Yeah...tires used can be important. Remember, the Flo wheels were designed around Conti GP4000SII tires (edit: 23C as I recall)

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http://bikeblather.blogspot.com/

Hahaha, I presume they didn't realise that the Shimano C50 and C60 are actually the exact same wheel with a different sticker on it?! At least their testing protocol appears robust on that basis...

LOL! I didn't know that! That's a surprising control 😂

Jim has stressed that tire choice is critical with the Enve 7.8 and that wheel needs a 25c tire. I think he had to pull out some tricks in order to get the 7.8/25c combo to work in a P5 IIRC. While not 100% clear, the test description seems to indicate a 23c tire was used with all wheels.

More than that, it seems they tested in a rider position described as "relaxed hoods." Without using aero bars to help lock in consistent position, this would seem to introduce additional error.

Then again, the C50/C60 data are impressive, unless... [Cue Larry David voice] it was an "accidental text on purpose"

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

The first-gen ones most definitely were not.

FLO initially recommended Michelin Pro 4 Comp tires which I bought. Then they tunnel-tested GP4000s tires which tested better. Anyone want to buy a Michelin Pro 4 Comp?

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Madison photographer Timothy Hughes | Instagram

who in the hell needs areo wheels to go 50kph on 583w???? let's get the numbers down to realistic values before making comparisons. I assume the rider had a small parachute attached

Think about the “meta” of the C50/C60 data though... are they banking on someone knowing it’s the same wheel so they say “hey, look at that, the same wheel tested the same, it must be repeatable.” Seems like a stretch. I spend an unhealthy amount of time on this stuff and I didn’t know that.

I’m genuinely curious about the 7.8. The idea of having a 25mm tire (likely 27 mm measured) is appealing especially if you were to run something like the Corsa Speed 5-10psi lower than normal.

The new Bontrager XXX wheels come in a "2", "4", and "6" version that are 28, 47, and 60 mm deep respectively. So there is no XXX version that is 50 mm deep. I would be curious to know exactly what wheels were tested because I was mildly looking at the XXX4. Still not convinced I want to go carbon braking surface but my old 404 aluminum clinchers are starting to act up. Interesting that they didn't test any of the HED wheels.

My reading of it was there were 2 phases of testing. The first phase was outdoors riding that was gathering data on yaw angles and transients. The second phase was wheel tests in a wind tunnel using the data gathered in phase one, with the main difference in this testing as compared to typical tests being the transient emphasis.

The results of phase 2 are then presented as a "distilled" single number prediction of an all-up drag number for a complete bike+rider system...at least that's the gist I'm getting. But, as I said, not totally clear...

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http://bikeblather.blogspot.com/

That’s my impression as well. It’s a shame more information wasn’t given on the protocol as the results are interesting and it seems like they came up with a higher yaw distribution than we’ve become accustomed to.

He confirmed in a comment that they're the XXX.

I suspect people didn't read the text closely and skipped to the charts, he says "The rim depths are split into classes to make it easier for comparison, they may not agree with the stated size from the supplier."


The Shimano C60 is also marked (50mm). Whether that means he tested them separately or not is a "who knows".

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The point is, ladies and gentleman, that speed, for lack of a better word, is good. Speed is right, Speed works. Speed clarifies, cuts through, and captures the essence of the evolutionary spirit.

I am not sure what can be learned from such incomplete data. Yaw angle is obviously a huge factor, which model 808 and 404? Which hubs? What fork were these on and at what blade width? What happened to Hed and Profile Design?
There are simply way too many unknowns to draw any conclusions.

Yeah it doesn't seem to be "comprehensive" without the Hed's (often the fastest).

On the XXX4, they actually brake pretty well - light years better than the old Aeolus', where you pretty much had to pray. Haven't ridden them in the rain though.

So I read this as a don't buy FLO...

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Washed up footy player turned Triathlete.

Certainly not a great showing here. That said, Flo has always been very transparent with their testing data and their wheels have tested fast elsewhere (TomA's data comes to mind). So I think we need significantly more information about how this test was set up.

Can't just be designed around a tire though... we need a tire and PSI and whether it has been a tire sitting and holding air for 3 weeks or brand new. ***partially in pink***

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Over and over and over again I've found the same results...if you don't test the 7.8 with a 25c tire, you haven't tested it properly. Tire choice and pressure is absolutely crucial to any wheel testing and, for that reason, it's practically impossible to conduct a test like this properly. If you try to make the testing "fair" by using the same tire and pressure for each wheel, you've likely produced near meaningless data. There are simply too many variables; it would take weeks to test all the different combinations. Then, of course, you'll need to repeat those results to give them value. Fun!

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Jim Manton / ERO Sports

Seems to contradict my test with the flo 60 vs the 808 and 404 which it beat by a good chunk. All with a 23 supersonic.
Added to that it was the front of a p4 which has a narrowish fork. So maybe that’s a factor.

Ultimately though, people just want the fastest wheel/tyre combination. If you wanted to know the outright fastest complete wheel system, why can't a list of wheels simply be tested in the purported 'fastest configuration'?

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29 years and counting

Whenever this topic comes up I always think we should view the wheel + tyre as a system. Test each wheel with the very best tyre that the manufacturer can recommend, or which has been shown in testing to work best with that wheel.

I mean, the idea of the thing is to find out how to go as fast as possible so just test everything in its fastest configuration.

If the manufacturer cannot recommend the tyre that works best with their wheel, or no additional test data is available, then screw 'em they can have a 28 on there as punishment because if they are trying to sell something to us based on its aerodynamic merit then they should have learned this by now, and be able to provide an answer.

For the "old Aeolus" do you mean the Aeolus Pro 5 and similar? This one:

https://www.trekbikes.com/...colorCode=black_grey

If so, that's disappointing, because that price had been tempting me for a while.

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The point is, ladies and gentleman, that speed, for lack of a better word, is good. Speed is right, Speed works. Speed clarifies, cuts through, and captures the essence of the evolutionary spirit.

It's been a few years, but I'm pretty sure this was the exact same opening and closing line for my thesis defense.

Yep, there's a lot I'm not clear on including how they gathered the data to generate the transient template and whether or not this took airflow velocity gradient into account (i.e. did they measure airflow magnitude and direction at a single height above the ground or did they do a sweep from the ground up - which would be very difficult to do well, I suspect. This is a pretty fundamental factor.
Also, is the wheel rotation mapped directly against airspeed, or does it take account of the fact groundspeed and airspeed (however that's measured) will not be the same except when travelling in a homogeneous body of still air - which is not what the test is about.

Bunch of horseshit test by Yoeleo , they finally figured out how to market/move their stock. They use to have YT channel with some chick talking/showing their frames and wheels... It was painful to watch, but with 500-600$ for set of wheels/frame people were watching.


They describe testing protocol without reviling testing protocol...relaxed hoods at 50km/h who was doing this test in UK ? Wiggo, Mr G or Froome?


You can't go wrong with those prices if you are on the budget, I just don't understand why people need validation from some BS test, like few watts would matter. You want to show off in front of friends: envy and zipp, no $, and want to lie to yourself you are faster get Yoyo.

If I offended anyone I'm sorry, I just call it how i see it.

Thus far, I'd purposely not mentioned that brand/wheel in hopes that nobody would ever consider buying a wheel made by a shady company that sounds suspiciously look "Yolo". I hear you with regards to this being a marketing ploy. That said, the results... the Shimano wheels in particular... seem too realistic to have been faked by someone who doesn't know that much about this stuff.

I will continue to buy Flo because they are transparent in their wind tunnel testing procedures.

Edited/fixed: not sure that's the same wheel as 2017 Aeolus 5 so don't know.

The *Pro* 5 is a new wheel that came out at the same time as the XXX though. I wonder how it compares to the old non-Pro models

Thanks for pointing that out! I'm going to delete my post because now I'm not sure it's the same wheel as last year.

That blog is totally not "realistic" there is nothing in it, numbers are "could be realistic" but the rest looks fake, except 2 random charts... anyone could come up with, just get the numbers 50-50% correct....
Having said that, those guys are doing carbon components for long time (they are not shady, since they are in business for long time), instead of trying to be the best, they should place them self just below (1-2W slower) Envy and Zip, with wheels that cost quarter of the price it would be no brainier choice for market their target. With current data posted they will just get laugh at. ENVY guys will get envy, zip guys will get zippy-zappy and everyone will call it BS. Otherwise none of Envy guys would even notice that blog, guys on the budget would still buy the product 1W slower and 70% less expensive.

They went to an awful lot of trouble and expense to come up with that really poor presentation.

What frame and fork were used? This has a big effect on wheel performance.
Why "relaxed hoods position" for aero wheels... and at 50km/hr?
Exactly how did they perform the "transient yaw angle" test, and what yaw angles were tested?
For a full rider on bike test we really need to see the repeatability.

I agree. The main reason I posted this was that I found it interesting that the Enve 7.8 and Bontrager Aeolus XXX 6 ended up so close to each other and that Flo, which has tested well elsewhere, tested so poorly. What I'm saying here is that maybe..... maybe.... something about this testing methodology, exposes strengths in some wheel designs and weaknesses in others that we have not previously seen.

Wait, so the people who did this test have a stake in one of the wheels tested? That's not clear to me from the site linked to.

I agree and I can't find a direct link... though that doesn't mean it shouldn't be ruled out.

Hey I know some guys who can do that haha

But what most people don't realize is that those dudes probably spent 20-50 hours planning everything before they ever set foot in the tunnel.

Like Jim said you'd need to devout some serious time tim finding the fastest wheel /tire combo. Then I suspect you'll need to redo that for every bike since fork blade are going to very in widths and blade widths won't be uniform either

Wind tunnel testing is waaaaaaaaaaaaaaay harder than most people think, even when we make it look easy.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

[quote desert dude Then I suspect you'll need to redo that for every bike since fork blade are going to very in widths and blade widths won't be uniform either[/quote]
This. It's a fun to look at these tests, but the wheel that is fastest by itself isn't necessarily going to be the fastest one in the frame. And the fastest wheel in once frame isn't going to be the fastest in another. Especially if you are looking at the difference between a beam bike which doesn't cover the back wheel at all versus a regular bike. Or between a tririg omni or ventum which there isn't a downtube and a cervelo p3 whose downtube is right behind the wheel.

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Matt

i'll 2nd that!
of course then you have frame/fork interactions but we'll ignore that for now...

my immediate reaction on seeing some no-name brand near the top of the results was that there is probably some influence there...

Jim@EROsports wrote:

Tire choice and pressure is absolutely crucial to any wheel testing and, for that reason, it's practically impossible to conduct a test like this properly. If you try to make the testing "fair" by using the same tire and pressure for each wheel, you've likely produced near meaningless data. There are simply too many variables; it would take weeks to test all the different combinations. Then, of course, you'll need to repeat those results to give them value. Fun!

I couldn't agree more, and it's the exact reason we've never done a FLO vs. Them study.


I have to say that I find it funny how the manufacturers are always made out to be the villains in these studies. As manufacturers, we certainly do not know everything, but I can tell you as a collective group, we have learned a lot about testing products. Honestly, most of us work together to help ensure the data we are producing is as good as possible. Some of the best advice we have ever received has come from our biggest competitors.


I'm not saying that all brands are 100% transparent and honest with their marketing, but I think most of our customers are smart enough to spot the fakers when they see them.


I think it's important for people to understand how the smallest changes in a wind tunnel can result in massive changes in drag. In most cases, these changes are so small or non-obvious that the people conducting the tests have no idea they are introducing error. Your protocol can render tens of thousands of dollars worth of wind tunnel time completely useless.


