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. First offered for sale in March 1990, 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