Safety must be a priority when checking tires for damage.
While technically known as “sidewall circumferential ruptures,” I think most of us in the tire industry call them “zipper ruptures.” Whichever term you prefer, these ruptures are a concern on truck and bus tires, as well as on LT tires that employ steel cord radial construction, whenever these tires may have been overloaded and/or under-inflated.
If you suspect that a zipper rupture may be an issue, you’ll need to inspect the tire thoroughly. In order to do so safely, you’ll want to (1) remove the valve core, (2) completely deflate the tire, (3) remove the wheel assembly from the vehicle, (4) demount the tire from the wheel assembly, and (4) inspect the tire both visually and with your hands.
According to a Tire Information Service Bulletin published by the U.S. Tire Manufacturers Association (USTMA), “tire service professionals could also utilize non-destructive inspection equipment, such as shearography, x-ray, or other non-destructive testing, to look for any anomalies present in the casing.”
That same Bulletin notes the following: “For all tires returning to service, a tire service professional should conduct a complete visual and hands-on inspection of the tire in a well-lit area and with a hand-held grazing light.”
Look, feel, listen
How can you tell if there’s a problem? The USTMA recommends looking for irregularities, including punctures, distortions, abrasions, undulations, ripples, and bulges on both the interior of the tire, as well as on the sidewall. In addition, you’ll want to check for any cuts, snags or chips that may have left the steel wire exposed.
In addition, the USTMA recommends feeling for irregularities, including soft spots in the sidewall flex area, along with distortions, undulations, ripples and bulges in the sidewall, and for protruding wire filaments.
Finally, the USTMA encourages tire technicians to listen for any snapping, popping or cracking sounds.
Inflation test
If the look, feel and listen test does not raise any red flags, the USTMA recommends conduction an inflation test: (1) mount the tire onto the wheel assembly and inflate it to 5 psi to seal the beads, (2) place the tire into a safety cage, (3) remove the valve core, (4) attach an OSHA compliant inflation device with a hose that’s long enough to allow you to step far enough from the tire, (5) inflate the tire to 20 psi (light truck and medium truck tires) or 40 psi (bus and refuse application tires).
Next, you’ll want to listen for any popping, crackling or snapping sounds, and look for distortions in the sidewall. If you don’t see or hear anything of concern, the USTMA recommends increasing the inflation pressure to 20 psi over the cold inflation pressure found on the tire sidewall, not exceeding 120 psi for light truck and medium truck tires, of 140 psi for bus and refuse application tires. Again, you’ll want to look and listen for the same red flags mentioned above.
If the tire exhibits potential zipper characteristics at any of the stages above, the USTMA says that it must be marked appropriately, made unserviceable and non-repairable and then scrapped.
They also offer the following warning, which applies to both the low and high inflation stages of the inspection process: “If any of these conditions are present during inflation—stop! Do not approach the tire. Before removing from the restraining device, completely deflate the tire remotely. Remove the clip-on air chuck.” Let’s stay safe out there!