Independent and crowdsourced testing is great, but people need to pay close attention to their protocols and heaven forbid, ask the manufacturers for advice. Take the following as an example. There have been several crowd-sourced studies on this forum. One, in particular, added hundreds of grams of drag worth of error to their results in how they set up their tires. Yes, hundreds of grams in just the tires. Conclusion, the results are useless.


We own a $2,000 pressure sensor that we use for all of our studies. It's accurate to +/- 0.1 psi or better. Why? Because tire pressure is critically important. Had the people conducting the above study called and asked for advice, we would have gladly loaned them the pressure sensor, and in a single conversation eliminated hundreds of grams of error. Honestly, the more good data, the better.


A while back we contacted all of the brightest minds in our industry to create a Collective Testing Protocol (CTP) that all manufacturers could adhere to. The idea was to develop a standard protocol—available to the public—that eliminated as much error as possible. Wind tunnels could then become certified to conduct CTP studies, and your results would be stamped with a CTP logo by an independent 3rd party. We had 100% buy-in when we presented the idea, but when the actual work had to be done, most of the people backed out. I still have the wheel protocol somewhere.


Anyway, my moment on the soapbox is over. We'll be discussing all of this stuff in future podcasts simply because we think it's important to share what we've learned with our audience.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Why heaven forbid? That is what you do. That is what we did for the bike setups, anyways. That is what Cervelo did for their P5-X competitive testing -- well, according to Cervelo they did, which is an assertion Trek disputes.

But yeah, I think the way to find out the fastest configuration of tires, pressure, and wheels for testing is not by spending dozens of hours in the tunnel prior to the study (for each wheel) but to simply ask the manufacturer what that optimal configuration is. If they do not know or do not participate, that's a huge red flag, and it should be noted in the output. A control tire and pressure could be used for those.

There are still the variables that nobody will agree on. You have chosen to test wheel only, and apparently wheel only closely aligns with wheel in the bike, per Tom A. Maybe on the Dimond Superfork, but on the 3T Strada I find it impossible to believe that my ultra wide Enve 4.5 ARs together with respective tires and pressures tests much differently as a system in that fork, with its couple mm worth of clearance to the fork, than those wheels would in, say, the new Ceepo, among others.


I just don't believe you, but you know that, because I've told you that before. I do not believe tire setup accounted +/- more than 10 watts (roughly) worth of error. I call bullshit, again.

Separately, I do think it's basically chicken shit that you haven't tested your wheels against two of the industry leaders, say Enve and Zipp of equivalent depth, while soliciting the information from those companies for optimal configuration. For all the time and money you have spent in and on aero testing, I don't understand why you couldn't spare an hour to do very basic competitive testing in line with the instruction of your competition.

Besides all that, this study strikes me as a total waste. Here we are right on the verge of rim-brake systems being extinct, and they go out and test the wheels facing extinction. Which brings up the next question: how will we test disc brake wheels? In a bike or not in a bike? Am I supposed to believe the location of the caliper (i.e. what bike) does not have interplay with the wheel itself?

They brake fine, comparable to Firecrests etc. Just get some decent pads (Black Prince).

But even plus minus 10 watt is a lot

You just lost a lot of credibility right there. If anything it makes the test results presented here that more believable. If drag was that influenced by such slight changes in pressure, all published results would be meaningless on the road anyway.

I am still going to ask you to explain the rationale behing the impact of tire pressure on wheel aero drag.

They collected wind tunnel data a couple years back where they varied tire pressure from 90-105 psi in 5 psi increments on the same wheel and same tire and found some significant differences.

Link to blog post: http://flocycling.blogspot.com/...pressure-change.html

Why do we lose credibility for telling people that tire pressure is important? I think if people understand how important it is, they will be able to make better decisions when inflating their own tires.

Here's a simple example. Standard floor pumps can be accurate to +/- 8psi. That's a huge range. Better designed floor pumps are accurate to +/-1psi, and you can purchase high accuracy gauges for reasonable prices. If our customers know this, they can make better decisions when inflating their tires.

With respect to the rationale behind pressure having an impact on drag, the shape of your tire changes with changes in pressure. We have hundreds if not thousands of measurements showing this. Changes in shape have an effect on your drag. It's as simple as that.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

The tire shape changes dramatically with pressure. Yes, we are chasing nearly unidentifiable differences between top wheels right now. 5psi matters. Read that blog post on Flo's blog.

I repeated did do a head to head in the wind tunnel. Same brand, size, model of tire at the same pressure except one was a few months old (less than 60 miles on the tires) showed notably different repeatable results just from being open and used. Head to head testing of wheels is something I won't attempt again since there are so many variables. I think to do it right, you need a very exact pressure gauge, same tire used on all the tests, etc.

This isn't "hundreds of grams of drag" difference though:


If tire selection and pressure are so important, then companies selling top tier wheels need to do the testing on multiple tires and pressures and give us the data so we can decide. Kudos to Flo for doing that better than anyone.

Pressure isn't the only variable to take into consideration when setting up your tires.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

[quote]Why do we lose credibility for telling people that tire pressure is important?[/quote]

You don't lose credibility. It's moronic to suggest that imo

The problem becomes race morning or the night before when someone is pumping up their tires they'd have a better chance of finding a natural redhead escort selling payday bars while riding an elephant inside transition than you will finding a pump that's +/- 1psi.

What your data does provide is a range where people should be trying to get their tires to on race morning

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Paydays? I love Paydays as ride food... :-)

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http://bikeblather.blogspot.com/

Do tell... picking off the little molding nubs?

ever since i started gravel and mountain biking more, i bought a topeak smartgauge (https://www.amazon.com/...Gauge/dp/B0051LQ0X4/) since i can feel a difference in traction with just a few psi difference and now i use it to verify the pressure on my road and tri bikes too. i would've never considered having an independent gauge before then and i'm surprised more roadies and triathletes don't use one given the usually poor resolution of bicycle pump gauges. of course i don't really know if it's accurate but at least it's been consistent for me

I completely agree that finding a pump on race morning would be hard. But you can build a small gauge with a bleed to keep in your race bag. Then setting your pressure is as simple as over inflating, connecting your gauge, and bleeding to the right psi.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Popular tires are made in such high volumes that they need more than one mold to hit production volumes. Let's assume there are 5 molds that are used to produce a specific tire. You'd think that two brand new tires from different molds would produce the same result... but they don't. In some cases, one mold is considerably faster than the others.

During our tire study we found one tire in particular that was faster than other identical make/model tires. We weren't sure why but after a few phone calls we learned that we had a tire from the best mold.

So to my earlier point about being careful with your protocol. Let's say you are testing two bikes. In order to save time—because wind tunnels aren't cheap—you get the bikes ready before going to the wind tunnel and buy 4 brand new tires—two for each bike. If you happen to put two tires from the fastest mold on Bike A and two tires from the slowest mold on Bike B, then Bike A has an unfair advantage. Add setting your pressure with a standard floor pump and you introduce potentially hundreds of grams of error.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

This seems a little backwards, but does highlight an avenue for optimization.

With pressure loss throughout the race (especially with latex tubes), temperature variation, leakage when removing the gauge etc... It's a fair assumption that the PSI won't be bang on throughout the race. Beyond that as the tire rolls down the road it's going to deform a bit, which I suspect will again have an impact on what the best PSI is.

So it would seem what I really want from a set of wheels is minimal areo sensitivity to pressure.

I find it ridiculous to throw numbers like 0.1 psi precision and hundreds of grams of drag errors. It's rubbish.

How much does tire pressure change while riding, braking and changes in envinronmental conditons?

I think if the aero drag changes that much with tire pressure, there is a problem with your selection of tire/wheel combo.

Do you think that or do you have data to prove it?

That would suggest opinion and not fact based on data. The data says it changes quite a bit. Again, we are trying to maximize very small differences. Again, it makes it so that you can only test what you are working with directly and not take any other test data beyond what it is. You need to test your stuff in a tunnel to maximize it, or at least do some virtual elevation testing to prove what works.

Don't forget, you need to set pressures based on ride start temperature, not temperature at 5:30 AM. Know your pressure rise versus at various temperatures. Gas laws help you here.

On my race cars, we tune to 0.1 psi. You can feel 0.2-0.3psi in handling differences. The tire shape changes with that small of a pressure difference.

Differences of 0.1psi are not resulting in large changes in drag, but 5psi changes do. Not everyone needs a $2,000 pressure sensor, but most can do better than a floor pump that is +/- 8psi.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Yes, PV=nRT. Doesn't take a genious to realize pressure will change quite a bit.

Do you also come up with optimal pressures for various tire wear levels?

No. I change them every couple races after seeing some data. They become crit tires instead

Appropriate screen name

Zing!

Personally that's what I do.

With regards to tire selection and tire pressure, it occurred to me when you first released all of your carbon rims and the related information about their development, that a better design process would be to do exactly what you did but for 3-5 different tires at 3-5 different pressures. Basically, you'd be looking at ~25 possible "leading edges" that you'd have to optimize the rest of the rim for. Undoubtedly it wouldn't be an optimum shape for a given tire but it might be a better shape the range of tires and pressures your rims would likely see in the real world.

To this end, Cannondale/Hed's new Knot 64 wheels intrigue me as it appears they are mostly tire/width agnostic up to ~28mm measured.

BTW what ever happened to your casing tension study?

I agree with you on this point. With wide forks, perhaps wheel only testing is sufficient. With narrow clearances I can't imagine that doesn't change and there's been some wind tunnel tests out there that show as much. I *believe* Grill did some testing with a P5 and an 808 front which showed the whole system was surprisingly picky with regards to tire selection... more so than wheel only testing would suggest.


I'm in agreement with you on this as well. Considering all of the testing Flo has done, it would have been rather trivial to compare their wheels to a 303/404/808 or Enve's equivalents. Just send them an email and ask them what tire they recommend.

Disc brakes may die but I'm going to hold on to my rim brake wheels for quite a while. Hearing the rotor go "ting, ting, ting..." while riding to the pool isn't the end of the world but it would drive me absolutely nuts on my TT bike. Given how baggage handlers treat bike cases, it seems like a guaranty that you'd have to true your rotors if you flew to a race.

Hundreds of grams is huge! If the mold the tire came out of and a few PSI makes that big of a difference, then we are kinda screwed. We'd need to take each individual tire to the wind tunnel and test it.

Aerosticks, the Cloud and Big Data are our answers.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

Except that, it's going to be few years before, A: they're working reliably, and B: people use them properly. There's going to be a ton of crap data out there for awhile.

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Jim Manton / ERO Sports

Oh I know, I was half joking because there are a lot of optimistic assumptions in there. But in theory, this could be the answer. Lots of (good) data, aggregated together, then the data analytics software sifts through it and teases out the answers.

Until then, we can head to Carson and see you!

---

Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

Just a general comment - not directed at you.

When I was testing wheels and tires to decide what we would specify on the Tactical I initially relied on the testing protocol that the tunnel operator/experts proposed. After all, they had years of experience and worked with many wheel and bike companies.

We wanted to determine tires after we had selected wheels.

They had us doing three sweeps at various yaw angles with different tires.

The sweeps don’t take long and you do them one after the other - then change tires and do it again. To save time you move quickly through the testing.

We were 3 hours into a total of 12 hours of testing when I saw a strange number pattern within the data sets. I decided that the data was not reliable.

I changed the protocol to include spinning up the wheel/tire until the tire temperatures stabilized at 30 mph and then we did each sweep - totally different outcomes. We did these at 95 Psi without rider weight so I still think we only got acceptable data - not great data but better data.

