Run Flat Tires: How They Work?

Although they first hit the market in the mid-1980s, run-flat tires (RFT) are more popular today than ever. As some automakers make them the standard for new vehicles, more and more consumers are asking about run-flat levels, their benefits, and how their use affects driving.

A flat tire often happens at the most inopportune time or place. Most people may call roadside assistance, but they’ll likely be waiting about 45 minutes to an hour. If you know how to change the spare, it’s a dirty job, and chances are you’re not properly dressed for it. Worse yet, your car may have no spare tire, and you might not know how to use the tire repair kit.

Enter the run-flat-tire. Run-flat or zero pressure tires can support the weight of a vehicle for a short period of time and give the driver about 100 miles of range to find a repair shop. While it sounds like the perfect solution, car owners and car buyers should be aware of the tradeoffs.

Run-flat tires are standard on 14% of new vehicles. While the number of vehicles with run-flat tires has doubled over the past decade, they seem to have hit a plateau. The total percentage of vehicles with emergency run-flat has risen to 13 to 14% in the last five years. Most vehicles from BMW, Mercedes-Benz, and Mini now have run-flat tire. Cadillac sedans also use run-flat tires.

What Are Run Flat Tires?

Run-flat tires are tires on which you can continue driving after a puncture so you can take the time to get to an auto shop or find a safe, level area to change your tire.

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However, you cannot drive it indefinitely. Check the manufacturer’s information to find out how fast and how far you can go with your run-flat tires. These flat tires allow continued operation even if some or all of the tire pressure is lost for up to 80 km at a top speed of up to 80 km/h.

How Do Run Flat Tires Work?

There are two primary types of run-flat tire systems: the self-supporting system and the support ring system.

In most self-supporting run-flat systems, the tire has a reinforced sidewall construction that continues to support the vehicle in the event of a loss of air. This design allows continued operation after the air pressure has been depressurized up to the manufacturer’s specified speed and distance.

Support ring run-flat tire systems, on the other hand, employ a ring of hard rubber or another structure that can support the vehicle’s weight in an air loss condition.

Since they continue performing even though they’re “flat,” all run-flat tires, regardless of the specific system type, may only be used on a vehicle equipped with a Tire Pressure Monitoring System (TPMS). The TPMS alerts you as soon as one of your tires loses pressure. Without it, you might not know you were driving on an underinflated tire.

if you still got a flat tire than, there is no consensus on whether or not run-flat tires can be repaired. Tire manufacturers often defer to the vehicle manufacturer’s replacement tire restrictions and recommendations.

Michelin North America Inc., for example, allows its run-flat tires (Zero Pressure) to be repaired under certain guidelines. However, repairing the original equipment run-flat tires on a BMW isn’t an option, per its owner’s manual.

Benefits Of Run Flat Tires

  • You don’t have to change your tire in dangerous or uncomfortable conditions. This is perhaps the biggest benefit of run-flat tires and is one of the reasons why they were designed. With conventional tires, you have to replace a flat on the spot or have your car towed.
  • In a puncture situation, run-flats are more stable than conventional tires. Since they’re made to support your vehicle even when they contain no air, run-flat tires will help you maintain better control in a complete air loss situation than conventional tires.

As consumers continue rating safety high on the list of features they look for in a vehicle, the popularity of run-flat tires is expected to grow. Since run-flat tires work reliably with interconnected technologies like TPMS, it may only be a matter of time before they become the norm rather than the exception in new vehicles.

The Pros and Cons of Run-Flat Tires/No Flat Tires

Self-Supporting Tire

The most common type of run-flat technology today is the self-supporting tire. The sidewalls of the tire are heavily reinforced to support the vehicle when the air pressure is low or when the tire has lost all of its pressure.

Pros:

  • You can drive on a flat tire: The main benefit of a self-supporting tire is that you can continue riding on a flat about 100 miles after the air has disappeared. No need to get out of the car in the cold or rain, or onto a busy freeway, or onto the street in any sketchy part of town. Drivers usually have to reduce their speed to around 80 km/h to get the maximum range. The instruction manual gives exact numbers for each tire/vehicle application.
  • Better stability after a blowout: Since this tire can carry the vehicle for miles without air, a sudden deflation leads to less weight transfer and destabilization of the tread. Steering and handling remain almost normal.
  • Lower vehicle weight: If the repair tools for spare wheels and tires are eliminated, the vehicle weight should theoretically decrease. But it won’t be as much as you might expect as run-flat properties weigh more than regular tires due to the added sidewall reinforcement.

Cons:

  • No spare: Vehicles don’t have a spare wheel or tire when you Run-flat, which means they don’t have a jack or tools either. Indeed, getting rid of the spare tire and reallocating that space for a different purpose (styling, third-row seating, interior, etc.) is a big reason automakers offer run-flat capabilities.
  • Reduced tread wear: People replaced their run-flat tires an average of 6,000 miles earlier than the owners who were using conventional tires. Opinions vary as to why, but one theory suggests that tire manufacturers apply a soft tread compound to a run-flat tire to counteract the rough ride. A side effect of the softer connection is the shorter service life of the profile. However, the owners said they were more satisfied with run-flat tires overall. They did not lag behind conventional tires in the survey.
  • Blowouts are still possible: If a driver ignores or notices the warnings and drives beyond the zero pressure range or the speed limit, the tire can crumble with the same destabilizing effects.
  • Hard to tell if it is low on air: A side effect of the stiffer construction is that the sidewalls do not bulge when the air pressure is low. It is therefore important to have a tire pressure monitoring system and to check the tire pressure regularly. Otherwise, you will never know when you will have a flat.
  • Harsher ride: The stiff sidewalls that allow run-flat work also results in a tougher ride. If the vehicle was shipped from the factory with run-flat tires, the automaker will usually tune the suspension to compensate for the rougher ride.
  • Cost: Run-flat tires are more expensive to replace. Prices vary depending on the type of tire and the place of purchase. However, it’s not uncommon for a run-flat tire to pay a premium of $40 to $65. In addition, many emergency levels cannot be repaired and often have to be replaced in pairs.
  • Less on-shelf availability: Since run-flat is not a top-selling tire, drivers shouldn’t expect to roll into any tire store and purchase them. This may be easier in larger cities, but if you’re a run-flat user on a road trip and are getting a flat near a small town, you will likely have to make a detour to find a suitable new tire. Or worse, you may have to stay overnight and wait 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.