So many dumb comments by Zipp.

Let's start with this one: majority of the 250g saved are from going hookless. Measure the dimensions of the hooks on your wheels and multiply the volume by the density of carbon. Hint, your answer will be somewhere in the 10g range.

28mm will not have lower RR than 25mm unless you're pumping them to the same pressure. Which you wouldn't. At the same vertical compliance, RR is essentially the same (within BRR error margins). In any case, if you want to have 23mm inner width to allow for bigger tires, you can still meet 105 rule by making the outside width greater. Just add hooks. They'll even allow you to run 75psi with those 25mm tires without popping off.

Don't even get me started on the "smooth interface" being more aero when the tire is wider than the rim. And then unironically followed by dimples right next to the interface.

I will say though, kudos on making a 75mm+ wheel sub-1600g. That's mighty impressive. Un-kudos for the asinine price. I thought hookless was what made the 303s so much cheaper. What happened to that logic?

I’m confused that you continue to make this claim about carbon volume between hooked and hookless. You are making the assumption that they remove the hooks and that is the difference between the rim styles. The real difference comes in the layup of the rim. Those manufacturers using hookless are consistently yielding much lighter rims because they don’t have to reinforce for the hooks and higher pressures. They’ve also gone all in on disc only which I would wager results in a lot of the weight reduction as most of the older rims didn’t differ a lot between rim and disc brake versions.

I am not sure there is a lot of benefit from TSE and wide tires for race depth wheels. Especially when aero figures into the equation.

The one thing that is clear about hookless is that these rims are less expensive to manufacture so it’s no surprise to see manufacturers go this direction while price points are not dropping (with exception of 303 options I guess)

I'm talking out of my rear here but with a disc brake only setup, you can use different potentially lighter layups, carbon and resin as you don't have the stressors of a braking surface. I do believe I heard (Enve maybe?) that hookless are cheaper and easier to manufacture as well, but I could be miss remembering.

No I think you are correct on the weight save from disc only. But something about the hookless configuration yields further weight reduction. The hooked rim and rim brake combo always seemed to be the big worry for carbon wheel manufacturers in the past.

I think you are remembering correctly for Enve too. I’ve had their hookless AR4.5s for 5 years and they definitely aren’t light weight rims. So something in the manufacturing process has definitely changed with these later rim iterations.

Layup won't affect density. And if you think there's a difference in reinforcement, I'd be interested in hearing the logic. If you need less reinforcement because of the lower max allowed pressure, then that's independent of hook or not. You can make a lighter hooked wheel if you limit it to 73psi max with 25% safety margin. The hooks on a tubeless setup don't need much reinforcement, especially if the tire that on there is hookless rated anyway. It won't push on the hook radially, just act as a safety device. The sidewall reinforcement will depend on pressure and nothing else (for disc-only) because the tire pushes perpendicular the walls whether there is a hook or not.

Rims getting lighter over time has been a trend before hookless. Deleting hooks isn't the reason. Princeton's 7580 weighs the same (or less depending on hub) than the 858 and has hooks.

Just as a logic check: Princeton's 7580 and the Enve SES 7.8 rims weigh 530g with hooks. Can you make them lighter without? Probably. But I'm saying it'll be closer to 10g than "the majority of 250g". If you want to argue whether its 10g vs an optimistic 50g, that's fine. But 25%? That's when it becomes an outrageous claim.

10g or 50g the fact remains these new hookless rims are lighter. So if Zipp's comment is dumb, then what is your explanation for the weight reduction? And how would you suggest they explain their improvements.

And contrary to your claim. layup will affect many characteristics. This is the point of using carbon in the first place.

It was conceded above that disc wheel only rims are likely the largest difference in overall weight, but you continue to focus on the hook/hookless aspect.

Our article: https://www.slowtwitch.com/...nd_858_NSW_8432.html

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Surely “you” can save a few grams by scrapping the specific heat resistant resin, the little bit of molded hook and reducing carbon to handle the decreased stated max pressures from 120 PSI to ~72.5 PSI (E.T.R.T.O. standard is 5 bar.) However for a variety of strength and impact related reasons I can’t imagine all that much can be scrapped, but that’s just pure uneducated speculation on my behalf. Especially given the heavier disc hubs, I’m impressed by the weight on the new 858, even if I’m not sold on 28mm tires and low pressures for the TT and track racing that I’d be doing with them. I guess I could rip some epic gravel races on them though.

I didn't say they aren't lighter. I'm saying they're taking us for idiots by claiming most of the 250g is from going hookless. We know that's not possible, and we know Zipp wants to shift fully to hookless so they have a reason to exaggerate any benefit.

My explanation? I didn't make the wheels, so I can't tell you if it's the hub, thinner walls, etc. But most likely most of it is just generic improvements in carbon and hubs that other brands made 5 years ago. Zipp had by far the heaviest wheels until this generation. After all this weight loss, the 808 is on par with SES 7.8

My suggestion would be to just be honest. Obviously not "just better margins for us" but at least don't oversell claims to the point that they can't pass a sniff test. "We saved 40g by eliminating hooks, 70g on hubs, and 130g be reducing wall thickness due to lower pressure limits" wouldn't stand out as odd.

Edit: To clarify, these wheels look excellent on paper. The marketing lines just rubbed me the wrong way. It reads like an adult explaining something to a kid in a nonsensical way, knowing they won't get it anyway.

I think we agree then

source?



says who?



faulty reasoning.



why? it's measurably true and one after another after another premium wheel company are discovering this.



what as MSRP of the last model year 808 per pair? pre inflation, pre supply chain problems, pre freight robbery?

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Dan Empfield
aka Slowman

https://www.slowtwitch.com/...nd_858_NSW_8432.html



The chart shows a 4-5 watt improvement (mostly due to aero). But the article mentions only 1 watt?

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blog

the article mentions a minimum of 1 watt. i have a follow up article that goes into more detail about watt savings; in which cases; in which wheels. that'll be published within the next 48hr. that chart you reference in your post is one of several that will be in the follow-up.

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Dan Empfield
aka Slowman

Hmmm...I'm going to need more info on this "rolling road" setup...since the only difference between the bottom 2 lines is tire width (same rim), and the setup really is only going to measure Crr differences (if "like a treadmill", then the only aero component measured is going to be rotational drag, which should be practically identical)...because I don't get how at the lower pressures the 28 and 30 tires have the same rolling resistance, and then 28 actually gets 1W faster above ~68 psi?

That's opposite of the previously measured "wider measured tire widths are faster at equivalent pressure" observations, which is exactly what the 25 line vs the other shows (since this is a "delta" plot).

I wonder what the accuracy and precision is of that test setup? Are the 2 tire width constructions actually "equivalent" (i.e. same casings and tread compound and thickness)?

And how is that "Hooked vs. Hookless"? It's 2 completely different inner rim widths and different label tire sizes. I suspect both of those things have a much bigger influence than hooks or not :-/

So many questions...

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http://bikeblather.blogspot.com/

the 1 watt is the aero savings. so they're indicating they have made 3-4w savings across the other areas which the little graph shows are all very small proportions of the total resistance - very impressive if true!

mind numbing amounts of testing on the Rolling Road trials, one particular guy, a particularly talented Crr crash test dummy, something between high dozens and low hundreds of runs. 25mm, 28mm, 30mm, each at various pressures. this is just Crr that's getting tested. so, the field testing, that's the combo of rolling resistance, wind resistance, and whatever biomechanical benefit/cost you get through an increase/decrease of power saved/lost in comfort and muscle vibration. but the rolling road testing is just about rolling resistance. the piece measured isn't that directly, it's the amount of power produced to remain at speed. at least, this is what i understand zipp to have done.

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Dan Empfield
aka Slowman

I don't know if your single word answers are just meant to engage or shut down, so I'll give benefit of doubt and go with the former.

Source for the 10g? On my knight and SES wheels it came out to ~10g. Depending on the hook dimensions of yours, it'll vary but be in that ballpark. Show me the old and new cross section of the Zipp wheels. Then show me how (most of) 250g savings came from the hook. Thats akin to the weight of the entire rim beds.

RE rolling resistance vs size and comfort level. Wider and lower pressure is faster in many real-use cases because of poor road surfaces not allowing low enough pressure with the narrower tires. But for any given surface, the narrowest possible that can still roll smoothly will be fastest (else we'd just jump to 40mm). Here is what I've seen claiming the same comfort level gives the same RR. They're not perfect, but it's more than Zipp provides.

BRR: https://www.bicyclerollingresistance.com/...prix-5000-comparison
Continental's engineer: https://road.cc/...e-right-tyres-279289

Why is it faulty reasoning that you can have both wider tires and still meet the 105 rule busy just making the whole thing wider? How can that even be faulty? Lol. Zipp said having the tire stretching wider is better than meeting 105, but you can have.... both.

Which companies have shown that the smooth interface is faster? Never seen a single data point that attributes a wheel's speed to that feature. Perhaps mavic with the CXR80 had something but those wheels can't be compared with/without strips since there's a big recess that sticks out where the strip sits. Roval and Hunt have gone the opposite way and exaggerated the step created by the hooks (one is hollow and the other is filled). They claim it's faster because it is easier to meet the 105 rule with bigger tires. The air can flow smoothly even if the surface has small gaps, as long as the two disjoint sections line up. So are Roval/Hunt the ones making wrong claims or is it Zipp? In any case, the smooth transition won't help you with smooth airflow if you have a 28mm tire ballooning to 30mm on a 23mm internal wheel that is 27mm on the outside.

Regarding the price. I said sub-1600g so clearly I'm talking about the 858. The Firecrests are competitive value. The 404FC was in my top 2 when I was purchasing new wheels last year and almost pulled the trigger when i saw them 20% off. Went with the i9.65 which is 7mm deeper, wider, still within 70g, and has hooks. I wonder how they managed that weight with those 150g hooks (just kidding around).

If there are contradicting "sources" and "measurably true" data for the claims you make, I'd be happy to read those if you're wiling to share them instead of replying in 1-2 words to each paragraph. I like reading about the tech side of these things but haven't found anything that actually shows that smooth interface is measurably more aero beyond the eye tunnel, hooks save many times more weight than the material they remove, etc. Only generic claims from the sales and marketing departments.

Well said. I feel like the cycling industry is run by marketing departments these days. For example they removed showing drag plots. They also stopped showing white papers/explanations on stuff that really needs explanations such as how they came up with rolling resistance numbers and why having tires much wider than the rim is now ok.

What I'd be curious is what some of the popular tires inflate to as actual width when mounted on those large inner width wheels...
(for example all the new cervelo tri bikes have 36mm clearance I believe, and insist on 4mm spacing on each sides, so anything that inflates to more than 28mm would be a no-go. And then the TSE discussion becomes irrelevant if it doesn't fit. I'm sure plenty of other bikes are in that regime?)

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https://besse.info/
https://www.strava.com/athletes/2012033

i'm no aero expert but it seems clear that there are some different approaches in the details, none of which are necessarily right or wrong.

we've seen a number of manufacturers recently go against 105 so its not just zipp which makes me think there must be some truth to it but i would like to see some proper explanation of the tradeoffs. it seems logical that smoothing the transition would help recapture the airflow as you are then more treating the tyre and rim as a single shape so maybe instead of 105% you're looking at closer to 100% but we have here 28mm tyres (or more) on 27mm rims so how can you recapture the airflow? unless there's some real magic you have to be counting on the tyre to play nicely with the flow which is unlikely.

i can imagine there comes a point at which the wide rims required to achieve 105 with increasingly wider tyres bring about other issues, though nobody has really explained that.

105 has enough backing that i trust it until someone can provide more than marketing spiel to indicate that their approach is at least as good

And it's not so much the directional claim, as much as the magnitudes. Same as when a bike manufacturer claims 20W over a strong benchmark

Since the whole idea is to go fast, I wonder if the real question on Crr should be about tire design for hooked and hookless rims. I would like a tire engineer to explain how the casing needs to change to work with a hookless rim. Are we going to see a hookless Veloflex Record or Corsa Speed that has the same low Crr, or does the bead and hook interface allow for a more supple casing? At the moment it seems like all the hookless tires I can think of are giving up 8-10 watts compared to the fastest hooked tires out there.

I will remain on the fence about hookless until the tire technology gets sorted out.

This is probably true. Tradeoff is mostly weight, I'd imagine. But check out 3T. They have some super wide wheels to maintain 105 with gravel tires

IRC makes tires that have a flap to fill the gap. Could be sized for hooked or hookeless. Lots of neat ideas coming out lately.

Didn't do Bontrager such tires a decade ago? I think I still have two of them in 20 mm or 23 mm.

Maybe. Don't remember the Bonti ones. Seems like the best solution if smooth transition is the goal

Mavic was making a gap filler for clinchers some 10 years ago

Yes, I mentioned it in post #18

This is my take on making wheels faster. I don't see it as a wheel manufacturer doing much more with current technology/materials. I see tyre manufacturers doing more to improve puncture resistance, reduce rolling resistance and mate their tyres to specific rims in specific ways making the overall wheel/tyre combo faster. Infact I am surprised in a way that wheel manufacturers keep producing generic rims. I would expect the fastest wheel set to come from a tyre manufacturer who works with a wheel manufacturer to produce rims specific to their tyres. Hows about a set of GP5000 wheels from Continental? A set of wheels developed around the GP5000 tyre but manufacturerd by somebody like DT Swiss or Swiss Side who can create the overall product, and badged as Continental.

