Hobbies Cars & Motorcycles Understanding Run Flat Tires The advantages of runflat tires are more than outweighed by the disadvantages. Share PINTEREST Email Print Michael Sheehan/Wikimedia Commons Cars & Motorcycles Cars Tires & Wheels Buying & Selling Basics How Tos Reviews Tools & Products Classic Cars Exotic Cars Corvettes Mustangs Motorcycles Used Cars SUVs Trucks ATVs & Off Road Public Transportation By Sean Phillips Updated April 25, 2019 Consumer Reports, Tire Program Leader Gene Peterson has said quite a bit about run flat tires and why he does not believe they should be used, except perhaps as building materials. Run-flat tires are built with very stiff sidewalls, enough so that if the tire loses pressure, the sidewalls will support the weight of the car. This can prevent loss of control caused by a blowout, for instance, and allows for continued driving until a repair can be accomplished in safety. These are important advantages, to be sure. They are, however, more than outweighed in Gene's opinion by the mountain of disadvantages. They Run Like Rocks With few exceptions, run flat tires run as they belong on the Flintstones' car. Start with a tread surface resting on jarringly stiff sidewalls. Add in a lot more unsprung weight. What you get equals neither high performance nor smooth ride. Often enough, there's not that much of a difference between how the tires ride when inflated and how they ride when flat. That's kind of a problem because... They Don't Look Flat Because the sidewalls don't collapse when the air is lost, you can't tell when a run flat is running flat just by looking at it. That's why run flat tires require the use of Tire Pressure Monitoring Systems. TPMS monitors are supposed to alert the driver when the tire has lost 25% of it”s proper pressure, but the systems are still somewhat wonky and expensive. This used to be kind of a problem for carmakers wishing to put run-flat tires on their cars but has become less so now that TPMS systems are required on all new cars. Knowing exactly when the tire is going flat is extremely important, because... They Have A Low Range When Flat Most run-flat tires will run for around 100 miles after going flat. That's a minimally decent range before complete failure, but putting on even a significant fraction of that mileage will damage the tire enough that it will need replacing. So if you have a flat that can't be repaired easily on the road, and you're 30 miles from somewhere that can, you're probably going to end up having to replace the tire anyway. You might think 'I can just put on the spare, and take the tire to be repaired! That's what a run-flat tire is for, right? To get over to the side and put on your spare before the tire gets damaged!' but you would then realize your mistake the moment you pulled over and checked your trunk, only to find that... There's No Spare? In almost every car that comes with OEM run-flat tires, the manufacturer has not seen fit to provide a spare. It seems to me that the major reason carmakers put on run-flat tires is not that they are any safer, but because it lets them feel justified in not adding the expense and extra weight of a spare rim and tire. According to Gene, these days only 16% of cars still carry a full-size spare. 75% have some form of temporary spare, usually a “donut.” 4.5% of cars have run flat tires with no spare, and 4.5% have a “repair kit” which usually amounts to a can of “fix-a-flat” and a portable compressor. Having no spare is bad enough. To me, getting a can of fix-a-flat in the trunk is like being slapped in the face by the carmaker. The unyielding sidewalls of run-flat tires transmit most impact forces to the wheels rather than soaking up impact as radial sidewalls do. This makes it more likely for impacts to bend or crack the wheel, causing damage that simply cannot be fixed by a can of fix-a-flat. What then? According to the carmaker, you're on your own, often in more ways than one... They Are Harder To Find and More Expensive Not too long ago, according to Gene, a Consumer Reports employee was testing a car by taking it on a trip to New Hampshire. While he was there one of the run flat tires were damaged beyond repair, and he took the car to the local dealer. The dealer didn't have the tire and sent him to a well-known tire chain store. The chain store couldn't get the right tire either. Eventually, to get him home, they sold the CR employee a non-run flat tire in the correct size, but would not actually take on the liability of installing a nonstandard configuration, so they sent him to yet another tire store that would. Three months later, Gene has still been unable to find a replacement tire. Granted, not all run flat tires are quite this difficult to replace, but many are not at all easy to find, and almost all run flat tires are quite a bit more expensive than non-run flats in the same size. My advice has always been that run flats tires are just not worth the hassle, the performance hit, and the expense. The best way of handling a deflation of a run-flat tire is precisely the same as a conventional tire – pull over as soon as possible and change the tire for the spare to avoid having to replace the tire, but car manufacturers have largely made that impossible. With TPMS monitors mandatory on all cars, drivers now usually have enough warning of deflation to save even a conventional tire before it is destroyed by deflation wear. Runflats just doesn't offer enough advantages to offset all the problems.