A series of skid-tester correlation studies are used to illustrate the difficulty of making "absolute" friction measurements on the tire-pavement pairing. The frictional demands of traffic are explained and the status of the theory of rubber friction is reviewed in the light of experimental findings. Special attention is given to the mechanisms of water displacement by the tire and the resulting coefficients on wet surfaces. The frictional performance of various tires in various operating modes is discussed and examples are given. Since theory is capable of dealing with real problems only in an approximate fashion, methods of obtaining tire performance by experimental means are reviewed at some length. Because tire friction changes with tread wear, current hypotheses on wear are cited.
Abstract