Originally Posted by
meanwhile
At 15mph good 32mm tyres will be faster than good 25s; search for the recent references to Jobst Brandt and rolling resistance on this sub-forum. (A Randoneur runs faster than the speed you've quoted, and 28 is faster than than 25 for a Rando - narrow tyres don't take the advantage until quite a high speed.) The marginal weight difference will also be almost irrelevant.
I'm really glad you're here preaching this good news. Seriously. I'm a convert.
After reading something you wrote to this effect a few months ago I bought some 700x50 (29x2.0) Marathon Supremes for my rain bike. Despite being fantastically wide, they are faster than the 700x42 Conti TownRides they replaced. I'm assuming that in this case the faster has more to do with the tire itself than the increase in width, but the increase in width doesn't seem to have hurt at all. The Marathon Supremes even feel like they roll better than the 700x28 RiBMos I run on my cross bike.
I'm guessing a two-inch-wide tire actually would register some negative wind-resistance effects if I were faster, but at around 18 mph where I usually cruise it doesn't seem to be a problem. Maybe I've just had too much of the Jobst Brandt kool aid to notice.
