Viscoelastic Properties of Truck Tire Compounds and the Related Heat Build-Up

Rubber compounds used in the manufacture of tread-cap, tread-base, and for the rubber-coating of the rayon cord for 12.00–20 tires have been varied in composition and, in consequence, their viscoelastic properties have been altered. Operating temperatures, in test-wheel runs, have been measured in the shoulder region of the tire close to the casing, using a needle-thermocouple. Multiple-regression has been used to investigate which combinations of viscoelastic properties of the rubber vulcanizates would give a linear, significant correlation to the heat build-up in the tire with a minimum residual. From the nature of the variables in the regression functions, conclusions have been drawn on the type of load occurring in the different components of the tire. It was found that the tread cap contributed to the heat build-up according to its loss compliance E″/|E*|2 and the carcass according to its loss-factor, E″/E′. Thus, the statistics show that the greater contribution to the heat build-up comes from the tread-base, according to its loss-factor also. The values of temperatures, calculated by the multiple-regression, show deviations of only a few degrees centigrade compared to the average temperatures of tires of the same construction. Therefore the operating temperatures of tires to be expected as a result of the compound variations can be estimated in advance. On individual tires greater deviations, up to 10°C, have been measured. These are due to inevitable inaccuracies in tire building and errors in temperature measurements.