Reinventing the Wheel

It was assumed, when the Michelin Group unveiled its revolutionary Pax run-flat tires in 1998 that the first U.S. application would be a sexy, high-priced sports car.

Four years later, Pax arrives on its first production vehicle for the U.S. market, but the application is the antithesis of a high-visibility sports car. The all-new '05 Honda Odyssey Touring model, which sells for about $35,000, comes equipped with Pax tires as standard equipment.

Michelin says a minivan is the ideal first application for Pax because the innovative tire and wheel design makes a vehicle safer — a key selling point for the family-hauling segment.

Unlike other run-flats, Pax is not a radial. It requires a new, dedicated, asymmetrical wheel design. The tire is mechanically locked to the wheel. Heavy stress on the tire actually clamps it more securely to the rim. Only a technician with a special machine can remove it.

Most conventional run-flat tires are good for about 60 miles (96 km) at 55 mph (88 km/h) with zero air pressure. Pax tires can run 125 miles (201 km), Michelin says.

Pax has an inner support ring (made of plastic or rubber) mounted to the inside of the wheel. During a blowout, the tire — as well as the load of the vehicle — collapses onto the support ring. Pax tires retain about 75% of their maneuvering power with zero air pressure.

When a Pax tire loses air pressure, a sensor inserted in each wheel relays the information to the driver — generally with a symbol on the instrument panel.

The sensing system on the Odyssey would meet the U.S. National Highway Traffic Safety Admin.'s proposed new standard to warn the driver when a tire is under-inflated. NHTSA wants to require active Tire Pressure Monitoring Systems — a radio-frequency sensor in each tire — for new vehicles phased in over three years beginning Sept. 1, 2005.

Pax also provides more cornering power, lower energy losses and less rolling resistance. With so many attributes, why has the Pax rollout come so slowly?

Price. A complete Pax assembly costs a whopping 75%-80% more than a regular wheel-tire package, a Michelin executive says. The company expects higher volumes to drive down price.

The technology also is heavy. A Pax assembly weighs about 15 lbs. (6.8 kg) more than a conventional wheel, which means a significant weight gain of 60 lbs. (27 kg) for four wheels — all of it undesirable unsprung mass.

The tread life is about the same as for a radial. Of course, a Pax tire must be replaced with a Pax tire, as a standard radial will not fit.

Honda and Michelin have invested in a nationwide network to supply Pax tires wherever they are needed by Odyssey customers.

More than 1,000 Honda dealers in the U.S. and some 200 independent tire retailers have received Pax tire-wheel assemblies. A technician need only remove and replace five lug nuts.

If an Odyssey owner has a flat Pax in a remote area — say, Yellowstone National Park — a logistics service will fly a new wheel-tire assembly to the nearest airport, then have it driven by courier directly to the consumer. Michelin vows it will deliver a Pax assembly anywhere in the continental U.S. within 12 hours.

Now that Pax has a high-volume U.S. application (Honda expects to sell annually about 24,000 Odyssey Touring models with Pax), Michelin hints other programs will arrive in the near future.

Nissan Motor Co. Ltd. will offer Pax on a U.S. vehicle in 2005, and another OEM will make Pax available on a minivan, also in 2005.

In Europe, several vehicles now offer Pax, including the Renault Scenic and Audi A6, A8 and, beginning in 2005, the A4. U.S. Audis do not offer Pax tires.

At a recent media event in Plymouth, MI, Michelin demonstrated Pax's capabilities on a number of handling courses.

In the most impressive demo, an Audi A8L with a flat rear tire performed remarkably well on a tight handling track. Even after several test drives at high speeds, the flat tire showed little, if any, wear.