KEY POINTS:
When 1000 people were asked what they most wanted in a new car, more than 87 per cent said run-flat tyres.
These run-flat - or extended mobility, continuous mobility, zero-pressure - tyres can be driven for some distance in the event of a puncture.
By contrast, self-sealing tyres use different methods to preserve inflation, but there is a limit to the amount of damage they can incur. These tyres simply cannot be driven without any inflation pressure.
In 1934, Goodyear introduced the Lifeguard safety inner tube that was designed to deflate slowly rather than blowing out. After several attempts Goodyear introduced the self-supporting tyre (SST) in 1978.
Italian tyre manufacturer Pirelli teamed up with Goodyear in 1983 to show a special asymmetrical wheel designed to lock the bead in. The same principle was soon applied by Dunlop with its high-performance run-flat tyres made for Porsche's 959 supercar. This design was also used in endurance racing but required special wheels that made it a costly exercise.
Michelin introduced a foam plastic insert that allows to car to continue after loss of pressure in the tyre. It is still widely used by car and motorcycle racers in events such as the Paris-Dakar rally. World Rally Championship cars also use mousse tyres, but their effectiveness is limited, since the foam heats up quickly and degrades at sustained high speeds.
The first run-flat tyre for a regular production vehicle first appeared on the 1994 Chevrolet Corvette. The Goodyear tyres then came standard on the Corvette from 1997 onward. This design used reinforced sidewalls that enabled the tyre to support its share of vehicle weight without collapsing measurably. The tyres could be mounted on standard wheels.
Michelin unveiled a different principle that centred on a solid inner wheel insert on which a pressure-less tyre could run safely for some distance. The new concept made run-flat capability possible without a large performance compromise.
The key elements of Michelin's system are special wheels with unique tyre bead locks and a solid insert that can fully support its share of the vehicle's weight and let it continue without any pressure.
At the 2002 Geneva show, Pirelli, Goodyear and Michelin had all adopted this concept for run-flat tyres. And, over the next couple of years, all the other major tyre manufacturers introduced their own run-flat tyres.
Most modern sports cars use low-profile tyres and ride comfort is not as big a concern on these as on other vehicles. A wide tread and low sidewalls generate maximum traction and responsiveness. A short sidewall is also easier to reinforce and flexes much less to begin with.
Due to a number of low-profile tyre failures, many sports vehicles are being fitted with run-flat technology as standard.
More research and development work is being done on highly automated, ultra-precise systems to manufacture run-flat tyres. Because of the specially designed wheels they use, these also require specific installation techniques and tyre-changing machines.
With run-flat tyres, there is no need for a spare wheel or a car jack. This frees up space for luggage, lowers cost and saves weight, making for a small gain in fuel economy.
Several high-visibility models such as BMW's Z4 and Z8 sports cars, the Lexus SC 430, the Mini Cooper and Cooper S, and the Rolls-Royce Phantom are all equipped with run-flat-type tyres. These have been engineered specifically in co-operation between the car and tyre manufacturer along the vehicle's development process.
Some run-flat tyres are available as replacement units. But they are generally more rigid, heavier and more expensive than conventional designs of the same size, especially when you factor in the cost of a pressure-monitoring system.
Run-flat tyres can also substantially affect ride comfort and the durability of some vehicle components in real-world driving - suspension parts, most notably. Ideally, a vehicle's structure and suspension components should be designed for the different nature and characteristics of run-flat tyres and vice-versa.
According to experts, all road-going production vehicles will eventually come standard with run-flat-type tyres. As OEM installation rates increase dramatically, so will the availability of fully adapted replacement units, the cost of which should follow the reverse trend.
All this is excellent news for drivers and passengers alike. As driver safety becomes more important, tyre technology is doing its part to make vehicles safer.
