Fewer Blowouts

February 16, 2007 | By | Reply More


3 Series run-flat

If you had X-ray vision, you could see that the sidewall on a 3 Series run-flat is different from that of a conventional tire.

Few things are more frightening to a driver than a blowout because several bad things start happening all at once. A trained, experienced driver may be able to bring his or her vehicle to a safe stop after a blowout. However, many drivers just hang on and hope for the best, or, worse, slam on the brakes. Even for an experienced driver, a blowout while driving on a highway with other vehicles nearby is scary.

“Run-flat” tires, which still support the car and provide control even when air pressure is lost, greatly reduce the danger of a blowout. Although run-flats have been available for many years, interest in these tires has surged recently.

BMW has offered run-flat tires as standard or optional equipment on selected models since the late 1990s. Equipped with run-flats, a BMW can be driven some distance even though the tire has no air in it. However, the maximum recommended speed for a run-flat without air is 50 mph. So, your customer can drive to your shop for tire replacement, just not at high speed.


With its stronger, reinforced sidewall, a run-flat tire can support a BMW even when all air pressure has been lost.

In addition to their other benefits, run-flats eliminate the hassle and potential risk of pulling onto the shoulder of a busy highway to replace a flat tire. These tires even offer a convenience benefit, freeing up trunk space because a spare tire and jack are not necessary with run-flats.

Three Types

Tire makers use one of three technologies or designs to address flat tire concerns.

  • Self-Sealing. Self-sealing tires have a thin, flexible liner bonded to the underside of the tire carcass that automatically seals punctures. However, the liner may fail, especially if a rock or nail causes a large hole in the tread.
  • Support Ring. Michelin’s PAX tire and wheel combination has a rubber ring bonded to the wheel that supports the weight of the vehicle after losing air pressure. These tires and wheels are of a unique size. You cannot mount PAX tires on any other wheel and PAX wheels will not accept any other tire.
  • Self Supporting. The most common run-flats have a sidewall strong enough to support the tire and car, for a limited time, after the loss of air pressure. The composition of the sidewall provides the additional strength. These tires also have a special bead that securely bonds the tire to the wheel to help prevent the bead from breaking loose. OE run-flats on BMWs are self supporting.

Drivers complained that the early generation run-flats were too hard, resulting in a harsher ride and reduce performance compared to a conventional tire. These complaints have just about disappeared with current run-flats. The tires have a less harsh ride and BMW has tweaked its suspension, steering, and braking to adapt to the unique characteristics of


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Category: BMW TechDrive, Tires + Wheels + Hubs + Bearings

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