On March 6, 2000, NHTSA began a preliminary inquiry This became a formal investigation on May 2 (PE00020). Ford argued that the Explorer was no more dangerous than any other SUV and that the accident rate for Explorers with Goodyear tires was far lower than for Explorers with Firestone tires. Some outside observers argued that both parties were to blame:
Ford Explorer Ford designed the first-generation Explorer by mounting an SUV cabin on a
Ford Ranger undercarriage. This cut production costs because Ford could use existing facilities, parts, and robots. But the extra upper cabin weight on the pickup chassis created a vehicle with a higher
center of gravity that was more likely to roll over in an accident. It was also more likely to sway during sharp turns because it used the same
leaf spring suspension as the Ranger. They did not widen the wheelbase, which would have required a substantial redesign. One consequence of lowering the tire pressure is increased tire temperatures which could lead to a tire failure. Firestone warrantied these tires at 26 psi for 11 years. the first-generation Explorer had one of the lowest fuel-economy ratings of any SUV sold in the United States, due at least in part to Ford's recommended tire pressure. While designing the second-generation Explorer, Ford made two changes to reduce weight and improve fuel economy. First, Ford replaced the Twin I-Beam suspension with a lighter-weight short- and long-arm suspension, but did not lower the engine. This raised the Explorer's center of gravity, making it more prone to rolling in an accident or sharp turn. Second, Ford reduced the amount of material in the roof. When the new model went on sale in 1995, it was discovered that this lighter roof was so weak that it would collapse under the weight of an overturned Explorer if the windshield were smashed in, as often happened in rollover accidents. After Ford Motor Company voluntarily recalled 13 million Firestone tires on May 21, 2001, Firestone requested that NHTSA investigate the handling and safety of Ford Explorers following a tread separation. Firestone argued that the Explorer is poorly designed and exhibits dangerous
oversteer in the foreseeable event that a tire fails while driving. Firestone hired a consulting engineer to analyze the performance of the Ford Explorer and other SUVs during a tread separation, this report showed that the Explorer had a greater tendency to
oversteer following a tread separation than other SUVs. NHTSA examined this report as well as real-world accident data and data provided by Ford concerning the design of the Explorer and denied Firestone's request. NHTSA stated that "[t]he many crashes following tread separations of tires on these vehicles that are documented in the Firestone claims database and that have been reported to ODI by consumers and others demonstrate that such a tire failure can lead to loss of control, particularly when it is a rear tire that fails and the vehicle is being driven at high speed. However, the fact that a vehicle exhibits linear range oversteer characteristics following a rear tire tread separation does not, in itself, indicate that the vehicle contains a safety-related defect. Moreover, the data available to ODI does not indicate that Explorers... are more likely to exhibit linear range oversteer characteristics following a rear tire tread separation than many of their peers."
Firestone tires The tires that were involved in these accidents were P235/75R15 ATX and ATX II tires and P235/75R15 and P255/70R16 Wilderness AT tires. These tires were installed as
OEM equipment on the
Ford Explorer,
Mercury Mountaineer,
Ford Bronco,
Ford Ranger,
Ford F-series pickup trucks,
Mazda B-series pickup trucks, and
Mazda Navajo between 1991 and 2000. ATX tires were originally developed in the late 1980s for use on Ford light trucks and SUVs and were first installed on Ford trucks and SUVs in 1991. The ATX II was designed to improve the ATX's ride and the fuel economy of the Explorer. which produced tires with a significantly higher
failure rate than the other two factories that manufactured these same tire models,
Wilson, North Carolina and
Joliette, Quebec. Wilderness AT tires manufactured before May 1998 had higher failure rates regardless of where they were manufactured and had a safety-related design defect according to NHTSA. where the tire tread peeled off from the body of the tire. Tread separation, due to the interaction of steel and rubber tire elements, has been a challenge in
radial tire design since their development by
Michelin in 1946. The failure of the subject tires "begin as belt-edge separation at the edge of the
second belt. This is the area of highest strain in a steel-belted radial tire, primarily due to the structural discontinuity created by the abrupt change in modulus from steel to rubber." The longer it takes the tread to separate the more the vehicle pulls in that direction.
Causes There were several primary causes for the tread separations: tire age, manufacturing facility,
operating temperature, tire design, as well as labor and management problems in Bridgestone/Firestone and at the Decatur, Illinois factory.
Tire age The belt wedge and skim rubber compounds change as they age. Skim rubber is a thin strip of rubber sandwiched between the inner and outer belts and the belt wedge is a thin strip of rubber installed along the outer edge of the tire between the two steel belts and in the area of highest stress on the tire. These changes reduce the ability of the tire to resist crack growth and belt separation. That is, once a crack formed within the tire, the crack would spread more readily than on comparable tires from the Joliette or Wilson factories. Researchers also tested belt adhesion strength by measuring the force that it would take to peel a strip of the second belt from the rest of the tire. ATX and ATX II tires manufactured at Decatur had lower belt adhesion strength than the same tires manufactured at Joliette or Wilson. However, there was insufficient evidence to conclude that this would weaken a tire or lead to a premature failure.
Operating temperature A tire's operating temperature will increase with higher vehicle load, speed, air temperature, and with lower tire inflation pressure. The combination of inflation pressure, speed, and vehicle load could increase the tire temperature as much as above the ambient air temperature.
Labor and management problems Bridgestone purchased Firestone in 1988 to compete with other large multinational tire companies and took on a considerable amount of debt to complete the purchase and upgrade Firestone's manufacturing facilities. At that time Firestone was losing a considerable amount of money each year which put a drain on Bridgestone's profits. Bridgestone pressured Firestone to cut manufacturing and labor costs to improve revenues. Critics and workers claim that this led Firestone to cut corners on production and to allow substandard tires to pass inspection that should have been rejected. This also led Firestone to pressure workers to accept new labor contracts that reduced pay and benefits and increased the hours that its factories were operating. In a deposition retired Firestone workers testified that quality control problems at the Decatur factory could have led workers to manufacture defective tires. One worker stated that, despite getting a company discount, he'd stopped purchasing Firestone tires years before the crisis developed because of quality control problems. Others stated that they had to inspect as many as 100 tires per hour which they believed were far too many tires to do an adequate job; that they rolled unvulcanized tire carcasses, also called a "green tire", across the factory floor which could allow debris from the floor to end up inside a completed tire; Firestone claimed that these were disgruntled workers who quit after a bitter strike. "We let the U.S. unit use its own culture. There was an element of mistake in that." during a time of labor unrest and a strike against Firestone carried out by the
United Rubber Workers (URW) and the
United Steel Workers (USW). By April 1994, the existing labor contract ended and workers continued to work at the factory until the URW called a general strike in July at Decatur and four other Firestone facilities. Almost immediately Firestone began hiring replacement workers at all their facilities and by January 1995 Firestone had hired 2,300 replacement workers who were paid thirty percent less. Over time union workers started to cross the picket line and by May 1995 there were 1,048 replacement workers and 371 permanent workers at Decatur. At that time the URW voted to unconditionally end the strike to block Firestone from hiring even more replacement workers and then holding a union decertification election. While the strike ended the labor negotiations continued. In July 1995 the URW had run out of money and was absorbed by the USW. During the time period from May 1995 to December 1996 union workers worked alongside non-union replacements. Labor negotiations between Firestone and the USW continued but many union workers could not return to work because their jobs had been replaced. The union described that time period as "brutal." ==Recall==