I've been experimenting with my bikes. Fatter tyres are comfier and slower. Except on really bad roads. On bad roads, fatter tyres can be faster as well as comfier.

When accelerating, or braking, or when going really fast - fatter tyres are even more slow than thinner ones.


For bad roads in my country, I'm still not sure whether 23 or 35 tyres are faster. So many bumps that fatter ones can sometimes be ridden faster, more comfortably. I'll experiment with 25 and 28 ones, to try and find "the sweet spot".