The Rolling Loss of Pneumatic Tires

Abstract

Abstract Tire energy loss has long been neglected as an area of scientific concern, in favor of other performance characteristics such as traction and wear. With the advent of federally mandated fuel economy goals, however, priorities have been shifted, and tire energy loss has now become a prime concern. Tires are responsible for a rather large fraction of the total energy expended by a passenger car or truck. For a typical passenger car driven steadily within the legal speed limit, the energy dissipated by the tires ranges between 3 and 7% of the total energy consumed by the vehicle. For a typical truck (18 wheels), these percentages can be about twice as high (see Section 7). Any reduction in tire rolling loss would therefore yield tangible fuel savings. In the past 5 years or so, the tire industry has reduced rolling loss by more than 25% (Hill and Moore). This is partly due to the rapidly increasing use of radial tires, lower loads, higher inflation pressures and less hysteretic materials. However, it is also partly due to the substantial efforts made by tire researchers to understand the general principles governing the loss of energy in tires. These principles are not intuitively apparent. Energy loss of tires is a very complex phenomenon, and there is little hope that it will ever be fully understood to the extent that energy efficient tires can be designed on the drawing board. But substantial progress has been made, as attested by a recent SAE Conference on Tire Rolling Losses in Boston, the first of its kind, organized to review the state-of-the-art and to stimulate further improvements. These are greatly needed. To meet the fuel economy target of 1980, a reduction of 15% of the present average rolling loss of radial tires is required (Tarpinian, Nybakken, and Mishory), and further improvements are necessary to meet the goals of 1985. Vigorous, and costly, efforts are being made—by industry and academic institutions alike—to come to grips with the rolling loss phenomenon. These efforts include mapping the interacting relations between rolling loss and the many tire parameters, building analytical models that would provide insight into these relations, and developing testing methods that would permit testing them with accuracy. This review is an attempt to organize the present knowledge into these categories and to suggest new avenues for further progress.