Firestone Requests NHTSA Investigation Into Ford Explorer
NASHVILLE, Tenn.--May 31, 2001--Citing the
findings of a well-respected vehicle expert, Bridgestone/Firestone,
Inc. President and CEO John T. Lampe today requested that the National
Highway Traffic Safety Administration (NHTSA) begin an investigation
into the safety of certain models of the Ford Explorer.
The company said its analysis clearly shows that a substantial
segment of Ford Explorers are "defectively designed," putting the
driver and the passengers at increased risk during routine,
foreseeable highway driving maneuvers following events such as a tread
separation. According to Lampe, "The company today presented the NHTSA
with a testing analysis of certain Explorers that shows there is a
serious safety issue with the vehicle. As a result, the company is
asking the agency to begin an investigation into this potential safety
Dr. Dennis A. Guenther, Professor of Mechanical Engineering at The
Ohio State University, conducted the study cited by Lampe. Dr.
Guenther's study shows that in most circumstances, certain models of
the Explorer will experience an "oversteer" condition following a
tread separation on a rear tire, a clearly foreseeable event.
The Firestone report released today on Dr. Dennis Guenther's study
quotes the professor saying: "An oversteer vehicle is not safe at
highway speeds in the hands of an average driver. This must be
regarded as a highway safety defect within the meaning of NHTSA's
Based on his initial findings, Dr. Guenther has concluded that the
Explorer as tested is defectively designed in that it has an
inadequate margin of control to permit control by average drivers in
the foreseeable event of tread separation during normal highway
driving in most load and turning circumstances. This makes the
Explorer's handling imprecise and unpredictable in foreseeable
circumstances, such as tread separation where precise and predictable
handling is essential to safe vehicle control.
As noted by Dr. Guenther, the engineering literature proves that a
tread separation does not ordinarily cause a vehicle to lose control.
Commenting on the issue of foreseeable circumstances, Lampe said,
"All tires can and some do fail. That's why vehicles carry a spare
tire. When tires fail, either from a tread separation or a road hazard
or other causes, drivers should be able to pull over, not rollover.
The Explorer does not appear to give the driver that margin of safety
to make it to the side of the road and change the tire."
Dr. Guenther's investigation has found that:
-- The Explorer as designed has a significantly lower amount of
understeer than other SUV's. In fact, the Explorers that were
tested had less than half the amount of understeer as the Jeep
Cherokee and Chevrolet Blazer. "Understeer" is a cornering
situation where the front of a vehicle turns less sharply than
the driver intends. (Virtually all passenger vehicles are
designed for understeer rather than for oversteer so the
vehicle can be easily controlled by the average driver. Car
designers can increase or decrease the amount of understeer in
a vehicle by many different means -- by adjusting spring
rates, shock absorber stiffness, frame stiffness, roll
damping, tire properties, tire pressure weight distribution,
and other component functions.) Understeer is compensated for
by the addition of more steering input.
-- The Explorer loses much of what understeer it has when it is
loaded to the vehicle design limit while the Cherokee and the
Blazer do not.
-- Following a tread separation on a rear tire, the Explorer
loses its small amount of understeer. This results in an
oversteer condition. A vehicle with an oversteer situation is
generally not controllable by most drivers, particularly at
highway speeds. "Oversteer" is a cornering condition where the
front of the vehicle turns more sharply than the driver
intends during a turn while the rear of the vehicle skids
around. For example, if a vehicle is in a turn and an
oversteering condition exists, the driver may have the
impression that the rear end of the vehicle is swinging out. A
vehicle with an oversteer condition is increasingly difficult
to control as speed increases.
The tests performed by Dr. Guenther were standard vehicle dynamics
test procedures. The vehicles tested were 1996 Ford Explorer 4-door
4X2, 2000 Ford Explorer 4-door 4X2, 2001 Jeep Cherokee 4-door 4X2, and
1996 Chevrolet Blazer 4-door 4X2. The tests were performed over the
last month at the Transportation Research Center, the same facility
that the NHTSA uses for a variety of vehicles tests.
Dr. Guenther's analysis will be continuing and Firestone has
committed to providing the NHTSA and Congress with updates as
additional information from the on-going study becomes available.
"Firestone's priority has and will continue to be the safety of
our customers. We will continue to provide information to the NHTSA,
the Congress and the public concerning the vehicle and the tire," said
Lampe. "As I have said many times in the past, it is critically
important to look at the tire and the vehicle as an integrated system.
What affects one, affects the other."
A copy of the letter sent to NHTSA Acting Administrator L. Robert
Shelton is below. Firestone has also sent a copy of its report
addressing Dr. Guenther's analysis to the Ford Motor Company. In
addition, a copy of Firestone's report on Dr. Guenther's analysis is
available through Firestone's media hotline, 877/201-2373.
BRIDGESTONE/FIRESTONE, INC. John T. Lampe
CHAIRMAN 50 Century Boulevard
CHIEF EXECUTIVE OFFICER Nashville, TN 37214
May 31, 2001
Mr. L. Robert Shelton
National Highway Traffic Safety Administration
400 7th Street, S.W.
Washington, D.C. 20590
Dear Mr. Shelton:
Today, I am requesting that the National Highway Traffic Safety
Administration open an investigation into the safety of a certain
models of Ford Explorers.
Testing done by Dr. Dennis Guenther, a Professor of Mechanical
Engineering at The Ohio State University, the results of which are now
in the possession of Bridgestone/Firestone, Inc., shows that certain
of the Explorer models will experience an "oversteer" condition in
most circumstances following a tread separation on a left rear tire,
an event which is clearly foreseeable. In his analysis, Dr. Guenther
says: "An oversteer vehicle is not safe at highway speeds in the hands
of an average driver. This must be regarded as a highway safety defect
within the meaning of the NHTSA's charter."
Based on his initial findings as reported to Firestone, Dr.
Guenther has concluded that the Explorers as tested are defectively
designed in that they have an inadequate margin of control (due to
insufficient understeer) to permit control by average drivers in the
foreseeable events of tread separation during normal highway driving
in most load and turning circumstances. This can make the Explorer's
handling imprecise and unpredictable in foreseeable circumstances,
such as tread separation, where precise and predictable handling is
essential to safe vehicle control.
As I have said many times in the past, it is critically important
to look at the tire and the vehicle as an integrated system. What
affects one, affects the other. We ask NHTSA to investigate to
determine the cause of the serious safety issue with a substantial
segment of Ford Explorers and to take the necessary steps to remedy
the potential defect so as to protect motor vehicle safety. A complete
copy of our analysis has been given to your office.
As always, we stand ready to offer you any assistance you think is
necessary. Thank you for your consideration.
John T. Lampe
cc: Dr. Dennis A. Guenther Professor The Ohio State University