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He who understands the WHY, will understand the HOW.

i would never try to shut down. you're too valuable around here for that. happy to engage. but there's a lot of ground you covered in your post, so let me just engage on one example, for starters.


if you look at BRR's tests - which we all have - one thing that sticks out obviously is that higher pressure always wins. even on larger tires. this speaks to a flaw in the protocol. drum testing - or at least BRR's drum testing - can't tweeze out "break point" to use jargon coined by a person participating in this very thread. when i look at BRR's data i stipulate to its reliability when testing compounds. but not pressures and since it's not reliable for pressures i'm highly suspicious of its reliability on tire widths.

so you have to move to field testing or, in zipp's case, field testing + a whole separate protocol on its rolling road. in that latter case you're testing power to maintain a given speed on the rolling road at various tire widths and pressures. in this case, they inoculate against different compounds by using the same tire made in different widths. what zipp found, as i understand it, is that not only is 28mm faster than 25mm, but 28mm on a rim build for that size is faster than their own rim optimized for 25mm with a 25mm tire installed.

by "faster" of course i'm talking only about road friction, not aerodynamics. but on that subject of aerodynamics, to pick up on another point you made, you don't like the idea that a smooth transition from wheel to tire is more seamless, because zipp already blows that up with dimples. i suggest these are different themes. zipp's dimples create mildly turbulent flow that keeps the air attached to the wheel longer. in theory. but the shape of an object is still important. a lousy shape isn't better than a good shape because it creates turbulence.

here is what i would have said if i was you: semi-toroidal wheels might be in the same class as the hooked-bead clinchers, so, if semi-toroidal works, hooked beads kind of work inside of that paradigm. but zipp has abandoned that wheel style. it wants a really clean flow from tire to wheel, front to back, and the idea of the dimples (whether they work or not) appears to me to prosecute a theory distinct from the general shape of the object.

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Dan Empfield
aka Slowman

I think we're on the same course here. The break point is what I was referring to when I said " any given surface, the narrowest possible that can still roll smoothly will be fastest". The BRR drum is not rough enough to find the break point, which explains why higher P always has lower RR. But can we agree that for any given surface roughness, the narrowest tire that allows for a low enough pressure to avoid the break point will be the fastest rolling?

I think of my points, this is one of the weaker ones since the mechanics are nuanced.

I'd be curious about your take on these two, aince they are more straightforward:
1. You can reduce weight by reducing density or volume. In engineering terms, how can eliminating the hooks account for "most of" the 250g+ savings? Where is this weight being eliminated given how little material is in that area to begin with? This statement is really odd since it is so far beyond passing the sniff test.
2. Why do the marketing materials say wider tires and a smooth transition are more important than the 105-rule? Is it just to state the relative impact? Because they are independent design decisions. You can have hookless beads for a smooth transition, throw on big tires, and still meet the 105 rule. Just need to expand the outer width. It can even be done using minimal additional weight, as Roval and Hunt have done (hollow or filled designs).

you're right when you say that we'd be riding 40mm if the bigger the tire the better the result. if you could make 40mm aero, then 40mm would be the ideal tire, yes? the problem with this idea is that it also flows the other way. why isn't 19mm best? well, it is. on the track. so, you're right again. it depends on the surface. washboard dirt, 40mm is the best, except when 53mm is better. so you're correct, it's the narrowest tire you can ride on a given road surface. what zipp feels is truest is this: on the most typical road surface found in TT and tri, 28mm outrolls 25mm. it might be truer to say 25mm is the best tire in germany, 30mm in new zealand. i know where zipp does its field trials, and it's not rough chip and seal with a bunch of potholes. it's a pretty representative road.

now, on the 105 rule, you'd be surprised how many wheel and tire companies either don't consider this or even in some cases don't know about it. but zipp certainly does. but it's kind of moot, because on almost every wheel i've tested over the past year or two that has hookless beads, the rule of 105 remains obeyed with a 28mm tire. cadex, zipp, hed, enve. road or tri. why? because the inner bead width is so wide. it's always a minimum of 23mm and up to 26mm. this pushes the outer width to 30mm+ and the inflated 28mm tire is about 29mm on these wheels. every wheel i get i pull out my caliper and check outside widths of the wheel and tire and i'm always between 105% and 110%, with 30mm tires still obeying the rule much of the time.

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Dan Empfield
aka Slowman

Ok...I have to address this, since it's a common refrain from some quarters ("Quarterly's"? <LOL>) that because breakpoint pressure doesn't show up in Crr vs pressure testing on rollers, then ALL of the data from them is "suspect".

Of course, that conveniently ignores the fact that the only reason the concept of breakpoint pressure was identified was because there was a divergence in the correlation between roller testing and field testing above a certain pressure (for a given road condition, setup, speed, etc.). In other words, you can't accept the concept of a breakpoint without acknowledging that below that pressure roller tests and field tests are highly correlated.

Couple that with the fact that for most reasonable surfaces (especially for TT or Tri events) the breakpoint pressures end up being at a point quite a bit higher than most would suspect, then it's logical to utilize roller testing to discern Crr differences for reasonable pressures...especially if one understands that due to the highly asymmetric loss function of running to high of a pressure, that it's prudent to err on the side of too low of pressure than too high.

So...look at the results in the lower pressure ranges and be confident the results reflect "on the road" performance. It's that simple, really.

That said, the "rolling road" testing is really the same as roller testing, just with less sensitivity to differences in Crr than rollers (due to the lack of the "amplification effect" of the rollers). My questions about the 28 vs 30 results further up in the thread still stand...they go against previous results on tire width (edit to add: and logic).

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http://bikeblather.blogspot.com/

To be more accurate, it's not that the BRR roller isn't rough enough, it's the fact that the setup doesn't necessarily reflect the damping effects of a large, floppy, human mass supported by the tire through the wheel and bike structure.

The Velonews testing that Zinn did with Wheel Energy recently using different roughness surfaces does appear to show a breakpoint, but that's because their load is applied with an air cylinder, which provides a small amount of damping (only ~10% of what would be required to simulate a human though, unfortunately). However the breakpoint shown there doesn't reflect what one would find in use, because of the low damping amount.

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http://bikeblather.blogspot.com/

Bontrager Aerowing TT was the model. For a short time, the best combo of aero and rolling resistance...until the Conti GP4000S came out.

VERY good aero (not only the gap filled, but the tread shape was parabolic). The thing that let it down was the Crr though, which was a combo of the relatively thick casing material, and the tread rubber compound not being as advanced as the Conti Black Chili options. Tread compound losses are critical for a tire with a parabolic shape since it's accomplished by using thicker rubber in the center. More rubber of "meh" loss properties isn't a winning combination. Plus, as I pointed out a long time ago, low Crr can make up for quite a lot of "aero sins" ;-)

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http://bikeblather.blogspot.com/

It's basically not suspending anything, so it's purely a hysteresis tester.

The issue I have with BRR's "pumped to same comfort" article is that I don't understand why equal drop against a flat surface is assumed to produce same suspension result on an arbitrary riding surface. The assumption differs from what static testing appears to imply, and I haven't seen any explanation from BRR as to why it was chosen.

To what degree does the damping of a human affect the results? If energy in a deflection gets far enough up a linkage of pivots and springs that it's no longer being directed along an obvious path to return to forward motion, does it really matter how aggressively it gets dissipated? (Is it even a good thing if such energy doesn't quickly dissipate?) And in this respect, how mechanically "close to the ground" is the rider?
Obviously there are situations like pumping where the rider is serving as a critical part of the suspension linkage, but the frequency and amplitude of the irregularities there are orders of magnitude different from roughness of a paved road surface.

Do you have the 105 rule backwards? The rim is supposed to be wider than the tire, and dollars to donuts none of the combinations you mention meet that criteria. 28mm and 30mm tires on a wide bead width tire will measure larger than nominal. Cadex 65 is 26mm wide, Zipp 808 is 27mm, and Enve 7.8 is around 27.5mm at the brake track (~29.5mm at its widest). A 28mm tire will measure 28mm+ on these.

you and i agree on the rule of 105. substantially all the new hookless road rims have outside widths greater than 30mm, in the 30mm to 31mm range, or fatter. 28mm tires on these rims, according to my caliper, are always <30mm wide inflated.

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Dan Empfield
aka Slowman

As I understand it, there's a 42.5kg static load. So yes, purely a hysteresis tester, which is fine for evaluating tire differences IMHO.


By definition, equal displacement for same load results from equivalent stiffness, no?


I think it helps to think of the bike+rider system similar to the simplifications used in automobile "quarter models", where 2 spring-mass-damper systems are connected in series. The spring-mass-damper system touching the ground represents the tire and bike structure, where the majority of the stiffness and damping is influenced by the tire properties. The other spring-mass-damper system represents the rider, and it's stiffness, energy losses, and mass.

Obviously, any energy that can "make it through" the 1st S-M-D system is going to be dissipated in the 2nd, especially considering the relatively large amount of damping represented there. However, if you can keep the stiffness of the 1st S-M-D (i.e. the tire) low enough, then (with a quality tire) due to the low hysteresis losses, the majority of the energy put into the system by road roughness can be nearly completely returned at the contact patch. Pump the tires up too much and that energy then makes it into the 2nd SMD system, and is lost as heat. Hence, the "breakpoint pressure" which is observed in field testing.

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http://bikeblather.blogspot.com/

Read the Silca blog post I linked. Pressing arbitrary rigid objects against a tire is a more complex situation than pressing arbitrary rigid objects against a simple idealized spring: the shape of the contact area affects measured spring rate.
In the static case, Poertner's data suggests that small sharp deflectors have a spring rate that's dominated by PSI dependence, with only minor dependence on tire width. As the curvature of the deflector decreases, the spring rate becomes more and more width-dependent.

It's not obvious to me why a flat surface in static testing is a good proxy for sharper irregularities in the dynamic rolling case.

Yes. What I'm asking is, how much (and in what ways) does the damping coefficient of the second SMD system affect paved performance? By emphasizing the damping of the human rider versus something like an air spring, you're suggesting that it may have a significant impact. It would be interesting if that's been looked into deeper.

Any update on that follow up article?

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no. well, yes. here's the update: not up yet. it's in the queue. i have 3 articles to get up on the site before that. each is in process. maybe tomorrow?

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Dan Empfield
aka Slowman

Probably because the "sharper irregularities" on the dynamic rolling case on typical pavement only really amount to extra flexing of the casing...think of it like an energy loss "bias" on top of what it would be for a perfectly smooth flat rolling case. As you pointed out, the "sharper" the object being pressed, the less the casing adds to the spring rate...in other words, deforming the casing at a more micro level only adds additional flexing losses, and not stiffness. Make sense?



The air spring of a tire as basically zero damping...the vast majority of the damping losses of the 1st SMD is in the tire casing and tread. One could argue that the effect of the damping in the 2nd SMD system is demonstrated by the existence of the breakpoint pressure. Whereby, for a particular case of equipment, speed, and (possibly rider) increasing pressure results in dramatically increasing losses in the total system, i.e. once the stiffness of the 1st SMD is increased beyond a certain point.

I think some of smaller feature data in that Silca demonstration can be somewhat misinterpreted in regards to the scale of typical pavement roughness.

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http://bikeblather.blogspot.com/

It seems like your argument is basically that irregularities of the non-highly-width-dependent scale in Silca's testing don't significantly contribute to suspension consequences in road riding at practical pressures, and that breakpoint pressure is dominated by broader-scale stuff. This is plausible, and I have no reason to believe that it's incorrect, but absent data I also don't see that it's self-evident.


Yes, I'm open to this idea. When I look at road surfaces, I don't know what filter to apply to isolate the things that do and don't matter to what tire setups and loads.


Yes, I'm talking in reference to the Wheel Energy air cylinder representing the 2nd SMD load, not the air within the tire.


I'm admittedly not a mechanical engineer, so I might be visualizing this poorly. I'm not entirely sure how you mean. Are you saying that, as damping in the 2nd system is reduced, the onset of inadequate suspension smushes out across a broader inflation range, experiencing a less-abrupt "breakpoint"? Or that the performance of tires as suspension simply matters less within the range of amplitudes and frequencies being discussed?

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Favorite Gear: Dimond | Cadex | Desoto Sport | Hoka One One

it's clear what they're saying if you pay attention. lower the breakpoint hypotenuse enough, the hysteresis becomes hysterical. generate some lift by inversing the rocky terrain, so long as the lever arm doesn't exceed the flow rate. get it?

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Dan Empfield
aka Slowman

So instead of power being generated by the relative motion of the pedals, with decreased resistance it becomes generated by modal reluctance?

you're close. modal reluctance is the cube of surface pressure just prior to stall, assuming you're running tubeless at anything below 30 kilopascals per stone of body weight. this has ramifications. when you feel the wheels stall, stop and pedal backwards.

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Dan Empfield
aka Slowman

We laugh but the work these guys are doing is amazing. Let me explain

Yesterday I went out and did some aero testing. I'm in Quebec, about 1hour North of Ottawa. There is a section of road roughly 1 mile of typical brutal Quebec roads, 1 mile of more recently paved.

Here is the map. The west section is the smooth part.




So I start between the two sections, go west, turn around, go east all the way, encountering rough roads half way back, turn around, repeat 3x

Here is the CDA with uncorrected rolling resistance, ie assuming the rolling resistance is constant. I use CDA for the lap, separating laps on smooth and rough sections.








