Another big gain that is often overlooked is tire weight. My 26x1.25's are much faster than the slick 26x2.125's. They're both slick, they both roll nicely. But the big ones are very heavy, so they're not as easy to get up to speed. But oh, the ride. They ride so very very nice! I'm thinking about switching back to them simply because the roads around here have gotten so bad, the 1.25's are jarring. I might even get some 1.75 or 1.9's in the future, to try to strike a balance between the two.