DETROIT (July 12, 2001)-—The National Highway Traffic Safety Administration is proposing a battery of tougher high-speed and endurance tests for tires.
But the proposal calls for only lab tests, which may not show how the tires are likely to perform on the road, according to General Motors Corp.
In a letter to NHTSA, GM safety engineers said the proposed new lab tests should be correlated with on-road testing. Tires, wheels, suspension systems, loads, road surfaces and other factors all affect tire durability.
But even road testing may not be enough to prevent another situation similar to the Firestone tire recall.
The problem: There are too many brands and combinations of tires and vehicles to test them all. Since cars and sport-utility vehicles have different suspension systems and varying weights and centers of gravity, lab tests can't anticipate all the stresses placed on tires.
“A tire is a complex composite structure. There are always going to be occasional flaws,” said Frank Kelley, dean of the University of Akron's Polymer Science and Engineering Department. “What we have is a growing expectation of perfection and durability at the lowest possible price.”
Bill Kemp, GM's executive director of safety communications, said lab testing shouldn't be the only measurement of durability.
“We support both (lab) and real-world testing. But we say real-world testing is more valuable,” he said. GM routinely stresses out tires on test vehicles for 45,000 miles in addition to conducting its own lab tests.
“Performance requirements for tires run on such laboratory tests will not correlate with any actual customer use at a combination of on-vehicle conditions,” GM said.
The car maker's letter is one of 14 submissions sent to NHTSA since last October. The agency is expected to issue its proposed testing procedures next month after it has weighed data received from auto makers and tire makers.
Part of the regulations mandated by Congress under the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act, signed into law by President Clinton last November, requires NHTSA to establish testing standards by June 1, 2002. Current safety tests measure durability at varying speeds and loads for a fixed time on a rotating drum. The government's safety standards have been on the books since 1968; many of the tests pertain to bias-ply tires, which are rarely used. All manufacturers have switched to radial tires.
NHTSA issued a preliminary outline of its proposed testing standards late last year. The outline, called a test matrix, dramatically increases the number of speed and endurance tests and measures tire performance based on load, speed, temperature and pressure and duration.
Ford Motor Co. has shared its test data with NHTSA and also hopes to help shape NHTSA's new standards. Ford engineers also believe lab tests should be correlated with relevant real-world testing.
“We are working with NHTSA to come up with more sophisticated tests,” said Ford spokesman Ken Zino.
As a result of two recalls involving potentially defective Firestone tires on Ford's Explorer sport-utility, the car maker has developed a series of test procedures that measure such things as temperature while the tire is in motion and how much force it takes to peel the tire tread from the case.
But those tests were conducted to determine the cause of the Firestone failures. And Ford won't suggest to NHTSA that all tires should undergo such rigorous tests.
Steve Butcher, vice president of the Rubber Manufacturers Association—which represents American tire manufacturers—said NHTSA's lab tests should be correlated with real-world driving situations, but he stopped short of calling for on-road testing standards.
If lab tests can simulate real-world conditions, that might be thorough enough, he said. He is waiting for NHTSA's next testing proposals before the RMA takes a final position.
NHTSA expects to issue its new testing procedures next month in a notice of proposed rule making. As for on-road testing, NHTSA spokesman Tim Hurd said: “We will certainly consider GM's proposal.”