I think that the different tire pressures - due to heat changes in the initial sweep runs changed the tire shape on the wheel which affected the numbers - but I never worked to formalize that issue - I just tried to normalize another input to get the data that would help support a decision on tire specification.

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Dan Kennison

facebook: @triPremierBike
http://www.PremierBike.com
http://www.PositionOneSports.com

The author has been on weightweenies discussing his test and protocol. thread here.

https://weightweenies.starbike.com/forum/viewtopic.php?f=113&t=153138&start=60


Thing I notice is he's used yaw from a control tower for his yaw values, which may not be representative of ground effects?
he's called BS on the pressure thing though.


would Canadian and some of he other more technically esteemed members of this forum be interested to have a chat with him?


He is actually a knowledgeable guy (he is an aerospace engineer by training) so this might be an interesting exercise from all. I'm sure everyone could learn from each other.

Thanks for posting!

Interesting yaw sweep. Granted at 30km/hr yaw will be higher than at greater speeds, but that is still very high yaw. I'm ok with the "pulsing". By their own statement, most of their test points will be in excess of stall angle.

I would have answered quicker but I had to go through the validation process.

1. We are not affiliated with Yoeleo at all. We are just a bunch of Engineers who build aeroplanes and race TT/Triathlons
2. I'm uploading data to show how tyre width effects overall aero performance. I will do this over the weekend.
3. The rider position was set with a laser to 10mm (FARO systems)
4. Tyre pressure was 8.25barG

Thanks

Hambini

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HELLO HAMBINI FANS!!!

Thanks Hambini!

Would love to see CdA for each wheel vs time added to the graph above.

Hi Chris,

I have eight of your wheels in the garage, so consider me a supporter. Your sincere interest in creating a quality product, evidence based approach to development and related transparency are a big part of what made me a customer. Your tire studies are a great example of providing value to customers by empowering us to make decisions that optimize your product.

You can control the narrative related to studies like this one by putting an optimized Flo 60 up against an optimized Zipp (or equivalent). Even better, put it on a control bike such as the popular Cervelo P3 and show us the integrated relationship. Easier said than done, I know.

Apologies to the thread if this is OT. Just wanted to take the opportunity to address some of the Flo related chatter on the thread.

Scott

Thank you for sharing this study. Threads like this draw me to ST, but are increasingly overshadowed by all the BS on the board.

Scott

Personally, I don't think that's Flo's job. I understand that engaging in any sort of testing pissing match with specific companies is a can of worms. Particularly when going up against companies with fully staffed legal and PR departments.

But we do have some independent testing of Flo vs. well-set-up benchmark wheels.

This is the *OLD* Flo 90. (full report here)

Thanks for chiming in and thanks for sharing your data! Could you tell us a little bit more about your protocol? It seems to me there was an emphasis on continuously changing the yaw vs moving to a yaw, waiting for the airflow to stabilize, measuring, moving to another yaw, etc. Please correct me if I misinterpreted that.

These kinds of statements really have me questioning the value of wind tunnel testing. If a $2K pressure sensor is needed to differentiate hundreds of grams of drag error, what's the value of wind tunnel tests if I am introducing a minimum of 'hundreds of grams' of error (e.g. ~ +/-200g = +/-20w) every time I inflate my tire with a $50 pump?

It seems like tunnel testing is a double edge sword. On the one hand, if you don't have it, you're going to get roasted. On the other hand, if you do have it and you use very sensitive controls, you may be able to tease apart differences, that unfortunately, the average rider will not be able to control for/use in a way that optimizes the advantage of that wheel.

@GreenPlease, I sure can.

To give you a bit of background. One of our colleagues entered the Ironman UK race and he wanted the fastest time possible. Not much we could do for his swimming or running but we could help him a lot on the bike. We work in Aerospace so have access to a fairly sophisticated wind tunnel. We borrowed some wheels and tested them in there along with adjusting his position (separate subject) to get him as fast as possible. This is where this data came from.

Prior to all of this we fitted out some bikes with sensors to work out where wind was coming from, it's direction and it's speed. We got several hundred rides and computed the data. From that we ran a Fast Fourier Transformation to turn the data into Ramp, Step, Sinusoidal inputs.

The flow over a bike is rarely steady state, it continuously pulses. This is combined with corrections from the rider and road furniture which alters the speed and yaw - even a passing car has an effect. The protocol you have probably seen is for 30km/h, there is another one for 50km/h. The main difference is there is much lower extremities of Yaw angle at higher speed.

You are correct in the sense the angle is changing in the tunnel. We've got the ability to do that whereas most people do not. They probably don't have as high resolution instrumentation to be able to get the numbers quickly and accurately. So what we can do in 20 minutes, may take someone a few hours at (for example) A2's wind tunnel.

As far as "Flo" Bashing goes. To be clear, I messaged Flo a few months ago and just recently informing them about possible issues with their wheels. They did not respond.

In our opinion (that's 100+ years of combined Aerodynamic experience), the Flo wheels that we tested should have better performance for their depth. They are welcome to say the tyres, pressures etc will influence the results but fundamentally we believe the profile is floored.

Thanks

Hambini

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HELLO HAMBINI FANS!!!

I find this part very intriguing, but I wonder about the magnitude of yaw and how your results are weighted. You appear to have much stronger winds (and higher yaw) than other field studies have determined are typical.

I'm guessing that in a tunnel you wouldn't find the Knot 64 wheels to be tire agnostic. I'm not sure how that would be possible.

The casing tension study is still underway. We have been studying pressure and rolling resistance extensively. That should lead to some pretty great data in the not too distant future. Data collection takes an eternity.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

And this is why we haven't done it. On top of that, "IF" we show our wheels in the lead, the first thing we'll hear is "FLO weighted the test in their favor". I've said for years that it would be fun and interesting to have a list of companies send a representative to the same tunnel and have a shootout. I think that's the only way to make people believe your results. But do you think companies will agree to that? Not a chance. We tried to have people come together to develop a collective testing protocol and even that was too risky for most.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

You'll never satisfy the Slowtwitch internet aero experts so I wouldn't worry about them.

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Make Inside Out Sports your next online tri shop! http://www.insideoutsports.com/

Relative to other rim profiles.

For the last 7 years, many times per day, I am asked the following questions.

1. What wheels should I buy?
2. How do your wheels compare to "some other brand?"

Here's my best answer.


Zipp, Enve, FLO, Hed, etc., all make really REALLY good wheels. Going from your stock training wheels to race wheels from any of the aforementioned brands will give you MOST of your advantage. After that, the performance difference gets much smaller. Let me explain.


Gear changes can without a doubt give you an advantage, but I think there are two categories of advantages. Certain gear changes give you large magnitude advantages, and others give you small magnitude advantages. Here are some examples of each.


Large Magnitude: Switching from a Mavic Open Pro wheelset to a FLO 60/90 in Kona will save you about 6 minutes and 20 seconds.
Small Magnitude: Switching from a FLO 60/90 to a FLO 90/90 is worth 1 second.


Large Magnitude: Using Gatorskins for an Ironman will cost you about 7 minutes vs. a tire with low rolling resistance.
Small Magnitude: The difference between two tires with low rolling resistance over an ironman... seconds.


When people start comparing Enve and Zipp—or any brands—I think it's important to realize that this is a small magnitude difference. For most people, large magnitude advantages should be the main priority. Here are a few examples.

• Get in shape. None of this matters if you're out of shape.
• Get a good aero fit.
• Get race wheels.
• Use good tires.

After the large magnitude changes are made, it's hard to say that there is a BEST. If two people spent a month in a wind tunnel finding the best solution for them, I could almost guarantee you that those two people will end up with different bikes, helmets etc. Why? Because they have different bodies. The shape of one athlete's legs may interact better with a FLO wheel and Conti tires than an Enve wheel with Michelin tires. Or vice versa. Also, If one particular frame is faster than another, but you can fit yourself on the frame in a position that allows you to produce optimal power, you probably shouldn't buy that frame.


Aside from aerodynamic performance, there are other things to consider when spending thousands of dollars for bicycle wheels.

1. Is customer service important to you? If brand A has terrible customer service, and brand B has excellent customer service, you should probably buy from brand B. Even if some guy on a forum said brand B is 1 watt slower than brand A. For example, my cell phone number is on our contact page. That is very important to some people while others don't care.
2. What is your budget? If you don't have a budget, buy whatever you want. If you do have a budget and your team gets a sweet deal on Enve wheels, then you should probably buy Enve wheels.
3. What do you want? (more for those without a budget) I just built a mountain bike. I had to decide what groupset I wanted. XO1 or XX1. I don't need XX1. X01 is an amazing groupset, and I'm likely never EVER going to see any difference by using XX1. I'd also tell all of my friends and customers to go with X01. What did I buy? XX1. Why? Because I wanted it. It's that simple. I know it really won't help me go any faster, or shift better, but I wanted the best, so I bought it, and it made me happy.

At the end of the day, make smart large magnitude choices. If you want to make small magnitude changes, you'll need to do a lot more work AND know that your small magnitude changes will likely be different than some guy on this forum. To optimize small magnitude changes, you'll need to visit a guy like Jim Manton (on this thread) or a wind tunnel.


I hope that makes sense,

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

You did? Where did you contact us?

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

“ fundamentally we believe the profile is floored“

Can you expand on the comment above? I’m not sure what you mean by “floored’?

Thanks for the study and for participating in this thread.

Scott

Fair enough. Thanks for your reply.

Edit; well said regarding large/small magnitude decisions.

Scott

that's when you just say "f*** it."

It looks like the wheel profile has been designed by an aero consultant that has been asked to make a wheel through very specific steady state conditions. Probably 50km/h <6 deg yaw. Air doesn't behave like that so when tested against real conditions the wheels perform poorly. If you peturb the bike and rider (ie simulate rocking) which is what most people do when they ride a bike, the airflow breaks away. It then reattaches moments later. The rocking is most noticeable when people go up a hill, they do it on the flat but it's not so visible.

Floored in this context - there is a design fault or poor design. I don't know the background behind the design of these wheels but it looks like there has been an over reliance on CFD and the boundary conditions have been so specific, the wheel really only operates well in those conditions.

Thanks

Hambini

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HELLO HAMBINI FANS!!!

@Chris Flo Cycling

Check your twitter account.

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HELLO HAMBINI FANS!!!

Flawed.

Apologies you are right it should be flawed. Sorry I'm not a native English speaker.

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HELLO HAMBINI FANS!!!

Got it, thanks. I appreciate the explanation.

Scott

This whole thing makes a compelling argument for the Speed Concept, assuming the Aeolus wheel testing so well here was specifcally designed for that frame?

Scott

You know, it's an interesting time we are in currently. I used to be Chief Aero Anal of my own setup. Lots of personal testing, for fun testing, etc. Different tires for different courses, etc. Multiple aero helmets. Going down the rabbit hole of everything adding up to a hopefully "most aero award" at a race in terms of watts:mph

But when you read threads like this, it just makes me feel like it's SO STUPID. It's totally not worth the time investment and financial investment that it requires for 99.8% of age group athletes. Hell, even most of the pros could do with less over analysis.

So now it's more - for me anyway - just buy what you want and make sound decisions about it and don't buy into all this lame ass paralysis by analysis aero shit.

/rant

I hear you.

That is basically what Chris said above in the context of large magnitude decisions. Make smart choices there and get on with The Work.

Scott

Yeah, I’ve come to that realization lately as well. Spending time reading and testing and analyzing to get the last few watts. Starts to take the fun out of why I started tri 10+ years ago. Hit the major stuff and don’t worry about the 0.5%.