You see, quite clearly and with good repeatability that my CDA took a hit. A BIG hit. 0.253 to 0.264 is HUGE
Smooth road is 0.253, 0.253, 0.251, rough 0.264, 0.263., 0.262.

(FYI, that is over 10watts at 30mph)

In green is barometric altitude (uncorrected). In blue is wind, I had a good head wind/tail wind going on.
In Orange is an indicator" or road roughness.

It is this road roughness that helps me to correct and recompute a new CRR. In theory those CDAs should all be the same, the CRRs should vary.

The problem is this orange indicator is not clearly defined. I have all kinds of vibration data but what I am trying to do is model, quantify, parametrize, describe......not sure what to call it....vibration and rough surface.

The nerds are trying (I think) to do this. This is the next frontier.

Long live the nerds !!

You all make fun...but then you also usually are first in line to take advantage of what all this type of discussion results in ;-)

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http://bikeblather.blogspot.com/

yup. true dat. the skill that i strive (and often fail) to exhibit - my lifelong objective at which i routinely fall short - is to make accessible complex ideas. i must first hold a complex idea in my head (debatable how often i succeed at this); and then translate it effectively.

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Dan Empfield
aka Slowman

My 2004 aluminum P3, Renn 575 and ancient Hed front wheel disagree. :p I've been riding since the late 80's and it's amazing to see the changes that have taken place. It's also good to keep on top of the latest and greatest so I have excuses for when people beat me on the bike!

Well...in this particular instance, we each were responding to questions of the other at a technical level that, in order to effectively make our points required using some words and concepts that may be slightly beyond the understanding of those not familiar with them. I was attempting to communicate to HTupolev only, just in a public manner. We could have done the discussion in PMs, but then that wouldn't allow those who ARE familiar with the concepts to follow along.

Now then, if you ask me (as you have in the past) to distill those concepts down into something more "easily digestible" to the general public, then I would do so...and most likely employ a measure of diagrams, graphs, and charts to better communicate the point. I think it was Feynman who said something along the lines of "You don't really know a subject until you can explain it to someone who doesn't have the same level of training as yourself" ;-)

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http://bikeblather.blogspot.com/

Well...sometimes the results of those types of discussions/tests/analyses is "What you have is pretty good already" :-)

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http://bikeblather.blogspot.com/

no doubt. and i wasn't indicting you; i was indicting myself. if there was a message in there for anybody else, it's just to remind us all that there are, and for 20 years have been, several hundred people on, logged in, and participating on this forum at any one time, day or night. this topic is of prime interest to them, because it directly affect their riding speed, riding experience, and riding purchases.

in fact, i was just discussing this with somebody a couple of days ago. just according to my observation the single biggest difference in how road and tri bike frames are made between, say, 8 years ago and beginning 2 or 3 years ago, is clearance. my road bike frames i purchased up until 2012 or 2014 were often not usable with tires wider than 25mm. over the past 3 or 4 years all my road bikes - for climbing, for general use, and my aero road bikes - have gigantic clearance. they're all rated for 32mm tires but they all take 35mm tires. i think this is a testament to where the industry is going. all today's relevant tri bikes can take 28mm tires easily.

this (they say) comports with their own testing, which often flows from the use of these bikes by their top cycling teams. i noted during the tour when pidcock rode away on that descent that the announcers (euro feed) commented on his tubeless tires, and one said that it was certainly the 25mm version of the tire (they could tell the make and model but not the width) i privately thought: not so fast. a fair number of teams are riding 30mm tubeless on stages with paves and that's almost certainly what got ridden during stage 5. if i were to guess i'd say pidcock may have been riding 28s during that mountain stage.

one difference is that other test paradigms besides drum testing are now used, and these highlight where drum testing is reliable and accurate, versus when drum testing is not the ideal tool. drum testing is hard to fault if you're testing compounds, for example. on the other hand, reliable differences in Crr among tires of different widths and pumped to different pressures appear harder for a drum rig to parse. but you know all of this better than i do.

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Dan Empfield
aka Slowman

Aaah...I see. Yes the Wheel Energy load, unlike many other similar testing machines that use a simple mass somewhat "rigidly" attached to the wheel, employs an air cylinder to create the load force. So, unlike the nearly complete lack of damping in the 2nd SMD for those typical setups, the Wheel Energy setup as at least a small amount of damping present in that part of the system. In discussions with Josh Poertner on this subject, he noted that this type of air cylinder typically has only ~10% of the amount of damping as what one would need to simulate the damping if an actual rider was the "test mass".



Here's some observations and conclusions that might help make things more clear:

-When roller testing tires on a setup with a rigid connection between the wheel and the test mass, Crr tends to continually decrease with increasing tire pressure. This is true for both smooth and rough roller surfaces, with the rough surface data showing basically an offset, or bias upwards. This implies 2 things:

• The lack of damping in the 2nd SMD system we discussed above results in the lack of a breakpoint pressure
• At the tire level, additional surface roughness results in additional flexing losses in the tire only.

- When field testing with a human representing the 2nd SMD of the system, there IS an observation of a pressure breakpoint. The location of this breakpoint, and the shape of the curve overall is highly dependent on the surface roughness and the speed encountered, and thus the energy input into the overall system through the tire. The fact that below the breakpoint pressure, especially with typical road pavement surface roughness, the shape of the curve matches that of the curves observed on the roller testing with "rigidly" attached masses points to the change of the 2nd SMD properties as the source of that breakpoint observation.


- When roller testing with a setup that DOES include an appreciable measure of damping in the application of the load to the wheel, such as the Wheel Energy setup, a breakpoint pressure IS observed for a given surface roughness, but typically at a higher pressure than what one would expect for the same tire, load, and roughness for field testing done with a live rider. Again, this implies that the amount of damping in the 2nd SMD system is important in the observation of the breakpoint.


- Lastly, all of the above observations are consistent with the concept of the 2 Spring-Mass-Damper (SMD) systems in series, like the model shown:

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http://bikeblather.blogspot.com/

Good stuff. My suspicion is that the parameter of interest is going to be the Power Spectral Density (PSD) of the road surface and speed combination, and roughly "higher PSD, higher resistance to forward motion (which is lumped in these analyses as Crr)"

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http://bikeblather.blogspot.com/

I might be misunderstanding what the test setups are doing. The way in which the BRR setup sets load isn't obvious from the photography nor is described on the website's "The Test" page, and the appearance of the rails around and above the tire made me think that the wheel was being rigidly locked in place for the test after the load had been applied. That is, I didn't think it was representing suspension of a rigidly-attached mass, I thought it was removing suspension entirely (i.e. 2nd SMD system is infinite-mass and has infinitely-stiff spring).

In practical terms, that's really not true as long as you are making comparisons in the range below breakpoint pressures, which for TT/Tri purposes actually ends up being a bit higher than some have been assuming lately (especially for wheels with upper pressure limitations ;-) So, roller testing is a very valid method of making those comparisons for which you are asking.

Now then, if you're looking for roller testing to identify where the breakpoint is for a particular setup, then you're probably more efficient making that evaluation with a field test, in that even IF you have a roller setup with adequate damping, breakpoint pressure is still highly dependent on the particular road/trail conditions, the speed, and the "rider properties".

Once again, in regards to "optimum" tire pressures, 'tis far better to err on the side of too low of pressure than too high.

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http://bikeblather.blogspot.com/

Yeah, the photographs aren't particularly enlightening on that front. Without putting in a direct question to Jarno, I'm only going by the description of the load applied being 42.5kg. I'm not sure why one would do the test in the manner you describe, with applying the load and then locking in the deflection. In any case, I think either situation would end up with effectively "removing suspension entirely", at least in a practical sense.

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http://bikeblather.blogspot.com/

that for sure makes sense. while i wouldn't stipulate to what you write above without some corroborating (field testing) evidence, you have a lot of experience that gives you a voice of authority on this topic.

when i see a test on BRR, and the best tire is almost always: 1) the widest tire; 2) that tire at the highest pressure; the question then becomes: what is the break point pressure for each tire at each size? this you can't get from drum testing in any way that i can see. but once you get it then sure, it makes sense that drum testing should be reliable at pressures beneath that.

here's the one thing, tho, that i come back to, which drum testing can't measure: what the is the biomechanical effect of vibration? you and i and many others have experienced what i take to be the effect of of muscle vibration in performance when on a gravel bike. obviously riding over washboard but i think the effect is there with more subtle vibration. for me, it's anything from power loss to ass soreness to shermer's neck. i don't even know that field testing gives you the entire picture, unless your field trials involved distances so exceptionally long that the protocol would be impractical.

and i could go on but i'd become even more boring so i'll stop here. there's a bunch of stuff on muscle vibration outside of our industry and avocation, not enough on muscle vibration inside our industry. this is why i like drum testing for what it is and what it does; and i like field testing because of what drum testing isn't designed to give you.

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Dan Empfield
aka Slowman

If the tire is loaded against the drum through vertical posts, it seems like letting the wheel "float" without troublesome play or stiction during the test might be tricky without a pretty decent linear bearing setup. I was under the impression that this was why some other test rigs suspend the wheel with an arm pivoting from the side.


Maybe. But it seems like vertical deflection transmitted through an extremely-stiff tire to a rigid load isn't necessarily going to tend toward returning to forward motion.

Think about the cartoonish extreme case of a wheel system rolling along a flat surface, which strikes a bump and bounces into the air, then lands on the flat surface away from the bump and continues on its way. That vertical deflection energy isn't returned to forward motion, even if there's almost zero damping in the wheel system; low damping just makes it take longer to dissipate (i.e. the wheeled system might bounce repeatedly). A squishier tire that produces a smaller bounce may lose less energy to vertical motion and have a higher forward speed after the bump.
Edit: And even if the system doesn't fully lose contact with the surface, a vertical lift in the system could give the tire less opportunity to push/roll off the back of the bump, even outside of considerations of hystersesis.

If you're talking about tires of the same manufacturer and model (assuming consistent construction across the model sizes), then yeah...but, that's just physics.

If you're talking across similar tires from different makers, then 1) above is demonstrably not true.

Also, I'm not of the opinion that trying to compare different tires across the ranges of sizes and pressures directly from that data is the most useful approach. Better is to avail oneself of something like the Silca pressure calculator which takes into account the system weight, the surface expected, the relative speed, and the measured tire width to come up with a pressure recommendation. Use that and then compare the tires AT the recommended pressures for each for a given application. That's going to make sure you're comparing them in the state they would most likely be used, and which is going to be well under any breakpoint pressure for the comparison. Make sense?


That is an excellent question...then again, it's long been my opinion that if vibration in the body is a concern (either for power demand or biomechanical issues) then you're probably not running a pressure low enough to prevent it. And if you are then concerned about tire/rim bottoming with the lower pressures, or pinch flatting, then you're not running tires wide enough for the pressures you want to run ;-)

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http://bikeblather.blogspot.com/

two things: correct me if i'm wrong, maybe i dreamed this, but it seems to me that if you're looking at the same tire (conti 5000 S TR, schwalbe pro one, etc.) that the 28mm tire will usually demonstrate lower rolling resistance than the 25mm tire if they're both pumped to the same pressure. obviously, tho, that's not a guide for real life.

on that question of vibration. the typical thinking is that you're on a typical road, with typical vibration-causing features, you normalize for pressure based in tire size, and ideally you get something like a typical Crr out a 23mm, 25mm, 28mm tire. those tires might have 100psi, 82psi, and 65psi respectively (let us say). back to the typical thinking: that 28mm tire would be more comfortable. is this true? i don't know. i think so. it seems so. this is what my brain tells me i'm experiencing. maybe the deflection in the tire is the same. same sag rate. same spring rate. across these various tires. but perhaps the damping is better in the wider tire. i don't know. but i think what i'm explaining is what is typically thought to occur.

except, of course, that you may well elect not to stipulate to the idea that it's possible to get a Crr out of a 28mm tire for this typical road that you can get out of a 25mm tire inflated to its optimal pressure. but this is the question. zipp says it's not only equal, but better. again, on a typical road. polished wood velodrome? zipp would tell you to ride a 19mm tire.

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Dan Empfield
aka Slowman

  
Bear with me.

Two points here,
a) you can do some good A vs B road condition testing
b) the contribution of nerds

Above I described the "smooth segment", "rough segment" testing and show very repeatable results
.253/.253/.251 on smooth, .264, .263, .262 on rough. Let's call it .252 and .263





The day before, I had done something similar except
2 longer, hillier longs runs on the smooth, 1 same route on rough segment
Different numbers : .264 vs .252 on the smooth
.271 vs .263 on the rough

(on 2 different days)

As above, orange shows road vibration




BUT.....

There was a 8 degree C difference between the two days

When you apply your correction factor for temperature, magic....

.254 vs .253 for smooth
.261 vs .263 for rough





All this to say that good, consistent, day to day results are possible, specifically for CRR testing and a big part of that is your work on correlation between ambient temperature and rolling resistance.

Yes, that's exactly what I said in my reply above. Across a particular model, wider (measured) tire is faster at a given pressure...no matter if the measured width increase is accomplished by a physically wider tire casing (i.e. tire sizes) on a given internal width rim, or by keeping the tire the same and increasing the rim internal width. Basically, "measured width is measured width" in regards to Crr and inflation pressures.

But, compare across the sizes at pressures "equalized" to the measured width, and the Crr differences become nil (for a given model).


