Eunice:

 A paper about the subject with pictures of a tire test machine and some charts:

http://www.millikenresearch.com/TTC_SAE_paper.pdf

 

Now you've found the mother load.  The Millikens know just about everything and anything having to do with tire characteristics as they relate to vehicle dynamics.

Also, if friction is proportional only to normal force, how can any tire generate more than 1g of traction without aerodynamic downforce?

Give up?

Modern tires are viscous/soft enough to mold themselves into the micro-structure of the pavement and provide sort of a gear-like interface with the road surface.  It's very tricky to make this happen at optimum levels and taken to extremes, some of the "gear teeth" break off, causing rapid wear (track "marbles").


--

Mike

2005 Carrera GT - Signal Yellow

2008 Tesla Roadster - Thunder Gray

1972 BMW 3.0 CSi - Nachtblau

2009 Bentley Arnage T - Black Saphire