Originally Posted by
msu2001la
Yes, also worth noting that when Zipp says "optimized" they're talking about more than just aerodynamics. They use the term "total system efficiency" which takes into account vibration and rolling resistance.
Still, I'd be surprised to learn that 25s are faster than 28s on anything they're saying is "optimized" around 28s. 25s might be more aero, but might also have more rolling resistance and/or more vibration.
Oh sure. I guess I'm only speaking from an aero perspective because RR differences on a steel drum between tire sizes have been shown to be negligible. BRR has a great article on this. A bigger tire is "faster" on a steel drum if you pump it up harder but pretty much the same at the same firmness. The only way a 28 is faster is if you can't achieve your optimal softness on 25s without pinching.
Ofc things might be slightly different IRL. But Zipp's marketing says they tested narrower tires at the same pressure and thus same contact patch size, which is nonsense.
IMO the only reason zipp is pushing wider tires is that they know tire manufacturers can't make TL tires that won't blow at the requisite higher pressures for narrow sizes on their cheaper hookless rims.
btw I'm not saying there is no benefit to large tires. The ability to run SUPER soft pressures and a larger, more square contact patch are all great things. But I don't think speed is a benefit of wider tires.