What Are Run-Flat Tires?

A flat tire always seems to happen at the most inopportune time or place. When it does, your options are generally to either call roadside assistance to install your spare tire or try to do it yourself. But these days, there's a chance your car doesn't even have a spare! One alternative to a spare tire used by many manufacturers is what’s known as run-flat tires. Run-flats, or zero-pressure tires, have additional reinforcement that allows them to support the weight of a vehicle for a short time, which buys you around 50 miles to get to a repair shop after a puncture or other related air loss. 

Run-flat tires are standard or optional on roughly 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, the trend seems to have hit a plateau recently. The overall percentage of vehicles available with run-flats has remained 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.

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

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, where getting out to fix a flat or even getting out of the vehicle is generally not an option.

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 for up to 50 miles after all the air has escaped. 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 around 50 mph to get the maximum range. This is because higher speeds will generate more heat and cause the tire to degrade faster. The owner's manual will have exact figures for each tire/vehicle application if the car came with run-flats. If the run-flats have been retrofitted, look on the tire sidewall or do an online search for the details.

• 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, which, in a conventional tire, can cause dangerous steering characteristics. Steering and handling will remain near normal with a run-flat in a similar situation.

• More room in the trunk: Most spare tires are located on the floor of the cargo area. Since there's no spare tire to take up space, automakers can maximize the storage space in the vehicle.

Cons:

• Less on-shelf availability: Because run-flats aren't as common as conventional tires, 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 driving a car with run-flats 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.
• 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 harsh 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. However, according to a 2018 J.D. Power owner survey, owners reported higher overall satisfaction with run-flat tires. 
• 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."
• Repairs are often not possible: A conventional tire with a puncture can generally be patched by a repair shop, but most manufacturers of run-flat tires don’t recommend doing repairs due to the differences in construction. Some repair shops may, in a pinch, still try a patch or plug, but don’t count on it.
• Difficult to tell if the tire is low on air: A side effect of the stiffer construction is that the sidewalls do not bulge if the air pressure is low. It is, therefore, critical to have a working tire pressure monitoring system or to manually check your tire pressure frequently. Otherwise, you might never know when you have a flat until it’s too late.
• 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.

Self-sealing tire

A self-sealing tire isn't a run-flat tire in the sense that it can operate without air, as is the case with self-supporting tires. 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 — about 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 tireshere are also products that can be added to a conventional tire to give them this self-sealing ability, though they’re not likely to work as well as the real thing.

Make an informed purchase

Run-flat tires seem to have more downsides than upsides, but many people (and vehicle manufacturers) swear by them. Before you buy, take the time to read customer reviews and know what tires come standard on any car you're considering.

FAQs

Can I put on regular tires instead of run-flats?
In most cases, yes. As the owner, you're free to put on whichever tire you think is best. If you're leasing the vehicle, however, we recommend sticking with the same tires the car came with. Many leasing companies require that the vehicle be returned with matching tires, often the same brand that it came with.

How long do run-flat tires last?
Looking at the Bridgestone DriveGuard run-flat, for example, it has a warranty of five years or 50,000-60,000 miles (depending on the speed rating). But in general, the life of any tire will depend on a variety of factors such as the conditions in which it was kept, the age, mileage and how well it was maintained.

Are run-flat tires good?
Yes, run-flats offer better stability in a blowout, help reduce weight in the vehicle, and keep you from having to change a tire in bad conditions. That being said, no tire is perfect. Take a look at the pros and cons here to decide for yourself.

Do I have to use run-flat tires on my BMW?
Not always. If you're leasing the vehicle, it is best to stick with the same run-flats that came with the vehicle to avoid any issues. A number of leasing companies require that the vehicle be returned with matching tires, often the same brand that it arrived with. If you own the car, however, you're free to put on whichever tires you like.