A more reliable, spareless solution is the run-flat tire. You can continue driving for at least 50 miles even after it has lost all of its inflation pressure. Although run-flats eliminate the spare tire and jack, you don't save any weight because run-flat tires are substantially heavier than normal ones.
Sounds like the perfect solution except for one major compromise—ride. The current run-flat tires achieve their airless performance primarily through reinforced sidewalls that are much stiffer than those on regular tires. As a result, the tires don't flex readily to assist in absorbing small, sharp bumps. The more rigid sidewalls also transmit more road noise into the cabin.
Due to their perceived value, four run-flats are also a bit more expensive than five conventional tires and a jack. This cost includes a tire-pressure warning system, to save dim drivers who might fail to notice that one run-flat has lost the benefit of air pressure. This cost penalty will disappear when such warning systems become government mandated in 2004.
Most cars using run-flat tires have been designed to work with them from the get-go, but some of these collaborations are more successful than others. The C5 Corvette has achieved an excellent combination of ride, noise, and handling with Goodyear Eagle F1 EMT run-flats. That said, you could still reduce the Vette's highway noise and improve compliance by fitting conventional tires of similar quality.
Other cars are less happy with run-flats. In the Lexus SC430, run-flats yield a welcome increase in trunk space in exchange for a jarring ride that incites serious structural quivering—at least here in the Midwest. The Mini Cooper also incurs a ride penalty with run-flats. Goodyear's Hopkins predicts these tradeoffs will be reduced with further development.
He also has high hopes for the Michelin-developed PAX System, which Goodyear is also adopting. Instead of stiff sidewalls, this approach relies on a plastic inner donut to support the tire in the event of air loss, reducing the ride compromise. But the PAX System also requires unique rims with positive bead locking, which has never been an easy sell, as Michelin learned with its TRX tires 20 years ago.
Flat tires are so rare I'd rather not compromise the performance of any car I own just to avoid carrying a spare. But I don't ever want to be stranded, either, so for now, the space-saver spare strikes me as the best solution. But if you think otherwise, don't wait until a bitterly cold night to learn what's in your car's spare-tire well
Car and driver
Need more information ? simply ask any driver using run flat tires
