A consumer group yesterday made public durability ratings for passenger car tires based on official government tests, and accused the Reagan administration of hiding the tire ratings from consumers by "burying them in a regulatory docket."
The Center for Auto Safety, which compiled the ratings from tests done by the National Highway Traffic Safety Administration, said there is a wide disparity in how well tires will wear, even among those produced by the same company.
The least expensive tires sometimes have the longest wear, according to the ratings. A Michelin tire -- the XH radial -- rolled to the top of the center's ratings while a Bridgestone 147V-70 tire skidded to the bottom.
NHTSA, which is part of the Department of Transportation, began grading tires on the basis of tread wear in 1979, but suspended the ratings in 1983, arguing that the tests used to rate the tires were unreliable. Two consumer groups -- Public Citizen and the Center for Auto Safety -- filed suit to reinstate the testings, and the United States Court of Appeals for the District of Columbia last year ordered the agency to resume the ratings.
The court order criticized the agency for "inaction" and "foot-dragging," saying, "It is hard to imagine a more sorry performance of a congressional mandate than that carried out by NHTSA."
While the Carter administration touted the tire ratings with a full-blown press conference, the Reagan appointees dumped them into NHTSA's files with no publicity, complained Clarence M. Ditlow III, executive director of the Center for Auto Safety.
"Although the department has resumed its tread-wear test program and sidewalls of new tires will soon have tread-wear ratings molded, DOT has not released a single grade to the public broadly, nor has it explained the reinstitution of the system," said the head of the group founded by Ralph Nader over a decade ago.
"Instead, the department has buried the invaluable tread-wear ratings deep in the bowels of a regulatory docket where no consumer is sure to go," Ditlow said.
But DOT officials say Ditlow's charges are full of hot air."That's just ridiculous," said Diane Steed, administrator of NHTSA. "Their whole contention of charges are just without foundation. We're not hiding this information -- it's available to any consumer who wants it over our toll-free agency hotline." Steed said that NHTSA is planning to publish the tread-wear testing results in a brochure available to the public.
The government tests assign each tire a rating number to reflect its estimated life; the higher the number, the longer the tire should last.
Under average driving conditions, a tire with a tread-wear rating of 100 should last for 20,000 miles, while one with a rating of 200 should last 40,000 miles, the auto safety group said.
The 134 radial tires included in the tests earned ratings ranging from 80 to 330. The highest ratings went to Michelin, which produced the only tires with a rating above 300. Its XH tire earned a tread-wear rating of 330 (66,000 miles) and its XA4 and XZ4 hit 310 (62,000 miles); the same company's XWX, however, rated only 100, close to the bottom of the list.
The Bridgestone 147V-70 was the mileage loser, with a rating of 80 (16,000 miles). "The reasons it has such a low tread wear is that is has a high performance and is designed for traction," said Shane Smith, spokesman for Bridgestone Tire Co. of America in Torrance, Calif. "It is not a regular passenger car tire that you would put on your car for everyday use. It is a tire for someone that wants very high performance and is not concerned so much by mileage."
The tires are tested in San Angelo, Tex., where they are installed on vehicles that are driven several hundred miles. Engineers for consulting companies hired by the tire industry then examine the tires for wear and grade them numerically.