I enjoyed the recent podcast with Ben Delaney re: buying speed, but… there was one thing, maybe a little thing, regarding rolling resistance that is so often misquoted that it’s become almost gospel. Specifically, the idea that wider tires are faster than narrower tires of a similar construction or within the same model.
It’s true (-ish) IF you’re considering equal tire pressure for both sizes. Nobody does that, though. For example, look at the chart from bicyclerollingresistance.com, comparing the rolling resistance of 4 sizes of the Conti 5000. The rolling resistance for the 32mm tire is lower than for the 25mm tire at 80psi (9 watts vs 10 watts). No one would run a 32mm at that pressure. Drop the pressure for the 32mm down to 60psi (still a tad high for all but the heaviest riders) and the resistance jumps to 10.3 watts. Now you’re looking at an ever so slightly higher resistance for the wider tire under conditions you’d more likely see IRL.
Another wrinkle to throw into the equation: once the tire width exceeds the rim width, aerodynamics suffers greatly, as well. Unless you’re riding very wide rims and riding on relatively rough pavement, the science doesn’t support the conclusion that wider tires are faster.
