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.
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
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.
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
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.
noted by Dr. Guenther, the engineering literature proves that
a tread separation does not ordinarily cause a vehicle to lose
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."
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.
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.
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.
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.
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."