I did some runs today with both Corsa Speed 2 (CS2) and Veloflex Record (VR). Early morning with no wind. The goal was to get a CdA estimate to use for CRR tests, and do some low-speed rolldown tests (5-13 mph) with set start-stop points (consistent elevation drop) to find CRR values using VE.

About 1/3 of the CRR results (9 tests total) are not consistent with the rest, including all 3 tests of the Veloflex. Perhaps there were some fluke wind gusts. I got consistent CS2 results both before and after those.

However the other 2/3 of the CRR results are extremely consistent, and I think the low speed rolldown test is extremely promising to detect small CRR differences.

I've got some additional work to do on the data, and I may need to re-run the tests, but progress is being made. And I don't want to jump the gun, but even with the variability in results, the Veloflex is looking solid. Though not as spectacular as the Aerocoach results suggest.

Actually, as long as your tires are not over-inflated for the surface, roller testing gives the BEST results when trying to evaluate tires for TT/Tri purposes. Rollers aren't the source of the VF Record result discrepancies...more likely is product changes.

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Nice work. I am trying to decide on running the Power TT again this year or switch to the Records. They are just so thin but so tempting. I ran them yesterday as a mock TT test but I know my roads are clean here.

Thanks! The Power TT is actually another one I want to measure, as Aerocoach shows the 23mm (25.6w) as far slower than the 25mm (22.2). This large discrepancy between 23mm and 25mm tires isn’t present in any other tire Xav tested.

I actually bought a pair of 23mm TTs based on BRR results for the 25mm version, but went to CS2 after seeing Xav’s results.

I’m having trouble finding the time & wind-free days to get the VFR vs. CS2 test done. But when I finally do I’ll aim to do a 23mm CS2 vs TT next!

I have a lot of faith in the rolldown test method with VE that I’ve worked out. The 3x CS2 runs 80 psi gave CRR results of .300 / .300 / .301 when I did VE, no tweaking needed. And one of the runs was done 45 minutes after the first 2, with testing the Records in between. The Record runs weren’t as consistent but both beat the CS2.

I’m still determined to get this done just need another chance between life and the weather.

I vary the "entry" speed at the start point (and thus, the stop point).

Interesting, for what purpose?

I have been working hard to get entry speeds consistent, in an effort to reduce the impact of error in the CdA estimate on the CRR delta between tires.

Also I don’t want end the run at a “stop point” of zero velocity. I want to end the run at the start point, just with less velocity (of course), so I can be sure of zero net elevation change and use that as a known value in VE.

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Do you have a protocol for warming up the tires before each run? I see a pretty big change in Crr on the rollers until everything gets up to a constant temperature, which I assume is the equilibrium point between international friction and heat loss through the roller and surrounding air. I definitively need to get out my new IR thermometer next time I do testing to see how much temp and pressure change from cold to whatever the equilibrium temp is.

It lets you double-check the estimated Crr and CdA.


I just estimate both CdA and Crr simultaneously from the data. There are two unknowns, so you need (at least) two equations to solve for the two unknowns. Varying the entry speed gives you the two equations.

To account for tire temperature, I used a SEEK Compact phone-mounted IR camera to measure tire temps before and after the runs.

https://www.thermal.com/compact-series.html

I did play around with this a bit. It was early morning and overcast, no real sun loading. I found that riding on the tires did not increase tire temps whatsoever, taken immediately upon a brake-less stop (using a hill to stop the bike).

The one thing that did drive tire temps up was braking. I didn’t do any high speed or repeated braking that day, but the light braking I did would drive the brake surface & tire temps up 3-8 degrees. Tires were almost exactly the same temp as the braking surface - I guess the heat conducts very quickly from the wheel compared with the low thermal mass of the tire.

The wheel-tire system then cooled to ambient after a few minutes.

Once I’d established that tire temps immediately post-run we’re exactly the same as pre-run (assuming no braking) then I’d just record tire temps before the run, ensure they weren’t elevated, and avoid braking. The roll downs are low speed (to maximize the ratio of tolling resistance to air drag) so this wasn’t actually too hard to do.

Got it. I remember this from your original VE paper and have tried it once before, though not too carefully.

Have you done direct CRR comparisons using this method? I’m curious how much precision you can reliably get for a delta CRR.

I think I actually am basically doing what you describe. I did a high speed run first to establish CdA using an estimated CRR. For the low speed run, instead of a standard VE test with the “zero elevation change low speed rolldown”.

