Heat Generation in Pneumatic Tires

A review of the entire literature on heat generation in tires shows that, while a considerable number of articles have reported the effect of running conditions, only the few cited here have provided clarification of the causes of heat generation. The overview presented here also has limitations in some respects, especially in that all the reported regression equations (except those for radial passenger car tires) have a large residual term. This is due to the scattering of the test results and the fact that only the viscoelastic properties of the tread and carcass stocks were varied, but not the tire cord and the other vulcanizates used. Tire cord properties have fixed properties, as far as the tire specialist is concerned and cannot be changed. A further regret is that almost all the investigations were carried out on laboratory test wheels, so that no experimental findings obtained from tires run on the road are included. This is so because road experiment conditions are difficult to make reproducible. On the whole, one can expect that the reported results would be qualitatively valid for tires run on the road, but the differences among different tire designs would probably not be as great, while surface friction effects would be more significant. Moreover, though the tire test parameters were different in the different laboratories, they remained constant in each test. No attempt was made to establish dependence on the load (except by Wesche), the internal pressure, the speed, the radius of the test wheel, etc., because each individual tire specialist is confronted, within his own development team, by certain standardized test conditions. The tires have to reach a sufficiently long running time under these conditions. Hence, they may not exceed certain limiting temperatures. Modifications of such requirements were not included in the scope of the present series of experiments. Almost all the authors took test samples for the measurement of viscoelastic properties from the tires, since correlations with laboratory-prepared test pieces were usually poorer. Nevertheless, in the course of compound development the tire chemist is forced to rely on laboratory test specimens and must establish relations to their properties. Consequently, the causes for the differences have to be elucidated for each individual case. In spite of these limitations, the state of the art, as presented here, permits reliable estimates to be made of the changes in tire running temperature that are caused by given changes in the recipes of the tire component stocks.