erly inflated, a bicycle tire exhibits rolling resistance that varies with the tire’s size, construction, and materials. This variability, even when slight, can be noticeable to the frequent bicyclist. However, large variations in the rolling resistance of tires used on motor vehicles may go completely unnoticed by the driver, since the vehicle’s engine does all the work. Despite paying the price of more frequent refueling, the driver may never make a connection between the tires and the rate of fuel consumption.

This study examines the contribution of tires to vehicle fuel economy, the variability in energy performance among tires, and technical and economic issues associated with means of improving tire energy performance. The focus is on replacement tires designed for passenger cars as well as vehicles defined as light trucks and used mainly for personal transportation.

Congress requested the study, presumably to help inform both consumers and policy makers. Most motorists will replace their tires every 3 to 5 years, but few are likely to know the effects of their tire purchases on the rate of fuel consumption of their vehicles, because little consumer information is available on this tire characteristic. While the extent of consumer interest in tire energy performance is unclear, it is reasonable to assume that motorists care more about this characteristic when fuel prices are high or rising. With respect to the public interest overall, the approximately 200 million replacement tires that are purchased each year by U.S. consumers have many collective effects on society. Most of the 160 million to 175 million passenger vehicles in the United States that are more than 3 or 4 years old are equipped with replacement tires (Davis and Diegel 2004, 3-9, 3-10). These vehicles make up about 75 percent of the passenger vehicle fleet. Replacement tires thus affect not only motor fuel consumption in the aggregate but also vehicle safety performance and the nation’s solid waste and recycling streams. Consequently, passenger tires have long been the subject of federal, state, and local regulations and environmental policies.

STUDY CHARGE AND SCOPE

Congress requested this study of national tire efficiency. The language of the request, which constitutes the study’s statement of task, can be found in the Preface. In short, Congress called for an evaluation of how lowering



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