Issue link: http://read.dmtmag.com/i/41477
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 gas, 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 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). 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. 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 and wheel 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 pressure marked on the sidewall. Do not exceed the maximum inflation pressure for the 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 pressure marked on the sidewall, and then be inspected. PART 2: MOUNTING AND DEMOUNTING TUBELESS TIRES In order for a tire to perform properly, it must be mounted on the correct size wheel. The following are general instructions for mounting and demounting MICHELIN® X One® tires. Specifics for 19.5" wheels are detailed in the Mounting Tubeless Tire section (Page 5). For additional detailed instructions on mounting and demounting truck tires on particular types of wheels, refer to the instructions of the wheelmanufacturer or the RMA wall charts. TUBELESS TIRE MOUNTING/DEMOUNTING USING A MOUNTING MACHINE There are several tire changing machines available for the mount and demount procedure. Consult the manufacturer's user manual for the machine you are using as each operates differently. Full lubrication of the wheel and beads is still required. Inflation process requirements remain the same. tubeless tires, including the MICHELIN® DIRECTIONAL TIRES Truck tires featuring directional tread designs have arrows molded into the shoulder/edge of the outer ribs to indicate the intended direction of tire rotation. It is important, to maximize tire performance, that directional tires be mounted correctly on wheels to ensure that the directionality is respected when mounted on the vehicle. For example, when mounting directional drive tires on a set of 8 wheels, use the drop centers as a reference. Four tires should be mounted with the arrows pointing to the left of the technician and four tires with the arrows pointing to the right. This ensures that when the assemblies are fitted onto the vehicle that all tires can be pointed in the desired direction of rotation. Directional steer tires should be mounted in a similar fashion, one each direction, to ensure both are pointed forward. Once directional tires are worn greater than 50%, there is generally no negative effect of running them in a direction opposite to the indicated direction of rotation. Operating directional tires from new to 50% worn in the opposite direction of that indicated on the tire will result in the premature onset of irregular wear, excessive noise levels, and significantly reduced tread life. 3 General Instructions