Yes. This is true, because the majority of the "spring rate" in the air spring known as "a tire" is driven by the air pressure. Lower air pressure means lower spring rate (less stiff). However, the other part of that spring rate is the effects of casing tension, which for a given tire increases with measured tire width for a given pressure. That behavior is driven by geometry. Dropping the pressure to get the same deflection for a given load is mostly counteracting that geometric effect of casing width...and as HTupelov pointed out above, is mostly in regards to "flatter" inputs, since the Silca data points out that the smaller radius the interacting object, the less effect casing width has on spring rate of the tire (i.e. for small object inputs, it's ALL about the pressure)


It's not about the damping in the tire...the air spring contained by the tire has nearly none, and more damping in a casing means more losses, and thus a slower tire. If anything, you want to minimize the damping in the tire. What you're feeling as better comfort is the softer air spring from the lower pressure that the wider tire allows.


Now we're getting back to my original question in post #15, where the Zipp data shows the 28 and the 30 tires on the same rim having equivalent Crr at the same pressures, and then the 28 having better Crr than the 30 at slightly higher pressures (still in the 65-72 psi range). Both of those observations "go against the grain" of a lot of other data. I would expect the 28 to have better Crr than the 25 at the same pressures, and be nearly the same at width adjusted pressures, but that result also depends greatly on how "equivalent" in construction the 2 sizes of tire actually are. And, also depends on the definition of "optimal pressure" being used ;-)

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http://bikeblather.blogspot.com/

Cool! Thanks for sharing that! I'm still amazed at how adding the Crr temperature compensation into my own VE spreadsheet made my results appreciably more repeatable. It's great to see it working out for others as well.

It's also amazing to me that it works so well since the value is basically from testing on a single tire. It would be interesting to see how (and if) the correction value changes over a wide range of tires...or if that original estimate is "good enough" :-) A project for another day, I guess...probably once I eventually retire and finally fabricate my own automated roller tester I've been promising myself for quite some time now <LOL>

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http://bikeblather.blogspot.com/

We repeated the tests with several tires. We did not use your formula exactly, we used the data from our tests. but the correction functions are very close. There were at least 5 tires involved.

Since, we also tried using it across days in outdoor testing but to be honest I only know one fool willing to do same courses, same position, same equipment over and over.

zipp has a lot of charts and i just included one as an example. i'll include some of the others as i get a free moment. they actually show the 28mm to have a lower Crr, at normalized (lower) pressure, on their rolling road, and that 28mm is faster in general - all factors included - in field testing. now, on the rolling road they're not testing Crr, they're testing power. roll the road at 24mph (say), how much power does it take to pedal the bike and remain aboard the rolling road and not go flying off the back? many dozens (or more) of trials at different pressures and widths.

i ask myself what might account for this and i don't know. there are other factors at play such as the aforementioned muscle vibration. i just find it all interesting but beyond that i've had a running argument with the wheel brands who use hookless beads and want to put 25mm tires on them. when i add it all up, take in all the factors, i have no quarrel with the hookless platform and find a lot things i like about it; but i just don't see it as a platform that works for a 25mm tire. the required pressures are too high for a rider above, say, 160lb or 170lb. so, if zipp's testing is repeatable by other brands and others like you, and if 28mm tires on typical bike racing and triathlon roads proves to roll even equally as fast (we can then talk about aerodynamics) the news is that it unlocks the utility of hookless as a viable platform.

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Dan Empfield
aka Slowman

Dan,
Would appreciate your advice if you are happy to share.
These wheels are hideously expensive down under here in Australia.
That being said, I can currently get the 808 NSW Tubeless DB wheelset for about $3500 AUD on sale. I am not sure how many generations of the 808 NSW's there have been, hence how old this technology is.
A tough question I know, but is there likely to be a massive difference in terms of time savings/watts with these wheels over the new ones you have talked about here?
I was an all Zipp person on my previous bikes, but since making the change to DB's have had to start from scratch again.
FYI: late 40's, 2:21 HIM bike split on my P3X running an 80mm Front and Rear disc by Parcours (2nd fastest age group split). Not sure it is worth it to spend anymore money on wheels as these certainly performed OK on the day.

there is not enough distance to sweat the time and money for the new wheels if the old wheels are considerably easier/cheaper. and there is one added value to the old wheels: you can use new or old tires; and you can use whatever pressure you want without consideration, which is not much of an issue with 28mm tires but it may well be if you're riding 25mm tires. you can ride 25mm tires with the new wheels, but i wouldn't recommend it because you may want to push that 72.5psi max and you can't safely do that, imo.

me? i would buy the new wheels, all things equal, because i'm done with 25mm tires, i'm all in on tubeless, i have scads of experience on everyone's hookless road wheels, and i have access to conforming tires for those wheels. but you live in a 4th world country down there (where i'm scheduled to visit in december, i'll bring provisions). i don't have confidence you'll have enough available tires. buy the old wheels.

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Dan Empfield
aka Slowman

If that's the case, then the rolling road is the same as a roller test...just that the "roller" is flat (i.e. roller radius increased to infinity). They might be bringing in some of the rider damping that could result in breakpoint observations, depending on the roughness of the moving section. But, I think I'd need to see how the moving section is supported before being able to judge if that's something that could be "teased out". Even so, that chart doesn't seem to be showing that anyway (i.e. breakpoint effects) and I find the data presentation a bit awkward, with it being normalized to the 25 tire results. More insight could be gained from seeing the power vs pressure plots, I believe...normalizing to the 25 removes some information that might be interesting to see.

So yeah...seeing more of the info in your article might be helpful...what's taking so long?? ;-)


Well...combine that with the common opinion (one held by myself as well) that road tubeless for measured tire widths 30mm or smaller doesn't gain advantages over running a tire with a latex tube...and in some cases, disadvantages...then yeah, I think I'd join you in the opinion that hookless is a tough sell for for even 28s. Especially since hookless construction eliminates the possibility of running a non-TLR tire as well.

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http://bikeblather.blogspot.com/

That is fucking insane.

i've been running conforming 28mm, 30mm and 32mm tubeless tires on just about every wheel made by every brand making hookless road (ENVE, HED, Zipp, CADEX). so far, i'm very happy. no spiking the football, not a flat since 2019 (when i began my hookless odyssey). but that's just so very n=1, and it's not hookless but tubeless that i credit for no flats. but... no rolldown tests. no chung. i'm JRA. i have no data, other than, you know, no flats. and, a pretty comfortable ride, to the limit of how comfortable a tire can make you.

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Dan Empfield
aka Slowman

I have a drum rig setup (the drum has 1m diameter) with a linear ball bearing to apply the normal force to the wheel through weights, i.e. the weights and the wheel both can move vertically. In addition a damper (a damper usually used in motor cycles to damp handle bar movements) with adjustable damping rate is connected to the linear transducer holding the weights.

Just an observation when an „obstacle“ is mounted on the drum surface or the tire on the wheel is not perfectly round (can happen). At certain combinations of normal force, tire, damping rate … the weights or the wheel respectively may begin to oscillate up and down (obviously a resonance of the oscillating system is attained) at a certain speed. Crr then goes up too, i.e. break point conditions?. Increasing speed further and the oscillation stops. Altering weight or damping rate or tire pressure … and the resonance arrives at a different speed region.

My N=1 is that I suffer the same rate of flats on 25-30mm tires, whether with latex tubes inside, or tubeless setups...perhaps 1-2 per year (over ~3-5K road miles per year). The only difference is that I might be successful plugging the puncture on the tubeless setup, saving a small amount of time vs. changing a tube. BUT, if I can't get a plug to work...then the roadside repair becomes significantly more difficult and messy. At those tire sizes (and my weight) the pressures run are too high, and the air volume too low, for effective sealing of even small punctures IME. Either way, I'm stopping. Best case with tubeless is that my stop is a few minutes shorter. Worst case, it's significantly longer and more messy. That's the calculus I base my opinion on. YMMV.

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http://bikeblather.blogspot.com/

This is exactly what I was saying in the beginning of this thread.

If Zipp's rolling road has the 28mm tire rolling faster than 25mm, then either they are not at a comfort equivalent pressure, or they cherry picked a surface roughness and speed that crossed the breakpoint for these tires (or worse, just the 25mm tire)

Where are you coming to in December Dan??
If you are over in Western Australia let some of us know and we can help you out with anything you might need.

thanks. staying east. visiting a friend in sydney. but i must say, the cost to travel to australia has so far kept us booking anything. hoping for prices to come down.

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Dan Empfield
aka Slowman

For their most recent 404/454 release they had their rolling road/real world testing simulating/on unpacked surfaces to get their crazy watt savings…

whats the real life time difference for Joe middle of the pack in a 140.6 vs a used $1,000 set of old firecrest on 23mm

Id have to believe they are the bulk of the buyers, as there are way more MOP then top tier guys

I’m racing on my wife’s nearly 10 year old 404’s. With 25mm GP 5000’s they haven’t failed me yet this year.

Reviving this thread since you posted data on the front page yesterday.

I am not sure I 100% understand

What we know
There is a tradeoff between wider/lower pressure/aero
We know that ideal pressure is very surface dependant.
We know that CRR is pressure dependant

In the article, I see nothing about the aero benefit/penalty for different widths. Am I missing something ?
While the show rolling resistance benefits, is there any indication of what type of surface this was on ?

How can I tell if this wheel is any faster than a 25mm tire on a reasonable road ?

the data, or the compilation and results from the data, from zipp on their new wheels is up on our front page.
tom, you wrote in a FB comment below that article, "Can you ask Zipp for the plots in raw power? These delta plots are a regular "dogs breakfast" in trying to understand what they're trying to say, and how things agree, or don't agree, with other data...and seems a bit "obfuscation-y". Some details on the rolling road setup would be nice. If you're wanting to call this "science", then details of the test methods should be revealed. No way to put the results in context without that."

i assume you're talking about the Crr data. i'll ask zipp about that. there is some additional color i can give you, tho it's not specifically what you're asking. there was 1 rider on the rolling road for all the runs. the weight was 85 kilos total, with the bike. i believe the entire suite of runs was 96. there were 4 pressures x 3 tire sizes for each wheel. the 808 firecrest and 858 NSW were tested. so, that's 24 total discrete plot points. that's how i can up with (in the article) 4 runs per discrete instance. what i don't know is what was done with those 4 points. average the 4? throw out the 2 on either side and average the other 2?

i disagree with you that the way zipp presented this increases obfuscation. the way they presented the data was designed to do exactly the opposite and i think they achieved that. the data they provided is designed to help their audience understand what these new wheels give you over the old wheels.

if i can spitball here a little: they aren't claiming science in this sense: they're not claiming that their charts, as presented, are ready for publication and will withstand all reasonable scrutiny. they're claiming science in this sense: science is what guided them, internally, on the choices they made. they're sharing their internal results with their readers; they're not presenting a paper to nature magazine.

but i agree with you that we can't just stop here and call it good. i have some of the same questions you do. i think we all know there is value to drum testing, and there are limitations to drum testing. but up 'til now drum testing has been the easiest, cheapest way to test tires, and so drum testing has been gospel. rider-aboard testing seems a step forward, but it's so infrequently used that i don't know that we all know what its limitations might be.

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Dan Empfield
aka Slowman

i'll tell you what i glean from the results:

1. there's about a 4w or 5w benefit in rolling resistance in the new wheels. per pair. you achieve that with a wider tire (28mm is best). in other words, the new wheels, with 28mm tires, run way better than the old versions of the same wheels with 25mm tires. the reason 25mm tires were tested on the old wheels is that the old wheels were optimized for that tire.

2. the new wheels are *provisionally* faster than the old wheels aerodynamically. but we don't know for 100 percent sure, because there was one big protocol difference in aero testing versus Crr testing: in the aero testing all their testing previously, and all their testing of all the wheels in this new series of testing, is done on the same tire: a zipp tangente 25mm. they chose this in order to retain continuity, test to test. the problem is this: these new wheels were designed around 28mm tires. so that's what we'll ride on these wheels. we don't know what the 28mm penalty is, aerodynamically, when it replaces the 25mm tire used in the aero tests.

but what i will tell you is this: when i slap a set of calipers on all these new hookless tires and rims, they all obey the rule of 105 with 28mm tires on. i know of almost no hookless road wheels with inner bead widths of less than 22.5mm. these wide inner beads push the width of the wheel, and i haven't measured any hookless rims that are less than 30mm in width on the outside. the 28mm tire is routinely 29mm inflated. so, you aren't riding a lollipop.

i've really pored over these charts. ask anything you want, i'll answer it as well as i can, and i'll inquire of zipp if you and tom and i or anyone else feels there's a question that should reasonably be asked.

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Dan Empfield
aka Slowman

Thanks for posting the write up however. It still leaves allot of questions unanswered regarding the rolling road itself. There is no information on either what surface they are trying to simulate with the rolling road: rough/smooth asphalt?, dirt/gravel? (for the 303 relaunch and their TSE numbers they were doing dirt roads to get the large efficiency gains). I am very curious what the surfaces look like and especially what the interface between the segments look like. Do they create smooth transitions or is there some sort of bump every time?

To clarify this, I would really like to see a PSD plot of the rolling road vs the road surfaces they are trying to simulate and pictures of the roads they are trying to simulate themselves. Additionally with a PSD we would be able to quantify the comfort increases, and reduction in rolling vibrational losses that we see to further provide color to their TSE story.

