Bridgestone/Firestone links tire problems to design, manufacturing process

NASHVILLE, Tenn. (Dec. 19)—Bridgestone/Firestone Inc. reported today that a combination of factors led to tread separation problems on the 6.5 million recalled ATX, ATX II and Wilderness AT tires. The company´s team of engineers, technical experts and statisticians identified individual factors that alone would not lead to increased tread separation claims rates, but acting in combination the factors appeared to explain the higher rates. The factors are: The shoulder pocket design of the P235/75R15 ATX tires could lead to cracking at the shoulder pocket bottom, which when combined with the other factors results in reduced resistance to belt detachment; low inflation pressure in the recalled tires increased the tires´ running temperature and would contribute to a decreased belt adhesion level; vehicle load levels and low standard tire pressure initially specified for the Explorer led to a decreased margin of safety; and the tires produced in Decatur, Ill., exhibited different belt adhesion characteristics, including lower initial adhesion, than those of the same size and line produced at other company plants. The Decatur plant uses rubber pellets blended with a lubricant to create the rubber that coats the tire´s steel belts, according to an Associated Press report. Other Bridgestone/Firestone facilities use a slab system, not the pellets.