I'm thinking the difference going from 28 to 25 will be much bigger compared to going from 25 to 23. I'd say you're going to notice a huge difference, but even with roads not smooth I think 25s should still be reasonably comfortable. Just don't go to 22s Today's groupride: Distance: 85km Duration: 2h47m. Avg. speed: 30,5 km/h. We rode varying terrain, so a lot of small short climbs here and there. We rode up the Thier D'Amry, which is a short climb. 300m, 11% avg. gradient, 18,9% max gradient. The recordholder on Strava did this in 39s at 30 km/h! That has to be close to a 1000W!