March 10, 2003

SUVs - Suddenly Upside-down Vehicles: Part I: Faulty Design

In 1982, Ford began production of the Bronco II, the original SUV and the precursor of the Ford Explorer. The Explorer is built on essentially the same chassis as the Bronco II, and the two vehicles have many similar characteristics. [View document].

During the development of the Bronco II, it became clear that Ford would not meet the company’s stated safety and engineering design goals. The car was too high and too narrow to "reduce rollover propensity" or "respond safely to large steering inputs which are typical of accident avoidance or emergency maneuvers." [View document].

As early as February 1981, Ford engineers identified the Bronco II’s poor stability index as a key problem with the vehicle. According to engineering documents from that time, for an additional cost of $83 per vehicle, Ford could have made a substantially safer car. [Excerpt | Full document] | [Excerpt | Full document]. These changes were rejected by Ford management, however, because they would have delayed production and sale of the vehicle. Ford did not widen the SUV three to four inches until model year 2002, almost 20 years after the engineers’ warnings.

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As part of vehicle development, test vehicles are driven on test tracks through several different types of turns and maneuvers. One such turn, a J-turn test, simulates a sharp turn to test the rollover propensity of the vehicle.

Internal Ford documents show that during a 1981 test drive the fully loaded Bronco II test vehicle tipped up on to its protective outrigger or had inside front wheel lift in every J-Turn run at a mere 30 MPH.  Engineers, including David Bickerstaff, who was later paid by Ford to lie about SUV safety in 30 lawsuits brought against Ford by rollover victims, recommended that Ford consider widening the Bronco II to increase the stability index—that is, make it more stable and reduce the vehicle’s propensity to roll over. 

Ford ignored the safety and design recommendations of its own engineers

A March 17, 1982 "Bronco II Handling Evaluation" document showed that more than 9 turns resulted in lift off, and 5 turns resulted in outrigger contact, which means that the vehicle tipped on its side.  With this document, Ford engineers presented Ford management with several options to decrease the likelihood of rollovers:

Development recommends pursuing items 1, 2, and 3 below if a small improvement in roll characteristics during a "J" turn maneuver is deemed acceptable, or pursuing item 4 below if a major improvement is required. Incorporation of item 4 would most likely cause a delay in Job #1.

1. Release a pitman arm that provides maximum toe steer and slows the steering system down. This action would affect turning diameter and require revised steering steps.

2. Release a higher ratio power steering gear.

3. Release a 1-1/8 inch diameter front stabilizer bar and delete all rear stabilizer bars.

4. Increase track width 3-4 inches.

— 3/17/82 Program Report. Page 2.

Ford chose Proposal 2 instead of the safer Proposal 4, which would have resulted in a "major improvement" of "roll characteristics," because increasing the track width would delay "Job #1," the scheduled date the first Bronco II would roll off the assembly line. In one test run configuration in early 1982, Ford engineers widened the prototype track two inches. This simple change prevented the vehicle from tipping over at speeds up to 60 MPH in the J-Turn, which was a drastic improvement from the original prototype.

Ford apparently did no other testing of a prototype with a widened track. In a subsequent Program Report in April 1982, Ford engineers repeated their recommendation that the Bronco II production vehicle needed to be widened 3-4 inches to reduce the possibility of vehicle rollover during sharp turns. This proposal was also rejected.

Graphical Pull Quote increase track width three to four inches

In addition to a delay in Job #1, management did not want to widen the track of the Bronco II because a wider vehicle would limit sales abroad. The narrow track of the vehicle would allow Ford to market the Bronco II in other countries, especially Japan.

Once it was clear that management would not permit the safer option of widening the vehicle 3-4 inches, Ford engineers, including Bickerstaff, evaluated other options to make the Bronco II less likely to roll. One Bickerstaff memo shows that engineers considered lowering the center of gravity of the vehicle by substituting 14-inch wheels for the programmed 15-inch wheels. Engineers also developed contingency plans to lower the tires, widen the track, and other changes in an attempt to decrease rollover propensity. Management finally agreed to widen the production level vehicle, but only 4/10 of an inch, not the recommended 3-4 inches.

1982 Bronco II Cancellation of Test Drives out of "concern about the safety of our track drivers"


The engineers’ recommendations for a 3-4 inch widening of the track were not based only on design principles, but also on first-hand experiences on the test-drive track. Internal Ford documents and court records show that in 1982, Ford suspended driving tests of the Bronco II for fear that its own professional test drivers would be injured or worse in a rollover accident.

A Ford engineer explained under oath why the tests were cancelled:

Q. Tell the Jury, if you will, what happened in the last limits J-turn test that Ford did at the Arizona Proving Ground in May, 1982. What happened to that Bronco II?

A. The . . . under the J-turn maneuver, the vehicle went up on two wheels, the outrigger failed, it dug into the cement and pole-vaulted the vehicle over.

Q. And it landed on its top.

A. It rolled over. Where it landed, I don’t recall.

Q. So is it correct, sir, that the reason the Ford Motor Company stopped limit J-turn testing of the Bronco II vehicle in May, 1982, and went to the computer simulation was concern about occupant safety?

A. Well, its concern about the safety of our track drivers, yes.

Q. Yes.

A. And our engineers.

Q. So you stopped doing the severe limits J-turn testing in May 1982, because you were concerned about your own test drivers. Right?

A. Right?

Q. You were concerned about the safety of your own test drivers. Right?

A. Yes. Because of the . . . we couldn’t depend on the outriggers supporting the vehicle.

Q. Now, that was eight months before job one. Is that right?

A. That is correct.

— Deposition of Ford Engineer James McClure, pages 109, lines 4-21 and page 110, lines 1-10.

"Ford conducted no further pre-production on-road safety testing of the Bronco II."  After abandoning live limits tests on the track, Ford used the ADAMS computer model for final limits testing. Ford’s report of the ADAMS simulation demonstrated again that the Bronco II Production Level Vehicle experienced inside two-wheel lift at 32 MPH during a Lane Change Maneuver test, which is an emergency avoidance maneuver. Ford did not simulate the Lane Change Maneuver at high speeds despite the computer model’s capacity to do so.