Run Flat Tyres

All the latest technology brings the modern motorist the run flat tyre - by whatever name you wish to call it - a tyre that you can drive on when the pressure has dropped.

Actually, it isn't new technology at all, just more modern interpretations of old ideas using modern materials. The first patent for a pneumatic tyre was taken out by Robert W. Thomson in 1846. Thomson called it the Aerial Wheel, and one of his patents included a tyre with multiple inner tubes - another of his suggestions was to fill the tyre cavity with horsehair or sponge to support the tyre and prevent it collapsing onto the rim. In essence both these methods are in practice today in one form of run flat tyre or another.

If that isn't enough to convince that run flat technology isn't new, then let's go back to a small conflict in Europe in the middle of the last century. The War Office supported research into self supporting tyres. In one version the air in the tyre was replaced by a rubber ring with voids in it - This was the PT Support tyre and it was expensive and heavy, but it worked. In one report a raid on enemy lines was subjected to three hours of air attack. Three of the vehicles were set alight, and one put out of action by gunfire. The remaining three all drove 70 miles back to safety with punctures in every tyre.

There was also a run flat that used thick sidewall construction and a rim filler to retain the beads in place. This was revisited in the 1960's with the Tyron band - still available and selling well around the world.

Today's modern run flat tyres are essentially designed around those original principles - though perhaps the tyre manufacturers might disagree.

There is the Goodyear Run-on Flat - this is a tyre which is designed with stiffer than normal sidewalls, which use a temperature resistant compound to fend of destruction by heat generated by running flat.

There is the Michelin Pax system, which uses a well filler and support system to keep the tyre on the wheel and prevent the tyre from being destroyed by the rim in the event of a flat tyre.

Continental has the integrated wheel system, IWS, a stiffer sidewalled tyre combined with a rim and bead system that retains the tyre on the wheel.

And in truck tyres there is the Greatec system which has a tube inside the tyre that when the tubeless tyre is punctured, the tube fills the void and supports the tyre in a "get-to-safety" role.

The key aim in all of these systems is to keep the tyre on the rim for as long as possible and to delay the destruction of the tyre, allowing the driver to make his way to a place of safety.

The one thing all these tyres have in common is the need for a tyre pressure monitoring system (TPMS).

TPMS is essentially a method of monitoring the level of pressure in a tyre and alerting the driver if there is a loss of pressure. Allowing him to reinflate the tyre or have the tyre swapped (usually a professional job as TPMS and run flat tyre equipped cars rarely have a spare tyre.

There are two basic types of TPMS, one is fed data by the vehicle ABS and traction control system which can identify a differential in wheel rotation - a flat tyre turns more slowly than an inflated tyre, so that differential can be used to flag up a pressure difference. The disadvantage of this system is that the vehicle needs to be moving for it to operate.

The other system uses chips in the wheel well of the wheel and tyre assembly to monitor pressure and report to the on board computer. This gives an instant pressure reading and can even be used to limit the speed of the vehicle. The minus point here is that these sensors mean that extra care has to be taken when fitting tyres, possibly even special equipment. They are also expensive to replace if damaged.

Most European vehicles with TPMS are manufactured with wheel mounted version.