WASHINGTON-Reducing the average rolling resistance of replacement tires by 10 percent can be done readily without appreciably compromising tire safety, according to a new study.
However, the fuel and cost savings to consumers will be worth it only if a tire´s service life is not shortened, stated the report by the Transportation Research Board within the National Research Board of the National Academies.
The study also said any regulation requiring the dissemination of tire rolling resistance information would be useless without vigilant attention to tire inflation and maintenance. That got plaudits from the Rubber Manufacturers Association. "We find a lot to agree with in this report," an RMA spokesman said.
Paul Fiore, director of government and business relations at the Tire Industry Association, said he, too, is encouraged by his first look at the report.
"It´s essentially saying that, all things being equal, there isn´t a great deal of evidence that rolling resistance makes all that much difference to fuel economy," Fiore said. "That´s something that everyone is going to be able to get behind."
"Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance," the work of a 12-member committee that includes tire industry, academia and energy activist group representatives, was issued April 4.
The committee met four times between April and October 2005, said Joseph D. Walter, adjunct professor of engineering at the University of Akron and a committee member, during a March 15 speech at the Clemson Tire Industry Conference, held at Hilton Head Island, S.C.
It also considered the existing scientific literature on rolling resistance; interviewed tire makers, auto makers and tire materials suppliers; and held public meetings with testimony from the tire industry, state and federal agencies and public interest groups, according to Walter.
The committee found copious information on how tire construction and materials, operating conditions and tire wear affect rolling resistance, Walter said. But it located only limited data on the rolling resistance characteristics of original equipment and replacement tires currently in use, and virtually none on the effect of lower rolling resistance and lower traction on vehicle accidents.
"It´s intuitive that if rolling resistance is reduced, a vehicle´s stopping distance will increase," said Walter, retired president and managing director of Bridgestone Technical Center Europe in Rome. "But how does that relate to increased traffic deaths? Even (the National Highway Traffic Safety Administration) doesn´t have that information."
Consumers today have little way of knowing how their aftermarket tire choices can affect gas mileage, the study said.
"Rolling resistance varies widely among replacement tires already on the market, even among tires that are comparable in price, size, traction, speed rating and wear resistance," it said.
A 10-percent reduction in average rolling resistance would translate to a fuel economy increase of 1 to 2 percent in most vehicles, the report said.
For individual motorists, this would equate to 6 to 12 gallons of fuel annually, it said. For the U.S., it would mean an annual savings of 1 billion to 2 billion gallons, equivalent to taking 2 million to 4 million cars and light trucks off the road.
It may not be practical, or even possible, to analyze the safety implications of making small changes in tread designs and materials to lower rolling resistance, the study said. The effect of lower rolling resistance on tire wear and scrap tire generation is difficult to measure because there are many ways to reduce rolling resistance.
"Reductions in tread thickness, volume and mass...may be undesirable if they lead to shorter tire lives and larger numbers of scrap tires," the report said. "However, continuing advances in tire technology hold much promise that rolling resistance can be reduced further without adverse effects on tire wear life and scrap tire populations."
The study recommends Congress authorize NHTSA to gather and report information on how motorists´ choice of replacement tires effects fuel economy.
NHTSA should seek the active participation of the tire industry in gathering and communicating this information, as well as the help of the Environmental Protection Agency, on how to make the information both widely available and easily understood, the study said.