FIRESTONE STATEMENT CONCERNING DR

This analysis is focused on the loss of control experienced by the Explorer in normal highway driving following a rear tire belt/tread separation (hereinafter “tread separation”).

Loss of control in this circumstance often results in the Explorer leaving the highway and rolling over or spinning into an angle relative to its path of travel on the roadway sufficient to cause rollover, with or without tripping, or other serious accidents. Because loss of control is a precursor to rollovers and other serious accidents, the hypothesis is suggested by common Explorer accident scenarios that the Explorer has a control problem leading to rollover and other crashes in the event of tread separation.

· the Explorer models he has tested, as designed, have a significantly lower amount of understeer than the other SUVs he has evaluated, less than half as much as the Jeep Cherokee and Chevrolet Blazer;

· the Explorer loses much of its small margin of understeer when it is loaded to gross vehicle weight rating; the Cherokee and the Blazer do not;

· the Explorer models tested, unlike the Cherokee and the Blazer, lose all of their understeer and become oversteer vehicles in most circumstances following tread separation on a left rear tire[1], the predominant tire position in Explorer tread separation crashes; the only exception in Dr. Guenther’s investigation is a light load configuration in a counter-clockwise turn, with the separated tire mounted on the left rear, a circumstance where the vehicle retains a very small amount of understeer;

· an oversteer vehicle is extremely difficult for most drivers to control, particularly at interstate highway speeds where it can become directionally unstable;

His conclusion based on these findings is that the Explorer is defectively designed in that it has an inadequate margin of control, due to insufficient understeer, in the foreseeable circumstance of tread separation during normal highway driving in most load and turning circumstances.

Understeer/Oversteer

The terms “understeer” and “oversteer”, while not particularly descriptive in themselves, are engineering terms that are used to characterize what is one of the most significant control relationships in driving an automobile in the linear range[2] – the amount of steering wheel input necessary to produce an amount of G’s of lateral acceleration, the side force that accomplishes turning of an automobile. It is measured and expressed in degrees of steering wheel input per G of lateral acceleration.

The amount of understeer or oversteer in a vehicle is measured by driving the vehicle in a constant radius circle at an increasing speed and recording the degrees of steer input per G of lateral acceleration. In an understeer vehicle a test driver, in terms of what he perceives and does in that circumstance, must steer toward the center of the circle, with increasing steer input as he increases speed, in order to stay on the path of the constant radius circle; that is the same thing the average driver experiences as he drives around a curve – he must steer to the inside of the curve in order to generate the side force necessary to turn the vehicle and stay on the curving path.

An oversteer vehicle behaves just the opposite. The test driver would have to steer away from the center of the circle in order to stay on the constant radius circle – he would have to “take steer out” in order to keep the car on the path of the circle as he increases speed. See Exhibit 2 for a technical definition of “understeer” and “oversteer”.

Automobile manufacturers do not intentionally design an oversteer characteristic into cars intended for ordinary drivers because “a vehicle that oversteers, by design or circumstance, is highly undesirable.” Exhibit 3. See also Bergman, “The Basic Nature of Vehicle Understeer-Oversteer” at page 11, col. 1 (1965). Ford, like any other automobile manufacturer, tries to build understeer into its cars. See, e.g., Exhibit 4. They do this because understeer is essential to safely control an automobile.

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. They adjust these and other elements which result in the amount and character of control available. Automobile designers, of course, may adjust these elements for reasons other than achieving or influencing controllability; they may, for example, make such adjustments to seek ride comfort, to achieve a “flat” European cornering feel, to improve rollover resistance, or for other reasons. Each of those trade-offs for such reasons, however, potentially affects the amount of understeer and the amount of control safety margin.

Cars differ from each other in how much control margin, or understeer, they have. How much understeer is necessary to provide a safe margin of control? The answer from an engineering perspective is: Enough to provide vehicle control in all foreseeable driving circumstances for the drivers intended for that vehicle.

