What are run flat tyres?

Last updated July 29, 2021

Run flat tyres are designed specifically to ensure your car continues driving safely after receiving a puncture. They’re able to do this thanks to a reinforced sidewall that continues to bear the car’s weight even when the air pressure drops.

With run flat tyres fitted to your car, you should be able to continue driving after receiving a puncture until it is safe and convenient to stop, albeit only for a limited distance and at reduced speeds. They effectively minimise the risk of a puncture causing a more serious incident.

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How do run flat tyres work?

Regular tyres support the weight of your car because of the sufficiently high air pressure they are filled to. Run flat tyres, on the other hand, are manufactured with an extra-thick, reinforced sidewall capable of supporting your car’s weight all on their own. They’re only designed to be able to do this for a limited period, but that’s better than nothing in a situation where you lose adequate air pressure.

On conventional tyres, you would have to pull over immediately after receiving a puncture to avoid driving dangerously. Run flat tyres can keep you going for a short period, typically enough to navigate to a garage or get home. How long they’ll keep you safe for varies based on a range of factors, including what vehicle you drive and what specific tyre model you use – there’s no consistent standard for how long a run flat tyre will last when punctured.

Run flat tyres are usually monitored by a Tyre Pressure Monitoring System (TPMS), which will alert the driver in the event of a puncture, or when the tyre pressure has dropped below a certain level.

Check if you have run flat tyres

Because run flat tyres look much the same as standard tyres, you could have them installed on your car and not even know it. These days, many manufacturers even fit cars with run flat tyres before they leave the factory, with leading car brands like BMW and Mini generally including them as standard.

If you check the boot of your car and you don’t have a cavity for a spare tyre or a puncture repair kit nestled under the floor, there’s a good chance you have run flat tyres. If you’re not sure, you can check with your car manufacturer. Get in touch with them and they should be able to tell you if your car came equipped with run flats.

Can run flat tyres be retrofitted?

Run flat tyres, like any other kind of tyre, can be fitted to your car as a replacement for your current tyres. However, it’s generally not advised to install them on a car without a TPMS because if they get punctured, your car will give little to no indication that the tyre’s pressure has dropped.

It’s also worth noting that run flat tyres can be a little pricier than conventional tyres, which could be an influencing factor in your decision.

Can run flat tyres be replaced with standard tyres?

Just as retrofitting run flat tyres on a car that came without them may not be advisable, doing the opposite can come with some downsides too.

If a car is fitted with run flat tyres by default, it will likely have no built-in room for a spare tyre, which could leave you stranded without an escape route if your new standard tyres sustain a puncture.

As well as the lack of spare tyre that’s common in cars that come with run flat tyres by default, the suspension on cars fitted with run flats is also usually set at a softer level to recreate a normal driving sensation. If a regular tyre is fitted instead, the soft suspension will make the ride feel softer, and the handling could be different to what you’re used to.

Remember, if you change your car tyres – either from run flat to standard or vice versa – you must notify your insurer to avoid your policy being invalidated.

Pros and cons of run flat tyres

The primary advantage of run flat tyres is the ability to drive after sustaining a puncture, providing the sidewall is damage-free. You might find yourself with more boot space, too, as you don't need to carry a spare wheel.

However, the main downside is that run flat tyres always have to be replaced and not repaired. The majority of reputable tyre retailers will not repair a run flat tyre, as damage isn’t as easy to spot thanks to the reinforced sidewall construction.

Can run flat tyres be mixed with conventional tyres?

There’s technically nothing stopping you from mixing run flat tyres with regular tyres, but there are several reasons you might want to avoid it. One of the main reasons is that different tyres have different handling characteristics and mixing them could make your car handle unpredictably.

Also, bear in mind that it’s illegal under UK law to mix cross-ply and radial-ply tyres, and to mix different tread patterns or tread depths on the same axle.

If you are in an emergency and find you have to mix your tyres, be sure to choose a similar tread pattern from the same manufacturer to sit on each axle, regardless of what type of tyre you are using.