I have access to some high quality accelerometers. I might actually do that experiment myself, setting my current tires at varying pressures and looking at the change in the PSDs, but controlling the speed and which part of pavement Im riding over exactly will introduce some noise the measurements as I would want to ride over the same segment 10s of times to get better data.

feel fry to hypergeek but please remember and respect your audience (and offer succinct background when appropriate). i assume you refer to power spectral density and i can see how this might be measured either with an accelerometer or a photometer. if zipp didn't do this at the point of testing they don't have that data for you.

perhaps if you find yourself in the proximity of indianapolis i might try to make a match between zipp and you for the purpose of seeing what their rolling road surface really is.

what they say that surface is is "standard" road, analogous to the eagle creek field loop they use. i could imagine, tho, that the entire contraption might have some give to it. imagine a treadmill that has x amount of bounce built in, but y amount of bounce simply due to the vibration of the entire unit. any additional bounce or vibration that unweights the rider might make the rolling road's results mimic a slightly rougher road than the belt surface itself. i'm wildly speculating here. i don't know.

i'm *provisionally convinced* by zipp's data, tho that phrase is kind of an oxymoron. i find the data compelling. just, my wild speculation would help answer the one question i have, which is, why is the ideal tire pressure so low in the 858 NSW graph? i'm provisionally convinced that the new wheel is fast, and faster than the old, and with the 28mm tire. i'm not yet convinced i'd run it at 50psi or lower.

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Dan Empfield
aka Slowman

Hi,
I have been following this thread in the past few days. I currently ride the 858 NSW from 2021. They came with the bike back then. I do like the feeling and of course the looks of the wheels, though I would like to ride 28 mm, at least in the rear.
My bike shop made me an offer to swap the 2 year old ones out for the new ones for 650$. I am thinking about pulling the trigger. How do you guys see the value here? I might be considering riding the new 858 NSW as they are, without a disc wheel in the rear in races?
Cheers.

first, i would make sure that your current bike easily accepts a 28mm tire. second, i would make an internal calculation on tires. is the tire you want to ride hookless compatible? we maintain a list of tires and while this would've been a real concern a year or two ago i don't think it's a concern anymore. but you should bear this in mind.

third, i'm done with 25mm tires. most of us are done with 23mm tires, just as we were done with 20mm tires before that, but i've gone this additional step. you need to make sure you're done with 25mm tires, at least on this bike. while you can ride these new wheels with 25mm tires i think you'd be throwing good money after bad to buy these new wheels only to continue to ride 25mm tires.

if all that is answered to your satisfaction, i think that's a pretty compelling deal. that's a $4,400 wheelset. to get a trade-in for faster, more comfortable, better handling wheels, yeah. if that wheelset came OE on your bike you spent north of $12,000 on your bike, which means you're not afraid to spend. i would do that deal, assuming that all the other conditions i mention above are met. this is really the case if you're over, say, 170 pounds, or 50 years of age, or both.

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Dan Empfield
aka Slowman

Here is why I get confused

if I take this chart



Just focusing on the "old wheel" (red line).

Would you agree the fact that there is no CRR difference between 60 and 100 PSI is strange ?

Do you not believe there are road surfaces where 110 PSI will be substantially better than 60 PSI with a 25mm tire ?

I would expect this (from this ST article)




And if so, if there is a .001 difference, that is close to 8watts better at 36km/h, bigger than the savings in the top chart.

Where does my logic break down ?

as to your first question, here is what i wrote in the front page article: "The 808 Firecrest chart has its own strange phenomenon. Both the 25mm tire on the old wheel and the 28mm tire on the new seem impervious to pressure changes. While the 858 NSW is very sensitive to tire pressures, not so this wheel, until you consider the new wheel with a 28mm tire mounted." so, yes. that's a point that needs investigation. the one thing i will credit zipp for is this: i asked them about that. i asked them a lot of questions. their decision was just to present the data, and they know full well that this question of yours (and mine) was going to come up. but rather than bend the line or throw out the data they just presented what they found.

yes, i for sure believe that road surface smoothness and tire pressure increases track. obviously. i could easily see, if you take all cases where a bike could be ridden in a timed race, that the best pressure for a given course would be 50psi and 150psi.

as to your logic, and whether it breaks down, i'm not sure i know what your thesis is.

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Dan Empfield
aka Slowman

I guess my logic is that if you are showing an improvement relative to something that is probably wrong do you believe there is an improvement ?

Clearance is fine, so there is no concern on compatibility.


As I said before, I would like to go 28mm.

Well, I am 32 years of age and 179 lb.

Sounds like I shouldn’t worry too much about throwing away money in this particular deal.
Just the Super-9 Disc doesn’t fit into the setup anymore then. Maybe I should think about selling that as well?

again, not following. what do you mean by "improvement relative to something probably wrong. "improvement" over something "wrong" means zipp previously did or made or reported something wrong, and the demonstrated improvement is unreliable because the previous data was unreliable. all this data was recently generated. perhaps you mean that zipp's methodology is probably wrong - because the tire Crr flatlines as pressure changes - ergo the improvement the data reports is unreliable. is that what you're saying?

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Dan Empfield
aka Slowman

yeah. sell the disc. ride the double 858s with 28s or even 30s. i know a guy at zipp who's riding this very set with a 28mm in the front and a 30mm in the back. your 179lb body will thank you, and the money you get from your disc will more than cover the trade-in cost. and you'll have more room in your garage, which your sig other will appreciate. quadruple win.

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Dan Empfield
aka Slowman

The TC858-25 data looks like the red line here,
TC808-25 data data looks like the Yellow line.
This leads me to believe they did all their tests rough/course surfaces.

So the question : "is this wheel faster on a smooth surface, at 110PSI" is not clear. (green line)

The test "looks like" they presented data for a very specific road condition.

i don't want to appear abstruse or argumentative. i'm just going to tell you how i approach this. the chart you present is from a slowtwitch article from about 3 years ago and, as well as i remember (from memory) relies on drum testing. what we know - what i think i know - is that drum testing has a problem, but that this problem is generally overlooked because while drum testing is not reliable at telling you a tire's optimal pressure on a given (or any) course, the relative values are reliable. meaning, it can't tell you what pressure your conti 5000 should run at, but it's reliable at telling how that tire stacks up against a schwalbe pro one tt. is that fair? are we agreed on that?

this testing on the rolling road caused me to ask two questions of the data: first, on the 808, why don't pressure increases require greater or less power expended by the rider? second, are the optimal pressures for the 858 unreasonably low?

but sauce for the goose is sauce for the gander. if relative values are acceptable for drum testing, why aren't relative values acceptable for rider-on rolling road testing?

we lost my favorite theologian this week. frederick buechner died at the age of 96. i remember reading many decades ago from a book of his and he tackled the inconsistencies in the synoptic gospels. how can irreconcilable data presented as fact occur in the inerrant word of god? buechner's answer? "somebody [matthew, mark, and/or luke] made a mistake."

this closely aligns with slowman's 7th law of epistodynamics: shit happens. but shit happens against the landscape of what we have that is valid. you believe that with drum testing. so do i. you don't believe that with rolling road testing. why do you accept the known problem with drum testing but reject rolling road testing? don't they both offer value in the *relative* even as we know there are issues in the *absolute*? if we can't stipulate to the reliably good while acknowledging the imperfect, then rolling resistance data and christianity both have a big problem.

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Dan Empfield
aka Slowman

actually the article was quoting a Silca article that was showing data on the road in real world conditions. BTW, this data lines up perfectly with my experience of testing on the road, hence why I believed it to be correct.

It showed trends in rolling resistance on different surfaces at different tire pressures.

It showed that on rough surfaces CRR trended up or flat like the trends Zipp shows with it's red lines

It showed that on good surfaces CRR dropped. We don't see this on the Zipp charts

It showed that on good surfaces at higher pressures, the CRR saving is as substantial as the improvements Zipp shows in it's charts .

Maybe, the data on the zipps are simulations of rough roads only. I don't know.

The real question for me is "are these wheels faster on a given course (say Kona)" ? I have never been to Kona, but if the roads are good, it's really not obvious from this data that these wheels are faster for that course.

When will this graph be corrected?

What needs to be corrected ?

There might even be a hookless disc for 28 mm tires on the horizon with their entire lineup converting.

let's stipulate that the chart you show reflects accurately the Crr on existing surfaces. that's a big assumption, because you have al morrison data, tom anhalt data, drum testing, field testing, all showing up on the same charts. still, these are smart folks (al, tom, josh) so let's just assume all of that is more or less accurate.

i don't see that in the data i presented in my article that zipp discusses variable road surfaces. perhaps i just still don't get your point. show me in the article i wrote where zipp is arguing road surface texture was even broached. for sure, the morrison test showed a higher optimized pressure. but let's stipulate it's accurate. that was a 23mm tire, tubed, on morrison's drum. it was not a 25mm or 28mm tire, tubeless, on a different surface using a different test rig paradigm.

all the testing zipp did was on one surface, that zipp considered representative of a typical event (triathlon or road race). what i would say - and did say - is that ideal pressures on zipp's chart seem curiously low for the 858 NSW. as i noted above, i'd like to know why that is. but we've come a long way since 100psi was the optimal pressure. we're not running 23mm tires anymore, many of us have moved past 25mm tires, and the pro peloton in europe went from completely-anti tubeless to "you must provide us tubeless!" in 1 year (from last year to this).

i would make these points:

1. did you ride 28s in your real world testing? it might be my imagination, but i get the impression that the things-that-roll cogniscenti are biased against that tire size, just as they were at one time (not that long ago) biased against 25mm, wider inner bead widths, disc brakes, clincher, then tubeless, then hookless. (but they weren't dumb; they were very obviously right about one thing: lower pressures.)

2. throw off any bias you might hold against 28mm tires, and embrace the possibility that this tire width in concert with tubeless, hookless, new well designs might conspire to create a system that reacts differently than what you're used to.

3. your say that your real world testing backs up drum testing, as i understand it. zipp says its field testing validates its rider-on rolling road Crr testing. i don't where that leaves us, except with more testing to do.

as i said in the beginning yes, there are some things that don't make sense to me, that need explanation, and i listed what those were. you think those inconsistencies make this an uncompelling wheel for kona. i find the data compelling, and believe the wheel ideal for kona. what accounts for the space between us?

i recognize both the apparent inconsistencies in rolling road testing and in drum testing, and i try to make sense of them both; and glean what's of value out of each. the experts minimize, gloss over, or reject the inconsistencies in drum testing. i look forward to the conversation we might have when we throw it all out there on the table and deal with the data we like and the data we don't like.

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Dan Empfield
aka Slowman

of this i'm sure: if there isn't now there will be. i'm not 100 percent on this, but i think perhaps blu and iden might be running a hookless CADEX disc. i have to run that down.

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Dan Empfield
aka Slowman

I don't see how iden could run a large hookless tire on wide internal rim when the trinity limits (according to Giant) are 25mm tires with 28mm external rim...

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https://besse.info/
https://www.strava.com/athletes/2012033

i'm not sure. i don't know. i guess i'm more thinking of what blu is running, because he can stick a motocross tire in that CADEX frame of his. i assume iden's running what blue is running but maybe not. also, i might have gotten bad info on what blu is running. that's why i've got inquiries on on that.

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Dan Empfield
aka Slowman

The annotation of the y axis on these graphs is wrong for years. I can‘t really trust such a proposition when a simple error isn‘t recognized for years.

In this way these ZIPP findings have the smell of marketing noise. What are the error bars with this rolling road? How are the test conditions not been chosen just to verify the own marketing claims? Are high Crr on these set up due to set up specific resonance effects?

Let me try this another way. When I read the article I look at the red line (old wheels, 25mm tires). This should be my reference, something I can relate to.

Then I look at the improvements with the new system.
My reference is the red line and the improvements are in the yellow/orange lines

The problem is the red line does not compute for me. If I cannot wrap my head around the "reference" I cannot appreciate the possible improvement

The reason the red line does not compute is that it doesn't match data I have seen from Tom, Silca or my own experience. So I try to understand it.

Then I realized the trend Zipp was showing matched the trend Silca showed for bad road surfaces. So maybe (I don't know) their data is based bad/rough surfaces. I don't know, but it's the only way I can make sense of the trend they see for the red line (my reference)

Maybe their data is valid for Paris Roubaix, but not my local formula 1 track.

I would be quite easy for them to just show a picture of the 'rolling road' you'd think?

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https://besse.info/
https://www.strava.com/athletes/2012033

Now I apologise if what I say is completely obvious and I've missed something in the previous posts, but I just wanted to check. There's a lot of really complex discussion here, but there's a 'simple' first stage.

A lot of the comments are about why there's not a difference in the red line as pressure changes. The answer is that this is a delta plot and that red line is the baseline of zero. So there are differences, it's just that line is set to be zero with the other lines based off that.

Where this entire chart falls down (to me) is that I can't see where the baselines are able to be set for portions of the graph that don't overlap. Which is where I think the request for the 'raw' data was coming from - show the crr/watts/elephant fart equivalents/whatever, just in raw, not the delta against a baseline that would appear to be somewhat contrived / synthesized/extrapolated.

In the first chart, "delta" is increasing as PSI is increasing (red line). I interpret this as "more watts are used" as the PSI increases.

In the second chart it's flat.

I always believed that until you hit the breakpoint, CRR would decrease with PSI then at breakpoint would go up. If neither of these charts are doing that, then we are close to, or beyond breakpoint ?

If we are at breakpoint at 65PSI (first chart), then maybe road surface is quite rough ?

