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What Are Run-Flat Tires?
by Larry Carley copyright AA1Car.com
Run-flat tires are a special type of tire that have internal sidewall reinforcements so the tires can support the weight of your vehicle if a tire loses air pressure because of a puncture or valve stem failure. Run-flats also have a special reinforced bead design that helps prevent the tire bead from separating from the wheel rim if the tire loses air pressure.
A little over one out of 10 new late model vehicles (about 12 percent) are now equipped with run-flat tires. They are used primarily as original equipment tires on certain luxury vehicles (European makes such as BMW, Mercedes and even MINI, also Cadillac) and sporty cars such as Corvettes.
Run-flat tires are made by Bridgestone, Continental, Dunlop, Goodyear, Kumho, Michelin and Pirelli.
Run-flats are a safer tire. A run-flat tire will continue to support the weight of your vehicle if the tire suddenly loses air pressure. This ability allows you retain steering control and stability. If an ordinary tire suddenly blows out, it may cause your vehicle to swerve, lose control and possibly roll over (a real risk with any SUV that has a high center of gravity)!
Ford had a serious rollover problem years ago with its Explorer models when the original equipment Firestone tires blew out. The sudden tire failures were often the result of the tires being under-inflated while driving the vehicle at highway speeds during hot weather. This lead to the requirement that ALL vehicles be equipped with Tire Pressure Monitoring Systems.
Extended mobility when a tire suffers a puncture. Most run-flats allow you to drive up to 50 miles at 50 mph with no air pressure in the tire. This reduces the risk of being stranded or having to call a tow truck if you get a puncture.
Run-flats eliminate the need for a spare tire and jack. This allows more storage room in the trunk of a passenger car or the cargo area in the back of a SUV. Eliminating the dead weight of a spare tire and jack also improves fuel economy slightly.
Run-flat tires are more expensive to manufacture so they may cost 30 percent more to twice as much as a regular tire. Prices can range from $200 to over $500 per tire! The higher cost can be a real surprise when a run-flat tire needs to be replaced.
A run-flat tire may NOT be repairable if the tire lost air and was driven on for too many miles. The further a run-flat is driven without air in the tire, the greater the possible damage to the sidewall reinforcements inside the tire. Most tire manufacturers say their run-flats should NOT be repaired if the tire has lost air regardless of how far it was driven upon. Many repair shops will also refuse to repair a damaged run-flat because of the liability risk. Even so, if a puncture is small (less than 4 mm) and is located in the main tread area of the tire (not the shoulder or sidewall), it may be possible to plug and patch a run-flat tire provided it was driven on less than 50 miles and it passes inspection for any signs of layer separation inside the tire (no wrinkles, cracks or splits inside or out).
Because run-flat tires have stiffer sidewalls, they are typically heavier and ride stiffer than ordinary tires. Run-flats may also be noisier too. To compensate for the increased weight and ride harshness, your vehicle's suspension may be calibrated with somewhat softer springs and shocks/struts.
Because the sidewalls on run-flats are stiffer, they won't bulge outward as much if a tire is low on air. This can make it harder to spot a low tire. Because of this, most run-flats are designed for use on vehicles with Tire Pressure Monitoring Systems.
The tread life of run-flat tires may be less than standard tires. To compensate for stiffer sidewalls, the tread compound may be a softer rubber. This decreases tread life. Some original equipment run-flat tires may wear out in as little as 20,000 to 30,000 miles! There have been class action lawsuits over run-flat tires on certain vehicles (such as Honda and BMW) because of poor treadwear and high replacement costs.
Most vehicle manufacturers recommend replacing run-flat tires with the same, not standard tires. Their rationale is that a vehicle's suspension that came originally equipped with run-flats may not ride or handle the same if standard tires are substituted for run-flats. There is some truth to that statement, but we know many people who have replaced run-flats with less expensive, smoother riding and longer lasting standard tires and would never buy run-flats again.
If only one run-flat tire is damaged and needs to be replaced, it MUST be replaced with a similar run-flat tire, not an ordinary tire. However, if you need to replace an entire set of four tires, then you can switch to standard tires if you don't want to buy another set of run-flats.
Run-flats and ordinary tires should not be intermixed on the same vehicle because of the differences in ride and handling characteristics.
If you do replace run-flats with a set of standard tires, keep in mind you won't have a spare or a jack to change a tire if it goes flat. You can buy a 5th wheel and tire and put it in the trunk and add a jack, or you can carry a can of aerosol tire sealer to reinflate and temporarily seal a flat tire (assuming the puncture is not too large and the tire has not suffered other damage).
Another type of tire that is designed to provide extended mobility when a puncture occurs is a self-sealing tire. The inside of the tire is coated with a special soft polymer material that can plug a small hole if a tire is punctured. The concept is similar to self-sealing pneumatic tires used on military vehicles that can seal bullet holes.
Self-sealing tires have ordinary sidewalls so the weight, ride quality and handling is the same as an ordinary tire. But the self-sealing layer adds cost, making them more expensive than standard tires (but slightly less expensive than run-flat tires).
Self-sealing tires are available in certain sizes from Continental, Goodyear, Hankook, Michelin and Pirelli.
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