It’s dilemmas like these that have more car makers offering run flat tires on new cars. Run flats can run for at least 50 additional miles following a puncture, giving you the ability to safely get home, or exit a highway and find a repair shop.
What are Run Flat Tires?
There are two main types of run flat tires: Self-Supporting, and Auxiliary Supported. Self-Supporting tires have stiffer and tougher rubber, which can temporarily carry the weight of the vehicle under lower tire pressure. If you do get Self-Supporting tires, you will need a tire pressure monitoring system (which is now government mandated standard equipment on new cars), because a driver may not notice their tire has lost pressure without it. Auxiliary supported tires don’t have stiffer and tougher rubber, but are attached to a special rim which has a steel support ring that is attached to the wheel and can support the weight of the vehicle.
Even though run flat tires have been around in production vehicles since 1994, the adoption as a mainstream replacement for conventional tires has been slow for many reasons. A top complaint is in regards to price. On average, run flat tires are about one third more expensive than regular tires. Sheri Hermann, Communication Coordinator from Continental Tire tells us “run flat tires provide convenience to a consumer, but conventional tires are typically lower in cost and have better ride qualities.”
That’s not the only complaint though. While the reduced weight of carrying around a spare might seem like an advantage, run flat tires also have an impact on your fuel economy. Thanks to the tires being heavier and thicker they can reduce fuel economy by 1-2%. Also, due to the stiffer and heavier design, the run flat doesn’t quite perform like its price would indicate. They can often be harsh on the road and don’t provide a lot of grip in low temperatures.
Lastly, when you do get a puncture, or lose tire pressure, it’s not quite as easy to get them repaired. While some run flat tires can be repaired, they need to spend some time off the rim, and need to be inspected to ensure they can be fixed. If they can’t, it’s time to buy new tires. Conversely, most punctures on a conventional tire can be fixed with a simple repair kit that costs just a few dollars.
Despite these obstacles and concerns, run flat tires are increasingly becoming standard equipment on new cars and the reasons are simple: safety and peace of mind. Not only do run flats ease concerns, but they make a vehicle easier to control in the case of a tire blow out.
Why Are Automakers using them?
Monty Roberts from BMW Product and Technology communications tells us that run flat tires are standard on most BMW models with the exception of some BMW M Models. He said specifically that run flat tires have several advantages and that they “Support BMW’s EfficientDynamics Strategy by eliminating the extra weight of the spare tire, jack and tools in the vehicle for better balance, dynamic handling and fuel efficiency.”
When asked about the criticism of run flat tires Roberts said “run flat tires by their design do have stiffer sidewalls than conventional tires, however, all current BMW models that use run flat tires have suspensions that were significantly developed for use with this technology.” He added “These suspensions have been developed and tuned for the best possible ride comfort. The safety benefits of run flat tires are so significant as to outweigh any possible trade-offs.”
When asked if owners could or should swap out their run flats either when a replacement tire is needed or because they’re looking for added performance, Roberts was unequivocal. “We do not recommend replacing run flat tires with conventional tires,” he said, “that deviates away from the original design, safety and suspension calibration technology that the run flats were originally designed for.”