Wheel setup structure now has an additional optional field "grip", which is a relative friction coefficient that alters the friction that was fetched from friction table. The grip value is supposed to reflect tire construction, but at the moment it's just a simple value applied to all surface types.
The table is currently defined as follows:
///Friction coefficients for average tire: sliding dry, sliding wet
static const float2 TIRE_FRICTION[] = {
float2(0.65, 0.50), // 0 Dirt
float2(0.35, 0.25), // 1 Grass
float2(0.45, 0.35), // 2 Moss
float2(0.75, 0.70), // 3 Rock
float2(0.65, 0.40), // 4 Soil
float2(0.55, 0.50), // 5 Gravel
float2(0.75, 0.55), // 6 Asphalt
float2(0.75, 0.45), // 7 AsphaltPaintWhite
float2(0.60, 0.50), // 8 Sand
float2(0.45, 0.35), // 9 ForestFloor
float2(0.75, 0.70), // 10 Concrete
float2(0.75, 0.45), // 11 AsphaltPaintYellow
float2(0.00, 0.00),
float2(0.00, 0.00),
float2(0.00, 0.00),
float2(0.15, 0.07), // 15 Snow
};
Maybe instead of a single grip value we could add several, for different material groups?