Tread Separation
The failures all involved tread separation[30][31] where the tire tread peeled off leading the tire to disintegrate.[32] 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."[2] 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.[2]
While a tread is separating from a tire the vehicle 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. Once the tread separation completes the vehicle ceases to pull in any direction. While the tread is separating the vehicle will oversteer while the tread-separating tire is on the outside of a turn.[33]
In 2000 Firestone added a nylon cap to reduce the problem of tread separation in all of its tire models installed on SUV's.[34]
https://en.wikipedia.org/wiki/Firestone_and_Ford_tire_controversy
