Originally Posted by
Schwinnsta
This wrong by pure physics. I am not talking about or getting into the argument of disk brakes.
The contact patch does not really enter into it as such. The braking force is the friction FORCE, which is the pressure force on the tire times the coefficient of friction of the tire. The pressure force is the pressure times the area of the contact patch. If you have a wider tire, the tire patch area increases, but the pressure will be lower as it a linear relationship to the weight divided by the area of the patch. Not trying to be a know-it-all. If I am wrong about this, one of you physicist types correct me. That said there are advantages to wider tires but braking is a function of the coefficient of friction of the tire.
Independence of the patch size (Coulomb law) is certainly a good first approximation, but going into more detail a larger patch for tires will less likely skid than small. In winter or on sand, we go with lower pressure. It may have to do with the persistence of contact or static vs kinematic friction in grains. The Coulomb law/model is itself empirical and more questionable at the extremes such as going into a skid.