Originally Posted by
Schwinnsta
I was assuming two tires different width made from the same compound so that coefficient of friction would not change only the width of the tire patch. Anyway, that was my assumption in the statement. That said, I would not think that these vary widely. I could be wrong on that point and maybe another thread should look at this. If there is much of a difference in stopping power of tires that would certainly something I would like to know when purchasing them.
Another assumption is that the tire remains in full contact with the road, the validity of which varies with tire width and pressure among other things. The point is that due to the texture of the road surface, the suspensive properties of pneumatics, and the well known aberrant behavior of rubber the coefficient of friction is simply not a constant property of the two materials as it is in some simpler scenarios (or equivalently we can simply say we're not dealing with "friction" but rather "traction"). Heck, according to Sheldon Brown it's even affected by the posture of the rider.
As I said it boils down to the fact that the coefficient of friction is an extremely complex quantity the determination of which in general is a
science in itself (and perhaps one of the most important ones of the modern age at that). So I don't think this is going to be settled in another thread either.