The final CRR and CdA combination does have to work for both runs. Although worth saying… I was initially worried about relying on high- and low- speed runs for precision work because CRR and Cd vary with speed, and I’m doing much of the low speed runs under 10mph, where I think this is probably significant and hard to control. That’s l part of what led me to low speed testing, where CdA errors are less of an issue, and rolldown testing, where speed profiles between low speed runs are very similar, further minimizing the impact of errors in absolute CdA / CRR values on “delta CRR”.

Ultimately it’s actually not that hard to validate a delta CRR method. You can do runs with the same tire at different pressures, where you have a small but roughly known CRR change (say, based on BRR’s data at 60-80-100 psi). If the deltas you measure lines up roughly with what was determined expect from 3rd party CRR tests at different pressures, then I’ll consider it validated.

I had some luck with this validation with the CS2s on the first day. I’ll ultimately post the validation data along with final results when I can get another full round of good tests done.

No ETA on all this unfortunately.

Only for proof of concept. I usually do powered runs, not coastdowns. Coastdowns take at least twice as long (cuz you have to go back up to the start) but they do have the advantage that you don't need to worry about the accuracy of the power meter -- so if I had a single-sided power meter I might do coastdowns. However, since you're relying on the speed being accurate, you absolutely need to measure loaded rollout carefully and use a wheel sensor rather than relying on something like GPS speed.

Wheel speed sensor for sure :-)

My original concept for the low speed run was powered. But with extremely low speeds (~6-12 mph range where RR losses are comparable to aero losses in terms of scale) I ran into some issues…

First I suspect that power meters lose accuracy at low power levels, since they are strain gage based (I used Garmin Vector 3). To stay in the 6-12 mph range, steady state power would be solidly under 20 watts (when using racing tires, skin suit, and aero tuck).

I also doubt I could pedal at that low power without gaps, that would further degrade the data.

One workaround I tried was using an “impulse” method where I pedaled for 7 second intervals every time I hit 6 mph to boost my speed to 12 mph, but I got messy results when I plotted VE. I assume this is an issue with data collection & recording with short bursts and a lot of on/off.

So to get good data collection at 6-12 mph, the only way I could think of was rolldowns.

The rolldown tests I did first were from point A to B where I guessed the elevation change.

The next set will be from point A (starting around 12-15 mph) back to point A (ending at 4-6 mph). Elev change will then be known (zero), not estimated. I have a loop picked out but could also use an out-and-back that turns around on a slope.

It's good that you're trying different protocols, measuring ambient temp, and refining your technique. Crr is small so you need good, repeatable, technique to get reliable results. When you have the right technique to estimate Crr, that carries over to estimating CdA because CdA is, relatively speaking, an easier nut to crack.

Crr increases quite a lot with speed on the roads where I tested... with the caveat that it could have been a mysterious "something else". Temperature effects Crr too.

BRR's data for Crr vs pressure would only be valid for the apparatus he was using. This would certainly not be valid on a road where vibration losses are a factor.

What you really want to do is compare the overall resistance of one tire vs another, at race speed and expected race conditions. If you are testing without airspeed measurement, then very low wind is your best bet, although you will miss aero differences. I suspect on most wheels the VFR will be aerodynamically better at yaw, because it is smaller.

Question is: What is the precision of your testing relative to the small difference in Crr you expect? Doing a bunch of test runs where you are trying to keep *all* variables the same (or compensate for the changes), will show you if you have a reasonable chance of picking the winning tire with any certainty. No tire swapping is necessary to do that.

Also, note that you need to nail the weighted rollout for each tire.

I won’t provide a watt savings, or actual CRR value. I’m looking for a % difference in CRR between CS2 and Record. If someone wants to figure out watts saved for Records, they’d have to baseline their watts for the CS2 off of all the data that’s out there, and apply the delta.

When I compare my results to Aerocoach’s and BRR’s results, I’ll convert their wattage results into a % compared with their baseline CS2 measurements (at 80psi for BRR).

So it’s true, my tests will be at 80 psi, smooth roads, low speeds, and a temperature dependent on the test day. Race conditions will definitely be at much higher speeds, and the other variables may or may not match. This would introduce error if the variables changed at different rates between the 2 tires, as conditions changed.

For example: hypothetically, the Record could have 10% lower CRR at 10 mph, but actually be 5% slower at 22 mph

Or one tire could do more to minimize vibration losses than the other on rough roads, in a way that doesn’t correlate with CRR.

