Run-Flat Tires

Run-flat tires have stiff, reinforced sidewalls that support the car's weight with zero air pressure, typically for about 50 miles at up to 50 mph. That lets you drive to a shop instead of changing a tire on the shoulder, and it lets automakers delete the spare to save weight and trunk space. BMW, Mini, many Mercedes, Cadillac and Lexus models come on run-flats from the factory, and those cars have no spare and often no jack.

They are for people who own a car that came with run-flats and want to keep the safety and convenience, and for drivers who cannot or do not want to change a tire on the roadside. They require a tire pressure monitoring system (TPMS), since a flat run-flat feels almost normal from the driver's seat.

The honest trade-offs are significant. Run-flats ride harder because of the stiff sidewalls, cost 20 to 40 percent more than the equivalent conventional tire, offer fewer choices in each size, and a punctured run-flat usually must be replaced rather than repaired once it has been driven flat. Tread life is often shorter. Many BMW and Mini owners switch to conventional tires and carry a plug kit and inflator, which is safe as long as all four tires are changed together. Newer designs like the Bridgestone DriveGuard Plus have narrowed the comfort gap and even carry mileage warranties. When shopping, look for the run-flat marking (RFT, ROF, SSR, ZP, DSST or EMT depending on brand), match the OE code if you want the factory tire, and check whether the size you need exists as a run-flat at all. Prices run from about 150 dollars for a 16-inch tire to 400 dollars for premium 20-inch performance sizes.