Quote:
Originally Posted by mattW
My question is what is the relationship between contact patch and traction... in physics we are taught that the contact patch is basically irrelevant to friction because as the area increases the force per unit area decreases. Here my a post about it in a different thread:
Is there any reason why what I said isn't true? I don't know anything from my own testing, that was just repeating what I learnt at University.
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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.
You can see this on a race track as the "marbles" that accumulate outside the racing groove. These"marbles" are bit of tread rubber that have been collected together by the tire rolling over them and then thrown out by the cornering force.