Run flat tires explained: markings, how far you can drive, and repairs

How run flat tires work

A regular tire relies on air pressure to carry the vehicle. When it goes flat, the sidewall gets crushed between the rim and the road. Bridgestone and Continental explain that a self supporting run flat tire uses stiffer, reinforced sidewalls that keep carrying the weight after air is lost, and stop the tire from slipping off the rim. Continental says its SSR tires fit standard rims. Michelin notes that some ZP tires marked SH M need special wheels, so never mount those on a standard wheel.

Run flat markings

• RFT or DriveGuard: Bridgestone run flat tires.
• ZP or EMT: Michelin Zero Pressure and Extended Mobility Tire.
• SSR: Continental Self Supporting Runflat.
• RF inside the size, such as 205/55 RF 16 or 245/45RF19: the general run flat marking under UN Regulation 30, according to Continental and the European Commission, which adds that a pictogram is shown too. Do not confuse this with RF as a separate marking next to the size, which means reinforced. See XL vs SL tires.
• EMT or RUN FLAT: Continental says the EMT marking is an alternative general run flat marking and will appear more often on its future SSR tires.

How far and how fast you can drive deflated

Sources: Bridgestone, Continental and Michelin. These are maximums. Michelin says the safe distance depends on speed, load, outside temperature, how much air was lost and the damage. Hard braking, cornering and sharp maneuvers greatly shorten it, and a deflated tire handles differently. If the tire starts to vibrate or the car becomes hard to control, stop. If your owner's manual gives a lower limit, follow it.

Why run flats need TPMS

Run flat tires ride so normally when deflated that you may not notice. Continental says SSR tires may only be used on vehicles with a tire pressure monitoring system, and recommends electronic stability control. Michelin says ZP tires must be used only with an operating low pressure warning system, or the limited warranty is void. Learn what the warning light means in our TPMS guide.

Can a run flat be repaired?

• Continental SSR: Continental says a tire repair is not allowed.
• Bridgestone DriveGuard: repairable in limited circumstances, depending on the damage, how much pressure was lost and how the car was driven.
• Michelin ZP: the fewer miles driven after air loss, the better the chance the tire can be reinflated or repaired and returned to service.

Where a repair is allowed, USTMA says a proper repair needs a patch and plug combination from the inside, never a plug alone, and the tire maker's own limits apply. See tire plug vs patch.

No spare, and replacing run flats

Cars built for run flats often carry no spare wheel or jack, which saves weight and trunk space. Michelin says only vehicles originally equipped with run flat tires should mount them, because those cars have suspension and chassis changes for them. Continental says SSR tires should only go on vehicles the maker approves with TPMS, recommends fitting them on all four positions, and advises against mixing them with standard tires. If you switch to regular tires, plan for a puncture: carry a spare or inflator kit and check our spare tire limits.