Most (all?) of the time that last 3 Watts isn’t going to make a difference place wise for me. This coming from someone who missed Kona by 68 seconds. It wasn’t not having the perfect wheel/tire/pressure combo, it was screwing up nutrition and hydration having to walk too much on the marathon. Spent too much focus and time chasing seconds and not enough doing things that cost me minutes

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Matt

If someone creates a Triathlon Psalms, this should be in it.

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Jim Manton / ERO Sports

I see you posted your results in August, but going all of the way back to mid June I didn't see anything else.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

I can appreciate your general recommendations to people. I've always liked the wheels you make and the price point that you sell them at, the down-to-earth approach that you guys have, and that's the very reason that I bought from you in order #1 (at least, I think it was the first pre-order) and again this past year.

But your answer doesn't get at my initial question...

If a wind tunnel test can be foiled simply by failing to control tire pressure down to a margin of accuracy that consumers don't have, do these tunnel results actually matter in the real world?

Effectively, I interpret comments about your $2K tire gauge as a sign that there is a 'theoretical' (wind tunnel) difference, that in 'practice' (real-world use), is lost in the margins of error.

Now, I don't mean to completely discount the validity of tunnels or aero testing (I've used the Chung method with a some degree of success), but I think we're at a point that some differences that we're being told about in the tunnel, in the end just get lost in the wash.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

ok. I'm going to take a long look at these affordable digital gauges.

This sentence is a real stretch:

"They probably don't have as high resolution instrumentation to be able to get the numbers quickly and accurately. So what we can do in 20 minutes, may take someone a few hours at (for example) A2's wind tunnel. "

Instrumentation is not an issue with getting numbers quickly, it's the control algorithms. Any signal conditioning produced in the last 20 years is going to be at least 16 bit and it's not unusual to have temp compensated .1% instruments except for temperature and humidity. 65,000 steps for 10" H2O is a pretty high resolution instrument. If you are going finer you'd better have some extraordinary calibration equipment or you'll be sending your stuff out every 90 days and then the metrology approach is questionable compared to end to end.

So you have a baro, a DP if using a nozzle, some other type of sensor if not, a DP from inlet to baro, some probes to measure eddys, temp, humidity and a few load cells for instrumentation. Any modern signal conditioners work really well unless you're using crxp from Omega.

We’ve had useful data from the TyreWiz. We still need to check the accuracy but the precision is there. I’m not sure i’d put them on a race bike for aero reasons, but I happily run them on back wheels during testing most of the time. When testing we still try and use a clients pump/gauge as that’s what they’ll have available later. So even if they aren’t actually putting a true 95PSI in they putting the optimum in, even if in reality that’s 87PSI.

In answer to an earlier question, tyre pressure will change by several PSI during a ride from temperature changes, and from air loss. We’re in the process of writing this up in a form that’s useful for riders.

Tyre temperature will influence Crr directly through effects in material properties as well as pressure. Even before we had the measurements we have now, it was always more consistent testing outdoors on cloudy days than in sunlight.

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Developing aero, fit and other fun stuff at Red is Faster

Don't forget to set your cold pressure 2-3 psi lower, because you know, tires do warm up when you ride them. Don't brake too hard on the course, that will throw your pressure off. I just don't know about where you should rack your bike. Shade and pressure will be much higher on the road. Sun and pressure will be way to high to start. Otoh rolling resistance goes down with increasing tire temperature. Sun it is!

Sounds easy enough :/.

Hi everyone,

it’s a very interesting discussion I followed on different forum, roadies and triathletes’, and even if I have not posted here for decades, I thought I could chime in … I think that the most important point in that discussion is how science deals with reality.

Both Flo Wheels and Hambini have a different point of view about wheels’ aerodynamics and both likely did their homework.

Flo seems to be a reputable wheels company, they did much studies about yaw angles, rims shapes, tires pressures and so on … they established a protocol, tested wheels and ended up with conclusions and products !

Hambini and his collegues, who seem to have experience of aeronautical engineering around high speed military airplanes, are at least as legitimate to work on wheels … but they seem to have another point of view, probably due to that aeronautical background, so a different protocol and new conclusions.

Being a scientific guy, I think that neither are totally right or wrong … they “published” different results about a common topic as scientists do every day, with slightly different protocols, analysis methods etc. ending up with different conclusions about the same “reality”.

Both points of view are interesting and have to be taken with a grain of salt … I can understand that after spending huge $$$ on tri equipment, some may be disappointed, lost in their reasoning but as a matter of fact, different points of view are exactly what I’m looking for in science to widen the spectrum of comprehension.

It seems that in recent years, people have more and more difficulties understanding that science is what it is … hypothesis, studies, measures and validation / invalidation of hypothesis, on and on … there can be no definitive conclusion, in my opinion, on any scientific topic … take sport or healthcare, climate, nutrition, agriculture, whatever you want.

Anyway, as Chris from Flo mentioned, we are talking about marginal gains compared to swapping from box to deep rims, etc. … and marginal gains are very difficult to measure because precision, accuracy and cost become more and more important in that situation.

So thanks to Hambini for his work … and thanks to Flo for their approach. I’d add that I have no dogs in the fight, no Flo wheels either etc.

Regards, E

What wheels do you ride?

Having switched from triathlete to recreational roadie in the past 10 years, I got less sensitive to aero gimmicks but I still ride custom wheels with Corima aero rims and Tune hubs when the weather is nice and shallow rims with bombproof hubs in the rain and winter's harsh conditions.

By the way, I essentially ride tubulars ... and I use to build my own wheels.

The aero question came back recently, just because I have a deep section wheels project in mind and was thinking about rim depth and shape ...

Regards, E

@hambini - great work.

stealing from your comments on weightweenies:

Myself and my 3 colleagues came to some broad conclusions

- If you are at mortal speeds, there is not much difference between any deep wheel.
- For general overall riding at 25-35km/h a 35 to 50mm wheel would be recommended.
- If you are going really fast, deeper is better.


I compiled your results as a drag-vs-rim depth chart, which shows that general trend of decreasing drag with depth, though drawing general conclusions (say "go for 65mm+") is possibly limited by the sample size.






But is it possible to generalise any other tips for spotting a fast wheel? (using eyeball aero)
eg is there any general trend with respect to rim width, shape, etc? eg lack of sharp edges/brake track lip, sharp corners at the trailing edge, toroidal, vee, square, rounded, etc.


The last point I think would be interesting to know more about is steering/yaw stability - something eg Swissside claim a lot of work on - the idea that making the bike handle well in fluctuating crosswinds will improve rider confidence, and hence the ability to keep mashing the pedals without backing off to steer, or worse come out of an aero tuck. Any thoughts? Is this why you suggest 35-50mm rims at lower speeds, or is it because the magnitude of the differences is just too small to care about?

@MattyK

Someone asked this question about crosswind stability on weightweenies so I have copied and my response

To emphasise this here are two popular standard aerofoils that are widely studied. NACA 0012 and 0024.

http://airfoiltools.com/airfoil/details?airfoil=n0012-il

http://airfoiltools.com/airfoil/details?airfoil=naca0024-il

If you look at the Cl vs alpha (graph on the top right), this is how the aerofoil generates lift when used on an aircraft, the alpha denotes attack angle and the CL is lift coefficient. If you change the orientation through 90 degrees and apply it to a bike, it is the force generated by wind when the yaw angle is anything other than zero.

The take away is to note that flow separation occurs around 12 degrees irrespective of the shape of the aerofoil. Having a blunt rim will take you up only to around 15 degrees (Reynolds number of ~100k) but it's a heavy price to pay at low yaw angles. Blunt aerofoils *generally* have poorer reattachment.


And for your other questions

Generally, if you experience a crosswind that is constant, the bike will be totally controllable and you simply tilt your body to compensate. If the wind gusts or pulses then this causes instability. For the average individual, they will be able to control a bike with a 50mm rim set at gusting crosswinds of 40km/h. At 80mm, it will be uncomfortable and may result in a meeting with the deck. Hence the guidance to go for 50mm as a general wheel. It is more important on the front wheel than the rear.

Hope that helps

Hambini

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HELLO HAMBINI FANS!!!

Also don't forget road surface "impedance". Optimal pressure is seemingly highly dependent on surface roughness. So you need to calculate a time-scaled mean impedance for all the road surfaces on a course, and then use that as input into an impedance-matching function solving for pressure. Taking into account losses over the day, and, of course, solar loading.

Even if you had a rectangular box, the break off point would be around 12 degrees.

Optimisation of the shape would only get you round a little further.

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HELLO HAMBINI FANS!!!

Not as much as you may think...don't forget that the "T" in that equation is in absolute temperature units (i.e. Kelvin, or Rankine) ;-)

Since V, n, and R are constant in this situation, you can simplify it to P/T = Constant. That means that P1/T1 = P2/T2. Rearranging you get P2 = P1 * T2/T1

Let's say the temperature rises from 10C (50F) to 30C (86F), in absolute temperature thats from 283K to 303K. T2/T1 = 303K/283K, or 1.07, meaning that the pressure goes up by only 7% over that HUGE temperature swing.

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http://bikeblather.blogspot.com/

Understood. I totally misread your previous post.

Reading all this, do you have any intuition on how these results could apply to bike frame choice? Will a frame with very deep tubing like Felt's IA be better suited for dynamic wind conditions or is the P5, which still seems to be the best low yaw choice, still be faster? Obviously this is a bit of a stretch to extrapolate these results and there are a lot of different frame designs, I'm just curious if you have any thoughts.

On a frame I would go for the deeper tubing. It's not like a wheel because it's not rotating. Additionally the rider's legs are disturbing a large proportion of the exposed area so the frame is much more immune to any gusts.

This is just my opinion, I haven't stuck anything in a wind tunnel to prove it.

Hope that helps

Hambini

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HELLO HAMBINI FANS!!!

I don't think it would be really hard to see a 20C delta.

A Quarc TyreWiz would be able to settle this if anyone has one.

Makes sense, thanks for replying

First you have to decide on what "quite a bit" means...and 20C is a pretty large temp swing...heck, 20F is as well.

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http://bikeblather.blogspot.com/

Inside a tire? With the sun and braking? I don't know.

DC Rainmaker should come out with a long term review of the Quark TyreWiz, hopefully he has plenty of data to share how tire pressure changes under various riding conditions.

TyreWiz is a handy gadget. :)

I’m going to write up what I’ve found when I get a moment free.

5PSI+ changes are definitely possible. The heatwave has finished here so I need to get out and see what the range is like with cloud cover.

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Developing aero, fit and other fun stuff at Red is Faster

Hambini,

Thanks for sharing your data and thoughts. Any thoughts on the Zipp 454 "hyper foil" design with regards to both aerodynamics and stability? Specialized tested the 454 and seemed to indicate it performed similarly to 50mm "toroidal" rim profile. Do you think there's any validity to Zipps' claims with regards to stability?

Sadly, some people here might take you seriously. Myself included. Perhaps that's why I'm single...

Very interesting !!

What do you think about the assumption that a U-shaped rim, having a more symetrical shape between the leading and trailing edges, creates a less important differential of "lift" (than a V-shaped rim) between the front and the rear of the wheel, thus more stability with less rotation around the axle of the fork ... don't know if my question is clear ?

Regards, E

For what it's worth, if you go back and look at the white paper Trek did on their D3 rim design (prior generation) that was exactly their theory. They seem to have since reversed course with their new rim design. Knight supposedly tries to balance lift between the rear of the leading portion of the rim (ahead of the fork) and the rear of the trailing portion of the rim (behind the fork) to minimize steering torque in crosswinds.

