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The effect of tire speed and temperature on rolling loss is described by two new tire characteristics: The speed factor indicates the relative change of rolling loss at a rapid speed change, and the temperature factor indicates the relative change of rolling loss at a tire temperature change. The two factors are derived from a general relation between rolling loss, tire temperature, and speed; this relation is valid for steady-state as well as transient conditions.

A brief discussion of the physical concept of tire energy loss and its relation to automobile performance is followed by a general definition of tire rolling loss. The effects of bearing losses, load, pressure, speed, road surface texture and other important factors on rolling loss are explained, and conclusions are drawn with respect to a fair representation of these factors in a generally accepted procedure for measuring tire rolling loss. General test requirements are outlined, and suggestions are made for a unified international test procedure.

A brief discussion of the physical concept of tire energy loss and its relation to automobile performance is followed by a general definition of tire rolling loss. The effects of bearing losses, load, pressure, speed, road surface texture and other important factors on rolling loss are explained, and conclusions are drawn with respect to a fair representation of these factors in a generally accepted procedure for measuring tire rolling loss. General test requirements are outlined, and suggestions are made for a unified international test procedure.

An interlaboratory test program was carried out by twelve test facilities with the objective to determine the degree of tire rolling resistance loss variations within and between laboratories. The same tires and test procedures were used throughout. Statistical data analysis involving all data as well as various data subgroups suggest that most of today's tire rolling loss test facilities have obtained an excellent level of performance. All measured and analyzed data are tabulated and displaced for each laboratory.

Tires built from compounds with equal storage moduli but different loss moduli for tread and body were subjected to designed tests on both roadwheel and twin rolls. The results allowed computation of the tread contribution to the total rolling loss, at various loads and pressures. On twin rolls, the relative tread contribution was much higher than it was on the roadwheel (typically, 60% vs 30%). On both machines, the loss contribution of the tread depended strongly on its loss modulus and on tire load; the effect of inflation pressure was small.

A linear relation between tire rolling loss and fuel consumption is derived experimentally for a tractortrailer operated at constant speed. The relation is used to investigate tire related fuel consumption and general effects of tire rolling loss changes. The results are compared with corresponding data of passenger cars .

A laboratory technique has been developed for producing road-like tire tread wear and obtaining quantitative results. The tire is operated on a flat-roadway test machine and subjected to a schedule of applied lateral and longitudinal forces to promote wear. Wear measurements are made using sensitive, electromechanical wear sensors. Some typical test data are shown. Operational experiences are cited and recommendations for technique improvement are made.

A general concept of tire energy loss is suggested, in which tire and roadway are considered a system, and tire energy loss is identified as the difference between input and output energies. From this concept, a uniform set of loss equations is derived covering not only the three commonly used test facilities, i.e., twin rolls, drum, and flat roadway, but also the major modes of tire operation including free-rolling, driving and braking. A few test results are discussed.

Nonsteady-state tire tests performed on Calspan's Tire Research Facility (TIRF) showed that at slip angle and load path frequencies of up to 0.2 rad/ft, attenuations of both lateral force and aligning torque are negligibly small. However, both quantities develop considerable lags at low path frequencies and, hence, show appreciable “dynamic” offsets, amounting to about 10% of the maximum steady-state values at 0.05 rad/ft (not uncommon in accident avoidance maneuvers). Actual, double-lane change maneuvers performed on a skid pad with an instrumented full-size passenger car indicated dynamic offsets of about ±90 lb for lateral force and ±17 ft-lb for aligning torque. These data were reproduced with good accuracy in simulations on TIRF in which both load and slip angle were varied simultaneously in accordance with typical time histories recorded in vehicle tests. It is suggested that these large offsets could significantly influence the dynamic response of vehicles.