What are run flat tyres?
Run flat tyres let you keep driving, at reduced speed and for a limited distance, after a puncture. Here is how they work, how to tell if you have them, and whether they are right for you.
How do run flat tyres work?
The sidewalls are reinforced so that, even with no air, the tyre can carry the car. Typically you can drive for up to 50 miles at up to 50 mph, which is usually enough to reach a garage. If it is further, you may need roadside assistance.
There are two main types. Self-supporting (SSR) tyres have a reinforced sidewall that stops the tyre being crushed between the road and the rim and stops it slipping off the rim. Support ring tyres have a lightweight metal ring inside that carries the car when the tyre deflates.
After a puncture on a run flat, get the tyre checked as soon as you can.
Do I have run flat tyres?
Run flats are often fitted as original equipment, so a car with no spare wheel and no repair kit probably has them. Check the sidewall to be sure. There is no standard code, so manufacturers use their own, including ROF (run on flat), EMT (extended mobility technology), RSC (run flat system component) and ZP (zero pressure). See also run flat tyres.
You need a pressure monitor
Run flats must be used with a tyre pressure monitoring system (TPMS). Because a run flat looks and feels normal even when it has lost air, the car warns you with a dashboard alert. For the system to work, all four wheels should be run flats. It is generally not recommended to fit run flats to a car without TPMS.
If you do have a puncture, do not ignore the 50-mile limit. Driving further can damage the wheel itself, which costs far more than a tyre.
Advantages
- No spare wheel, so more boot space and less weight, which can help fuel economy.
- No wheel change at the roadside, which can be dangerous, especially on a motorway.
- More control after a puncture, thanks to the strengthened sidewall.
- Less prone to blowouts, where air is lost very quickly.
Disadvantages
A puncture on a Sunday evening may mean waiting until Monday to find an open garage, and the extra miles can push you over the 50-mile limit. Run flats also generally cost more than standard tyres, and in most cases they are replaced rather than repaired.
Can I swap run flats for normal tyres?
It is usually not a good idea. If your car has no spare wheel well, a normal tyre puncture would leave you stranded. Any change to or from run flats is a material change to the vehicle, so tell your insurer and check your warranty. If you buy a second-hand car with no spare, check that its tyres really are run flats.
Can a run flat be repaired?
Some manufacturers say a repair is possible under certain conditions, if the work meets British Standard BS AU 159. In general, repair is not advised: once the reinforced sidewall has been compromised, the tyre’s strength and safety are much reduced. And if the tyre has been driven on flat, nobody can tell how far, so many fitters will refuse to repair it. If in doubt, ask the manufacturer.
If a run flat has been punctured, we can supply and fit a replacement where you are. Call us.