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Firestone's Request for a Defect Investigation on the Handling of Ford Explorers After a Rear Tire Tread Separation


On May 31, 2001, Bridgestone/Firestone, Inc. (Firestone) submitted a "request" that NHTSA open a safety defect investigation regarding the handling and control characteristics of Ford Explorer sport utility vehicles (SUV) following a tread separation on a rear tire.  The request was filed shortly after Ford Motor Company (Ford) announced on May 22, 2001 that it would provide free replacements for all Firestone Wilderness AT tires on Ford vehicles.  It was part of Firestone's effort to argue that the crashes (many of which involved rollovers) that occurred in Explorers following tread separations of Firestone ATX and Wilderness AT tires were to a large extent due to the design of the Explorer rather than a defect in the tires.

Memo and Tables: 

  • Complete Memo
  • Analysis of A Report for a Defect Investigation Submitted by Bridgestone/Firestone Inc.
  • Table 1 - Vehicles and Test Conditions Used in Dr. Guenther's Testing
  • Table 2 - Comparison of Understeer Gradients Measured at Different Facilities
  • Table 3A - Understeer Gradients for SUV Models with Data Available from Multiple Sources
  • Table 3b - Understeer Gradients for SUV Models with Data Available from One Source
  • Table 4A - Comparison of Understeer Gradient
  • Table 4B - Comparison of Understeer Gradient Values Lightly Loaded
  • Table 5 - Understeer Gradient (UG) Change Lightly Loaded to GVWR for 1996 to 2000 Model Year
  • Table 6 - Understeer Gradient Change Lightly Loaded for 24 various Model Year
  • Table 7 - Understeer Gradient Values with ""Detreaded" rear tire in Lightly Loaded Condition
  • Table 8 - Analysis of Effect of Rear Tire Tread Separation on Understeer Gradient
  • Table 9 and 10 - Consequences of Tread Separation of Subject Tires on Various Types of Vehicle
  • Figure A-1- Simple 2 Degree of Freedom Car, Moment Components