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Commercial Tires

Zipper Rupture Bulletin Issued

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Think about the thousands of truck tire debris pieces alongside many major roadways, almost every one responsible for an unscheduled (and expensive) service stop.

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It has been well documented that many of these failed tires share several common traits  they were underinflated and fitted to an inner dual tire position. Consider that, for every one of these tires, many others continued on without the benefit of proper inflation for the load being carried until noticed in a runflat condition or found to be inflation-deprived during a routine tire change or service interval.

It is noteworthy that industry guidelines, endorsed by all manufacturers of medium radial truck tires and supported by the Technology & Maintenance Council (TMC), state that any tire inflated to less than 80% of its maintenance specified inflation pressure should be considered flat, removed from the rim, and inspected for punctures or other damage before returning to service.

When steel ply tires are operated in underinflated or overloaded conditions, the ply cords are deflected beyond their design limits, much like bending a coat hanger or piece of baling wire repeatedly until it breaks. Ultimately, a fatigue failure occurs in the upper sidewall area, beginning with the fracture of one or more ply cords, then progressing circumferentially, resembling a “zipper” opening. This often results in immediate air loss with explosive force and can be extremely hazardous to anyone in the immediate area.  

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In one sense a tribute to advances in modern radial tire technology, many of these “overworked” tires show little or no visual clues of their working history. Innerliners of older bias-ply tires showed discoloration, often accompanied by localized liner distortion, when run underinflated, making visual detection fairly reliable – not so for modern tubeless radials.

For years the industry has worked to develop some type of non-destructive, shop friendly inspection criteria to separate those overworked tires suitable for returning to service from those that should be scrapped. Failure to detect potential “zipper breaks” can result in premature casing failures, road service expenses, retread investment in unworthy casings, and, most serious of all, injury to tire servicing technicians or retread plant workers.

The S.2 Tire and Wheel Study Group of the TMC has gathered the input of all major truck tire manufacturers, collected samples of suspect run-flat and underinflated radial tires from fleets, and evaluated test procedures designed to reliably separate tires which should be scrapped from those that can be safely returned to service. The result of several years of this work is a detailed three-step inspection procedure.

The Rubber Manufacturers Association (RMA) has just published this information in a new bulletin titled, “Inspection Procedures to Identify Potential Sidewall Zipper Ruptures in Steel Cord Radial Truck, Bus and Light Truck Tires.” It can be ordered from the RMA Web site publication section (www.rma.org), or by phone at 800-325-5095, or fax at 330-725-5095.

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These industry standardized inspection procedures should be posted in all tire shop areas, preferably in wall chart form, reviewed with all tire servicing technicians, and included in tire servicing training materials. Also, the Tire Industry Association (TIA) offers a training video, “Detecting Potential Zipper Ruptures in Steel Cord Radial Tires in Tire Servicing Operations,” (www.tireindustry.org).

You can’t afford the potential liability of not adhering to these newly published guidelines. Other benefits include keeping undamaged casings in service with confidence, reducing unnecessary scrap, and reducing future road service calls – all good signs for your bottom line.

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