Firestone tire research focusing on belt fatigue

NASHVILLE, Tenn (Oct. 17)—The independent expert hired by Bridgestone/Firestone Inc. to investigate possible problems with its Firestone P-metric light truck tires is focusing on the fatigue properties of the rubber layer between the tire´s steel belts. ``All evidence to date points to a slowly developing fatigue crack that propagates through the belt wedge material and then subsequently into the belt skim between the steel belts,´´ wrote Sanjay Govindjee, the University of California-Berkeley associate professor of civil engineering brought in to conduct an independent investigation, in a letter to Bridgestone/Firestone. ``At some stage, the cracks reach a critical size and the tires subsequently fail.´´ Ganjay also wrote that the problem is a ``quite complex interaction of the effects of tire design, the manufacturability of the tire, and loading conditions. Ganjay expects to have a preliminary technical report done by the end of October and a final report early in 2001.