I've got 25s on my road bike and 32s of the same tire on my hybrid. Even with about a five pound increase in weight and a more upright position on the hybrid, the difference over a 50-mile ride is about 1 mph. If I'm riding with a group the road bike definitely has the advantage for sprints but the hybrid is a more comfortable ride on rough roads. IMHO the advantages vs. disadvantages to the two tire sizes are about a wash.