Run flat tyres are designed so that you can drive on them even when they are punctured and have no air in them. They have very stiff sides that will bear the weight of the car even without air in them.
How run flat tyres work
Also known as Self-Supporting Run flat tyres or SSRs, run flat tyres are designed to enable you to at least continue driving and get to safety if you have a puncture.
Calling them run flat is actually a bit of a misnomer because the tyres don’t actually let your car run on flat tyres. Running with no air would be the more accurate but less catchy description.
Think of tyres as a bag of air. The weight of the car is supported by the air; the tyre simply holds that air. When the air escapes following a puncture, normal tyres collapse under the weight of the car – the familiar flat tyre.
Run flat tyres have a very stiff sidewall. These are designed to support the car even if there’s no air in the tyre. You can then continue driving, although ideally at reduced speed and for a short distance.
How do you know your car has run flat tyres?
Look at the tyres and they should say somewhere on the writing on the side that they’re run flat. If you’re still unsure, look in the car’s user manual. If the car was fitted with SSR tyres in the factory and it’s old, remember it may have switched to conventional non-run flat tyres at some point in its life.
How do you know if a run flat is punctured?
It’s frequently tricky to know if a car has SSR tyres. That’s why car makers and tyre companies came up with the Tyre Pressure Monitoring System (TPMS). These were designed to tell drivers when their tyres’ air pressure has fallen below the set level so they didn’t keep on driving on the tyres until they failed completely.
If you’re interested in having SSR tyres fitted to your car, it must have a TPMS. All cars since 2014 have been fitted with Tyre Pressure Monitoring Systems (TPMS). These keep an eye on tyre pressures and tell you if your tyre is losing air.
How far can you drive on a run flat tyre?
Most tyre makers say you can cover 50 miles on a run flat tyre that’s been punctured. But you should not go any faster than 50mph.
Would we drive more than 50 miles on one? Probably not. They are designed to enable you to keep moving in an emergency. That is, they will get you off the motorway or help you to make it to the nearest tyre fitter. They aren’t really supposed to get you home, if home is a couple of hours away.
Can you change from run flat to ‘normal’ tyres?
If you don’t like the firm ride a run flat tyre will give your car, you can replace them with non-SSR tyres. But you should change all the tyres at once rather than having a mix of them with conventional rubber.
Also if you change to conventional tyres, your car probably won’t have anything to help you if you suffer a puncture. If you do switch to conventional tyres, it’s probably best to buy an inflation kit or a space saver spare wheel.
Are there any downsides to run flat tyres?
Due to the way they’re built, these tyres can result in cars feeling like they have a very firm and unforgiving ride. Cars with run flat tyres such as BMWs and MINIs were frequently slammed for having a harsh ride. What do we mean by that?
When you drive along your car encounters lumps, bumps and undulations in the road surface. Its suspension is designed to iron these out by yielding to them, thereby insulating the car’s interior. But tyres also play their part with the sidewall helping a car to absorb bumps.
As run flat tyres have a very stiff sidewall, there’s not as much ‘give’ in them and it makes the car feel firmer.
Are run flat tyres more expensive?
Run flat tyres can also be more expensive than standard tyres and they might be less easy to source should you need a replacement. If your car is fitted with SSR tyres and you have a puncture, you should replace it with the make and model of tyre that the car’s manufacturer recommends in the handbook.
Another thing to be aware of is if you have a puncture with a run flat tyre, you’ll need to replace it with a new tyre. See below.
What about having run flat tyres repaired?
You may find that tyre repairers won’t fix damaged run flats, even if the puncture is the legal area for repairs. This is because a run flat tyre is likely to have been driven for some distance at speed without having sufficient air in it. This can result in the tyre suffering structural damage internally which is hard to identify and could cause the tyre to fail at speed in the future.
Can you fit run flat tyres to any rim?
To have run flat tyres on a car, it must have TPMS fitted to it. You can get aftermarket systems. Assuming it does, the majority of these tyres that are made by quality makers, such as Continental, Goodyear and Michelin, can be fitted to any standard wheel rims.
I’ve been writing about cars and motoring for more than 25 years. My career started on a long-departed classic car weekly magazine called AutoClassic. I’ve since pitched up at Autosport, Auto Express, the News of the World, Sunday Times and most recently the Daily Telegraph. When I’m not writing about cars and motoring, I’m probably doing some kind of sport or working in my garden.