Or is one tire could be faster at 50F, but the other tire is faster at 90F…. Or at least less slow.

These are all possible. I would think these impacts are minimal but I can’t prove this. I definitely welcome any insight here!

The most prominent & risky difference with race conditions, I think, is the slow speed of this test, around 10 mph.

For CRR vs speed we do have some data… When BRR did their test of CRR vs speed they found an a average increase of 12% CRR from 9mph to 22.5. There was a range of 6.6% to 14.5% between the 6 tires tested. But the article stated that all variation here was within the margin of error, so they could actually all have varied by the same %.

If there is in fact a dramatic difference in how much CRR increases from 9 to 22 mph between Records and CS2, say 5% vs 15%, then this would definitely throw off my results. Based on the BRR data, I wouldn’t expect these to be actually off by more than a few % points, if at all. But it’s a good point, and I’ll make sure this + the temp differences a stated assumption & potential source of error.

Overall I don’t think these assumptions are much (if any) worse than the assumptions made for various lab testing. I don’t know from any test results that GP5000s are slower than CS2s at a tire temp of 105F, or at 40F… but I think we all still assume the CS2s are still faster at those temps. Same goes for smooth vs rough roads, I understand that supple tires manage impedance losses better, but it the CS2 and Records are both in the “extremely supple” category, and nobody (I’m aware of) has publicized big differences in impedance losses between otherwise similar tires.



I hear you. I’m really trying! But I don’t know what I can make more race-specific, given the constraints I’ve got on speed required to amplify the CRR signal. Any specific ideas are most welcome, this whole thread had been a huge help for me to refine my process and consider new variables.

I’ve outlined above why I think this test will still lead to worthwhile results in spite of the differences against race day. But like any test, the results are imperfect representations of the actual use case, and while I think the assumptions are reasonable, they are far from perfect and will make any “close call” results suspect.

Yes the assumptions are too vague to generate specific error bars, so it will be up to every reader to make conclusions about precision against the real world. But in this world of aero & CRR, let’s be real, let’s be real, this is ALWAYS the case. We always have to assume to extrapolate. We don’t race on drums and in tunnels :-).

What I can do is to be sure to include these assumptions when I ultimately discuss results.

Ultimately this test isn’t meant to be better than the other public test results on these tires, just another data point to help people make decisions.

It’s worth repeating, the delta CRR between CS2 and NEW Records was something like 20% in Aerocoach’s tests, while BRR found them almost equal. That’s a massive difference. I think even my test has a good chance of falling clearly on one side or the other.



My initial day of runs, with one high speed tun for CdA, and about a dozen roll downs with CS2s and Records, came up with .00300/.00300/.00301 for the CS2s. Two were consecutive, one was almost an hour later, after a wheel swap. The Records weren’t as consistent. Could have been wind coming into play. So precision is TBD. There are some bugs to work out but also reasons to be optimistic about the precision.

Good point about testing on different days! But I’ll tell you, it’s brutally hard for me to find test days/times with no wind, minimal sun, and a few hours of free time. If I also needed to temperature match test days, I’d be lucky to get 2 tests in a year!

What I really need is a second identical set of 38mm Sunrise wheels. At $320 on Amazon it’s actually tempting… I wonder what the resale value is for these things?

If anyone would want to take a lightly used set of those off my hands, send a PM :-)

Also thanks again for everyone giving their input. Making this thing defensible is turning out to a lot of work, and all worthwhile.

I’ve heard it said that Records are skinnier but I measured at several points around the rim:

24.0-24.1 Corsa Speeds
23.8-24.0 Records

So skinnier but by very little. Maybe at 25mph I’d have to worry about that but at 10mph I think I can disregard - therein lies the advantage of going slow.


Great point! I’ll bring a scale next time to get real time weights. The tires are a couple hundred grams different & it doesn’t seem unreasonable that I’d gain or lose enough body weight from food & fluids to impact results.

Most data files only have speed resolution of 0.1 mph or 0.1 km/h (for this reason, I usually do all my measurements and calculations in metric). You want to get loaded wheel circumference right, but if you're off by a mm or two it's not going to screw up your estimates much. Likewise, you might lose a tiny bit of weight during a run but if it's not too much it won't screw you up much. I try not to make my tests last too long, since these things can change, but if you do some error analysis you can see that the effect of being a tiny bit off isn't huge. So try to get it right but don't lose sleep about changes during a test.

Did an early morning run over the weekend. Extremely low wind. Tire temps consistently measured 51F.