Understood, I guess what I was trying to get is your thoughts on steering torque caused by an imbalance of the leading and trailing edges of the wheel.
1) Does Cl vs alpha look similar when the profile is travelling backwards?
2) Does Flow separation occur similarly when the profile is travelling backwards?

The other question would be:
Given a blank sheet, and a speed of ~30-40 kmh, what sort of wheel would you design (or look for feature-wise)? Or is it too hard to just guess without doing the testing?

Cheers!

This post is getting slightly derailed by tire pressure discussion rather than aero differences. Whilst it is true tire pressure varies with ambient temp these differences are fairly easy to calculate and have been done in various spreadsheets such as this one (https://goo.gl/99PG6Z). For example if you had a 25mm and inflated inside at 20degC you would inflate at 87psi to get 90 psi outside at 30degC. However ambient temp causes pressure differences more than volume change because volume is constrained by the casing. OK now I am getting distracted! The point is tire pressure has a very small effect on tire size in MTB, Cx and road. 25psi might give a 1-2mm change in tire width or height (see http://forums.mtbr.com/...im-width-756818.html). In turn this also a tiny effect on aerodynamics measured as few seconds over 40km or 90km. Of course tire pressure will have a big effect on CRR but thats not the topic. For any wheel manufacturer to say the results are invalidated by choice of pressure in the tire is really over reaching (unless they are invalidating their own results, which is rare indeed!). This will be the least of all possible variables. There is probably more difference in the aerodynamics of two identical tire out of the box due to manufacturing & installation differences than the same tyre in two tests at 85psi and 90psi.

Now on the topic of these results, what is interesting to me is the slight re-ordering between 30kph and 50kph which implies some wheels/tire combos cope better with deep vs shallow yaws. What I like about this test is that they appear to have tried to make the wind tunnel protocol simulate outdoor wind variation.

@MattyK

It's not the amount of torque that makes the wheel unstable. It's the hap hazardness.

If you had constant cross wind then you would tilt your body to compensate. What generally happens is the wind pulses and you find yourself with either too much or too little body tilt and the instability arises.

However to answer your questions

1. Cl to alpha would cut off at a smaller angle backwards and the Cl term would be lower. Basically the line would be a shallower slope. This is summarised by lifting line theory, the maths is a bit heavy but it's here https://en.wikipedia.org/.../Lifting-line_theory
2. Flow separation will still occur around 12 degrees for reasonable geometry.

Hope that helps
hambini

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HELLO HAMBINI FANS!!!

Good stuff in the D3 whitepaper: https://www.google.com/...GxtN4hrYidZmZ0jAg2oS

"It’s easy to design a rim cross section to have good rim-leading performance. In fact, the rim-leading cross
section mimics the shape of the KVF tube shape found on the Trek Speed Concept [1], where the tire acts
as the truncated airfoil tail. Like the KVF airfoils, the rim-leading side can be designed to mitigate flow
separation—the key challenge in bicycle aerodynamics. As a result, the rim-leading side of the wheel can
achieve very low or even negative drag until finally stalling at a relatively high yaw angle, as shown in the
previous figure.
It’s a different story on the tire-leading side of the wheel, where the tire leads the rim into the wind—an
obvious but critical observation. The tire’s circular cross section is a very poor start of an airfoil. As we know
from the Speed Concept white paper, circles have early flow separation and, as a result, very high drag. This
flow separation off the tire is the largest source of aerodynamic drag for the entire wheel. As such, it is the
largest opportunity for potential drag savings, and therefore the primary focus of the Aeolus D3 design."

Leads me to believe that small tires are best....

Also, Hambini has added the Reynolds wheels... and they are the best. Yes, this rim shape is the new winner:

I just notice the link in the OP has been updated with a lot of additional information. I'll update the title.

Interestingly, the Reynolds, Enve 7.8, and the new Bontrager rims all share a very similar rim shape. I'll add that Venn Cycling also came up with a very similar rim shape about a year ago http://www.venn-cycling.com/.../ctl-rims#venn507tcc

Sadly, they're not offered in the fancy-pants filament wound construction :( yet.

It's funny how we went from pointy to oval and back to pointy. Only now the pointy rims are much wider. Wider than the tire. I guess back in the day you could have achieved the same thing with a very narrow tire, which the smart people did. With less drag than modern rims also I'd wager if you are matching Cd but making the A smaller.

It looks like Reynolds has actually made their rims less extreme (pointiness) than they were a couple years ago. They used to be concave at the very end of the tail.

I found the paper on the D3 very interesting regarding the performance of the trailing vs leading edge of the rim. I figured the tire leading part would perform better (subject to good tire choice), but they say the opposite. I wouldn't expect round to be bad for the leading edge, you just need the proper shape and width of rim behind it.

Trek has been at the bleeding edge of bike aero for a while IMO. I recall that one of Carl's departing remarks was that their in-house CFD had gotten so refined that they almost didn't have to go to the tunnel to test as 99% of the time their CFD predictions matched what they saw in the tunnel. The only area where they still "struggled" was with helmet design.

A personal suspicion of mine is that the Mavic CXR 60 with a 23mm Corsa Speed and Mavic's "tire" strip fitted is a very fast combination.

I find it interesting to compare the Enve 7.8 to the XXX 6 and the Venn 507. All very similar shapes. It would appear that the longer the aerofoil the less of a need there is to truncate it into a "toroid" shape.

Thank you for stating (and backing up) what I have been intuitively believing all along. thanks

Have they? Both rruff and I have been attempting on the weight weenies thread to get more detail about the results of their data gathering step, and in particular the apparent wind probability distribution, and how that squares (or doesn't) with the wind tunnel test protocol. No luck so far...

I've asked for some sort of data or calculations that show this particular protocol is actually better at predicting "real world" performance than simple CdA vs. yaw angle data taken in steady-state wind tunnel conditions...which actually work quite well (e.g. modeling like BestBikeSplit). Again, no luck...

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http://bikeblather.blogspot.com/

Doc...care to comment on the variability of the wind conditions during the data runs for this?:


I recall you saying conditions were quite gusty, no?

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http://bikeblather.blogspot.com/

It does kill me when people are suspicious when a company does well in their own testing. Because they should do well in their own tests. Since they should be making a test that evaluates what makes the best wheel, they should be designing their wheel to do well in that test. It is not automatically dishonest, it just the outcome of a well designed wheel. The thing that all these companies should do is to provide detail of their protocol and why they chose that protocol, so that consumers can evaluate if the company optimized for the right conditions.

Flo obviously does a very good job in detailing their protocol and why they do it. Bontrager is similar.

I don't know if an industry standard protocol is the best idea, because what is the best protocol? Will it constantly be revised when new tires come to market?

Quite gusty indeed.

Despite this, the wind tunnel (steady flow) data were strongly predictive of 'real world' power requirements.

That is presumably because 1) parts of the bike+rider system exhibiting significant yaw sensitivity we're only a small part of the whole, and/or 2) the time scale over which yaw angle may have flucuated was too small to matter (such that knowing just the overall average as we did was sufficient).

Thanks for the trip down memory lane... that study is >20 y old now!

Well our protocol was tire independent. The protocol was designed to ensure you had good measurements but gave you the freedom to use any combination of wheels, tires, and pressure that you wanted.

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Chris Thornham
Co-Founder And Previous Owner Of FLO Cycling

Yeah...I tried to show "hambini" that as an example of how steady-state data appears to predict power requirements under somewhat variable conditions (i.e. wind velocity with SD ~ 0.4 m/s according to the paper...so, +/- 3-sigma of ~4.3km/h). I asked for any evidence that his new protocol works any better at predicting "real world" performance than steady-state data...with no answer to that question :-/

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http://bikeblather.blogspot.com/

Up to 5 years ago I had read every SAE paper there is on aerodynamics when I was involved in road vehicle efficiency. So I figured the auto industry would have looked into transient flow analysis. I don't have access to everything that is published anymore, but a quick google search landed the following:

https://www.google.ca/...8LCLxOo1mnJTZ4_B_ctv

I'm sure more can be found on the subject and I feel there is something non negligible at play here that applies to the field of cycling as well.

I don't believe transient flow evaluation is related to yaw angle distribution specifically, but really to turbulent flow, which is something wind tunnels typically try to avoid by smoothing out the flow as much as they can.

If we talk about yaw angles distribution I really think they should generally be low, but again I feel that is an unrelated concept. Wind gradient diminishes with height following a power law and factoring an hellmann exponent for the environment you're cycling through, so the closer to the ground you get the lower the wind speed is with varying degree, which have a direct impact on effective yaw angles measured at the wheel. Technically there are differences between the top and bottom of the wheel, exacerbated by the rotation of the wheel itself, but I do not know whether these are significant or not.

Our wind tunnel vs. field test data indicate otherwise.

Yeah...as I mentioned above, I've tried to point that out to Hambini on the WeightWeenies thread on this...and when either I or rruff try to ask questions about the data gathering and protocol, we basically get shouted down and accused of being shills.

https://weightweenies.starbike.com/...=153138&start=60

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http://bikeblather.blogspot.com/

What makes the most sense, laminar or turbulent flow? Good enough doesn't mean something else isn't better. You just don't know how to explain divergences from the model that might very well be explained by something you haven't tested for. I don't pretend I know, I just don't dismiss it.

It certainly can't be ruled out that variability in the field test data that is not explained by the wind tunnel data is due, at least in part, to turbulent vs. highly laminar flow.

At a maximum, though, this means that the effect amounts to only 3%.

Having built, validated, and performed numerous experiments using my own wind tunnel, I'm betting that the true effect is actually much less than this.

Well that was a bizarre read. Entertaining in a train wrecky sorta way. The discussion seems rational enough until it suddenly took a left turn at Albuquerque. WJW.

Do you think a 40 second blast in your study 20 years ago is a good validator against a wind tunnel test?

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HELLO HAMBINI FANS!!!

The longer the period of data collection, the more closely the sample mean would approach the population mean.

IOW, if anything limiting the test segment to only a little over 400 m would tend to reduce the correlation between the measured and predicted values. Yet, the R^2 was 0.97, i.e., steady-state modeling accounted for all but 3% of the variation.

More than anything I'm curious to know why the Flo wheels performed so poorly. Everything else on there (random Chinese wheels excepted) ended up about where I would assume they would. Also, Hambini seems to have largely confirmed that narrower = faster for tires which is what I've mostly seen as well from independent wind tunnel data.

Side note: I wish Schwalbe would update their 22mm "Ironman" tubeless tire with a faster compound.

I've been saying this since I joined ST... no relation to Reynolds personally. I never liked the design philosophy behind Zipps and their copycats, so it's funny to see everyone come around.

If you approach Albuquerque from the east, take a left and go about 100 miles, you end up where I live... ;)

I've never been that fond of the idealized environment of the typical wind tunnel test. Introducing realistic instability in the flow field plus time varying yaw of the article being tested makes a lot of sense to me. I was hoping for a very interesting discussion and hopefully an improved protocol for bike aero testing. But it devolved into paranoid ad hominim so severe that I believed Hambini was a total fraud. Lately it has improved a bit and he keeps posting more data. Maybe we'll get the full story eventually.

The most interesting thing I learned in that thread is that aero engineers in the UK are allowed to use restricted corporate wind tunnels for personal projects. Boggles my mind. I would have stayed in the business longer if they'd let us have that kind of fun ;)

We put it to you that you were simply using the air as your wind tunnel and not a fan.

If we (and we have) go out and do several 40 second blasts and plot them together the correlation is no where near 0.97 against a power meter using your equations.

