NASHVILLE, Tenn.—Bridgestone/Firestone Inc. is focusing its "root cause" investigation into its recalled 15-inch P-metric light truck tires on tire design, tire components and external factors.
Specifically, BFS is looking at differences in design between the Firestone Wilderness AT and the Radial ATX, on the materials that make up the "interbelt" between the tires' twin steel belts, and on the manufacturing process at its Decatur, Ill., plant, where the bulk of the tread-separation-plagued tires were made.
In addition, the company continues to investigate possible vehicle influences on the problem, saying the majority of claims show the tread separation occurred on a rear tire, with a clear majority of these claims involving the left rear tire. Most of the claims filed involve the Ford Explorer sport-utility vehicle.
Word of the investigation's direction came as BFS has completed nearly 77 percent of the recall, with more than 5 million tires replaced to date out of an estimated 6.5 million on the road on Aug. 9, when the recall was announced.
Among its findings, BFS has discovered that:
Tread separation claims on 15-inch ATX tires made at the BFS plant in Decatur, Ill., were more than 10 times those made on 15-inch Wilderness AT tires manufactured at the same facility.
"The disparity in the rate of tread separations between the two tires has led the company to closely analyze how the two tires differ in design," the company said.
Wilderness AT tires made at Decatur had many more claims than the same tires made at plants in Wilson, N.C., or Joliette, Quebec—leading BFS to examine manufacturing practices at Decatur.
The vast majority of claims on the ATX and Wilderness AT tires involve rear tires, leading the company to research "how the loading or stress from a vehicle affects the overall strength and performance of a tire."
BFS said it is "taking a hard look" at the components and materials in the ATX and Wilderness AT tires, particularly the interbelt material "which is an important factor in the strength between the steel belts." It also is studying factors that cause heat buildup in the belt-edge area.
All of this is substantially what Mr. Lampe and other BFS officials told Senate and House investigators in public hearings back in September. However, their message has been questioned openly by other stakeholders in the recall.
Plaintiffs' attorneys and consumer advocates insist all ATX and Wilderness AT tires—not just 15-inch tires or those made in Decatur—are inherently defective.
Ford Motor Co.—which installed most of the recalled tires as original equipment on its Explorer and other SUVs—insists the tire alone is at fault, and that the vehicle does not factor into the problem at all.
Bridgestone/Firestone's OE business with Ford totals about $330 million of its annual tire sales of approximately $5.5 billion, a BFS spokesman said.
Meanwhile, Sanjay Govindjee, an engineering professor at the University of California at Berkeley hired by Bridgestone/Firestone to conduct an independent investigation into the root causes, released preliminary results of his study last month. He is expected to submit his final report to BFS around the beginning of 2001.