Firestone Announces the Completion
of the Independent Expert's Analysis
- Dr. Sanjay Govindjee Confirms No Single Factor
- Findings Shared with Public
Nashville, Tenn. February 2, 2001-
Firestone today announced the completion of Dr. Sanjay Govindjee's analysis
and technical report detailing why the recalled ATX and Decatur-produced
Wilderness AT tires, primarily on Ford Explorers, experienced a higher
rate of tread separation claims. Dr. Govindjee's findings and analysis
independently confirm that there was no single causal factor.
"In all cases, failure rates for the recalled
tires are fractions of a percent and thus determining a single cause
for the tire failures is an unrealistic expectation," said Dr.
Govindjee, an associate professor of civil engineering at the University
of California at Berkeley. "From a mechanical and materials engineering
perspective, the phenomena of belt separation in these tires resulted
from a crack that grew in the rubber between the two belts. This cracking
is influenced by a number of factors, including climate, design of the
tire, manufacturing differences at Firestone's Decatur plant and usage
factors."
Dr. Govindjee examined recalled tires to determine
what could cause a fatigue crack or belt separation to grow between
the two steel belt layers of the tires. His analysis, which included
standard testing and new lab and field testing, found that climate played
a critical role in reducing the material properties or capacity of the
tires. For example, tires from warmer climates showed a substantial
degradation in their material properties; further, tires that were run
at high speeds, in highly loaded vehicles or at low inflation displayed
pronounced heat build-up. While the effect of temperature on the capacity
of the interbelt materials was confirmed, he also found the demands
on the tires from extra loading were important in pushing a fatigue
crack to grow. Further, his analysis showed that the interbelt material
properties of the tires in question produced in Decatur, were substantially
different from those at other plants and were more subject to fatigue.
His analysis also found design differences in the Radial ATX could lead
to a higher propensity to fatigue than the Wilderness AT.
Dr. Govindjee focused on a mechanical and materials
engineering analysis and, as a result, his report has some differences
in scope and focus from Firestone's internal investigation, released
December 19, 2000. His overall conclusions provide additional information
consistent with the company's findings.
"Firestone's technical staff is now thoroughly
reviewing Dr. Govindjee's report as part of our quality assurance and
continuous improvement program," said John Lampe, Bridgestone/Firestone
Chairman, CEO and President. "We thank Dr. Govindjee for his hard
work. I am confident that with our own internal review, combined with
Dr. Govindjee's analysis, we have determined why some of our tires experienced
a higher rate of tread separation claims and that our recall in August
was more than adequate to protect the public."
To determine how these factors affect tire life, Dr.
Govindjee used information provided from Firestone and its research
center and laboratory, independent laboratories and a survey of material
properties from returned tires. His analytical work included the assessment
of tire loading on the Ford Explorer, analysis of heating factors -
which included an analysis of tire inflation pressure, loading and speed
- and extensive finite element modeling.
In addition, Dr. Govindjee used field data on Ford
Explorers regarding actual dynamic loading or forces placed on the tires
by the vehicle. This data was collected at Firestone's test track in
Acuña, Mexico on a 1998 Ford XLT Explorer four-wheel drive. Measurements
were performed at four different inflation pressures, four different
cargo loads and at different speeds.
Dr. Govindjee was retained by Firestone in September
to provide an independent analysis of its recalled tires. While Firestone
provided information and data requested by Dr. Govindjee, his work was
conducted independently from the company's own internal review and analysis.
Firestone has provided Dr. Govindjee's report and findings
to the National Highway Traffic Safety Administration and other governmental
groups.
"I am grateful to Dr. Govindjee for his efforts
in this analysis," said Lampe. "Finding the root cause of
why a small percentage of our P235/75R15 ATX and Decatur-produced Wilderness
AT tires suffered tread separations was a priority for this company,
and we know it was extremely important to our customers. 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. 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.
And it supports my firm belief that our company today is building the
world class tires for which this company has been known over the past
100 years."
A full copy of Dr. Govindjee's report is downloadable
in Portable Document Format(PDF) and can be viewed with Adobe's free Acrobat
Reader.
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