40s is a very short interval and the fact it's in the middle of an airfield bares little resemblance to road conditions. Why do loads of users on here quote it as the basis of data to compare against ours beggars belief?

Regards
Sachin, Pete, Jeremy, Steve, Mark, Terry

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HELLO HAMBINI FANS!!!

We simply tested in the weather conditions that prevailed that day (the only day available to us).

As it turned out, it was quite windy (and chilly), due to the passage of what Texans call a "Blue Norther" cold front. The measured ground level wind speeds are provided in the paper, but to put them in context, picture a large flag snapping in the wind, the landyard clanging against the flag pole, moderately thick tree branches swaying, etc.

If, as you claim, you have not been able to replicate our observations, I suggest that you write them up for publication in a peer-reviewed journal, so that they can vetted by many eyes.

Finally, as I pointed out before, the shorter the period of data collection, the greater the error in the measured (vs. actual) value. Thus, if anything lengthening the outdoor trials (or the wind tunnel runs, which IIRC were 30 s at each yaw angle) would be expected to improve, not reduce, the correlation between the turbulent (outdoors) and steady (wind tunnel) flow conditions.

Having had a discussion internally, we have decided to send our data for peer review. We think it would be good to assist our bicycle colleagues to improve their aerodynamics.

With regards your comments about the shorter duration giving a worse correlation. The following were noted:

- the wind by your own measurements was not particularly strong . Approx 7km/h even though anecdotal evidence is suggesting it was gusty.
- You were in an open area

If you take a spot measurement which for a 40 second burst is. It's going to give an answer that is more akin to a sedate environment such as a wind tunnel than If you were to ride for 10km and be exposed to the pressure differentials caused by temperature variations, passing vehicles, natural wind variation and rider adjustments.

What we find mind boggling is the cohort of users on here deem it to show a strong correlation between a wind tunnel and field testing and use it as the basis to dismiss transient effects. You yourself have commented you believe an error to be of 3%.

Thankyou for your time

Peter Williams PhD


I have used Sachin's forum account as the validation system is very slow.

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HELLO HAMBINI FANS!!!

1. Wind speed was measured at 1 m off the ground. As others have pointed out, the wind speed at 10 m height (typically used in weather reports) would have been significantly greater.

2. Wind speed was measured several times during each run, and the average value used in further calculations. The between-run SD as given in our paper is therefore an underestimate of the within-run variability.

3. Based on the available dates, my conclusion is that the difference between steady and transient conditions appears to be 3% *at a maximum*, at least when testing the entire bike+rider system and using older equipment.

With respect to the latter, while I think that it would be interesting to repeat our study using a more modern bicycle, nothing you/your colleague hambini has posted has convinced me that testing under transient vs. steady state conditions would make a significant difference in this context.

Finally, I will say that I find hambini's persona here (and weightweenies) quite off-putting, exhibiting all of the negative qualites stereotypically associated with being British and/or an engineer.

Hello Andrew

In response to your comments.

1. If you are in an open area the difference in speed between 0.5m and 30m is considered to be negligible. This is in JAA and FAA guidelines for take off parameters, the exact paragraph is lost in my memory. You were on an airfield so it would apply.

2. Noted

3. Noted. I suspect that the weighting of the rider will be more of a constituent of the total drag than the wheels. However your study was conducted in conditions that do not correlate well with ours based on road data. The conclusion from our data is your wind tunnel data is lower than would be experienced on the road.

With regards personas. Everyone is different. The group of engineers in the Aero department here is well and truly multicultural and bring something to the table. I have watched this thread, indeed it is a topic of conversation for our lunch times. I have seen the types of questions that have been asked. Once an answer is given. The answer is systematically taken to task because of a small detail that was omitted. Requests to display data in formats that modern aero engineers are not accustomed to because they are considered dated are met with hostility. Once data is given, more data is requested, this self perpetuating cycle for someone who is providing it for free and without prompting is unjust.

The two answer giving forums on here and starbike have been shared internally for peer review... ironically. Whilst some of Sachin's antics are deliberately designed to wind individuals up. He has not given any information that is inaccurate. What is deemed as being evasive is quite simply Aerospace engineers working in units that bicycle engineers or those connected to the industry seem incapable of grasping, the majority of data was already included but required some manipulation to make it less technical.

In my lifetime I have seen the industry evolve and technology and practices being trickled down to other industries, the use of carbon being a good example. In the field of Aerodynamics that trickle does not seem to have occurred. I read an article in a UK cycling publication written by Simon Smart, he was formally at Red Bull Racing Formula 1, he commented that in his opinion the aerodynamics in the cycling industry were less developed than they should be. After following these two answer giving forums, I would tend to agree.

Thankyou for your time and I wish you a pleasant day

Peter

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HELLO HAMBINI FANS!!!

As others have indicated, wind speed as measured at 1 m and 10 m would likely have differed by a factor of at least two. This is consistent with how I would describe the wind using the Beaufort scale, i.e., as a 4 or 5 (although when I ran back to the control building from the taxiway, I could definitely feel the wind pushing me along, which would make it more like a 6).

(Beaufort scale for those unfamiliar with it: https://simple.wikipedia.org/wiki/Beaufort_scale)

ETA: Here is a pic of Phil White (Cervelo founder) assisting with the field testing. Note the tousled hair and windbreaker wrapped over his hands to keep warm. He is kneeling next to the runway that we used - the black strip in the background is actually the grassy median separating the runway from the adjacent taxiway. Out of the image to the left is a line of trees next to the taxiway. I think that somewhere Jim has a picture of one of the jets that used the taxiway and runway during our testing, which IIRC shows the trees. I will see if I can dredge it up.




I believe the phrase that applies is "taking the piss." As I indicated, I find it both stereotypical and off-putting. You/your group may or may not have important contributions to make here, but his behavior is doing you no good.

For that matter, neither does reliance on appeals to authority, i.e., mentioning the opinions of others who reportedly agree with you.

Andrew,


Your dismissal of information presented is frankly staggering, quite arrogant and xenophobic.

It is with respect that I will pass no further comment

Thanks

Peter

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HELLO HAMBINI FANS!!!

What information am I dismissing?

peter, at al, a few notes:

validation: everyone is vetted before validation. all validation happens within minutes or, at most, a very few hours. we do this because this is a very busy forum - one of the 2 or 3 largest in all endurance sport - and is the target of spammers dozens of times per day. but you don't see any spam here, because we try to make sure you're you, and that you belong here, before your account is validated. no one is in the validation queue, so, either you are validated or, if you aren't it's because you didn't pass muster. if you don't have a validated account i recommend you create the account once again and, in the question we ask you during the sign-up process, reference something about this discussion we're having. we have 90,000 registered users, so it's not hard, just, i need something in your account that tells me you're you and you belong here.

personalities: everybody hates andy coggan. except those who don't (which includes me, but i had to practice hard). my guess is that everybody hates hambini except those who don't. so, when you get hambini and coggan in the same forum, what do you think is going to happen in a hen house full of chickens, and 2 cocks? so, my advice, don't take things personally. otherwise, the urgency of your message is lost, and the cycling world loses your voice. i doubt thinks went any smoother in the weightweenies forum. this is cycling. this is the milieu. figure it out.

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Dan Empfield
aka Slowman

Why, might I ask, are you singling me out? I was a late entry into this thread, have not had any disagreeable interactions with hambini or Peter (until his last somewhat bizarre message), and have not been involved in the exchanges on weightweenies.

IOW, I think you are pointing fingers in the wrong direction.

i just noticed the last couple of posts, and commented on them. but i have this sense that this is a moving discussion - like a progressive dinner - and you all are having the same argument from forum to forum. i just think that whomever are all the players - hambini, peter, the other 3 engineers there, you, tom anhalt - you all need to find a way to talk things through, just in case the hambini folks have something good to add to this discussion.

my sense is that the hambini crew are like so many others who've waltzed into cycling with zero regard for product or protocol that existed before they got here. but i might be wrong about that and even if i'm right about that sometimes folks learn to appreciate how incredibly precise and difficult this industry is (just try to make a crank, chainrings, a BB, and a frame, stick it all together, and see if the chainrings spin true; and then make that happen in a $69 complete bike).

but, hey! they're new here! and we need to be welcoming, and i know you guys! and i mean this in love: who do we think we're shitting here? the slowtwitch family is a nuanced group. so, we have 2 nuanced groups, with enough PhDs in this discussion to populate both starting lineups of a basketball game. it would be nice if we could all find a way to get past the idiosycracies, regardless of who is most idiosyncratic.

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Dan Empfield
aka Slowman

The answer to that is long. The short answer is don't be offended. We want a octagon cage match performed with civility and professionalism. Slowman singled out because you're one of the (few) regular posters that we can throw into the octagon and expect to go toe to toe with someone who *appears* to have a legit aerospace background.

I hope it works out because there's a suggestion that Hambini could provide some significant value to the discussion of cycling aerodynamics.

I will simply repeat what I said above: I am a late entry into this thread, have only posted a few times, and have not been involved in the discussion on weightweenies.

IOW, your "sense", at least in my case, is wrong.

So I am clearly WAY late to the party here!!

So sad to me to see how little credit Zipp got for any of this... when we launched Firecrest in 2010, we did with its some amazing supporting data including 3 prior years of AIAA papers developed with Matt Godo... we were the first to talk about transient behavior, and then developed the models for handling stability..the first to extensively use the Aerostick to test and later validate handling improvements...etc, all of the other stuff mentioned here from every other single company has benefited from the work done to develop Firecrest (especially the work of Matt Godo.. we even became the first non-military winner of an Innovation Excellence Award at SuperComputing 2012), which makes me super proud, so hard to see it forgotten so quickly. Rant over.

I really like the way the Hambini crew have tried to put numerous variables into one single test.. it's an interesting attempt to blend real world data into something new and better. One of our secrets at Zipp was that our tunnel protocol went 0-30 and then built the curve stepping back to zero.. so it started with detached flow and measured when it all came back together rather than the other way around which led to shapes that seemed to be more forgiving of transients. Many wheels (and bikes) have large hysteresis when comparing 0-30 to 30-0

Past all of that, I have no horse in this race so my questions are all based on logistics:

1. What tunnel was this done in and who/how was it paid for? I see the it says weekend project for engineers, but with a 1600 second (26+ minute) protocol run time per velocity regime, you are looking at ~1hour per run time per setup assuming spin-up/spin-down time turn on of data acquisition, etc..then assuming a minimum ~30 minute de-fixture/change wheels/re-fixture, re-zero, and water the rider time this makes for 1:30 absolute minimum time required per wheel model if you're running it like an F1 pit crew.. I count ~30 fan-on hours here plus probably 50% more in fan-off time plus 2x that amount in post processing.. and that's assuming everything is perfect all the time. So that's a long way of asking if you are trying to monetize this in some way or if it was covered by other means?

2. Is the tunnel used for other things?
3. Did you have to tear it down and set it up each weekend or whatever to do this over a few months?
4. Was the same rider used for every test and if so, how did you find somebody who could/would ride a 26 minute tunnel protocol back to back at the required level of physiological stability required to net a +/-2.5% max error?
5. Is the tunnel temperature and pressure stable or is this accounted for in post processing? I'm assuming this took a few months to complete so ambient had to vary quite a bit?

If nothing else, I love seeing the discussion on these topics as we try to move the state of the art to the next level.
Josh

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Just... no. You can't seriously believe that. I don't want to go back to one ounce of that nonsense, so can we just move forward instead of reinventing the recent history?

