rates regardless of where they were manufactured and had a safety-related design defect according to NHTSA. Tread separation 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 fast. 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. Reasons suggested include additional heat from the exhaust, higher weight on the driver's side because vehicles are often driven without any passengers or higher temperatures in the middle of the road than on the shoulders. 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, IL factory. Tire age The belt wedge and