What Are Run-Flat Tires?

A flat tire often happens at the most inopportune time or place. When it does, you might call roadside assistance to install a spare tire. You might try to do it yourself. But there's a chance your car doesn't even have a spare. One alternative to a spare is a set of run-flat tires, which buy you time — about 50 miles, generally — to get to a repair shop after a puncture or other related air loss. These tires have additional reinforcement that allows run-flats, or zero-pressure tires, to support the weight of a vehicle for a short time.

While run-flat tires may sound like the perfect solution, car owners and car shoppers should know about the trade-offs with run-flat tires.

Run-flat tires are standard or optional on 16.1% of new vehicles, according to Edmunds data. While the number of vehicles available with run-flat tires has doubled in the last decade, they seem to have hit a plateau. The overall percentage of vehicles available with run-flats has remained plateaued at 14%-16% for the last several years. You'll now find run-flats on the majority of vehicles from BMW, Mercedes-Benz and Mini. Many Cadillac models also employ run-flat tires.

Self-supporting tire

The most common type of run-flat technology in use today is the self-supporting tire. In most cases, the tire's sidewalls are heavily reinforced to support the vehicle when the air pressure is low or even when the tire has lost all its pressure. Another less common method to reinforce a run-flat tire is with an internal ring of hard rubber running along the center of the tire or wheel. Think of it like a thin doughnut between the wheel and tire tread that can bear the weight of the car in the event the tire loses air. This is typically the preference for military vehicles, armored cars and high-stakes security services.

Pros:

• You can drive on a flat tire: The primary benefit of a self-supporting tire is that it allows you to keep driving on a flat up to 50 miles after all the air has gone. You don't have to get out of the car in the cold, or the rain, or onto a busy highway or on the street in a sketchy part of town. Drivers will usually have to reduce speed to about 50 mph to get the maximum range. The owner's manual will have exact figures for each tire/vehicle application.




• Better stability after a blowout: Because this tire can support the vehicle for miles without air, a sudden deflation results in less weight transfer and tread destabilization. Steering and handling will remain near normal.




• Lower vehicle weight: With the spare wheel and tire repair tools eliminated, vehicle weight should theoretically go down. But it won't be as much as you might expect since run-flats weigh more than regular tires due to the added sidewall reinforcement.




• More room in the trunk: Most spare tires are located on the floor of the cargo area. With no spare to take up space, automakers can use that to maximize the storage space in the vehicle.

Cons:

• No spare: Vehicles equipped with run-flats do not carry a spare wheel and tire, which means they don't have a jack or tools either. In fact, eliminating the spare tire and reallocating that space to some other purpose (styling, a third-row seat, interior room, etc.) is a big reason why carmakers offer run-flats.




• Reduced tread wear: A study by J.D. Power found that people replaced their run-flat tires an average of 6,000 miles sooner than owners using conventional tires. Opinions differ on the reason, but one theory is that tiremakers put a soft tread compound on a run-flat tire to counter the hard ride. A side effect of the softer compound is a shorter tread life. Actual data on the longevity of run-flat tires has been hard to find. But according to a 2018 J.D. Power owner survey, owners reported higher overall satisfaction with run-flat tires. They did not lag behind conventional tires in the survey.




• Blowouts are still possible: If a driver fails to heed or notice the warnings and drives beyond the zero-pressure range or above the speed limitation, the tire can begin to disintegrate, with the same destabilizing effects. Additionally, if the puncture occurs on the sidewall or if the tire hits a large object, the driver will have to call a tow truck. The J.D. Power study found that "customers with vehicles equipped with run-flat tires are nearly twice as likely as those with vehicles equipped with conventional tires to have to replace a tire due to a flat or blowout."




• Hard to tell if it is low on air: A side effect of the stiffer construction is that the sidewalls do not bulge if the air pressure is low. Therefore, it is critical to have a working tire pressure monitoring system and check your tire pressure frequently. Otherwise, you'll never know when you have a flat.




• Harsher ride: The stiff sidewalls that make a run-flat work also result in a harsher ride. If the vehicle came with run-flat tires from the factory, the automaker has usually tuned the suspension to offset the rougher ride.




• Cost: Run-flat tires are more expensive to replace. Prices will vary by tire type and purchase location, but it's not uncommon to pay a $40-$65 premium for a run-flat tire. Also, many run-flats cannot be repaired and often need to be replaced in pairs.




• Less on-shelf availability: Because run-flats aren't a big-selling tire, drivers shouldn't expect to roll into just any tire shop and buy them. It may be easier to do so in larger cities, but if you're a run-flat user on a road trip and get a flat near a small town, you'll probably have to make a detour to find a suitable new tire. Or worse, you may have to stay overnight, waiting for the tire to be shipped.

Self-sealing tire

A self-sealing tire isn't a run-flat tire in the sense that it can operate without air. Instead, it has a layer of sealant inside the tire that can maintain the air pressure in the event of a puncture. If you get a nail in the tire and remove it, the sealant will fill the puncture as long as it is near the center of the tread and is not larger than 5 millimeters.

The biggest advantage of the self-sealing tire is that it resembles a traditional tire. It can be mixed and matched with standard tires, and the tread life is the same. The downsides are the higher cost (roughly the same premium as a run-flat tire) and restricted availability.

This type of tire isn't standard on new vehicles but is worth mentioning since it is available as a replacement tire. Continental and Pirelli are two tiremakers that produce self-sealing tires.

Make an informed purchase

Run-flat tires seem to have more downsides than upsides, but many people swear by them. Take the time to read customer reviews and know what tires come standard on a car before you buy.