Slowman wrote:
stevej wrote:
Slowman wrote:
don't you think it's generally accepted that wider tires offer less rolling resistance than narrower tires - up to a certain width, with that width being probably 30mm to 32mm - and the limiting factor is aero?
It seems to be generally accepted but I don't know why. I personally don't subscribe to it as I don't think we have definitive data on it. We have sites like BRR that show a 28mm rolling faster than a 25mm at the same pressure but that doesn't translate to the real world. I think this confuses many and it leads to a false narrative. Lets assume 80 psi is the break point pressure for the 25mm tire, you wouldn't run the 28mm at 80psi. You would run it at say 75psi. What is the crr at the breakpoint pressure of the 28mm tire vs the 25mm tire at 80psi? This has been discussed several times on here and I forget who it was but someone mentioned that the crr would be roughly the same.
if you lowered the pressure, going from 25c to 28c, by only 5psi then the 28c would well outperform 25c on a drum roller. it's more like 10 psi or more.
here's why i think teams are moving to 28c with the proviso that some of this is a guess and some is what i've actually heard.
1. handles better, corners better.
2. more comfortable.
3. less chance of puncture.
4. is faster for this reason: the wider tire with lesser pressure, while rolling equally well as or slightly better than the thinner, higher pressured tire, does much better at sucking up bad or irregular patches of asphalt, and the speed delta between 25c and 28c is much bigger over those bad patches, ruts, jumps, curbs, etc.
I was using 5 psi delta as an example. Whether it’s 5, 8, 10, or 12 psi delta, the question still remains.
What are teams doing during TT’s? Are they running 25s or 28s? This seems to be a better comparison for tri. I’m not sure the criteria for selecting tire size is the same for a typical road stage (assume no cobbles and relatively smooth surface) vs a TT stage. It seems to me based on pictures I’ve seen that the top guys are running 25mm tires during TT stages but maybe I missed something. Perhaps Marc can chime in here.
I agree with #1 and #2 above. Not sure I understand #3. Could you elaborate?
#4 - so do 28mm tires roll equally as well as 25mm or do the 28mm tires roll faster? Marketing speak says they roll faster but then you just said something different and different from the original post I quoted.
Disclaimer: I run 28mm tires on my road bike on 19mm internal width wheels. I like them and will continue to ride them on my road bike. I run 25mm tires on my tri bike on 23mm internal width rims (Aeolus rsl 75s) as my training setup. I can see/understand the hype with 28mm tires and feel my tri bike setup could really use them for training purposes. What I don’t know is if I go to 28mm tires, am I gaining or giving up something? If so, how much? I don’t care about giving up something for training purposes So 28mm is a no brainer for my next set of tires on my training setup. But for racing purposes and getting every last .1 watts that I can, I’m not sure yet.
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