page_title: Firestone and Ford tire controversy
section_title: Tread separation
hierarchical_section_title: Firestone and Ford tire controversy / Investigation and possible causes / Firestone tires / Tread separation
caption_attribution_description: English: Separation pattern on the tire carcass of a failed Wilson P235/75R15 Wilderness AT tire, manufactured in Sep 96
context_page_description: The Firestone and Ford tire controversy was a period of unusually high failures of P235/75R15 ATX, ATX II, and Wilderness AT Firestone tires installed on the Ford Explorer and other related vehicles.
  The tire failures are linked to 271 fatalities and over eight hundred injuries in the United States with more injuries and fatalities occurring internationally, it led Bridgestone/Firestone and Ford Motor Company to recall and replace 23 million tires, it cut the market value of Bridgestone/Firestone in half, Firestone closed the Decatur, Illinois factory where the tires were manufactured, several executives in Bridgestone and Ford resigned or were fired, it led Congress to pass the TREAD Act, and it brought an end to the nearly 100 year corporate relationship between Ford Motor Company and Firestone.
context_section_description: The failures all involved tread separation 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." Once a tread separation begins it can grow along the circumference of the tire or laterally across the width of the tire leading to cracks that grow between the belts. As separation progressed it could grow to form large crescent shaped areas along one or both sides of the tire. If those areas grew large enough they could separate catastrophically, especially at high speeds where the separation was aided by the centrifugal force of the spinning tire.
  Vehicles with tread-separating tires were difficult to control especially when the failing tire was on a rear wheel and when the vehicle was moving at a high rate of speed.
  A vehicle with a tread-separating rear tire will pull towards the side of the vehicle with the failed tire. The longer it takes the tread to separate the more the vehicle pulls in that direction. While the tread is separating the vehicle will oversteer while the tread-separating tire is on the outside of a turn. Once the tread separation has completed the vehicle will cease pulling in any direction.
  Tread separations for Firestone ATX, ATX II and Wilderness AT tires were significantly worse than for comparable tires manufactured by other companies including the Goodyear Wrangler RT/S which was also installed on new Ford Explorers.
  The tread-separating tire was most frequently the left-rear wheel of the vehicle, possibly because of additional heat from the exhaust, higher weight on the driver side because vehicles are often driven without any passengers, or because of higher temperatures in the middle of the road than on the shoulders.
caption: Tire Tread Separation of a Firestone P235/75R15 Wilderness AT tire
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