Originally Posted by
mschwett
the issue i have with BRR (which i love reading!) is that the differences are so tiny in this kind of tire (a few watts max) that they’re totally swamped by aerodynamics, which is not discussed. i know that i only see consistent/measurable differences in speeds on segments which have pretty high averages, meaning some descending. the 28mm tires i’m on now come closer to the ideal profile with my current rims, and i definitely am braking more on descents that i do multiple times a week. wouldn’t be surprised if there was another 2mph at 35+. but it’s not really useful, since i’m braking it off, and at the more typical 15-20 average i see no difference at all other than a rougher ride.
Of course looking at that chart, you should also likely be comparing the 23s at 100 or so PSI to 32s at about 60psi. In addition from aero perspective, the assumption is generally all-else-being equal. Ie. a bike that's built to take 32mm+ tires, conceivably isn't going to be as aero as a bike built that could only take max 25mm tires. Nor could said bike likely be built to the same weight as a bike that hasn't been built to take only narrower tires. IOW, there's a number of factors.