1/27/2011 | 2 MINUTE READ

No Air? No Problem!

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Another run-flat tire?   Not exactly.


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Another run-flat tire?

Not exactly. But before I go into the details of Michelin’s Pax tire, let’s review the current state-of-the-art. Zero-pressure/extended-mobility tires have reinforced sidewalls that carry the weight of the vehicle when the tire loses air pressure. This leads to a stiffer ride, poor fuel economy due to higher rolling resistance, and limitations in its repairability. When the tire deflates, the vehicle rides on two small oval contact patches at the wheel rim. Zero-pressure/extended-mobility tires, therefore, are limited in the gross vehicle weight they can carry, which limits the vehicles that can use them.

What’s the answer?

Michelin’s Pax System uses a new tire and wheel assembly system to eliminate these problems. The wheel design includes an integral inner support ring that locks onto the center of the wheel rim; it is made of textile reinforced injection molded polyurethane by Dow Automotive. A gel lubricant on the inner surface of the tire keeps the tire from overheating due to friction between the tire and ring. The deflated tire drops onto its contact patch, which means a Pax System tire loses only about 25% of its cornering power and can be driven up to 125 miles at 55 mph. A tire pressure monitoring system is included to warn the driver of a deflated tire. Finally, the shorter sidewalls aren’t as stiff as the zero-pressure tires, allow a larger wheel to be used with without increasing tire diameter, and can be made of low-rolling resistance materials. Minivans, SUVs, pickups, and cars can use the system.

A unique wheel and tire?

This isn’t Michelin’s unlamented proprietary TRX tire all over again for the simple reason that Pirelli, Goodyear, Toyo and Sumitomo have licensed the system and will produce their own tires for it. All major wheel suppliers have made or designed a Pax-compatible wheel, including some makers better known for their aftermarket activities. Therefore, buyers aren’t locked into a single provider.

Can they be serviced?

Honda’s Odyssey minivan is the first North American market vehicle to use the Pax System. Each Honda dealer will have a complete wheel and tire assembly in-stock, while Michelin dealers will be able to dismount the tire, fix it and remount it. In case of an emergency, Michelin says it can have a wheel and tire assembly bolted on within 12 hours, anywhere in the U.S.—even the Grand Canyon. Also, a tech bulletin was sent to 11,000 tire dealers with a toll-free number they can call to get an assembly sent to them overnight. Audi will put the system on the A4 in 2005.

Weight and cost?

Let’s start by saying the design allows OEMs to eliminate the spare tire, jack, and the space necessary to carry them. And the brakes can be larger. On the Odyssey, the 18-in. Pax assemblies weigh about 15 lb. more each than the 16-in. wheel and tire assemblies, and the cost of the support ring is under $50. The difference in the cost of the wheels and tires themselves is negligible, though the increase in unsprung weight obviously is not.