Maybe I am reading this all wrong or I don't understand (wouldn't be a first)

Hang on, too many charts and too many red lines ;-) This was the chart I was referring to.

Yes, but look at first chart (and my post just above)

if you look at only that instance in zipp's recent testing on which you have reliable data - 25mm tires on an 858 NSW - the optimal pressure is low. this argues for exactly what you're saying: that the road surface on zipp's rolling road must be course. but it isn't course.

so i fall back on 2 possible explanations: first, that there's something else in the rolling road. vibration that occurs in the whole testing apparatus, causing the rider to unweight, even just a little, but constantly, making the rolling road test as if the surface is coarser than it is. but this is a wild guess on my part. second, that i would bet that almost all of the data that you, tom, al, have is based on tubed systems. please correct me if i'm wrong. zipp's is tubeless. is there a different optimal pressure for the same tire on the same road, tube v tubeless? is the inner bead width of the rim on the testing you've done similar to the [old] zipp 858 NSW, realizing that that wheel is not that old (i think from memory it was debuted at the 2019 IM).

so, you're right in the data you're looking at, if i understand you correctly. what i write above is what's running around in my head as i try to square that circle. but...

the point i'm trying to make, perhaps poorly, is what do yo do with the data you do see? that regardless of road surface, regardless of pressure, the new wheel with the 28mm tires outperforms the old. consistently. by 4 or 5 watts per pair. i take [what i think is] your point, that if this delta only exists on rough, chip & seal pavement, does it exist in kona? 4 watts is a big gap to close. how smooth does a road need to get in order for the old wheel to be as fast as the new? that's the wager.

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Dan Empfield
aka Slowman

i don't know if this is helpful, but the red line as the baseline is the paradigm used for the wind tunnel test data that zipp offered.

that's not the paradigm for the rolling resistance tests. if you look at the red line on the Crr chart for the 858 that red line is, well, "unstraight." what i pointed out in my article, and what marcag also mentions if i understand him right, is that line should *not* be straight in the Crr chart for the 808. as the pressure goes up and down that line should change. but it doesn't.

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Dan Empfield
aka Slowman

Agreed


I think we are converging :-)

If we saw the chart on a smooth road would there still be 4 watts at 110-110 PSI ? Or would it be 2 ?

Then if we had the aero penalty for the 28 tire would that be 2w there ?

there are too many things wrong with this data to have been generated for marketing purposes. as marcag and i have been discussing, the ideal pressures are too low during the 858 Crr test. the Crr doesn't change enough when pressures change during the 808 test. this is not the set of graphs you publish if what you want is to produce a marketing buzz.

i traveled back to indy, spent some time there, looked at their field testing, talked to their engineers, toured about every square foot of the factory, and maybe i'm fooled. maybe there's some 3D judo going on here and they intentionally through a curve ball by producing imperfect graphs in order to convince me that it wasn't marketing hype when in fact it was. but you have to be kind of a conspiracy theorist to think so.

why are there no error bars? because it's not a white paper. it's not intended for peer review. in which case, you might say, don't publish anything at all. then zipp would be criticized here, as manufacturers always are, when they launch a product without accompanying data.

by the way, off topic, but i've always wondered, perhaps everybody knows this but me, sorry if that's the case, but are you part of the hugi family? that hugi family?

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Dan Empfield
aka Slowman

for sure, if 110psi was the best pressure we'd have a very different outcome. but in that case - on that surface - perhaps 25mm might be too wide.

this is one reason why i have contended - to the consternation of several of our partners who help keep the lights on - that hookless is a 28mm tire phenomenon. and up. 28mm the minimum tire width. once you go hookless you wed yourself to the idea that it's at least 28mm you'll be riding. otherwise, the pressures are too high. you can't ride hookless beyond 5 bar. so, what road is that? to circle back to your point. is hookless and 28mm kona? or paris roubaix?

in point of fact, paris roubaix is 30mm or 32mm. tubeless. that's what the pro peloton rides right now. off topic, but pidcock did that descent, unless i misremember, on a new dura ace wheelset, tubeless, inner bead width of 22.4mm. when i read what was written about that descent it was assumed that he rode a 25mm tire, but i think that's a big claim to make. if i had $5 i'd take that bet and wager he was on 28mm.

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Dan Empfield
aka Slowman

  

On the aero side of things, I found what you wrote interesting

"However, as I read the notes on the test the one notable item is that 25mm tires were used throughout in the wind tunnel tests. (Not in rolling resistance, but wind tunnel.) I don’t have any wind data using a 28mm tire on either of these new wheels. While it would have made some sense to test this wheel with a 28mm tire, Zipp chose the 25mm size – in fact they used Zipp Tangente tires for their aero testing – because of all the historical data they have in the tunnel that used this tire."

I had a flash back to this



I wonder if we have hit the peak of aero on wheels

That's one way to look at it. But I'd argue Zipp would phrase it slightly differently as finally looking at wheels as a system optimization problem instead of just an aero optimization problem.

I was surprised with this forum's past wind tunnel test fetishization, this recent testing wasn't covered here (afaik). Which at least indicates the one maxim that if you don't want to agonize over which wheelset to buy, just buy some HEDs, as they've finished 2nd-3rd in about every wind tunnel test ever, as far as I can remember. The DT Swiss wheels were an interesting outlier, though.

Though I agree this set of data by Zipp is perplexing, and raises more questions than are answered.

Hoo boy...I go out for a ride on a Sunday morning and all confusion breaks out... ;-)

So...all this talk about "what do these charts even mean?" is ALL because of the data presentation. That is, the use of the "delta" charts with no clue as to what the reference curve looks like, and with poor explanation. Is the one curve flat because that's the delta to itself? OK, so what does the actual curve look like. THIS is why I said it was a "dog's breakfast" trying to make heads or tails of what is actually being presented.

In addition, being able to discern power values on their "rolling road" to within 1W...I'm highly skeptical. It's not that I don't' think they're good engineers, it's that I know how difficult it is to get that kind of precision with simple roller tests. Their "rolling road" is just going to ADD uncertainty, not to mention that the flat surface doesn't take advantage of the "amplification" effect of rollers in determining tire hysteresis properties. Show the setup and why we can have confidence in the results.

And then they say the aero data is with a 25mm tire (for comparison sake to past data) but then don't also show what it is with the 28? I'm sorry...that's just not kosher...especially if they say they don't show the Crr data on the older wheels with the wider tires. Sure, it was "optimized" around the 25mm, but THAT is an aero effect, not Crr. It reads like they're cherry picking the results.

I really don't know what to say. Zipp data used to be quite transparent (relatively speaking, for the industry), but this whole thing just doesn't make sense. Looks like I'm not the only one to feel that way, judging by this thread...

Here's an important thing to remember about the chart above from Silca...it shows BOTH roller data AND field test data...and, for similar surfaces, they MATCH up until the breakpoint pressure. That shows that roller testing is a GOOD proxy for on road Crr for most typical roads, and not only is a "quick and easy" way to determine this, but also accurate. Here's the thing...if Zipp's rolling road data isn't matching either roller testing trends OR field test data (as you mentioned, they said they weren't happy with their results and haven't shown them), then maybe that says something more about the applicability of their treadmill? It IS the outlier apparently...

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http://bikeblather.blogspot.com/

Hmmm...maybe I'm missing something...the y-axis is labeled as Crr, and the values are of a range I'd expect for the data. Please educate me on what's incorrect. Genuinely curious.

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http://bikeblather.blogspot.com/

The answer to that is demonstrably "no" (when using a latex tube). Asked and answered, your honor. Plenty of data to confirm this.


The point I'm trying to make, perhaps poorly, is based on the data presented, I can't make ANYTHING with the data I see. And that's because, IMO, the data have been poorly presented.

How about THIS wager, how much slower aerodynamically does that new wheel get with the 28 on there, instead of the 25 in the data presented? Is it 4-5W? More? This is a big reason I endeavored to present a combined aero+Crr estimate when I showed the results from the "Win Tunnel Playtime" on my blog.

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http://bikeblather.blogspot.com/

Exactly...if you are coming up with data that's supposedly "different" than what has been seen previously, don't change the format of the data presentation. Especially if you don't show the baseline curve that you're normalizing to on a "delta" plot...it all just looks like something is trying to be hidden IMO.

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http://bikeblather.blogspot.com/

I had to look twice, but notice the y axis. Notice .002, .004, .006 then .007, .009....

Sorry. My fault :-)

Aaah...interesting...I wonder if that's ever been pointed out to Josh.

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http://bikeblather.blogspot.com/

Nope...you weren't the only one confused by those plots and their presentation. Not our fault...

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http://bikeblather.blogspot.com/

 
do you think there is the possibility of a relatively common range of road surfaces where this system will not be optimal due to it's inability to support higher tire pressure and no aero advantage due to it's width ?

To be honest...I really don't know what to make of any of it, one way or the other ¯\_(ツ)_/¯

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http://bikeblather.blogspot.com/

going back to simple matters for a moment, can i get clarification on the external width please.
the cyclingtips article says "23mm internal and 27mm external rim widths" and i've seen those same specs elsewhere on both these wheels and other recent model zipps. zipp don't seem to give external width on their website and i don't think i've seen external width specs anywhere else.

30mm is still marginal on rule of 105 for a tyre likely to measure 29mm+ inflated but its a damn sight better than 27mm

I agree with the general sentiment that the charts are a bit inscrutable.

Like, what is "delta power"? When there's no apparent zero-delta data covering the entire x-axis, or reference to what "zero" refers to, what is it a "delta" from? Is the whole thing actually just an absolute chart where the y-axis has a constant bias, or is it referenced to some other data set?

I would love it if you could try to make a match between Zipp and I! I would be happy to fly out to Indianapolis if that happens! I am also very curious how they're testing/modeling their wheels, as they are showing large rolling resistance

Is hypergeek a Zipp representative here on slowtwitch? Yes I am referring to power spectral density measurements. I imagine they have them as it's more or less required to compare vibrations of two bodies especially to validate that one test is simulating real world vibrations. That being said I can understand why they created the rolling road, in order to shorten the testing loop on rolling resistance/width/pressure changes. But echoing what TomA has said, I don't believe they can achieve 1 or even 2 watt resolution/repeatability without ten or hundreds of runs due to the fact that there is a floppy human on top plus there's still steering involved.

Also to provide another point of info, on Bigham's hour record attempt they lowered the pressure from the traditional ~200 psi to ~130 psi and round rolling resistance reductions even on the very smooth track surface even with centripetal forces providing additional load on the tires. So I am starting to believe that quite low pressures are the way to go on road.

Interesting...and it matches some data shared with me a long time ago about some informal tests done at the Carson, CA velodrome. Do you happen to know what the track surface is at the velodrome Bigham used? The speculation at the time was that if tire pressures are too high (i.e. 200 psi), then the compliance of the track itself starts coming into play.

I did some tests around the local high school running track one time, which has a "compliant surface"...it had a quite dramatic effect on the measured Crr. Additionally, I know that Josh has seen in his Silca testing differences in Crr for freshly laid asphalt vs. the same surface that has "cured" for a few months. In other words, surface compliance matters ;-)

Of course, surface compliance is basically why MTB tests usually result in: "the fastest pressure is the lowest you can run without pinch flatting" :-)

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http://bikeblather.blogspot.com/

you're right. i misreported. at least on the 808 firecrest. i made an assumption based on everyone's wider internals, and failed to remember the big differences between the 404 and the 353 NSW. here are some examples:





above are a couple of CADEX wheels i have on road bikes of mine right now.



above is the ENVE 6.7



even the newer wheels that aren't hookless are fat on the outer width. this is the new bontrager 75 and i don't even know that it's 32+mm. it's lenticular (to my caliper) and my caliper isn't long enough to (necessarily) catch the widest part of the rim.



here above is the 353 NSW. (i love this wheel.) this is probably the closest analog to the 858 NSW, in terms of construction, but i don't have that 858 NSW and so didn't have the chance to measure it.

i believe i've met my own site's max for number of attachments, so i'll post about the 404 and the 808 firecrest in the next post.

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Dan Empfield
aka Slowman

following on my post just above, here's the 404 firecrest released maybe 2 years ago? i think?



this is kind of an outlier on wheels like this, with fat inner bead widths and especially (but not exclusively) hookless. this should've given me a clue about the 808 firecrest just launched.



here's the 808 firecrest. i suspect - but don't know for sure, because i don't have it - the 858 NSW is fatter. but i don't know. cyclingtips was right, at least about the 808.

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Dan Empfield
aka Slowman

delta force, delta drag, delta power. i don't know why you don't know what this means, unless i didn't explain it well enough in the article (which might be the case). it's the difference between the performance of prior wheels zipp made and these new wheels they replace. as i understand it, you're asking for the underlying data from the prior wheels, that are a few years old. maybe that's available, when those wheels were launched. but that's another set of data; another topic; of scant relevance to what zipp is trying to show here.

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Dan Empfield
aka Slowman

what's confusing you? perhaps i can help. i have questions, for sure. but none of these charts have me confused.

