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Continues Efforts to Identify Root Cause
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News of November 07, 2000
Bridgestone/Firestone
Continues Efforts to Identify Root Cause
Recall
nearly 75 percent complete
NASHVILLE,
Tenn. - Bridgestone/Firestone said 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.
(November
6, 2000)
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