With these you can make bumpy and slippery surfaces. The first pack of 11 lines is the default material.
It is used for textures which don't have any numbers in the beginning of their identifier in PT2. So those numbers are the key for defining texture's physics.
To make some texture use material 2, for example, put "2" to the beginning of its name. (So "grass7"-texture should be renamed into "2grass7".
And as I just said, don't put any numbers to the beginning of the identifier to make the texture use default material's attributes. (physics)
// material '0' , grass (in this case, but could be asphalt/dirt/sand too)
1.5 // Car wall friction. (Used when you have flipped over, and the car is sliding on its roof or sides)
0.7 // Tyre road friction.
1.0 // Down force.
7.5 // Bumpiness.
0 // Tyre sound index. [No effect]
0 // Crash sound index. [No effect]
0 // Scrape noise index. [No effect]
2 // Sparkiness.
1 // Room for expansion.
SKIDMARK.MAT // Skid mark material, see the following list.