Originally Posted by
Hokiedad4
Like most things, the answer is, It depends. Under most conditions and on most road bikes, 28-mm tires will have less rolling resistance than 35-mm.
I think there's more debate in this forum between 25-mm and 28-mm.
I think this is a much more complicated question than most people think. I think the greatest difference has to do with the surface you are riding on and how fast you ride.
IF EVERYTHING ELSE IS EQUAL at low speeds a wider tire will have less rolling resistance because, at equal air pressure, it has to deform less. On a bumpy road a larger, lower pressure tire will be faster than a narrow, hard one because it bounces upward less. The energy expended to lift you up with each bounce, isn't moving you down the road.
As your speed increases, aero drag becomes progressively more significant. That favors narrow tires for folks who average greater than 15 MPH and wider tires for people who average less. As you progress beyond 15 MPH the benefit of narrower tires increases.