But few use them on truck tires like the Firestones. Firestone corporate partner Bridgestone does use abbreviated nylon strips to cover the edges of the steel belts in its Dueler truck tires. Nylon belts are used on nearly all Pirelli's U.S.-market tires, including truck tires, according to Mark Peist, product manager for Pirelli. Often, not good enough, says an expert. The adhesive gives up the ghost, or gets hard and powdery.
Small things can affect how the tire layers adhere.
Tires built in the winter worked fine because the relative humidity went down and the adhesive worked well. In the summer, the humidity went up and the adhesive didn't hold as well. Another factor that could draw attention from investigators is quality control at Firestone plants. Firestone's Decatur, Ill., factory is blamed for many of the suspect tires. That plant has been embroiled in contentiousness since 1994, when United Rubber Workers local 713, now United Steel Workers 713 as a result of a merger, struck.