[adam728]

Originally Posted by CapriRacer

The old adage that the contact area doesn't affect friction doesn't work for tires.

Go look closely at the pavement outside your house. No, No, I mean "down on your hand s and knees" close. Notice, it has a texture. I'll call this macrotexture to distinguish it from the irregularities on the microscopic level.

This macrotexture allows the relatively soft rubber to penetrate that texture and provides more grip than ordinary friction provides. Under severe situations - such as hard cornering and emergency braking - the rubber gets torn off and that generates more traction. The result of course this that the part of the tread rubber is worn off.

This is very true, and often a point missed by many people. This is the reason I can climb Bump Rock at 8 psi, but not 12 psi (slickrock feature on a trail here, surface is much like concrete).

Ever screw around on very smooth concrete (like in a parking garage) vs textured concrete you'd find on a road surface? Much less traction on the smooth surface, even thought the material is the same. It's the "macrotexture".