Runflat Tyres
Return to Motor Vehicles Index
Runflat tyres are becoming a common accessory on new vehicles. This fact sheet seeks to explain how they work, their benefits, and things you need to consider if you have a vehicle with runflat tyres.
How they work
In conventional tyres, the pressurised air contained within the tyre supports the weight of the car. However, recently tyres have been developed which are able to support the weight of the car by themselves, for a short period of time. These are known as runflat tyres.
Runflat tyres have been developed in order to minimise the risks associated with a tyre puncture. A puncture can lead to the driver losing control of the vehicle due to the deflated tyre’s loss of shape and structure.
In everyday operating conditions, runflat tyres work like conventional tyres. They still contain air; to reduce the load that the runflat system has to bear, to spread the weight of the vehicle evenly on the road surface, and to maximise the contact patch between the car and the road.
The advantage with runflat tyres is that they can operate without air in them, for a relatively short distance and low speeds, as their basic shape is kept by rigid components. This rigidity helps a driver maintain control of the vehicle if the tyre loses pressure, and removes the need to change a tyre immediately.
There are currently two different types of runflat tyre –
Re-enforced sidewall
One way that a tyre can be adapted to support the weight of the vehicle is to increase the thickness and strength of the sidewall. Although the tyre will bulge outwards without pressurised air inside, it will not completely collapse and become unseated from the rim, as a conventional tyre can.
Internal support ring
The internal support ring is a less common design of runflat tyre. When the tyre becomes deflated, it rests upon the internal ring, which supports the vehicle and maintains both the tyre’s shape, and its contact with the road.
Runflat tyres and your vehicle
Runflat tyres offer a better level of safety than conventional tyres if they have a puncture - although they should be treated with care so as not to lose this benefit, or put you at further risk when using them.
Do not travel long distances or at high speeds on a punctured runflat tyre. You should ensure that you know your runflat tyres’ maximum speed and distance, this information can be found on the sidewall of the tyre or by contacting the tyre manufacturer. Never exceed the maximum speed and distance stipulated by the tyre manufacturer. If one of your runflat tyres has a puncture, you should replace it at the earliest opportunity available.
If a runflat tyre has been used without internal pressure, then damage can occur to the tyre. The damage may be internal and is not always visible. Runflat tyres that have been used whilst deflated should always be replaced, rather than repaired, if they have suffered damage.
As many runflat tyres offer good ride comfort whist deflated, it is often hard for the driver to feel that a tyre is deflated by physical means. In order to detect a deflated runflat tyre, your vehicle needs a Tyre Pressure Monitoring System (TPMS), and you need to be aware how it will communicate a loss of tyre pressure. You should never retrofit a runflat tyre to a vehicle without a TPMS.
You should seek expert advice from your vehicle manufacturer before retrofitting a runflat tyre if your vehicle has TPMS. As the tyre is more rigid, vehicles that have them as standard may require softer suspensions to compensate for the lost ride comfort. Guidance should also be sought from the tyre manufacturer.
It is still vital to check tyre pressures regularly to ensure they are inflated to the manufacturer’s recommended pressure, and to also check the tyres for damage. The chances of needing the runflat capabilities of the tyre are much reduced if the tyre is well maintained.
Advice and information about other aspects of tyre safety can also be found on the RoSPA website. This link will take you to Tyre Information.
To view PDF documents on the RoSPA website you will need to download and install a free copy of Adobe Acrobat Reader. If you have problems accessing PDF documents on this website visit our Download Help page.
|
RoSPA is a registered charity: Registered Charity No: 207823 Patron: Her Majesty the Queen RoSPA Head Office: Edgbaston Park, 353 Bristol Road, Edgbaston, Birmingham B5 7ST, UK |
 |