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."