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Dan Empfield
aka Slowman

of all the posts i awoke to this morning, yours is the most interesting. here is what i took josh's anecdote to mean (when i first read it, and now). josh was giving an example of what you can predict when the rule of 105 is disobeyed. in the case of the wheel designed around a 28mm tire, what josh was saying (i think) is that this wheel disobeyed the rule of 105 with a 28mm tire on it, and if you replace it with a 25mm tire the rule is obeyed so the wheel will test (at least marginally) better.

that said, there's a lot about this new wheel (whatever it is) that may still make the new wheel faster, and if you look at zipp's data here on Crr you can see why. just above i've posted some pics of wheel widths, and what is typical among these new wheels - hooked and hookless - are external rim widths of 30.5mm to 32mm (the 808 firecrest notwithstanding). this makes these wheels good candidates for rule of 105 obedience with 28mm tires installed (which typically measure about 29mm inflated on these wheels).

as to your question of whether the wheels are capable of improvement, sure. but that's the wrong question. the game changer over the last 5 or so years is disc brakes. when you decouple rim braking from the whole system you get to make changes to the whole system not possible. the flashiest examples, maybe, are the bikes with really wide stays and blades that seek to overcome interference drag. the CADEX, the KU, the Shiv Disc. once you look at systems then you can imagine wheel design that works best in a system like that which, i've always felt, calls for (among other things) narrow hub flanges. which is exactlyl what i had steve hed build for me back in the mid 1990s, when i had kinesis build me a fork with wider blades. what we did at QR back then didn't come close to the designs i name above, but what we did worked pretty well, i think, based on what we had to work with.

what will change is the approach. we're making motorcycles now. motorcycles without engines. that requires new thinking. the whole idea of taking a wheel to the wind tunnel will vanish.

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Dan Empfield
aka Slowman

It was a wooden track. He did testing at Grenchen Switzerland. I'm not familiar with the track, so I can't say if it's more or less compliant than other wooden tracks.


I totally agree that a significantly softer surface would create higher rolling resistance. It's basic tribology. With this recent realization. I'm much more willing to accept lower pressures being better. But I'm a bit less convinced on wider tires at same casing tension/equivalent pressure without seeing the rolling road setup. However the easy part is knowing lower is better. The hard part is figuring out how much lower.


I'm also super curious what layup tricks Zipp is playing to try and get the claimed very large hysteresis gains between the 404/454.

You (and I) wondered why they didn't provide 28mm aero data. I wondered if the reason is 28 is less aero than 25 or 26 as Josh found.

I have no doubt there is still room for system improvement. I do believe in opportunity with fork width and fork/wheel interaction.

I also remember a podcast with one of the Look engineers who said wide was an opportunity for tri spokes to make a comeback. That may be interesting

I am chomping at the bit to get a new bike but have to admit I would not know what to but if I had to tomorrow morning. At this point I'd probably go Hed-hooked.

I just need to find a person that has these wheels. I have all I need to prove/disprove their performance on road. I just don't have the wheels and I'm not paying that price to find out :-)

maybe you're right. but i think it's more likely that it's what they said it was: you'll note that the entire round of testing, and what they displayed, had a common theme: testing the current wheels against their prior wheels, and showing you and me the difference in performance between them. they choose a testing paradigm for the wind tunnel that parallels everything they've done for years. but in my opinion there was a blind spot in their thinking. what changed this year is the move to 28mm as the optimized width.

i'll just clue you in on something i didn't write previously because i didn't think it was relevant, but maybe it is. when the zipp folks first came out with their new hookless wheels, and that was back in 2019 or so, they were prickly every time i said that i thought this was brilliant tech, but best for 28mm. they were really insistent that i understood that these wheels were usable with 25mm tires, with the exception of the 303 Firecrest and the 353 NSW. fast forward to today, i don't write for zipp, i don't speak for zipp, but i think i sense a change in posture. as the Crr testing has proven (to their satisfaction) the utility of this wider tire, i sense they're all in on 28mm now.

i write this because i wonder when the wind tunnel testing was done, and when the Crr testing was done. i wonder where along the progression in their thinking this change occurred (if there was a change). if the wind tunnel testing was done quite a while ago i could see why they might've just stuck with the 25mm tire for continuity purposes. if zipp were to take these wheels to the tunnel today, they might test them with 28mm tires. but i'm just guessing.

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Dan Empfield
aka Slowman

I guess I wasn't clear enough above. The most confusing (or, perhaps, a better term would be "least enlightening") graphs are the delta plots, with no explanation of the baseline at each data point. It would be REALLY easy for them to show the baseline curve, and the rest of the curves for that matter, and THEN show the delta plot. The delta plot is really just a refinement of the data presentation. Without the original data, it's tough to put into context...especially if it shows (as these plots seem to indicate) unexpected behavior based on previous data/knowledge/modeling.

edit to add: Secondly, is the lack of details and transparency in the rolling road setup and protocol. IF they're using that data to point to these products somehow behaving differently than others do, then I think additional scrutiny of that methodology is warranted. Especially if the data from that methodology somehow doesn't match well with previously established methods.

It just seems like a bunch of hand waving right now...reminds me of the "old days" of wheel claims, actually ("It's faster...trust us!")

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http://bikeblather.blogspot.com/

i don't suffer from the lack of that underlying data you ask for. i don't feel i need that data to understand what zipp is trying to express with these graphs. however, i respect your view and honor your background in this, so i don't mean to minimize your desire to see the data not supplied.

as to the rolling road, i might misremember but i think this is the second time "lack of transparency" has been used as a descriptor in this thread and, again, unless i misremember you've been the user both times. to me, this connotes and intentional act to withhold data. i gave you the protocol. rider aboard, 85 kilos rider + bike, roll up to speed for 30sec, the test runs for 90sec, rider dismounts. there were 96 total runs. there were 24 set ups tested (a given wheel with a given tire width at a given pressure). to me, dividing 96 by 24, that means they performed 4 runs per set up. zipp says the rolling road is a "standard" to use their word road surface, analogous to their eagle creek field testing circuit.

if what you want is a picture of the rolling road, i'm pretty sure one could be provided. do you want the speed of the rolling road? the speed of each test? i'll ask. but i don't see the lack of transparency you see. perhaps you could tell me what it is you don't see and i'll see if i can get it for you. just, if you're going to ask for data beyond that which is typically given by drum testers, such as you or al or BRR, then i have to cry foul. sauce for the goose and all that.

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Dan Empfield
aka Slowman

Check me if I'm wrong...but doesn't the "rule of 105%" apply to the WIDEST section of the rim, which is not necessarily right at the rim edge (i.e. what we used to call the "brake track")? Just thought I'd point that out for future measurements you take.

Also, don't forget that this ROT is referring to the point at which aero degrades "too far", and not so much the "optimum" ratio for aerodynamics. THAT is why an 25mm tire on these new wheels may be still significantly faster than if they have 28mm tires on them. It's OK for Zipp to test the new wheels with the 25mm tire "for consistency of comparison sake" to older data, but they really need to show what happens when it has the 28mm tire on there, since that's how it's going to be used (per their recommendations). You KNOW they have that data (if they didn't take that data, that brings up some big questions), so not showing it implies there's something there they don't want the consumers to see.

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http://bikeblather.blogspot.com/

you're right. my caliper arms are only so long. zipp makes it a little easier, because it's kind of off the toroidal train. where it's harder is when the rim is toroidal and when i asked bontrager if that rim is, they just haven't replied. but it's wider as you get farther from (what used to be) the brake track, and the widest i can measure with my calipers is 32mm and change. as you'll see in my post above with attached pics. i think with both zipp, ENVE and CADEX i'm getting a pretty reliable outside width.

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Dan Empfield
aka Slowman

Correct me if I’m wrong but the pressure drop was because instead of the 200+psi max of tubular tires, conti clinchers have a much lower max pressure (109psi I believe) so for Dan to be running the systems around 130 psi, 21 psi over the recommendation, that says a lot to me.

“The velodrome itself is 250 m (270 yd) meters long, made of Siberian spruce wood and is applied according to the UCI standards.”

Yes, I recall your description of the number of runs above...but, what's missing is some sort of description of the equipment used and how the method was "validated". Here's a short list of things off the top of my head that could be helpful:

• How was power measured? What's the accuracy and precision of the equipment? Is the power measurement inclusive of drivetrain losses? If not, how is that handled (i.e. is gear selection fixed? Something else?)
• How well does the method detect a "known" change in Crr (i.e. the "Tom Compton Challenge"), such as what happens when mass is added to the setup? Does the Crr change in the expected way? What's the smallest change detectable reliably?
• What's the surface roughness which the test setup is attempting to duplicate? How well does it mimic that "specification"? (This is where the PSD data referenced earlier would come in handy to evaluate how well the test setup duplicates the intended surface).
• Was the same rider and bike used for all tests? If not, how do we know their "damping" is similar (for pressures above breakpoint)?
• How does the data compare (numerically) to what is found using simple roller tests and field tests? If it differs, then how...and what are the possible sources of the differences?
• How tightly is ambient temperature controlled in the test location? If it's not, is the temperature compensated for in the results (due to the somewhat important temperature effects of Crr)?

I believe all of the above have been reported and investigated for both roller and field test methodologies. I understand the desire of the Zipp Engineers to use their "rolling road" as a proxy for field testing. It eliminates translational aero drag AND puts to rest any arguments against validity from people who don't understand the "equivalence" of rollers to flat surfaces...in other words, it's slightly more "real world" for some consumers. That said, it is going to have it's own quirks, and being able to understand those quirks is the way we can put their results in context. It's just like understanding that roller testing (when done carefully) is extremely good for evaluating tire hysteresis properties (and thus Crr) for pressures below the "breakpoint" of the system. Again, it's all about context.

edit: I thought of one more (very important IMHO) piece of info on the treadmill:

• What is the thickness and material of the moving belt, and how is it supported? How does that compare to an actual road surface in terms of compliance and damping?

As mentioned above with the Bigham track discussion, surface compliance matters in these sorts of things. If the "rolling road" adds compliance and damping into the system, the results can be different than "real world".

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http://bikeblather.blogspot.com/

I think the issue is exactly that there isn't enough transparency with this testing. All the claims they are trying to make are that their rolling road is a good simulation of real world with no data to back it up or even details on what type of road surface is being simulated especially as road surfaces are super variable.

Along the same note people even don't believe wind tunnel test and that's very well established with decades of validation and everyone is well aware of the assumptions and limitations involved in wind tunnel testing. Asking other engineers to believe an entirely novel setup without any validation or even pictures/description of the setup shown to them is going to be an uphill struggle. Listing out the number of runs, rider weights, how long they road for before testing isn't really useful in my opinion. That's small peanuts and is taken as a given that those things are controlled. The real important questions are as mentioned before behind the actual rolling road setup. As if that doens't simulate road riding or the representative surfaces I or others ride on, the results won't be meaningful no matter how much control there is of test setup. I want to believe that it simulates actual roads well, but having experience building test apparatus to simulate real life events, I know how difficult that is.

This is part of the reason the track "data point" I mentioned is so impactful to me. We know the test apratrus is good (the track), the main source of error (the rider) likely well controlled due to rider skill, and the test setup is likely good. Plus this is on very smooth surfaces which is a regime with sparse low pressure data. If much lower pressures are good on smooth surfaces, then it's a given that they will be good on rougher surfaces. Instead most of the testing thus far has been on quite rough surfaces which makes me believe that the benefits aren't there on smoother surfaces, and that this testing (if it is an accurate simulation of road riding) represents rougher surfaces to show a larger benefit.

Echoing what Tom said I'd like to know the following about the rolling road testing and will likely have more follow on questions once I see a diagram of the rolling road setup and a picture/cross-section of the surface. However I'll assume the Zipp engineers have the normal environmental, sensor setup, and sample preparation variables well under control.

• Do you have a diagram of the surface of the rolling road setup?
• How is each section/plank of the rolling road supported when rotating through the treadmill/how large is each section?
• What does the transition between sections/planks of the rolling road look like?
• Do you see periodic events correlating to the load/unloading of a new section/plank or the transition between sections?
• How is the micro/macrotexture on each section/plank of the rolling road applied?
• What surfaces are you trying to simulate?
• Do you have PSD's between the rolling road and the surfaces you are trying to simulate?

I know what it means philosophically. I don't know how the charts are trying to represent it.

For instance, if the "delta" is the difference from the old wheel, then why does the first chart have values for the old wheel that aren't at zero on the y-axis? Shouldn't it be at zero difference from itself? The second chart does have the old wheel at zero, does this mean that the first chart is referenced to the 808 data? But even then, the 808 data doesn't cover the entire portion of the x-axis used by the other wheels, so what is the new-wheel data at those pressures in reference to?


I'm asking how the charts show the change from that underlying data to the new wheels.

i'm not going to bother zipp with this. i'm just going to answer it and if i'm wrong zipp can correct me when they read it.

the power was measured using a quarq power meter on the bike of the sole person on the only bike used for all 96 runs. accuracy? it's the accuracy of a quarq power meter. there's at least a half-dozen ways i can think of, off top of my head, for dropping the 90-second captures into data analysis. gear selection was fixed, because speed was constant for all runs. drivetrain losses are not material to because the actual power is not relevant (who cares how much power it takes a given rider to ride his bike at 20mph on a rolling road?) the only thing that's relevant is the delta in power between the set-ups.

the surface roughness has been asked and answered at least 3 times in this thread. what is relevant, that i don't know - also mentioned at some length in this thread - is the vibration in the entire system which could - just using my intuition - add to the "roughness" of the road. i think this is worth investigating.

was the same rider used for all the tests? yes. as i pointed out in posts twice above. how does the data differ from field tests? the data, per zipp, syncs well with their fields tests, which they perform at eagle creek park, on a circuit, and which i stated at least twice, both in this thread and i believe in the article on the front page.

how tightly is the ambient temp controlled in the test location? again, just my intuition, but in the 25,000 square foot factory where i built my bikes i hit on the idea of setting the thermostat on my HVAC. this has not been mentioned, explicitly, so for those who have this question: zipp's rolling road is inside its building, not outside.

