Rubber friction on self-affine road tracks

A basic theoretical concept of rubber friction on rough surfaces is present ed that relates the frictional force to the dissipated energy of the rubber during sliding stochastic excitations on a broad frequency scale. It is sh own that this is of high relevance for tire traction and allows for a predi ction of the likely level of friction of tread compounds on the basis of vi scoelastic data.. The impact of both, the frequency dependent loss- and sto rage modulus on the frictional force during sliding of tires on rough track s, is demonstrated quantitatively for different sliding velocities. The eff ect of the surface roughness of road hacks is described by three characteri stic surface descriptors, i.e., the fractal dimension and the correlation l engths parallel and normal to the surface. These descriptors can be obtaine d from a fractal analysis of the road texture via stylus- or laser measurem ents. In particular, it is shown that the applied model of rubber friction is in agreement with the classical friction data of Grosch, who found a bro ad maximum for the friction coefficient with increasing sliding speed. The broadness of the friction maximum is shown to be directly related to the br oadness of the roughness scale of the surface.