Bridgestone/Firestone Continues Efforts to Identify Root Cause
7 November 2000
Bridgestone/Firestone Continues Efforts to Identify Root Cause
Recall nearly 75 percent complete
NASHVILLE, Tenn., Nov. 6 Bridgestone/Firestone said today
that it has surpassed the 4.8 million mark in its safety recall of 6.5 million
tires, and that its scientific process to isolate the root cause or causes of
accidents associated with a small percentage of its tires, is centering on the
design of the recalled tires and the manufacturing process at its Decatur,
Ill. facility.
"No one is more interested in finding the answer than we are," said John
T. Lampe, chairman, chief executive officer and president of
Bridgestone/Firestone, Inc. "Our technical team reports that we are
concentrating our efforts on a number of factors, including tire design, the
tire's components and external factors, all of which warrant further
examination," he said.
Lampe added that as the company continues to search for the cause or
causes, it will provide periodic updates on the status of the company's
internal analysis.
Tire Design and Components
Clear difference appears to exist between ATX and same-size Wilderness AT
tires
As part of the company's analysis it is examining every aspect of the
tire's design, including tread design and the placement of the tire's
components within the makeup of the tire itself.
This is a significant area of examination because according to the
company, its data shows a clear difference in the rate of tread separation
claims between the P235/75R15 Wilderness AT tire and the same size Radial ATX.
These Wilderness AT claims are less than one-tenth of that experienced by the
P235/75R15 ATX tire made in Decatur. 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.
In addition to examining the differences in the individual design of each
tire, the company said it is taking a hard look at the various components and
materials that comprise each tire, including the interbelt material which is
an important factor in the strength between the steel belts. The interbelt
area includes the steel cords that are made into two belts coated with rubber
and a strip of rubber between the edges of the two belts. The company is
looking closely at the interbelt area because that is where tread separations
tend to occur.
Manufacturing Variability in Decatur
Beyond its focus on tire design, the company is also examining the
manufacturing process employed at its Decatur plant. Specifically, the
company is analyzing how its Decatur-made Wilderness AT tires perform in
relation to those Wilderness AT tires made at its other plants. A review of
the company's claims data shows that its Wilderness AT tires made in its
plants in Wilson, N.C. and Joliette, Quebec, have a much lower number of
performance-related problems.
In addition, while the claims rate for its Decatur-made P235/75R15
Wilderness AT peaked in 1996, the first year the tire was produced at that
plant, that rate was still significantly lower than the ATX claims rate. The
rate of claims for the Wilderness AT tire dropped in 1997 and continued to
decline in subsequent years.
Heat and Stress Impact Tire Performance
Running on an under-inflated tire significantly increases the heat and
stress that the tire experiences, especially when carrying heavy loads,
traveling at high speeds (note, speed limits have been increasing over the
last several years) or driving in high temperature climates. Proper tire
inflation is important because all tires can lose about 1 pound per square
inch of pressure per month.
The company said it is looking at factors that generate excessive heat and
weaken the tire's construction in the belt-edge area, making the tire more
susceptible to failure.
Vehicle-Tire Interaction
According to the company's data, the vast majority of claims on the
recalled tires involve a rear tire, and the clear majority of those claims
involve the left rear tire. In order to fully understand this phenomenon, the
company said it must fully understand how the loading or stress from a vehicle
affects the overall strength and performance of the tire.
"Based on the company's review to date, our technical teams believe the
performance issue with the tire ultimately will be the cumulative effect of
tire design, tire components and the interaction of the tire with the
vehicle," said Lampe. "Bridgestone/Firestone will continue to update the
public periodically as our extensive examination continues."
In addition to the company's own analysis, the examination by Dr. Sanjay
Govindjee, the independent materials expert retained by the company, is
ongoing.