The foreseeable circumstances of driving include many things – the coefficient of friction of the roadway surface, wind gusts, ice and snow, vehicle load, component wear and failure, the effect of heat and use on the fit and flexibility of suspension system components, and many others. One foreseeable circumstance, of course, is tires wearing out and eventually failing, including tread separation, the most common mode of wearout failure for steel belted radial tires. All of these circumstances can cause an increase in the need for understeer or directly decrease the amount of understeer available in the vehicle. For example, tread separation will change tire properties related to understeer, decreasing cornering stiffness and traction provided by belt and tread.

One of the car designer’s engineering obligations is to quantify the amount of understeer and other vehicle control characteristics required to compensate and account for such varying and foreseeable events, the inevitable changes in driving circumstances. By that quantification he determines the amount of understeer, the margin of control, that must be designed into the car.

Tread Separation

Tread separation is a failure mode usual in steel belted radial tires. See, e.g. Exhibit 5. The majority of Firestone tires incurring a tread separation, without some causally related damage to the tire, are high mileage tires with long use. The causes of this form of failure are heat, loading, oxidation and cyclic stressing, all of which weaken the rubber bond between the layers of steel belts, which centrifugal force can then pull apart. It is an inevitable result of the chemical and physical properties of rubber tires and how they are commonly used.

Those who are unfamiliar with tires or with accident reconstruction tend to describe tread separations or accidents associated with tread separations as if they are explosive events in which the vehicle is thrown out of control by the force of the separation. The scientific literature and testing commissioned by automobile manufacturers and others, however, has repeatedly demonstrated that this is not correct.

For example, Carr Engineering, vehicle dynamics experts regularly retained by Ford to testify in automotive litigation, carried out testing on behalf of Ford relating to, among other things, the forces involved in tread separation. Their findings in those tests led them to conclude:

“During the tread separation event, the tire did pull the vehicle slightly to one side but the driver kept a straight line path with a small steering correction. This amplitude of steer angle is small and on the order required to keep a vehicle in the lane on curved highways or in a straight path during other events such as wind gusts or driving through water puddles at highway speeds.” Exhibit 6. (Test vehicles included a 1993 Ford Explorer, 1986 Ford Bronco II, 1986 Ford Bronco II XLT, 1994 Dodge Intrepid, 1987 Ford Club Wagon van, 1990 Ford Bronco, 1990 Ford Aerostar van, 1987 Toyota van).

Other automotive researchers, including plaintiff experts pursuing forensic inquires, academic researchers, and Firestone, have arrived at the same conclusion based on numerous tests, including tests involving the Explorer and the Firestone tires mounted on it as original equipment. For example:

“Test results by this author corroborate work by Gardner who measured that steering wheel inputs during tread separation are of the order of magnitude of lane change maneuvers during high speed travel.”

Klein, et al. “Anatomy of Accidents Following Tire Disablements” (1999). Exhibit 7. (Test vehicles were 1989 Pathfinder and 1982 Chevrolet pickup.)

· “Maintaining control of the vehicle after tread/belt separation requires a steering torque similar to that required for a lane change maneuver.”

“The results of the testing show that the forces developed during a tread/belt detachment are well within the range of a driver’s ability to control a vehicle.”

Gardner, “The Role of Tread/Belt Detachment In Accident Causation” (1998). Exhibit 8. (Test vehicles were Ford Explorer, Camry Station Wagon, and Chevy Truck C2500.)

· “Little or no corrective steering action was needed to maintain control of the vehicle during the tread separation events.” Fay, et al., “Drag and Steering Effect from Tire Tread Belt Separation and Loss” (1999). Exhibit 5. (Test vehicle was 1993 Ford Taurus.)

Descriptions of tread separation related accidents also sometimes fail to accurately capture the sequential nature of those accidents. Engineering analysis and accident reconstruction require that tread separation and accidents associated with them be broken down into their separate parts. For those purposes, the accident events should be viewed as three separate and sequential elements:

This is characterized by vibration felt generally in the vehicle, (see, e.g., Exhibits 5 and 7) as the tire is deformed from a smooth circle to an irregular “circle” by movement of the tread and belt. This vibration is something most drivers have experienced in connection with a failed tire, whether a puncture blow-out or a tread separation or some other mode of tire failure.

The vibration serves as notice that something is wrong with a tire, a message that most drivers understand as requiring them to take their foot off the gas, check the traffic around them, and begin to move to the shoulder of the highway to change the tire.

