Having a tyre puncture or blow out at high speed can be dangerous. Any puncture is inconvenient, and changing a wheel can be difficult in some situations and impossible for some drivers, resulting in a call to a breakdown service and a lengthy delay.
Run flat tyres promise a solution to these problems – after getting a puncture, they allow you to carry on driving for up to 50 miles at speeds of up to 50mph.
At first sight, you would think that this kind of performance would be attractive enough to make run flat tyres popular with motorists. However, they are not especially popular and few manufacturers offer them as standard fitment; they are largely restricted to premium manufacturers such as BMW, Audi and Mercedes-Benz.
How Do Run Flat Tyres Work?
A standard tyre will crumple immediately if it is deflated, leaving the tyre unusable and possibly damaged.
Run flat tyres do not do this. They remain correctly shaped and usable by having very strong, stiff sidewalls that can support the weight of the car, even when the tyre is not inflated.
If you look at an unfitted run flat tyre alongside a standard tyre, the difference is obvious – the sidewalls of the run flat tyre are very much thicker and the tyre is correspondingly heavier than a standard tyre.
Driving With Run Flat Tyres
We drove a slalom course with all tyres correctly inflated and then let all the air out of one of the run flat tyres before repeating the course to see what (if any) the difference was.
Driving the course with the tyres correctly inflated was predictably impressive – the tyre was new and the BMW 5-Series is a fine-handling car. Tyre noise and handling seemed completely normal and there was no sign that we were not using standard tyres.
We then deflated one of the run flat tyres completely. It sagged very slightly compared to the fully-inflated tyres, but most drivers would not notice the difference and it was certainly not enough to cause problems.
Driving the slalom course with the deflated run flat tyre was interesting. The car’s handling was still very good, although there were two differences:
- A very slight loss of grip on tight turns – you had to push the car quite hard to notice this;
- Increased tyre noise when the tyre was loaded into corners – a rumbling noise.
Both of these would be quite easy to live with in normal driving conditions. In any case, run flat tyres are only designed for up to 50 miles of driving after deflation.
Run Flat Tyres – Downsides
Run flat tyres appear to offer great safety and convenience benefits, but they are not yet very popular, so what are the downsides?
- Cars must have a Tyre Pressure Monitoring System (TPMS) to alert the driver when they have a puncture – otherwise the driver might not notice, resulting in the tyre eventually breaking up. Many cars do not yet come with TPMS as standard.
- Run flat tyres are about 30%-40% more expensive than the corresponding standard tyres, they are not so readily available at tyre centres and they are more complex to fit.
- Run flat tyres are historically stiffer than standard tyres, which can result in a harsher ride in some cars. However, recent run flat tyres have improved greatly and the differences are now much less noticeable.
- You still need a spare wheel – unless all of your driving is very local, 50 miles is not enough to negate the need for a spare wheel to get you home or to your destination without needing to visit a tyre centre.
Will Run Flat Tyres Become The Norm?
I think that run flat tyres might well end up becoming the norm, not least because of a new piece of EU legislation being introduced in 2012 which requires all new cars to be fitted with a Tyre Pressure Monitoring System (TPMS).
A TPMS monitors the pressure in each of a car’s tyres and shows an alert on the dashboard if a tyre’s pressure falls too low. This is useful for safety and tyre maintenance, as it reduces the chances of driving on underinflated tyres, which causes increased fuel consumption. (As our surveys have found, many drivers do not routinely check their car’s tyre pressures.)
A TPMS is an essential part of a run flat installation, but until recently they have been found only on upmarket cars. In my opinion the new law will rapidly open up a large new market for run flat tyres – the family car market.
I believe that this female and family-focused market sector could be more receptive to run flat tyres than the premium car market, which is where most run flat tyres are currently sold. The safety and convenience of never being stranded with a sudden puncture is most likely to appeal to women drivers and anyone who ferries young children around on local journeys. The only remaining issue is the cost of run flat tyres, but I am sure this will gradually fall.
MOT Includes TPMS from 2012
One final note is that from 2012, TPMS systems will be tested as part of the MOT. This only applies to cars which have TPMS systems but it means that your TPMS system must be working properly or your car will fail its MOT.
The most common source of TPMS faults is wheel sensor failures. Replacement items are available from main dealers as well as a number of independent suppliers – often cheaper.