Firestone Requests NHTSA Investigation
into Ford Explorer Safety
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
defect."
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
charter."
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 attached
along with Firestone's Report
and Dr. Guenther's Analysis.
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.
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