Originally Posted by Kestrel
Well as far as drag slicks go, there's more to it then just simply more rubber on the ground. The compounds are different, the tread is different, and, going to my next point...
... the reason is IMHO geometry. You're right, in a static situation where the tire does not deform, more rubber does not equal more traction because the pressure on the tire patch is the same. However, a wider tire of the same diameter is under less force per unit area, and thus areas like the sidewall benefit from having to deal with less forces, making the tire stiffer, meaning that when it comes to a dynamic maneuver, more tire remains in contact with the ground.
Of course, this is just something I came up with in about 3 min. So I could be wrong
h:
Point taken. I can also bring some physics into this... now, you also have to remember that most of physics, especially basic physics, is for 'ideal world' applications. F = f * N is the equation used to determine the amount of friction. This equation means "The frictional force is equal to the frictional coefficient times the normal force." Contact area has nothing to do with this equation.