Tire Report Places No Blame

There was no single factor that caused tread separation on Firestone ATX and Wilderness AT tires recalled last summer, an independent analysis released Friday shows.

Dr. Sanjay Govindjee, an associate professor of civil engineering at the University of California at Berkeley, was hired by Bridgestone/Firestone Inc. to analyze the problem after the tires were linked to 148 deaths in the U.S.

Govindjee found that climate was a primary factor, but other factors included design; manufacturing differences among different Bridgestone/Firestone plants, especially the Decatur, Ill., plant; and usage.

"The variable that seems to be most important is the physical load of the tire, that is the weight of the vehicle itself," he said.

Bridgestone/Firestone recalled 6.5 million tires in August amid a federal investigation into accusations of design and manufacturing defects that caused blowouts and tread separations leading to hundreds of crashes. Most of the tires were installed as original equipment on Ford Motor Co.'s popular Explorer sport utility vehicle.

The corporate heads of the Japanese parent corporation, Bridgestone Corp., and its U.S. subsidiary, Nashville-based Bridgestone/Firestone, have both stepped down amid harsh criticism of the company's handling of the problem. Bridgestone Corp.'s stock has plummeted, and hundreds of lawsuits have been filed seeking damages for injuries or deaths blamed on the tires.

Govindjee refused to discuss whether Ford shared in the responsibility for the tire failures. Bridgestone/Firestone contends Ford suggested a tire inflation rate too low for a vehicle the size and weight of the Explorer.

Govindjee said assessing fault was the government's role.

"From what I've seen, the report is consistent with previously released findings of Ford and Firestone," Ford spokesman Ken Zino said.

While excess heat tended to increase the incidence of failure, Govindjee found, tires made at Bridgestone/Firestone's Decatur, Ill., plant were "substantially differet" and more subject to fatigue.

Govindjee also found that design differences led to a higher propensity to fail in the Radial ATX than in the Wilderness AT.

For Govindjee's analysis, Bridgestone/Firestone provided data he requested, but his work was independent of the company's internal review and analysis, he said.

Bridgestone/Firestone has provided his findings to the National Highway Traffic Safety Administration, which is investigating the recall.

"Dr. Govindjee's report is another step forward in assuring that the difficulties we encountered last year with this one particular tire size and type won't happen again," Bridgestone/Firestone Chairman John Lampe said.

"His report confirms and reinforces our earlier internal findings. It assures me that our company has taken the necessary and appropriate corrective steps to deal with this difficult situation."