I thought wind resistance increased exponentially with speed where rolling resistance increases linearly? Wouldn’t that mean that different test speeds could at least theoretically favour different tyres? E.g. If the 28mm was the most aerodynamic but also had the highest rolling resistance, then the higher the speed the more the aerodynamic advantage would come into play. So it might be the slowest tyre at lower speeds/wattage but the fastest tyre at higher speeds/watts
Which might explain why the Worldtour with very high speeds seem to still prefer 28mm (and I’m assuming the Worldtour is fairly optimised on tyres these days given that guys like Josh Poertner and Dan Bigham are advising the teams). Though could also be explained by wheel sponsors - the Rovals in the video are pretty wide at 35mm external width on the front (I think), that’s wider than a lot of the teams are using. And/or Worldtour races are generally on good tarmac (other than the cobbled races obviously).
Yup, which is why if you vary speed and power you can estimate both CdA and Crr, and thereby determine how much difference you’d see at low speeds vs. high.
(Also, if you do the protocol and analysis well, the “sample size” increases so you can calculate the variability in your estimates of CdA and Crr).
In your experience, have you observed a pattern where at some width tires become too wide for a given average speed (assuming the rule of 105 is followed). Or is this something that can’t be generalized?
Well, first of all, I can only test with my bike, and on my bike the widest tire I can fit is a 28. But more generally, yes, there should be a width where the Crr decrease is offset by an increase in CdA if you ride fast enough. We see that on the velodrome where the speeds are high and the surface is very smooth, and that’s well-predicted by the physics, which is reassuring. So although I can’t test beyond 28 on my bike, I’d expect a similar thing on the road. Obviously, the road surface comes into play, but for a given Crr and CdA, you can calculate the “cross-over” point. Note that Crr scales just like road gradient, so you get a different cross-over on a flat road than you would on a hilly or rolling route.
I had my first puncture on my last outdoor ride of the 2023 season, so id ballpark about 8000km’s without issue. It did seal with a plug (eventually, half hour of pfaffing about) to get me home, but I’ll probably replace it in the spring. They are an absolute bastard to seat on my rims, so I would switch to something else, but I have another Pirelli new in box.
Have just taken delivery of Conti GP 5000 all season in 32s, Will be fitting them tomorrow and christening them this weekend; will report back with initial impressions. Based on the BRR data, they tick just about every box for me. I’d have liked the ability to run a 30 at the front, but (for some reason) Conti don’t offer them in that size!
Tarmac SL7 installed 32c All Season TRs on September 4th. About 1010 miles so far. Rode them thru the end of October and then switched to my gravel bike. Only rode 5000 AS TRs twice in December, twice in January, and then had Tarmac serviced last week and started riding the Tarmac again last night. Compared to my Checkpoint with 42c S-Works Pathfinders, the 5000 AS TRs at 60psi (I’m 91+kg) have some nice “float” over rough roads (the Pathfinders are even better). Really happy with them given they have better protection versus more supple tires.
Plus with all our crap roads I think the rolling resistance is likely lower than running a 28c tire - an opinion that is apparently backed up with non-scientific testing by NorCal Cycling recent video
Recently got my new do it all bike, the Canyon Grail which comes with DTSwiss GRC 1400 carbon rims 42mm deep and Schwalbe g one rs evo gravel tires. Did a few rides and they felt slower than my 60mm deep rims with gp5000 28mm tires. Checked out byciclerollingresistence, but their test only showed less than 5 watts difference between the tyres.
So today I did a little test. A 16km continuous loop without stops at my z2 pace on both wheelsets sitting upright with hands on the hoods. Tests done back to back.
GRC 1400 with Schwalbe: 27.5km/h at 171W
60mm rims with gp5000 28mm: 28.7km/h at 171W
That’s a huge difference I did not expect. Must have been a combo of rolling resistance, less aero rim/tyre combo and larger tyres making me less aero by raising the bike and rider. This was only at z2. The difference will be even bigger at race pace. The 28mm was faster across all segments headwind, tailwind and crosswind. I expect the roads would have to be pretty rough for the wider tyre to be faster.
I think 32 vs 28 of the same model tire us a more interesting comparison. For a gravel tire vs one of the best dedicated road tires, that actually seems like a pretty good result.
I’m honestly impressed with how fast the 40mm Schwalbes are, relative to what’d be considered a very quick road setup.
I’d also echo that IME tires that “feel slower” is often just a matter of lower pressure and slightly less twitchy steering due to the larger tire. Both make the bike feel less responsive, but are not necessarily slower. In this case your fat tires are definitely slower, albeit not a ton.
I’m currently running 32mm GP5000 TRs on 3T Discus 40|44 wheels (hooked 29mm ID rim). These blow up to ~36mm measured, and I’m running around 50PSI. This setup feels less responsive than 28mm tires at higher PSI, but based on my semi-careful testing it’s a good deal faster than non-aero road wheels with 28s and way, way more comfy.
You are right. I may have overlooked some data thinking the difference would be less.
In looking for the optimal setup for my trip to the alps later this year I have switched out the Schwalbes for 32mm GP 5000 S TR. I’ll run the same test again and see how that compares to the 28mm on 60mm deep rims. I really want the extra grip and crosswind stability for the descends, so I hope there’s minimal difference in speed. Though thats ofc less of a factor when only going 10kph up a mountain.
