Run Flat Tyres - What you need to know
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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 a puncture on a cold, dark night, 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 c. 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, 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.
Fitting 'Conventional' Tyres to a Run Flat Equipped Vehicle
If your car was originally supplied with Run Flat tyres, then it is possible to change to 'conventional' tyres. However, if the vehicle was designed with Run Flat tyres in mind, bear in mind you could be left stranded without a spare! Make sure you also buy a new spare tyre and tyre changing equipment.
Why change from run flat to conventional tyres?
We are not recommending that you change the type of tyre your vehicle was originally supplied with. Changing to normal tyres could affect the handling of your car, so you must always consult the manufacturer before making this type of change.
However, some people choose to do this for the following reasons:
- Conventional tyres are generally cheaper than run flat tyres and have better availability
- Some drivers find that conventional tyres give a smoother, less bumpy ride than run flat tyres
- In line with most leading tyre retailers, National will not repair a run flat tyre following a puncture
See below for the some industry views on this subject **
Can Run Flat tyres be repaired?
In line with most leading tyre retailers, National Tyres 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. For a brand specific answer you can contact the manufacturers below, but generally it will be hard to find a retailer who will be willing to repair a run flat tyre.
|Brand||Run Flat Tyre Descriptions||Technical Enquiry No|
|Bridgestone||RFT (Run lat Tyre)||01926 488 595|
|Continental||SSR (Self Supporting Run Flat||01788 552 937|
|Dunlop||DSST (Dunlop Self Supporting Tyre)||01902 327 070|
|Goodyear||EMT (ExtendedMobility Tyre)||01902 327 070|
|Michelin||ZP (Zero Pressure)||0845 366 1535|
|Pirelli||Tyre identified as a "Run Flat" tyre||0870 240 9996|
Fitting Run Flat to an older vehicle ('retro fitting')
If you are considering changing to run flat tyres on a vehicle that was previously fitted with 'normal' tyres, then there are several points to consider:
- Tyre Pressure Monitoring System
Run flats must only be installed on a car which has TPMS/tyre pressure monitoring system. TPMS alerts the driver to a puncture so they are aware that they have a limited time to replace their tyre, and so they drive within the limits of their deflated tyre (see our section on tyre-pressure for more detail)
- Vehicle Suspension
You should also note that you may need some changes made to your vehicle's suspension. Because of their stiffer construction, run flat tyres contribute to a vehicle's suspension when fitted as original equipment.
Mixing Conventional Tyres with Run Flat Tyres
As a general rule of thumb, you should avoid mixing different tyre types on a vehicle. This is also true of combining conventional and run flat tyres on a car – as their handling characteristics may differ, they should not be mixed on a vehicle.
Mixing Different Tyre Brands
Again, it is the case that different brand tyres can have different handling characteristics, so you should follow the advice of the tyre manufacturer if you plan to mix different brands of tyres (this is also the case with conventional tyres). We would always recommend fitting the same brand and type of tyre across the axles of the vehicle, i.e. so both front tyres match each other.
Life span 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.
Can you use Run Flat tyres on caravans and Trailers?
As mentioned previously, run flat tyres can only be used on vehicles fitted with TPMS (tyre pressure monitoring system). As caravans and trailers are not currently fitted with TPMS, they should not therefore be equipped with run flat tyres.
** Industry Views on Replacing Run Flat Tyres with Conventional Tyres
National Tyres and Autocare
National recommend replacing like with like, i.e. keeping run flat tyres if that is what your vehicle was originally equipped with. This is because the vehicle manufacturer has set the vehicle's suspension to suit run flat tyres, so changing to conventional ones could have an adverse effect on handling.
However, if you do choose to change to conventional tyres, don't forget to purchase a spare wheel and tyre – or failing that, a can of tyre sealant to give a temporary repair./p>
Also, if you choose to replace with conventional tyres, then note:
- make sure you fit the correct tyre size, speed rating and load index
- don't mix conventional and run flat tyres across the vehicle, i.e. replace all four tyres at the same time
- get advice from your insurance company to make sure your cover remains valid
The BTMA (2005) stated that retro-fitting conventional tyres in place of run flat tyres would:
'remove the run-flat capability, potentially leaving the driver immobile in a case of deflation and could compromise vehicle handling. It is therefore recommended to consult with the vehicle manufacturer before replacing SSTs with conventional tyres'.
BMW promote run flat technology because of its advantages for driver comfort and safety. They point out that when run flats are fitted as original equipment, then vehicles' braking and suspension are set up accordingly, so changing to conventional tyres may affect the handling characteristics of your car. However, they do say it is possible to fit conventional tyres.
Tyresafe recommend that drivers do not change their vehicle set up from run flat to conventional, because of the adverse affects this could have on vehicle handling due to the vehicle set up.