Testing, described above and set forth more fully in Exhibits 5 through 8, establishes that the actual tread separation is a benign event in terms of the amount and duration of forces exerted on the automobile laterally, longitudinally and vertically.

In the period immediately following tread separation on a rear tire any SUV will lose some understeer because the tire properties contributing to control of the vehicle – cornering stiffness, traction, etc. – will have been reduced because of removal of the tread and one of the steel belts. It is the controllability of the Explorer in this circumstance that Dr. Guenther is investigating.

ENGINEERING EVALUATION OF EXPLORER DIRECTIONAL CONTROL

Dr. Guenther was retained by counsel to assist them in the preparation of Firestone’s defense in the personal injury litigation arising out of Explorer crash and rollover accidents. While he made measurements of and inspected various Explorers and engaged in some accident reconstruction at the direction of counsel, he did not undertake the dynamics testing and data analysis underlying his conclusions concerning the controllability of the Explorer until last month.

Firestone had expected that Ford, as part of a root cause analysis, would focus on the vehicle and provide Firestone, NHTSA and the Congress information about the vehicle’s handling in a tread separation event. Ford has 15 years of experience in the design and development of and litigation about the Explorer. They have that information. Firestone requested Ford participation in investigation of the vehicle in October of last year. In spite of repeated follow up requests, Ford made no response to Firestone. It became clear that Dr. Guenther’s engineering evaluation of the Explorer would be important not only in defense of the litigation but in addressing congressional, regulatory and public concerns about automotive safety relating to loss of control and rollover of the Explorer when it experienced tread separation.

Testing Conducted

The tests were carried out at the Transportation Research Center, Inc. (TRC) test facility near East Liberty, Ohio. The facility is used on a contract basis by numerous automobile manufacturers, component suppliers, and state and national regulatory authorities to conduct automotive safety testing. It was used by NHTSA, for example, in 1997-98 to conduct extensive tests of maneuvers that may induce on-road untripped rollover in various vehicles, including the Ford Explorer. See Exhibit 9. Ford used TRC in development testing of the UN-105, the version of the Explorer offered in 1995 and subsequent years.

The purpose of the testing program, which is ongoing, is to examine the margin of control in the Explorer as designed and, comparatively, in peer SUVs in the circumstance following rear tire tread separation. Due to the complexities and non-linearity of vehicles, Dr. Guenther chose to explore the linear range as a preliminary investigation. In the linear range, a principal parameter of control is the understeer/oversteer gradient (other parameters such as steering response time and gain, and steering frequency response are also being examined as they may relate to loss of control in the event of tire tread separation).

Each vehicle was tested with its original equipment (OE) tires. The 1996 Explorer was tested with both OE Firestone tires and OE Goodyear tires recommended by Ford.

The instrumentation and sensors used to acquire this data is identified in Exhibit 10.

The tests conducted are universally recognized standard tests used by automobile manufacturers, including Ford, and other researchers in vehicle dynamics for establishing the values investigated. The tests are as follows:

The vehicle is driven on the test pad area in a straight line at a constant speed. The driver then rapidly turns the steering wheel until it hits a mechanical stop. Steering wheel stops are set to attain a desired lateral acceleration at the test speeds. This steer angle is held until steady-state response is established.

Tests were run in both directions (right turn/left turn) and at two speeds (60 mph and 40 mph). The test was run both with four good tires and with the left rear tire detreaded by cutting between the steel belts; test runs with the detreaded tire were done only at the slower 40 mph speed. Test runs were done at both light load (curb plus driver and instrumentation) and heavy load (gross vehicle weight rating).

The test is used to measure vehicle response times as related to lateral acceleration and yaw velocity response, and to measure the gain of these responses in relation to steering wheel input (output divided by input).

The vehicle is driven around a 200 foot constant radius circle with increasing speed. The driver adjusts the steering angle (by turning the steering wheel) as necessary to keep the vehicle on the path of the circle.

Test runs were done in both directions, clockwise and counter-clockwise, with four good tires and with the left rear tire detreaded. Test runs were done at light load (curb plus driver and instrumentation) and heavy load (gross vehicle weight rating).

