Issue link: http://read.dmtmag.com/i/34501
ZIPPER RUPTURES A fatigue-related damage, with or without a rupture, occurs in the sidewall flex area of steel radial light and medium truck tires when it is subjected to excessive flexing or heat. This zipper rupture is a spontaneous burst of compressed air, and the resulting rupture can range in length anywhere from 12 inches to 3 feet circumferentially around the tire. This is caused by the damage and weakening of the radial steel cables as a result of run-flat, underinflation, or overload. Eventually, the air pressure becomes too great for the weakened cables to hold, and the area ruptures with tremendous force. The RMA (Rubber Manufacturers Association) states that permanent tire damage due to underinflation and/or overloading cannot always be detected. Any tire known or suspected of having been run at less than 80% of normal recommended operating pressure and/or overloaded, could possibly have permanent structural damage (steel cord fatigue). TIRE INSPECTION Tire inspection should always include a thorough inspection of both sidewalls and inner liner, as this may reveal any potential damage condition that would cause the tire to become scrap. Examine the inner liner for creases, wrinkling, discoloration, or insufficient repairs, and examine the exterior for signs of bumps or undulations, as well as broken cords, any of which could be potential out of service causes. Proper OSHA regulations must be followed when putting any tire/rim back in service. After the tire has been inflated to 20 psi in a safety cage, it should undergo another sidewall inspection for distortions, undulations, or popping noises indicating a breaking of the steel cords. If this is the case, immediately fully deflate and scrap the tire. If no damage is detected, continue to inflate to the maximum air pressure marked on the sidewall. Do not exceed the maximum inflation pressure for the rim or wheel. Any tire suspected of having been run underinflated and/or overloaded must remain in the safety cage, be inflated to 20 psi OVER maximum air pressure marked on the sidewall, and then be inspected. The RMA has issued a revised Tire Industry Service Bulletin for procedures to address zipper ruptures in certain commercial vehicle tires. The purpose of the bulletin is to describe the inspection procedures for identifying potential sidewall circumferential ruptures (also known as “zipper ruptures”) on truck/bus tires and light-truck tires of steel cord radial construction. Zipper ruptures can be extremely hazardous to tire repair technicians. Careful adherence to proper repair procedures is crucial. For more information contact RMA at info@rma.org or visit www.rma.org. Dual Cage MICHELIN X One Tire Cage ® ® Be sure to reduce pressure to regular operating pressure before placing back in service if the tire has been deemed serviceable. Section Two: Mounting the Tire 17