In Firestone Tire Study, Expert Finds
Vehicle Weight Was Key in Failure

By CLARE ANSBERRY
Staff Reporter of THE WALL STREET JOURNAL

An outside expert hired by Bridgestone/Firestone Inc. backed the company's findings that there is no single cause for its tire failures, but also singled out vehicle weight as a key factor in belt separations and said data show a similar rate of complaints between certain recalled and nonrecalled tires.

The conclusions of the five-month study keep alive troubling questions for Firestone, a unit of Bridgestone Corp. of Japan, and Ford Motor Co. as both companies attempt to move beyond a crisis that began in August when Firestone recalled 6.5 million tires that had been linked to 148 deaths in the U.S. and 48 overseas, from accidents mainly involving the Ford Explorer. Indeed a panel of outside tire experts, assembled by plaintiffs' attorneys, is expected to present on Wednesday the results of its own study with more details about manufacturing and design problems related to the recall.

Meanwhile, the investigation by the National Highway Traffic and Safety Administration, which was supposed to be completed in March, is expected to take much longer.

In September, Firestone hired Sanjay Govindjee, an associate professor of civil engineering at the University of Berkeley with expertise in studying how materials such as rubber react to stress, to analyze why Firestone's recalled Wilderness AT tires produced at the company's Decatur, Ill., plant and all ATX tires experienced a higher rate of tread separations.

Dr. Govindjee concluded that the separations resulted from a crack that grew in the rubber between the two steel belts. He said several factors can accelerate the spread of the crack through the tires, including hot weather, speed, the tire's design, tire inflation and weight of the vehicle. Of all those, he concluded, the weight of the vehicle is critical. "The other factors certainly play a role, but for the cases examined, vehicle load always dominated," he stated in his report.

That finding raises the question of whether the Explorer was too heavy for the Firestone tires. Ford spokesman Ken Zino says the Explorer's load rating is "well within the range" of similar vehicles. "Our view is that the tire is unduly sensitive," says Mr. Zino, and that the weight of any vehicles on such tires would cause cracks to grow. Ford has made some changes in its 2002 Explorer, adding larger tires capable of carrying more weight. The company also announced last fall that it would begin providing to consumers more information on how much weight vehicles could safely carry.

Dr. Govindjee said he couldn't comment on the suitability of the Firestone tires on Ford's Explorer because it is outside his expertise. Firestone officials likewise said they aren't vehicle experts.

However, Firestone spokeswoman Christine Karbowiak said the company's own four-month study, completed in December, found that vehicle-load levels, coupled with tire pressure initially specified for the Ford Explorer, "played a role" in the tire failures. Firestone has maintained the 26 pounds a square inch initially recommended by Ford didn't provide enough of a safety margin. Ford has since changed its recommended tire pressure to a range of 26 pounds to 30 pounds a square inch. Dr. Govindjee likewise cited low inflation as a contributing factor, saying it reduces the ability of the tire to resist cracking because it causes heat to build up within the tire. Heat causes the materials in the tire to degrade.

One point in Dr. Govindjee's study was quickly seized upon by consumer groups pushing for a wider recall of Firestone tires. Dr. Govindjee noted that warranty-adjustment data on all Firestone consumer tires showed similar rates of complaints between the recalled Wilderness AT tires produced at Decatur and nonrecalled Wilderness tires made at the company's plants in Wilson, N.C., and Joliette in Quebec. "This means that the tires were equally problematic regardless of the plant in which they were manufactured, and that all Wilderness AT tires could crack and separate," said Joan Claybrook, a former official with the NHTSA who heads Public Citizen, a Washington-based consumer advocates' group.

The tire maker said warranty-adjustment data include all consumer complaints, such as tires that make too much noise, and aren't considered by the industry as a performance measure. Moreover, the company notes that even with this wider base, complaints were "a small fraction of a percent" and that the August recall was more than adequate. Dr. Govindjee wouldn't comment on the suitability of the recall, saying he was "not an expert in recall."

Sean Kane, who heads the consumer group Strategic Safety, says while the study acknowledges that the age of a tire contributes to its breakdown, it doesn't quantify the risk to drivers as their own tires age. That is of special concern, he says, because the materials begin breaking down within the tire long before the tread wears out. Consumers normally replace their tires only when the tread is worn. "Wilderness tires have not been on the road long enough," he says, to manifest internal problems.

Dr. Govindjee issued what he called a "caveat" regarding the higher rate of failures on the ATX tires. "ATX tires have been in production for a longer period than [Wilderness] AT tires. Thus age could be playing a role in some of the observed differences." Firestone officials said the difference reflects improvements made in the AT tires, which replaced the ATX tires in 1996.

The study has been submitted to the NHTSA, which is continuing its investigation of whether the recall should be broadened. NHTSA spokesman Rae Tyson declined to comment on Dr. Govindjee's report but confirmed that the agency had received it. A person familiar with the NHTSA probe said it is now likely to last well beyond March, the original deadline set by the Clinton administration last fall. The agency has been in negotiations recently with an independent lab that will conduct tests on both the recalled and nonrecalled Firestone tires.

-- Timothy Aeppel in Pittsburgh and Stephen Power in Washington contributed to this article.