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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blog

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 !!