Maybe engineering works totally differently in the UK, but when someone makes bold revolutionary claims, then other engineers are *really* going to want to see the details that back up those claims. The average Joe won't care because they don't understand the technical aspects anyway. But engineers who are interested in the topic get really excited about this stuff. And of course they'll want to go over the details thoroughly and will have many ideas and critiques.

Those details would be your field testing instrumentation, protocol, and data collected. And then how you replicated "real world conditions" in the tunnel, and the data collected. I know it's a lot of work, but if you are engineers you surely understand that "everyone has been doing it wrong (for decades), we did it right, here are the numbers, trust us" isn't going to cut it.

I'd be extremely surprised if you did everything perfectly on the first try. This was a hobby project after all, not a well funded research endeavor. So I hope you aren't too concerned about defending it on that level. Adjustments will surely be made. It's a learning process.

I for one have a very positive attitude regarding the concept of using unsteady flow or motion in wind tunnel testing. In the real world, wind is very "unsteady" and the bike and rider constantly making subtle corrections. Also the large reduction in drag at high yaw that is commonly reported in WT tests (for wheels, frames, and even riders on bikes) has never happened in the real world for me or most of the people I know.

Hi Josh. Some of your questions have been answered in the WW thread at least in a cursory way (but don't waste your time!). We haven't seen details of their protocol or setup however. Hopefully that will be reported eventually. It's a hobby project and they basically led with results. Full details might take awhile.

Apparently in the UK engineers are allowed to use their restricted corporate facilities for personal projects. Blows my mind, but.... I guess Airbus (or some other company?) paid for this indirectly. The specific tunnel wasn't identified.

I also wondered about the inclusion of a rider for these tests since that introduces a lot of variability. Hambini mentioned that they took care to ensure that the rider's position was consistent. I still think that is an issue, particularly when testing over a long period of time. They are estimating +-2.5% error which is quite a lot when you consider that the wheels are the only variable and they are small % of the total drag. For instance when you look at the 30km/hr chart here: https://www.hambini.com/...hich-one-is-fastest/ a wheel reported as 185W would have overlapping error bars with every wheel tested except for the Ksyrium.

I hope that they are advancing the "state of the art" as well. I like the concept anyway.

I like the test. I have a pair of Shimano C50 that I got for 500 USD 4 years ago that seem to be doing extremely well for the price tag.
I also like the bike bottom brackets you're making and selling on your site. I will get one of these next time mine is due for a change. I really like the idea of having only to swap the bearings later on.

I haven't really understood yet why your test protocol supposedly models reality in a better way than traditional approaches where one would determine the most relevant yaw angles seen in reality and then focus on these. Afterall race courses are seldomly routed through perfect loops with wind coming from the same direction during all this time. But then I'm only on page 8 on the weightweenie thread so far and probably I will get to the point where thats covered. Just because its been done in a certain way in the past doesn't mean that its the best way to look at it.

I absolutely don't think that you need to point out at every chance you get that you are an aerospace engineer. I get how you would lead with that during the introduction of your work, but reading it now in every second or third post of yours over various forums complete with pictures of military aircraft for illustration now that kinda seems totally stupid. And there is quite some condescending tone that people are getting annoyed by no point in denying that. Theres been quite some interesting points raised and scientific explanations given and those speak for themselves so no need for the crap between the lines.

Just to put some color on wind speed at 0.5m as it relates to cycling. On long rural rides, because it's more pleasant.

For standard reported numbers at 10m wind speed at 0.5m will be:

45% lower passing by a mowed airfield
60% lower spinning between a field of wheat and field of barley
75% lower passing by an oak
And 84% lower Just before you get to the pub.

I'll chime in because I think I understand the concept at least. Typical "real" wind has more variability than you see in the tunnel. It's constantly changing in direction and intensity. Plus the rider and bike move from side to side, and the wheel will pivot slightly as you move down the road. They are attempting to model this by moving the bike +rider back and forth in the tunnel a small amount, while simultaneously running through a varying yaw protocol. They don't stop at a particular yaw and wait for the drag to settle as it typically done. Hambini also mentioned louvers at one point but I don't know if they are manipulating the flow-field as well.

BTW, I'm WMW in the weightweenies thread but rruff everywhere else.

Thanks for chiming in Josh. Personally I don’t have a dog in this fight. As a neutral and somewhat educated observer I just found it interesting that Hambini’s results stacked up about the way I would have expected. I know Zipp has put a lot of R&D into their rims and came up with a shape that both Roval and Bontrager (D3) seemed to settle on as well after doing their own R&D. A few years hence and both Enve and Bontrager (XXX) produce new rim shapes that are remarkably similar to each other. As far as white papers go I place more faith in Trek/Bontrager than just about any other company (no offense to Zipp) so in the case of the XXX I believe Bontrager when they say it is both faster and more stable than their prior D3 rim shape. The fact that three others came up with a similar shape... seemingly independently... tells me it likely is a (slightly) better mouse trap.

That said, rims like the Enve 7.8 and 808 are so different in shape but so similar in performance it leads me to believe there’s more than one viable approach. The big question mark, in my mind, is why the Flos performed so poorly.

[quote GreenPlease The big question mark, in my mind, is why the Flos performed so poorly.[/quote]


Yeah. Even if the whole data collection/yaw distribution issue is problematic, that chart labelled "Steady State vs. Transient Drag Characteristics" is compelling purely as a standalone thing.

Also I used to scoff at Zipp's dimples. My scoffing is tapering off a bit now....

Here's another wrinkle: I just looked back at a "yaw-weighted average drag" of Mavic's new "Cosmic Ultimate" wheels (which are pretty sweet btw) and noticed something unusual about the yaw weighting. Take a look:



See it? I'm not talking about the unusually good Aeolus 3 performance. Take a good long stare. Is it me or is Mavic placing an unusual emphasis between 10 and 20 degrees of yaw (and not for the sake of winning their own tunnel shootout it would seem)? Doing rough approximations, it does appear that the final value they give for each wheel weights primarily measurements inside of 10 degrees of yaw but... what's with all of those data points out past 10 degrees?

I'd also like to point out that, despite some tongue-in-cheek marketing, Mavic has been pretty tenacious in sticking with NACA derived shapes.

When close to the stall angle, the data tend to become more variable, as very small differences in yaw angle result in much larger changes in drag. It therefore makes sense that they have collected more data between 10 and 20 deg - in fact, I did exactly the same thing when testing the flat-faced MRC brake in my wind tunnel, collecting data at 12.5, as well as 10 and 15, deg of yaw to try to better understand the source of asymmetry.

They come with black prince pads, and all the items to go tubeless. They are a great value. I never even think about the braking. They just work. I have a set on my trek now. The tubeless part is a PIA. Ran 24 Bontrager tires and it took 2 of us to get on. The rear seated great and has not leaked. The front looses a little in a week.

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http://www.TriScottsdale.org

GreenPlease wrote:

<snip> post #1 </snip>

Great topic - and I'm glad to see folks challenging the status quo when it comes to how best evaluate wheels in a tunnel. The vertical and horizontal gust simulations (louvers) that are alluded to by the folks doing the testing is really interesting! I'd like to hear more about this. 👍

Side note: glad to see that post #2 in this thread related to tires! Warms my heart! :-) I can still remember the shock on the Rolf wheels aerodynamic consultant in the 90's when I put skinny tires on wheels that were being tested in the tunnel at A&M and minds were seemingly blown! haha.

Now, I just wish post #3 would have something to do with "watts to spin"! haha. ;-)

Unsteady aerodynamics are very interesting to me => here are my thoughts on the topic from 12+ years ago:

http://biketechreview.com/...adence-and-cda#11354



you'll note the caveat in the quote above: " it is also assumed that beta angle sweeps in the tunnel are done for all cases one is trying to model"...i think there is a dearth of information/tunnel data regarding a wheel that is simultaneously experiencing sideslip and "roll" => maybe this protocol can provide insight into this?

anyway, good stuff - I really appreciate that a group is trying to move the needle on the topic!

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=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================

i recall a comment from Paul Lew about the original Reynolds Aero line a few years ago basically saying (as best i recall and i'm sure i'm mixing up the terminology but hopefully i can convey the point) that the more V shaped rims are low drag whereas the more U shaped are high lift (negative drag sail effect) - producing opposite forces along different vectors such that the resolved vector sum may amount to much the same system performance. of course the different shapes have pros and cons in terms of rim structure and handling which is mentioned in the Princeton thread

i found this - note the quote i was thinking of but along the same lines

The best way to think of this is that for a given depth of wheel, they are all going to have really similar surface areas... so the amount of total force that has to be resolved is going to be somewhat similar. This is how the whole Firecrest thing came about... once we had deep wheels that could output drag numbers nearly identical to a disc, we believed that there would be little more speed to be found, but that we should focus on handling as the real problem with deep wheels was that in the conditions where they were most advantageous to run (in the wind) people didn't want to ride them.. So all of the surface of the wheel has some forces on it, the question is how do you resolve and distribute them to minimize drag, side force and steering torque. Ultimately we learned that it becomes a bit of a shell game where every possible solution has some tradeoff and once the system is highly optimized the tradeoffs generally become nearly 1:1 where 10 grams of drag reduction just becomes 10 grams of side force, etc..

I don't have access to all my old Zipp stuff, but here's a link to a presentation Matt Godo gave in 2011 using our 2009-2010 benchmarking study for Firecrest.. there are other presentations that show not only steering torque (he called it turning moment) but wattage to spin as well as the transient effects of turbulent and vortex shedding. Also shown here but only minimally are the visualization tools we developed to understand where on the wheels the forces were acting which allowed the calculations of steering torques and centers of pressure (Cp) which we determined to be the biggest factor in handling.

Once you eliminate the low hanging fruit of big pressure drags related to separations of flow, the only way left to sufficiently lower the drag further is to utilize aerodynamic forces have to be turned into a combination of side lift and forward lift.. The goal with Firecrest was to balance the front and rear half of the wheel so that the center of pressure remained in front of the steering axis at all angles with little fore-aft movement. You see on the graph that a front disc wheel and our own 1080 have a rearward center of pressure..and while this 'rudder effect' seems initially like a self stabilizing feature, it isn't. This is due to the way a bicycle initiates a turn.. for a bicycle to turn left, the contact patch has to move to the right, so the wheel initially has to turn right which then makes the bike lean left... this is why you fall over when you get pinned up against a curb or in a rut, you can't lean away from the curb because the wheel needs to go in the curb direction to move the contact patch to allow you to lean the other way.

Similarly, we found with the wheels..if a wheel turns into a gust wind (sounds like a good idea) the contact patch moves toward the wind, but the rider lean then goes the other way which pushes the bike/rider system along the direction of the wind and the only way to correct it is a pretty significant steer into the lean direction to move the contact patch to the other side... with Cp in front of the steering axis, a gust of wind initiates a lean/turn back into the wind.. it's much more stable.

So the problem turns out that some wheel designs, particularly ones that have sharper inner diameters is that the center of pressure will cross the steering axis at some angle..as you have larger movements of Cp with yaw in these designs. Cp crossing the steering axis means that the wheel behaves one way in certain conditions and the opposite way in other conditions, and that's even worse than just having Cp on the wrong side of the axis.. One way around this would be to have the Cp start well ahead of steering axis and then come back with yaw..this would give you proportionally higher torque values at low yaw, but at least the handling would be predictable..