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Dan Empfield
aka Slowman

no. i don't have a diagram. it was my assumption that the rolling road zipp owns is the same that was manufactured by the folks who make the inside ride rollers. it's a big, expensive, manufactured product. it's a known product, though i haven't seen it sold in quite a few years. if having a picture of the rolling road would help you, i'm happy to ask zipp for one. but is this going to help you? because, if you've already made up your mind i'm not going to waste my time. please advise.

as with tom's questions - which i answered - i'll answer your question again even though i've answered it several times here in this thread. the "surface" zipp is "trying to simulate" is what zipp calls "standard" road. what you would see on a typical asphalt, average asphalt road, and zipp considers the queen k hwy on the big island "standard."

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Dan Empfield
aka Slowman

the aero testing charts are as you say they should be. the "old" wheel sits at zero in the Y axis. there is 100 percent consistency on how all the charts are presented on data gained from the wind tunnel.

the Crr charts are presented differently. i am not bothered by the difference in how these charts are presented. i understand why the Y axis is not zeroed. i don't find this cumbersome. i don't find this data hard to read or parse. i don't know what to tell you.

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Dan Empfield
aka Slowman

Is this in the running for the Nerdiest Thread in ST History?

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Favorite Gear: Dimond | Cadex | Desoto Sport | Hoka One One

jcbesse wrote:

I would be quite easy for them to just show a picture of the 'rolling road' you'd think?

The do on their website

https://www.sram.com/en/life/stories/life-on-the-rollingroad


https://www.sram.com/en/zipp/campaigns/total-system-efficiency

OK then...and myself having had quite a long term experience with Quarq PMs (I was a beta tester for them at one time, after all), I also know that the data quality is only as good as the care is taken during their use. It's imperative that the torque slope is checked (and adjusted, if possible) and to "zero early, and zero often" ;-)



...unless drivetrain losses are changing across the runs, that is. Are we SURE gear selection was the same? You appear to assume it was because the speed was fixed, but is that the case? I don't know...there's no data showing one way or the other.

Additionally, how "fixed" was the speed, i.e. what's the +/- on the speed setting? Did they calculate Crr for each run (which would cancel out speed and power variation), or just compare watts? In other words, if you want to compare "delta power", you need to compare on an apples to apples basis. For roller testing, I don't try to tightly control the speed (in fact, I try to control cadence for a given gear combo), but then I use the speed, power, wheel load, and ambient temperature to calculate the equivalent Crr on the flat at 20C ambient. THAT is what gets compared, not the raw test values. That's the thing, if you have a good model, you don't necessarily need to control all the variables, just record their values and use the model.



Right...and it's been asked for good reason. You say they claim it's comparable...we're all asking "how comparable?" My intuition is telling me that based on the results, there may be some additional compliance and/or damping introduced in the running surface that's different than typical pavement. That's one way that continually lower pressures would lead to lower power requirements on surfaces consistent with typical pavement roughness.




Right...they say it "syncs well", and yet you said they aren't willing to reveal that data for some reason. It really should be the "golden data set", no?




Yeah...see, that's the thing...even HVAC systems can have quite a wide range (relatively speaking) of temperature swings throughout a day. I often run long-term thermal tests at my office and detect local temperature swings in particular areas of the office of a few degrees C. That's plenty of temperature change to affect Crr results, especially if one is looking to resolve them to within 1W (as their plots imply). So, if they aren't monitoring the temperature, and/or compensating for the temperature effects on Crr...well, that throws up some red flags to me.

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http://bikeblather.blogspot.com/

Quarq PM. it is my assumption that SRAM understands best practices using that PM. same gear throughout. you're right. i don't know for dead sure. but i'd be shocked if this were not the case. same speed throughout. changing the speed on the rolling road would be no different than changing wind speed in the wind tunnel. do we ask those performing wind tunnel tests that question?

the road surface. i agree, the question is asked with good reason. it's a very fair question. no quarrel there. i just would like to know that at some point i won't have to answer this again.

as to the field testing data. they're not ready to publish that yet. they are comfortable, as of now, that the field testing they've done syncs with the rolling road tests. but they're not ready to publish. it is my guess that field testing will become the norm for this brand. but let me tell you my takeaway. the fact that they say the field testing syncs means that there is some degree of validation of their rolling road testing. the fact that they aren't ready to publish their field testing means there's an asterisk on that "sync" statement of theirs. it means we can only attach minimal to moderate faith in that. where you are on minimal to moderate, i wouldn't quarrel with your characterization. once they publish, my faith grows. until they publish, my faith is counterbalanced with doubt. as all faith is. (that's the nature of faith.)

HVAC. i guess i'd need to see how the differences between 71°f air temp and 73.5°f air temp impact the Crr results. i'm not smart enough to know.

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Dan Empfield
aka Slowman

A really cool triathlon site has the answer to EVERYTHING

https://forum.slowtwitch.com/...D_P7791676/#p7791676

I am anxious to see this because so far, the "red lines" don't align to other field testing data, including the results Zipped published from CDA/CRR testing in Kona.

In your article you say

The 25mm tire on that wheel performed better at 65psi than at 75psi or 85psi. This will not sit well with those who live and die by drum testing results, which show exactly the opposite. How does one square this circle? Maybe Zipp’s data is wrong. But we also know that drum testing has a flaw, which is, it cannot tell you when its reliable data becomes unreliable, that is, at which pressure system vibration overwhelms the value of high pressure.

Their own data collected in Kona goes against this for 25mm tires.
Josh's field testing goes against this.
Members on this forum show road data that goes against this.

I have no doubt there is an explanation, I just want to know what it is

Thanks for that...those links led me to David Morse's "white paper" on the subject, that answers a few of the questions asked above (including PSD plots): https://www.sram.com/...s/tse-explained2.pdf

The constantly lessening power requirements with reducing pressure, for even a 28c tire, still is hard for me to fathom...unless the road surface roughness is REALLY bad, and/or the surface has additional compliance/damping than typical pavement...



...or, unless it means that their wider internal widths widen the measured tire widths so far that even 30 psi is above the breakpoint pressure for those tires, speed, and road conditions? I'm not sure if that's exactly a good thing, if that's the case...for a variety of reasons.

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http://bikeblather.blogspot.com/

  
Here is their data for good roads (Kona). Green 28mm, red 25mm, blue 23mm

lewis, in that article, was the test rider for all these Crr tests on the new 808/858.

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Dan Empfield
aka Slowman

Well...in the white paper I linked to just above, they state it's run at speeds "up to 20mph", so that's not exactly clear. But again, it doesn't matter if they control the speed tightly IF they measure the speed and combine it with the power and mass to calculate Crr. If they don't do that, then yes, the need to control it tightly, since higher speeds require higher power at the same Crr.


If the wind tunnel reports in drag force, but they don't say at what speed, then we ABSOLUTELY ask for the wind speed. The drag force value has no context. However, if they report in CdA, then test wind speed isn't as necessary (just want to make sure it's in a representative Re number regime). It's the same with my description of watts vs. Crr above.

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http://bikeblather.blogspot.com/

we ask for wind speed because we can translate drag to time or power. we don't ask someone performing a comparative wind tunnel test if they raised or lowered the speed while testing different bikes or wheels. at least i don't. that would be kind of insulting i think. but, if you want me to ask i'll ask.

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Dan Empfield
aka Slowman

Yeah...that's more of what would be expected, at least for general trends and the ranges of minimum Crr.

Even so, the shapes of those highly smoothed curves aren't exactly what I would expect based on previous data and theory.

edit: not to mention that 40kph is significantly faster than the 20 mph max (32.2kph) reported for the rolling road setup. All things being equal, greater speed would tend to shift breakpoint pressure to the left, not right. In other words, if the treadmill truly represents pavement, then the data should look similar to that plot, but with the power minimums shifted to slightly higher pressures.

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http://bikeblather.blogspot.com/

So...a quick calc using the stipulated temp range above (which is only ~1.4C range, or ~1/2 of what I've seen in HVAC controlled office environments), and mass and speed claimed (85kg, 20mph), shows that temperature difference can cause the Crr results to vary by up ~0.5W (with a reasonably assumed Crr of .0030 for the application).

That doesn't seem like much...until you look at charts showing 1W differences, that is...and understand there are other sources of error contributing as well ;-)

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http://bikeblather.blogspot.com/

Found another longer video with more details on the Rolling Road.




It looks like they're able to put different "belts" on the treadmill in an attempt to simulate different road surfaces. The ones shown in the videos on the SRAM website have some pretty nasty bumps in them (like riding in a rumble strip or on washboard dirt roads). Even if those were removed, The texture of the normal slats looks like they would provides a fairly "rough" surface, like riding on a boardwalk vs smooth asphalt. It's possible the plot you showed is from one of those really rough belts (maybe since they're showing the gravel king comparison?).

FWIW, there're 4 tris in Eagle Creek every year. The road surface inside the park is pretty good for for Indiana and it would make a good place for VE/Chung testing (lots of potential loops w low car traffic). It's been a couple of years since I've raced it, but I don't remember any chip seal or the thunk-thunk of expansion cracking, but at the same time, it wasn't freshly paved asphalt either. It's what I'd call "normal roads" like Zipp and Dan have been saying they're trying to represent. The data to show that the Rolling Road is actually replicating that though.......

when i was at zipp a couple of months ago i had it on my schedule to see the rolling road. but a covid incident forestalled that plan. as i see it now, from this video, it's a much more sophisticated device than i thought. to cajer's point on a PSD plot, i wonder what's built into the software analysis zipp has when translating video from its camera. 200,000 frames per second.

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Dan Empfield
aka Slowman

Hmmm...seeing as the "planks" appear to be some type of polymer (Delrin, or Nylon?) material, and in the slow-speed video in the second link shows them deflecting somewhat, I think my suspicion of additional compliance/damping in their system is what is making their plots look the way they do. Unfortunately, that surface doesn't have the same properties as pavement.

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http://bikeblather.blogspot.com/

Something that’s been nagging at me, and just because you brought it up: reporting measurement error doesn’t seem to be in the kit-bag for engineers (perhaps I should say industry engineers?). Recalling the Zipp data in question here has 4 runs for each setup, so it’s possible to show this.

Put another way, to you point (and BergHugi above?) – is all this just hair splitting if the test sensitivity is a relevant amount less than the size of the error? Dan argued above that Zipp (and other companies?) don’t show error bars because this is not up for peer review. That seems like strawman rationale if we’re seriously interested in teasing this apart.

Looking at pictures each plank appears to be in the range of 2-4 inches wide. So if they are running the system at 20 mph and there is additional damping (as it appears from the data), we would expect to see some features around 90/180 Hz in the PSDs. But they only show them up to 50 hz.

Looking at the PSD's themselves they appear to be quite noisy, either the runs weren't long enough/not enough runs were used or they used too large of a window. As is it's hard to make a comparison between the real road/rolling road.

However I imagine the rolling road is extremely good for tuning mountain biking or gravel suspension as the only features as the features they are looking at are the bumps they add in.



That's likely because we are both looking at small deltas and the bike industry doesn't have that much money for development meaning they aren't able to do allot of runs to reduce errors. So it's best for them not to report them.

you industry experts crack me up!

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Dan Empfield
aka Slowman

 
This is probably a silly question, but hey.....

Why doesn't ST set up a road test with a well accepted method (like Chung testing) to validate some of the data/claims made by the manufacturers ?

BTW, the TSE paper is actually really interesting. Not too many manufacturers release this amount of info. I still believe the P5 whitepaper was the reference of what a great report could/should be.

i think you're on the right track, and i would be game. we've helped facilitate this kind of thing a number of times before. i do think there's a built-in bias against any kind of tire testing that's not drum testing, because a lot of people have invested time, money and reputations in drum testing and there's a lot of data around it that creates a momentum for drum testing to continue as the preeminent tech. as we see here, a number of people have formed opinions about granular specs of the rolling road (e.g., road surface characteristics) on the basis of a youtube video. so, if you want to use anything like rolldown, get ready to get stabbed.

what i like is your knowledge and your eagerness. what i would counsel is that you perhaps take some time to actually consider whether this pretty sophisticated machinery is a step up from rolldown or circuit testing using chung or similar. i'm in agreement that zipp's characterization of the road surface might be right and it might be not. if it's not, the road surface is more likely to mimic a less smooth actual road. but there only way to know is to test it and see.

but you would probably have to reconsider making statements challenging the integrity of the company if you think you might like to be part of a team that ferrets this out. in my 35 or so years in this industry i have very rarely (or never) come across top tier manufacturers who hide stuff or make stuff up when they present data on their new product. sometimes the data doesn't withstand scrutiny. but that's bad test protocol rather than subterfuge.

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Dan Empfield
aka Slowman

where did I ever challenge the integrity of the company ?

sorry! wrong user! muddled brain. please accept my apology. you're gold.

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Dan Empfield
aka Slowman

No problem. Thanks

Yeah I'd like to see CRR and aero for both wheels with both tire sizes. Otherwise Zipp is assigning the RR gains that come from a larger tire to the new wheels but not for the old. What tire size they're "optimized" for is rather meaningless in this context. The old wheel might save the same 4W on RR with a 28mm tire.