Too many variables to say whether one width is faster than the other. I will say this though, 2 seasons ago I ordered some new tires. My road bike doesn't have a lot of room for wider tires, so I ordered the same 25's. The actual measurement when mounted was 28. The new 28's are faster than the old 25's, but they are a different brand. I do run them at a little lower pressure, not too great a difference tho. Seems like pro racers are running wider tires and getting away from the skinny, higher pressure tires of the past, if that's any indication.