The test is used to measure understeer and oversteer (degrees of road wheel steer per Gs of lateral acceleration).

Sinusoidal sweep steering tests are frequently used to determine the linear response of vehicles. The vehicle in these tests were driven on a long straightaway with the driver steering with slowly increasing frequency up to approximately 3 to 4 hz followed by decreasing frequency. The test was run at a nominal speed of 66 mph.

The test measures lateral acceleration gain, yaw velocity gain, and phase angles at the frequencies tested (up to 3 to 4 hz).

The results of the constant radius circle tests are set forth in data sheets and charts attached hereto as Exhibit 11. Data reduction continues with respect to the step steer and frequency response tests.

Constant Radius Circle – This standard method of measuring understeer/oversteer gradient establishes that the Explorer, with four good tires, has a relatively small amount of understeer compared to other SUVs – less than half the amount found in the Blazer and the Cherokee. In fact, the Cherokee has about the same understeer with a detreaded tire as the Explorer with four good tires. These findings are consistent with NHTSA vehicle characterization tests which found that the Explorer had the lowest amount of understeer of the 12 vehicles on which it conducted rollover-inducing maneuver tests. See Exhibit 9 at page 20.

The test results show that, unlike the other SUVs tested, the Explorer loses its small margin of understeer when it experiences a tread separation and becomes an oversteer vehicle.

This is true whether the Explorer is operated on Goodyear OE tires recommended by Ford or on Firestone OE tires.

The Explorer’s oversteer characteristic is worse in the loaded condition. The only circumstance in which it does not become oversteer with a detreaded tire is when it is lightly loaded (curb plus driver and instrumentation) and the detreaded tire is on the inside rear position (left rear in a counter-clockwise turn); in test runs in that configuration the Explorer is almost neutral steer with respect to the understeer/oversteer gradient.

An oversteer vehicle is not safe at highway speeds in the hands of an average driver. Sometimes a driver may achieve directional control, sometimes he may not, particularly where he has to deal with the unfamiliar and unpredictable oversteer handling through a steering input/vehicle response characterized by a slow response time and a following large gain.

In addition to his dynamic testing, Dr. Guenther has carried out several accident reconstructions involving Explorer crashes and reviewed numerous police accident reports concerning such accidents. Explorer rollover accidents, as reflected in those reconstructions and police accident reports, frequently occur

· with some apparent effort at driver steering control reflected in change(s) of vehicle heading and path of travel.

CONCLUSION

The Explorer is an oversteer vehicle in most circumstances after it experiences tread separation. Oversteer can make a vehicle directionally unstable and subject to loss of control in the hands of most drivers. This is a vehicle problem, not a tire problem. The vehicle performs the same following tread separation on the Goodyear tire as it does the Firestone tire. This must be regarded as a highway safety defect within the meaning of the National Traffic and Motor Vehicle Safety Act.

Exhibit 2 Gillespie, T.D., “Fundamentals of Vehicle Dynamics (1992) (published by

Exhibit 3 Dickerson, et al., “Vehicle Handling with Tire Tread Separation (1999); Bergman, “The Basic Nature of Vehicle Understeer-Oversteer” (1965)

Exhibit 5 Fay, et al., “Drag and Steering Effects of Under and Deflated Tires”

Exhibit 6 Letter from Carr Engineering to Wheeler, Trigg and Kennedy dated January 23,

Exhibit 7 Klein, et al., “Anatomy of Accidents Following Tire Disablement.” (1999)

Exhibit 8 Gardner, “The Role of Tread/Belt Detachment In Accident Causation”

* Dr. Guenther is a Professor of Mechanical Engineering at The Ohio State University. He is frequently engaged by NHTSA and automobile manufacturers as a consultant on automotive safety matters. He has testified on numerous occasions at the request of automobile manufacturers as an expert on automobile control issues, rollover, and accident reconstruction. He has published over 100 articles on automotive safety matters. His resume is attached as Exhibit 1.

[1] Left rear tread separation is the most common finding in Explorer accidents involving tread separation and is the condition examined to date.

[2] Linear range in this context refers to normal everyday driving by average drivers.