WASHINGTON-The Rubber Manufacturers Association has issued a service bulletin providing an explanation for ``zipper'' failures and steps technicians can take to prevent the blowouts. Steel ply cords in the upper sidewall area of underinflated light and medium truck tires can become overflexed, causing structural fatigue. Weakened cords may break while being serviced, the RMA said.
Especially susceptible are tires with less than 80 percent of their recommended operating cold inflation pressures or those that are run while flat.
The condition generally occurs in tires that have been punctured or repaired in the crown area and radial truck tires used in dual applications, the RMA said.
Discoloration of the innerliner and/or ripples or bulges in the upper sidewall may be signs of weakened cords, the RMA said. Technicians should place suspected tires in a safety cage, inflate them to a maximum of 20 psi for a visual inspection and then deflate them for a physical inspection.
Remember: The Occupational Safety and Health Administration requires all truck tires be inflated in an approved safety cage in conjunction with the use of an extension air hose equipped with a clip-on air chuck, the RMA added.