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Servicing run-flat tires Stiffer sidewalls are just one issue of concern By Bob Ulrich and Ann Neal
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hat does a dealer need to know to service a run-flat tire versus a non-run-flat tire? That is the question we asked the experts on your behalf. And who better to ask first than the mounting and balancing equipment manufacturers? Pete Liebetreu, senior product manager for Hunter Engineering Co., had both a short and long answer. “The short answer? A lot!” he said. “Run-flats are much more than ‘just a harder tire.’ Just like non-run-flat tires can vary widely, so can run-flats. As a general rule they have stiffer sidewalls than conventional tires, so they are more difficult to mount and demount. “This is especially true for top bead demounting and mounting. You almost always need, at minimum, a single press arm or, even better, multiple press arms to service them professionally.” Liebetreu said size matters when it comes to servicing run-flat tires. Smaller diameter run-flats (i.e., 17 – and 18-inch sizes) are often more difficult to handle then their larger counterparts. “Tall (high aspect ratio) sidewalls are also usually harder to mount than low profile run-flats because the taller the sidewall, the stiffer the construction.” Tire dealers should also keep in mind that not all run-flats are equally stiff. “It depends on the specific design for the specific application,” said Liebetreu. “The OEM usually determines the stiffness that is acceptable based on the desired ride and handling goals.” The stiffness in a run-flat tire compared to a conventional tire plays an important part in the vehicle’s overall suspension performance. So substituting non-run-flats or run-flats with a different stiffness characteristic can have ride quality implications that a dealer might not see when they are replacing the original run-flats, he said. “Because run-flats are already so stiff, those vehicles also can be more sensitive to road force variations. When balanced, they should also be road force checked and corrected as well.” As part of its Basic Automotive Tire Service Training Series, the Tire Industry Association has a training module detailing how to demount and mount run-flat tires.
What the tire makers say Tire manufacturers say the differences between run-flat tires and conventional tires are minimal yet prominent. “Servicing run-flat product in regards to the normal protocol for inflation checks, rotation and visual inspection is the same as that for a traditional tire,” said Gerardo Andrade, senior manager of market quality for Pirelli Tire North America Inc. “One difference that dealers and service technicians might notice is that vehicles using a run-flat product must be equipped with TPMS or a similar approved monitoring system which should be taken into account when servicing the tire.” Bob Abram, senior manager of product planning for Yokohama
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“We have a different bead filler, reinforcement in the sidewall and different bead bundle for the Advan Sport ZPS versus the standard Advan Sport,” says Yokohama’s Bob Abram. “The rayon body plies are also different than many of our other tires.”
Tire Corp., said due to the unique construction of a zero-pressure tire — and the tire pressure monitoring system (TPMS) with which it is associated — more care should be taken when dismounting and/or mounting. According to Yokohama’s ZPS (Zero Pressure System) Technical Service Guidelines, run-flat tires should never be mixed with tires that do not have run-flat technology. In addition, “Never mix run-flat tires of different brands or technology.” Juan Britos, senior technical services specialist for Hankook Tire America Corp., said the only major difference between servicing regular and run-flat tires is the type of mounting equipment needed. “Run-flat tires require multi-armed mounting equipment to support the tire. Other than that, the two styles are serviced in a similar manner.” Goodyear Tire & Rubber Co.’s Goodyear (ROF, or Run On Flat) and Dunlop (SST, or Self-Supporting Technology) run-flat tires feature a patented sidewall construction that allows continued driving on a flat tire for up to 50 miles at 50 mph in normal conditions. However, the tire may have to be replaced if driven to these limits, said Bob Toth, director of industry relations.
MTD September 2017
