What are run-flat tyres?

Punctures happen. In fact, punctures happen a lot. Almost a third of UK motorists experience one each year and they’re a top reason for breakdown callouts.

Run-flat tyres promise to put paid to the prospect of being stranded with a puncture. Changing a wheel is a messy business that’s difficult in all but the best circumstances and almost 40% of motorists are unsure how to fit a spare wheel, anyway.

Having run-flat tyres means there’s no need to stop if you get a puncture, as they allow you to drive on a deflated tyre – albeit for a limited distance and at reduced speeds.

BMW has led the way in run-flats, fitting them as standard to many of its models. The same goes for MINI, which is owned by the German giant. But while run-flats are a great idea, some drivers find them more of a hindrance than a help. We look into what you can expect if you buy a car with run-flat tyres.

How do run-flat tyres work?

The principle behind run-flats is pretty simple. Thanks to an extra-stiff sidewall, a run-flat tyre has enough strength in its side – even when there’s no air in it – to support the weight of the car without being dangerous to drive or damaging the wheels.

That means if you or your car’s tyre-pressure monitoring system detects a puncture, you can just keep driving – although you’ll need to be a lot more careful, as the car’s handling and stopping distances will be adversely affected.

Audi advises its cars can be driven at speeds ‘between 30 and 50kph’ (18-31mph) when fitted with run-flats, while BMW says you can do ‘up to 80kph’ (49mph) for ‘up to 150km’ (93 miles). Those are maximum limits, though, so if your car is fitted with run-flat tyres it’s important to check the exact figures.

Advantages

The main advantage of run-flat tyres is that you can carry on driving if you get a puncture – assuming the sidewall itself hasn’t been significantly damaged. True, you have to be careful how, how much and how fast you drive, but the distance limits run-flats come with should allow you to get to a garage or tyre fitters fairly easily.

Because of their strong sidewalls, run-flat tyres are also said to be less prone to blowouts – a rapid and potentially dangerous loss of air from the tyre.

Another advantage is there’s no need to carry a spare wheel, meaning the car’s boot can be a little bigger, or have under-floor storage where the spare would normally sit.

Disadvantages

Run-flat tyres work really well in many cases, but there are some circumstances in which they’re less than ideal. If you get a puncture late on a Sunday evening, for example, you may have to wait until Monday to find an open garage to fix it. It’s also possible your journey length will exceed the tyre’s limits, particularly if you’ve got to drive to your destination before making a second excursion to a garage the next day.

Speaking of fixes, because the sidewall may have been damaged, run-flat tyres must generally be replaced rather than repaired after a puncture. Run-flat tyres are also more expensive to buy than standard tyres, adding further cost.

Some drivers feel cars with run-flat tyres are slightly less enjoyable to drive, or aren’t as good at soaking up potholes and broken tarmac as cars fitted with conventional tyres. That’s because the stiffer sidewalls are less adept at absorbing bumps, and they also add ‘unsprung’ weight (mass that isn’t supported by the car’s suspension) meaning the suspension is less effective.

How can I tell if my car has run-flat tyres?

Most run-flat tyres will have ‘run flat’ printed on their sidewalls, but if you’re in doubt, call your dealer or a garage with the tyre details to find out.

Can I swap run-flats for normal tyres if I don’t like them?

Yes, although it’s a good idea to check with the manufacturer first, as your car’s suspension may have been configured specifically to work with run-flats.

It’s also important to note you should never mix run-flats with conventional tyres, so you’ll have to swap all four at the same time.

Do also make sure you buy a spare wheel, jack and wheel brace when you make the change. If there isn’t anywhere to put these, you’ll have to make do with a can of tyre sealant and a compressor – although there are limits to the types of puncture tyre sealant can fix.

What about the other way round?

This is a bit of a grey area, and again we’d recommend consulting with your car’s manufacturer due to potential suspension issues. Run-flat tyres should only be fitted if you car has a tyre-pressure monitoring system, too.