August 19, 2014Run Flat Tyres – What are they?
When a run-flat tyre is punctured, the weight of the car is supported by the specially strengthened sidewalls; designed to carry the weight of the car and withstand speeds of up to 50 mph for a limited distance.
Because the exact nature of the damage, the speed at which it occurred, and the distance subsequently driven are all factors that would affect the internal integrity of the tyre and its subsequent safe use following a repair. As these “known unknowns” represent a serious safety issue it is, therefore, our policy NOT to repair run-flat tyres.
Run Flat Tyres – what are they?
Run-flat (or self-supporting) tyres are specially designed to keep working for a short while even after they suffer a puncture. So if you get one there’s no need for an uncomfortable roadside tyre change – you should be able to safely drive home* or to your nearest garage to get your tyre changed. Run-flat tyres also reduce the dangers of a potentially dangerous tyre blow out due to their unique construction.
How do they work?
Run-flat tyres are built with reinforced sidewalls. Normally, a car is supported by the air in your tyres, and once you have a puncture they collapse. However, run-flat tyres have tough rubber inserts which temporarily hold up the weight of your vehicle even after a puncture.
How long can you drive on a punctured run flat tyre?
* Once a run flat tyre suffers a puncture, you can’t keep driving on it forever – usually you will be able to drive at a low speed (30 mph) for another 50 miles – plenty of time to get to your nearest garage. The exact range depends on variables like your driving speed, the load of your vehicle and driving conditions.
Vehicles fitted with Run Flat as ‘Original Equipment’ (OE)
An increasing amount of vehicle manufacturers are opting to fit new cars with run-flat tyres – so when you buy, for example, a new BMW 5 series or Mini, then it will come with four run-flat tyres. This means that it will not have a spare tyre or tyre changing equipment included as standard.
Can Run Flat tyres be repaired?
In line with most leading tyre retailers, we will not repair a run flat tyre following a puncture. Most manufacturers advise against repairing run flat tyres. If the deflated tyre has been driven on, it could have compromised its strength and it is impossible for a fitter to know if the tyre was driven on for longer/faster than recommended after a puncture.
These photographs were taken at one of our branches and illustrate the dangers of repairing run on flat tyres. The vehicle owner was surprised that another company repaired the tyres once we explained that you cannot tell what damage has been done to them while they were less inflated. These tyres failed when in use which is very dangerous; the company that repaired them may have thought that they were doing the vehicle driver a good deed by trying to save him money.
Lifespan of Run Flat Tyres
The materials used to manufacture run-flat tyres are similar or identical to conventional tyres, so their wear rates should be comparable. Keeping the correct air pressure in your tyres (no matter what type) is the best way to ensure a longer life from your tyres.
Run Flats on Vehicles Towing Caravans/Trailers
If your car is fitted with run flats and you are using it to tow another vehicle, e.g. a caravan or trailer, then particular care must be taken. The extra weight of a towed vehicle puts any tyre under additional stress, and this is particularly true of a run-flat tyre. This means that even if you observe the speed limit set by your run flat manufacturer, there could still be problems with the stability of your car and towed vehicle. To keep safe, it is recommended that you reduce the overall speed and distance travelled on a punctured run flat. Check with your vehicle manufacturer’s handbook for more detail.