October 6, 2009
Bridgestone Potenza RE050A. Click image to enlarge
By Paul Williams; photos courtesy Bridgestone
Run-flat tires are becoming more common as original equipment on new vehicles. They save space, weight, and are designed to increase safety. But owners of vehicles with run-flat tires are asking, “In the event of a puncture, can a run-flat tire be repaired?”
The answers are “yes,” “no,” and “maybe,” depending on who you ask. For the definitive answer, read on.
The use of Bridgestone run-flat tires on the BMW 3 Series was the first large-scale, original equipment (OE) application of these tires in the North American market. At the time, there was a directive from tire-supplier Bridgestone to retailers not to repair damaged run-flat tires, instead sending them back to headquarters for inspection. Mark Kuykendall, Bridgestone’s Engineering Manager for Bridgestone Light Vehicle and Truck Tires, explained, “Initially, we didn’t want the tires repaired because we didn’t have sufficient field data.”
In other words, although the tires had been tested in controlled situations, there wasn’t data from thousands of applications over time upon which to base general conclusions concerning the effectiveness of run-flat tire repairs. Being cautious, Bridgestone requested that retailers fit a new tire, and send damaged/worn tires back for inspection, ultimately determining that the tires can safely be repaired.
Consequently, Bridgestone issued a Repair Procedure in May, 2005 for run-flat tires.
The procedure specifies that the inside of the tire must be professionally inspected (which means the tire must be off the wheel), and if it passes, then a patch/plug combination will effect a satisfactory repair.
This is confirmed by local Ottawa tire retailer, Frisby Tire. Manager Francis Peori states that his shop has successfully repaired many run-flat tires using the patch/plug method. “No problem at all,” says Mr. Peori, who has consulted with representatives of the major brands that make run-flat tires, including Bridgestone.
As an aside, it’s possible that the initial directive by Bridgestone not to repair its run-flat tires has circulated more widely than expected, leading to the mistaken conclusion that run-flat tires are not to be repaired, period. This conclusion is obsolete.
In some situations, however the tire won’t pass inspection and can’t be repaired. Contributing factors would be excessive heat compromising the structure of the tire (run-flats do run hotter than conventional tires), excessive load, and/or running the tire with no pressure for too long at excessive speeds.
How long is too long, and what’s too fast? The International Standards Organization (ISO) indicates that for a tire to be called “run-flat” it must be able to run at 80 km/h for 80 kilometres with no pressure. Beyond these minimums, your chances of successfully repairing the tire decrease.
Another indication of whether the tire can be repaired is via the car’s Tire Pressure Monitoring System (TPMS), which is part of the run-flat specification.
The TPMS system is informed by sensors in the wheels, and typically generates a two-stage warning consisting of a visual (light) and audible phase. When the light comes on, Mr. Kuykendall suggests, it means the pressure is low; when the audible warning sounds, indicating that the pressure is minimal or gone; you effectively have a “flat” tire (although it won’t look flat, as the sidewall provides support).