However, the CS2 data is no good. I realized after a few runs that the tires hadn’t seated fully, and was creating a subtle bump as they rolled. I couldn’t get it to seat for the life of me, even pumping to 120 psi. Looks to be an issue with the factory tape job on the set of Superteam wheels I used… I’ve noticed this issue before but was always able to seat with other tires. Oh well, another day of testing without conclusive results.

But I did get a few things out of this test.

- The VE out-and-back-low-speed-rolldown (OBLS?) method seems to give results consistent within a couple percent.

- The Records tested 4.5% faster… than a pair of CS2s that hadn’t fully seated. So the CS2s may have been at a penalty and the Records might not actually be faster at all. However that variable is unknown, plus I cut the test short (so the sample size was small, and I didn’t re-test the CS2s after the Records to ensure the process was stable).

Note: Aerocoach results show the new Records to be well over 16% faster than CS2. BRR showed Records to be 4% slower than CS2 (at 120 psi).

For reference, the gap between GP5000s and CS2 on BRR (80psi) is just under 20%.

VFR
.00298
.00296
.00283
.00287
.00293
Avg: .00291

CS2 (front & rear not fully seated)
.307
.310
.304
Avg: .00304

- I’m just going to pull the trigger on a second set of 38mm deep 25mm wide Sunrise wheels. I’m feeling really good about the method and am having a good bit of fun with this. I’ll do some more CRR tests in the future, next up will be 23mm CS2 vs. 23mm Michelins Power TTs.

I should have a much better test set done within a couple of weeks. But I thought these results were interesting enough to share.

Thanks for the input and confirming my tests. IME and with my own protocol (no OBLS but loop with a mix of coast down and small power applied), I got Crr under 0.003 and VF23 not in any way 20% faster than CS23.

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Hi Rob, apologies on my lack of understanding earlier... I thought you were testing these at race speed, but I see you are doing slow tests. Also, by "weighted rollout" I meant an accurate tire circumference/ speed measurement.

Instead of buying new identical wheels, you could try just swapping with a set you have. Wheel A tire A vs wheel B tire B. Then wheel A tire B vs wheel B tire A. Of course having identical wheels would be better, but...

If you enjoy testing I'd highly recommend the CdACrr app, written by the guy who replied above (bugno). https://cdacrr.blogspot.com/
I haven't tested for a couple years, and I see he's been making updates. There is a long thread about it on this forum. https://forum.slowtwitch.com/...system)_P5881854-12/

Thank you for doing this! I was thinking about getting some VFRs in case I race this summer, but I have Vittoria Pista 23s, and if the VFR is only a tiny bit smaller and a tiny bit lower Crr (maybe!) I doubt it's worth it.

My goodness there are a lot of interesting & useful discussions in that thread. Not sure how I’ve not come across it before!

Some things It helped confirm for me were my observations on tire temp - the ground temp is relevant, not just air temp. And ground temp would be weighted more heavily for my runs because they’re at low speeds, short durations, and on carbon wheels. Surprised this wasn’t mentioned but brake track temps appear massively more impactful to tire temp than anything else. A single brake event from 20mph might bump tire temps up by 5-10F.

If I ever find myself with more time to dedicate to the aero side of things I’d pick up that wind sensor and the app for sure. Much easier price to swallow than for the current set of commercial bike CdA wind sensors.

For now though, I think I’ll stick with the CRR side of things.

I’ve already bought the 2nd set of matching wheels so it will be way easier to actually plan & execute tests. Truth is I’ve got a newborn in the home so hobby time is a premium :-)

Still have a 2nd run of CS2 vs VFR, then Michelins Time Trial 23mm will be up next.

I’d also love to put the new Michelin Power Cup against the GP5000. I have the Continentals in 23 and 25mm but would need a pair of the Michelins (have too many tires around to justify those for riding, but perhaps for science…).

Glad it was helpful! While I really wanted the VFRs to live up to the hype, I’m also very pleased with the outcome of saving others the time, money, and overall hassle that such a low-mileage tire brings - while not actually gaining meaningful benefit over the alternatives.

With that said, I did race the VFRs at an Olympic last weekend :-) Only fair to wear them a bit since the CS2s have a couple hundred miles on them.

Thanks for all of your testing and time! Tried run the VFR in the TT at elite nationals and got a flat coming out of a corner just before the turn around. No idea what cut the tire but I almost crashed when in aero as it dropped and started to slide so quickly. Going back to Vittoria speeds once I’m out of these.