Here's a Cp plot we did for the 808 with Intelligent light...sorry, I'm limited to public domain stuff, but we had hundreds of these plots and graphs showing different rim shapes and the movements of the Cp's...it's super interesting stuff! Anyway, you can see that we designed for a Cp that was as low as possible and as close to the steering axis as possible without crossing it. The Cp moving rearward with yaw means that as side force increases the lever arm relative to steering axis is decreasing.. still looking for the graphs on this, but the goal is a graph that has pretty flat steering torque regardless of wind angle.

Long story short, the 808 in the Hambini test is now an ~8 year old shape...I have no doubt that there are faster shapes and designs at this depth. Heck, we had identified dozens of them before I left Zipp at the end of 2013.. but we never found one that was worth the tradeoff in handling, which is not in any way meant to say that it isn't possible. We were also beginning the study of the waveform inner diameter rims when I left and that more than tripled the design elements in a rim opening even more options for tuning. On a separate pathway we had begun using a mathematical technique called simulated annealing to seek other possible solutions for this when I left, which showed that for a given optimization parameter, there were groupings of solution sets that were competitive, but at the same time, the solution pathway we were one was pretty robust and hadn't been fully explored. Sadly you need infinite resources for that!!

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Does this help? I just created a quick Monte Carlo simulation in Excel to see what sort of standard deviation produces that outcome:



So that is with a range of true power values and number of data points similar to those in the study. R^2 = 0.97 is achieved with a standard deviation of measured power around 15W. Because it's a Monte Carlo simulation, the result changes each time I run it, so I've just run it 10 times and taken the average R^2, and it was 0.9751. So if anything, the SD should be a little higher than 15W. Does that make the amount of variation seem less implausibly low?

You could have just calculated the SD of all of the power values using the R^2 and SEE given in the paper.

That said, I have no clue what you are trying to achieve.

If I go out and aero test, then I can't really relate to an R^2 value, because I have a single true CdA, and lots of observations of measured CdA, so R^2 isn't relevant. What I can relate to is the standard deviation, because I can look at the standard deviation of my measured CdAs.

What you have calculated does not tell you what you want to know.

You'll have to elaborate, as I believe it tells me exactly what I wanted to know.

It appears that you wish to know the between-run variation in power within a single individual, so you can relate that figure to the variability you see in field testing. The data in the paper, however, represents the between-run variation in power across multiple individuals. Furthermore, each individual only did a single run under a given condition (i.e., speed and direction).

Now if it is the within-run variation in power (either within or across individuals) that interests you, you can't determine that from the data either, as only the average value was used in further calculations.

Or just read the paper:

"Mean values were 172.8 ± 14.7 W for SRM versus 172.0 ± 15.2 W for the model"

(I forgot that the overall means and SDs were in there.)

That is handled okay by what I did. Each random number is a sample from a normal distribution with a mean of the true power in the column to the left, and a standard deviation of the value in that cell. It's a single sample from the distribution that would be expected for that one person, i.e. the model is of variation within a single individual. The graph then calculates the r^2 across individuals like you did. So the model shows the variation within each individual that gives rise to that r^2 across individuals.

Picture two cyclists tested at multiple speeds, each under perfectly still conditions and while holding perfectly constant power on perfectly level ground. Also assume that the model is perfect, i.e., within a given individual the R^2 between modeled and predicted power is 1.00. Finally, assume that one cyclist is much heavier and less aerodynamic than the other. In this scenario:

1) the within-run variation in power is zero (assumed);

2) the between-run variation in power at a single speed is zero (corollary from first assumptions in first sentence);

3) R^2 between modeled and predicted power when you pool all of the data is less than 1.00.

IOW, as I said before the answer that you are seeking cannot be determined from the regression analysis, because the latter was performed by pooling averaged data across individuals.

Do you mean measured (the graph from the study is labelled as measured power vs predicted power)? In any case, I don't see how 3 follows. If the two are perfectly correlated, you'll just have a load of points (x1,x1), (x2,x2) etc, even if they've come from different riders, and r^2 will be 1.00.

Or are you saying each point on the graph represents some sort of average? Even if that were the case, averaging (x1,x1), (x2,x2) etc will still give (y1,y1), i.e. it won't move the correlation away from 1.00.

Thanks for all the insight Josh. Interesting point about "once we had a design that was nearly as fast as a disc". I'd never thought about it that way but, once you pull watts to spin out, many modern wheels are nearly as fast as a disc at low yaw so there really is not a lot left on the table in terms of aerodynamic gains.

When you say "wave form inner diameter rims" I assume you mean the 454 and 858 rim shapes? What are your thoughts on those wheels out of curiosity? How do you think that design fares with regards to managing the center of pressure?

I'm also curious to hear your thoughts on the new Bontrager XXX wheels as they make some big claims with regards to side force to drag but... as you pointed out... it's not just about side force but also where the center of pressure is and how stable its location is (something I'd literally never thought of until you just brought it up).

One more question, just because I'm curious to know if you and/or Zipp looked into it, what are your thoughts about wheel design and frame and fork interactions? Can they be done separately or should they be viewed as a system? Can wheel design be frame/fork agnostic? Are wider forks less sensitive to wheel selection?

Thanks for that. You probably have us much design and wind tunnel experience with aero wheels as anyone on the planet so it's great to have your input!

What are your thoughts regarding the premise of Hambini's testing protocol; that small oscillations in the flowfield and transient yaw movements (more closely modeling outdoor riding conditions) can have a significant effect on the drag and stability results?

Good question. Despite Josh's protestations about leaving out Zipp, zipp.com is unfortunately a veritable desert of tech information that goes beyond marketing pablum.

There is a slight hint as to their thinking on one of their "whitepapers", :




Sort of interesting that they call the "normal conditions" 5-16.25 degrees. That's more consistent with Hambini than the ST-approved notion that 0-10 is "normal conditions." Especially that 0-5 is completely left out.

But I could be reading way too much into that cartoonish graph.

Zipp has always favored that high yaw regime. So did all the other wheel manufacturers AFAIK... until recently. I don't know if there was ever a scientific justification for it, but deep rims have very low drag in the 10-15deg yaw zone, so....

Finally some people actually went out and measured it: https://www.slowtwitch.com/...Yaw_Angles_5844.html

Paging Skippykitten (James Webb)! He's been developing his RiF aerostick for awhile now so he should have a very good idea regarding real wind conditions and variability.

Yes - that's what I meant by the ST-approved notion of yaw angles.

I just wish that page had more information. Few go much deeper than "bicycle mounted sensor". Only Flo, as far as I can tell, goes so far as to specify a specific model and sampling frequency. Flo calls 1Hz "high frequency," but that's *not* high frequency for transient analysis.

My point being that a vaned yaw/beta sensor already has some built in "mechanical low pass filtering". It's, by its nature, intended to be a steady-state direction sensor. Then for sampling rate it's not clear if data is being integrated over that one second, and 1Hz is just the recorded sampling rate, or if it's truly an instantaneous sample. If integrated, that's another filtering effect. In the Coggan paper the wind direction sensor was on a control tower somewhere, apparently?

My point here is I'm just wondering if Zipp knows more about this transient, more chaotic "wind buffeting" right at the surface layer. Suggested by Hambini. Rather than this smoothed vane-calculated vector, possibly integrated over a time period of at least a second.

We're jumping all over Hambini for not telling us much about his data collection apparatus and methods. But we're also, as far as I can tell, not eating our own dog food. No one has really specific apparatus or methods with sufficient detail to attempt complete replication of results. Except maybe Flo.

Hello joshsilca and All,

Future stall and gust control gains may be had by the automatic articulating of portions of the wheel (or vanes on spokes) to match changing flow conditions.

Did you experiment with this concept at Zipp?



While this slat design shown here was preceeded in prop planes .... the version here in the Me 262 ... was later copied almost exactly for the F-86 and FJ-2 and performance was excellent. (Personal experience USMC FJ-2)



The slats require no power other than the motion of aircraft and no control inputs from pilots ,,,, the relative simplicity of using gravity and reduced air pressure to deploy the slats and increased air pressure to retract it is a good example of using changing enviromental conditions to cause 'automatic' device changes to adapt for optimum performance.

For aircraft slats provide a higher angle of attack for wing sections and a delayed stall.

For bicycle wheels slats could be used to delay wheel stall in gusts and also have a dumping feature to prevent an upset with forceful gusts values beyond the stall controlled values.

Aircraft slats shown here have enough mass to move relatively slowly. Bicycle wheel slats could be light as a feather and move very quickly.

The slat has a counterpart found in the wings of some birds, the alula, a feather or group of feathers which the bird can extend under control of its "thumb". [Wiki]



A bicycle front wheel with both the characteristics of a full disk like a Zipp Super-9 Disk (low drag) and a Zipp 202 (good control in windy conditions) should sell well.

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Cheers, Neal

+1 mph Faster

Great question! 😉

Scott

Good point about how that sensor may bias low in its readings.

I've got an Alphamantis Aerostick I'm dusting off for some "playing around". It's a pitot tube device, so shouldn't have any mechanical "low pass" action...IIRC, wind speed and yaw angle are transmitted at 4Hz on ANT+.

I'll have to check what the internal sampling frequency is and if the 4Hz transmitted data is averaged or downsampled.

I'll let everyone know what I observe...

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http://bikeblather.blogspot.com/

Maybe this is a dumb question, but how does it calculate angle? Is more than one pitot tube needed to capture direction? I thought a pitot tube only captured a linear velocity along the tube axis.

I was trying to look up the sensor Flo used, and it doesn't seem to be in production anymore. But the same company has newer more solid-state-like sensors that seem to use arrays of transducers to presumably do some vector math to calculate direction. Kind of interesting.

Sorry, my thought experiment was ill-formed - ignore it.

To answer your specific question, though, each point on the graph is indeed an average value (as described in the paper, which you seem not to have read).

The airport control tower, correct, and direction data were only obtained at the end of each run (by radioing the tower and asking.)

(This was pre 9/11, so Jim was able to gain access to the airport taxiway simply by asking nicely. The airport was still open, though, so there were several times we had to all scramble out of the way of a corporate jet that had just landed or was getting ready to take off. A bit surreal, that.)

If they did, why woudn't they have told us? It's a big marketing bonus if they are accounting for conditions that others aren't.

They'd want others to continue to not account for those conditions? Trade secret kind of stuff.

The tip is multiport, with 3 precisely machined openings in the rounded end. One in the center and one on either side of it. Each of those ports are hooked up to a pressure sensor. Additionally, there is a ring of tiny holes further back on the tip on the cylindrical part. Those are there to get the free stream pressure.

Apparent wind angle and magnitude are determined from the output of all three of the tip port pressures, in comparison to the "ring" pressure.

I took a quick look at some previous data files had, and I mis-remembered. Although the WASP unit I'm using to receive the ANT+ signal can handle the 4Hz data, it looks like the files are recorded at 1Hz.

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http://bikeblather.blogspot.com/

i built a beta probe a few years ago and published some results on my blog - from what I remember, I experienced a lot more beta in the testing I did compared to what has been promoted here in slowtwitch-land:


http://biketechreview.com/...rement-at-a-distance


http://biketechreview.com/...le-probe-calibration


http://biketechreview.com/...9-overtaken-by-a-car



http://biketechreview.com/...g/520-laps-with-wind

http://biketechreview.com/...log/521-gps-and-beta



and here is a parts list of my setup - oh, yeah - garage science at its best! ;-)

http://biketechreview.com/...t_biketechreview.pdf



I _generally_ remember cobbling up the arduino sketch that drove the data acquisition...and the reported betas in the links/images above were most likely average values over a given reporting interval...iow, reported betas have been damped.




ETA: glad to see someone else chiming in on damped beta measurements of the past ... :-)


https://forum.slowtwitch.com/...ost=4803288#p4803288

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