Thanks for posting this. I have the same question (same wheels and tyres).

....but additionally, does the answer change for old Turbo cottons (only used for racing, maybe 1000km max on them).

Well the TT that is in stock is only the 23mm at the current time. The faster TT is the 25mm version, that is the one from the test but it is also super wide. Not sure how wide it is on the Super 9. But both tire choices you are probably giving up some aero. I definitely wouldn't run the Turbo Cotton on the front because of aero penalty. You know what I am going to recommend but of the choices I would probably go with the GP TT 23mm front, and 23mm rear.

Fwiw, which I do have 2x of the 25mm TT for sale, 1 of which I think is listed in the classifieds.

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I put the 25mm on the rear and it looked good to me. Thomas i did not measure since it looked good enough. I also some how managed to hit every pothole and article of crap in the road know to man at Timberman which was quite a feat considering how good the road conditions were and that 23m SS / 25m TT held up very well.

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

I rode 23mm SS at TImberman, front and rear. What rim are you running the 25mm TT on? That matters a lot.

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zipp disc rear/ 808 front

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

I actually happened to roll a 23c GP TT just this past weekend. It basically was tied with the 24c Turbo Cotton (.0028 vs .0029 respectively), but actually measured slightly wider than the TC (24.6mm vs 24.25mm, mounted on a Mavic Open Pro at 120 psi), so make of that what you will...

That also points out the importance of "as mounted" tire widths vs relying on listed sizes ;-)

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So you mean that the CRR was pretty well a wash but the GPTT 23 likely had increased CdA?

Any comment on old TC (~1000km max) vs new GP TT?

I think that is what Tom A meant for the rolling resistance yes.
For the CdA, wider does not always mean less aero as it is rim dependant... though as a general rule it makes sense but it can be wrong (like GP 4000S II 700x25 which is quite ok on modern rims).

The only aero test I've seen for GP TT is from Swiss Side on their Hadron 625 wheel (see below) and show poor aero for the TT after 7.5° of yaw... bad news. Good news is under 5° it seems to be on par of slightly better than GP4000S 700x23...
Now if we consider (and I'm not saying this statement is true) that on modern rims a tyre that is aero on one is often aero on another (that's the case for GP4000S 700x23, GP Attack 700x22 and GP Supersonic 70x23 for which we've seen results on more than one rim in more than one wind tunnel) then we can expect GP TT to be quite good at low yaws on most modern rims. And we also know that Turbo Cotton 700x24 is not so good at low yaws since it's also been tested on more than one modern rim.
So GP TT rolls slightly better, is slightly better at low yaws aerodynamically and in my experience is quite reliable... this is why it is my tire of choice for most races though I would probably now consider Force 700x24 (since the rims I use are wide enough for it)) on a very windy day...

Pragmatically; are you basing this decision on 0.2w? Such a small difference is meaningless outside a laboratory.

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29 years and counting

Thanks for the detail.

....that BBS estimates 70% of my next major race has yaws 5-10% (40% positive and 30% negative) muddies the waters further.

25mm TT

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

Tom's article says the low CRR outweighs the aero penalty.

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If your running a 25m TT on the rear wheel and your not running a beam bike i think its fair to say that the rear wheel is even more protected from the wind?

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

Your picture below doesn't look too bad. I can assure the tire doesn't look like that on HED JET+, but the again we are talking about ID of 17.25 versus 21

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Fwiw, the lab is also running tests at 18mph, and that doesn't include a second tire, nor the aero penalty + the tire is up to 50 grams lighter. Marginal gains add up.

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Yep, because the lab is not factoring in yaw angle, rim size, and other variables. The lower CRR of 0.2W per tire means 0.4W can be saved.

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http://bikeblather.blogspot.com/...sheriff-in-town.html

Read this. This is why I ran a 24mm up front.

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To expand on this, I'd wager that the TT is faster than the TC from a CdA perspective. I only say this because of the way the tread is put on the tire. There is a big edge on the TC from having a glued on tread the GPTT doesn't have this.

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Heath Dotson
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Yeah...I consider anything within .0001 of each other to be basically tied. I don't think the methodology is good enough to really discern anything finer...plus, tire to tire variability can affect things as well




The used TC will have slightly lower Crr than a new one, but also will have most likely gotten slightly wider.

You're talking about fine differences here though...in the end, it's probably best to just pick the tire that you feel most comfortable with running and that looks the best on your setup ;-)

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Just like how I prefer to talk about aero drag in terms of CdA (instead of grams or watts), this is also why I think it's best to talk about tires in terms of Crr ;-)

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Yes it would be great if people spoke in Crr but I also understand that that it is only really meaningful/understandable to the geeks. Watts is even a stretch for the average triathlete. But regardless, this is how some of this bad information proliferates just by not reading charts correctly.

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Right and I have now read that piece maybe 5x times over the course of the last 2 years. The problem is that the picture we have has changed.

For one, it is data from Specialized. We don't know some of the other parameters like what the tire pressure on the rim, how long the tires had been mounted, had the tires been used before (ie. pumped up, not rolled, and casing expanded). We know have a clearer picture on how important some of those parameters can be. The Turbo cotton is still a great choice, I talked with Weiss about his setup at Timberman, he rolled a TC on the rear - not the front.

As a front? I don't know, I don't like it is as much on the front. Crr is less important on the front and aero more important. There are better options IMO. Regardless, while the aero picture of a new TC mounted on 808 might be ok given the trade-offs, that tire is going to look very different than the tire mounted to say a HED JET+. And that tire mounted to HED JET+ broken-in, I can't even imagine and then the aero picture really starts to change.

What it all comes down to is that if we are going to have these discussion we almost need to talk about the entire system including, which tire, at what psi, for which wheel. The new 105% rule Josh gave us is driving my view.

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Regardless, we need to be looking at it from a wheel-system prospective. The tire + the psi + the rim + how broken in the tire is width wise. I like the GP TT, I like the TC, but I would still prefer the SS.

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No need to speculate...the TC used on my Jet 6+ Black had ~700mi on it at the time of testing: http://bikeblather.blogspot.com/...playtime-part-1.html



It still didn't do too horribly overall when the aero drag was combined with the Crr:




I would be careful in thinking of the 105% value Josh gave as a hard and fast "rule"...it's a general guideline, especially if other info isn't known. In other words, it shouldn't necessarily be a "driver" in tire selection ;-)

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