INNOVATION Michelin unveils new no-flat technology

Michelin calls flat-resistant tires the biggest change since radials.
KNIGHT RIDDER NEWSPAPERS
DETROIT -- Flat tires aren't likely to disappear any time soon, but for some drivers, changing a flat by the side of the road is becoming a thing of the past.
Since the early 1990s, one solution has been run-flat tires, which keep rolling even after losing all their air. But these tires have been available mostly on sports cars, not on the kinds of vehicles most people drive such as sport-utility vehicles or minivans.
French tire maker Michelin has developed a system that extends run-flat capability to minivans and SUVs while also eliminating some of the drawbacks of traditional run-flats, also known as self-supporting tires.
In September, Michelin's system, called PAX, became available for the first time on a mainstream, family vehicle in the United States. It is now standard equipment on the Honda Odyssey Touring Edition, the high-end version of the minivan.
The company that in 1946 invented the radial tire -- now the industry standard -- says it has another hit on its hands.
"We believe the Michelin PAX system represents the most significant development in tire technology since the radial tire revolution itself," said Tom Chubb, vice president of marketing for Michelin's Automotive Industry Division.
Radials replaced bias-ply tires, which had less traction, shorter life and were more susceptible to tears and punctures than modern tires.
"Remember that 50 years ago, no one had ever heard of the radial tire, and it was considered a pretty radical invention at the time," said Chubb.
Joining in
Other companies are also betting on PAX technology. Michelin has licensed it to four of its competitors -- Goodyear, Pirelli, Toyo and Sumitomo -- while some tire makers are developing rival systems.
All tires use air pressure to support the weight of the vehicle under normal conditions. Self-supporting tires -- the most common type of run-flats -- have reinforced sidewalls that hold up the vehicle even if a tire has zero air pressure.
But self-supporting tires have drawbacks. They don't take bumps as well as regular tires, so automakers that want a smoother ride must tweak their suspension systems to compensate. Secondly, they have higher rolling resistance, which lowers fuel economy. Lastly, experts say stiffening the sidewalls doesn't help when the tires get past a certain diameter, meaning they can't hold up most minivans or SUVs, the BMW X5 and Toyota Sienna being notable exceptions.
For those reasons, run-flat tires have until recently mostly been limited to sporty cars, such as the Dodge Viper and Chevrolet Corvette.
Michelin hopes to change that with PAX, which doesn't rely on a stiffened sidewall to keep a vehicle rolling in the event of flat, but rather on the combination of a modified wheel, a special technique for keeping the tire on the wheel and a polyurethane support ring that sits inside the tire.
The PAX system allows a driver to keep going for up to 125 miles at up to 55 mph with a completely deflated tire, often with little discernible difference in handling. It also eliminates the need for a spare. An electronic tire-pressure monitoring system is needed to alert drivers to the loss of air pressure and to inform drivers how long they can drive the vehicle safely.
Replacing PAX tires will cost about 10 percent more than regular tires, said Don Baldwin, Michelin's director of technical marketing. Vehicles have to be designed especially for use with the tires, so they are not available in the replacement parts market.
The key to PAX is an anchoring system that keeps the tire firmly attached to the wheel even as it loses air. Specifically, it stabilizes the bead of the tire. If you look through the opening of a tire, the bead is the rubber-coated band of wire that runs along the circumference and rests on the wheel.
How it works
When a driver gets a flat on normal tires, the tire pulls away from the wheel, leaving the wheel's rim exposed. Subsequently, the vehicle rides on its rim rather than on rubber.
Michelin says the PAX system anchors the tire to the wheel in such a way that even with hard steering, the tire stays connected, and actually holds on tighter with more vertical load. With the tire still in place, instead of riding on the rim the vehicle rides on the polyurethane support ring inside the tire. The tire might look flat, but the vehicle is still drivable.
Indeed, during a recent Michelin demonstration in Plymouth, Mich., a driver in an Odyssey barely reacted as an explosive charge blew a hole in a tire sidewall. He drove the minivan nearly 100 miles before returning to the test site.
He said the federal government's TREAD Act, which calls for tire-pressure monitors on all vehicles, will also encourage use of run-flat tires, since such monitors are part of the run-flat system.
"When the TREAD Act came in place, one of the huge obstacles to run-flat tires went away," Gingo said.
Under a proposed rule from the National Highway Traffic Safety Administration, the monitors would be required by 2007.