Michelin PAX System

PAX was an automobile run-flat tire system developed and manufactured by Michelin in the 2000s. It utilizes a special type of rim and tire to allow temporary use of a wheel if its tire is punctured. The core of Michelin's PAX system is the semi-rigid ring installed onto the rim using special equipment. It provided support to the tire and its sidewall to allow emergency operation at limited speed until such time as the tire can be replaced.

Cars that used the system include supercars like the Bugatti Veyron EB 16.4, luxury cars like the Rolls-Royce Phantom, and more common vehicles like the Honda Odyssey and Nissan Quest.

History

Prior developments

Prior to the introduction of PAX, Michelin and Goodyear produced other pneumatic tires that could temporarily support themselves without air pressure. These tires were modified with a stiffer, heavier sidewall which could support the weight of a vehicle at speed without losing control. This design allowed a vehicle to be driven at a limited speed to a service station.

The heavier sidewalls and special bead construction allowed a driver to drive a car with little or no air pressure at a limited speed (approximately 50 mph) over some specified distance to a service station, or at least off the roadway out of immediate danger. In a conventional pneumatic tire, loss of pressure at speed would result in the collapse of the soft tire sidewalls such that the metal wheel edges would slice through the collapsed sidewalls, which would likely result in an accident, possibly fatal, as well as the destruction of the tire, and possibly the wheel. These tires required the introduction of an electronic tire pressure monitoring system to indicate low tire pressure to a driver. With conventional tires, low pressure is obvious, due to sidewall deformation; but with reinforced sidewall run-flat tires, low pressure is difficult to detect until the tire fails.

The Goodyear EMT (Extended Mobility Tire), with a reduced sidewall, was introduced with the 1994 Chevrolet Corvette. Michelin also introduced a similar tire in the mid-1990s called the Zero Pressure System, distinguished from conventional tires by the designator "ZP."

Development and release

Technical details

The PAX system approached the problem differently, requiring a system of parts, not just a different tire. Rather than extra stiff and supportive sidewalls, the PAX system relies on a newly designed asymmetric wheel, a supportive insert and a similarly asymmetric tire combination to provide an extended run-flat capability of up to 125 miles at 50 or 55 mph. The PAX system weighed approximately the same as four conventional tires plus a spare. So although comparable PAX tires were heavier than conventional counterparts, they were not that much heavier (Michelin claims four PAX System assemblies are equal to the weight of 4.7 standard tire-wheel assemblies). However, rotating mass and unsprung weight of the wheels and tires on the ground increased, which is a disadvantage. In addition, no spare tire had to be carried, so that PAX-equipped vehicles weighed no more than conventionally equipped vehicles, and had more storage space without the spare tire. Michelin said that the retail replacement cost of the PAX tires would be approximately equal to the cost of five conventional tires. The true cost was approximately US$1200 or $1600 for snow tires in 2008 for Odyssey which is higher than some conventional tires. PAX tires allegedly had a smoother ride and provided better gas mileage than the comparable conventional tire but owner impressions vary greatly. PAX tires provided peace of mind and real safety and added mobility that no conventional tire could but limited availability and cost of PAX tires and service reduced owner satisfaction. As with the zero-pressure type run flats, a tire pressure monitoring system (TPMS) was mandatory. TPMS became mandatory on all cars soon afterward.

The soft PAX sidewall allows for a more comfortable ride compared to run flat tires which work by having stiff sidewalls. When flat, the PAX tire sidewalls collapse until the weight of the car is riding on an internal polymer support ring mounted to an asymmetric wheel. That is the outside diameter of the wheel is smaller than the inside diameter of the wheel. This asymmetric wheel and tire design allows the tire to lock onto the wheel, rather than coming off at speed and/or while turning. So a PAX wheel that appears to be about 18 inches from the outside of the car (the side facing out), will look more like 19 inches on the inside of the wheel (the side facing the suspension).

Vehicles equipped

United States

2004–2008 Rolls-Royce Phantom[22][23][24]
2004–2011 Bugatti Veyron [25][26]
2005–2009 Honda Odyssey Touring

External links

Run-Flat Tires:A New Standard Rising - MSN Autos

References

Robert W. Dalton. Michelin working to prove it can reinvent the wheel Company introduces tire that can still run while flat Spartanburg Herald Journal, 1998-01-06, retrieved 2025-03-12^
Jeff Daniels. Michelin bets on a flat runner October 1997^
Michelin touts Pax's control after pressure loss

Lawsuit

In March 2007, a federal class-action lawsuit against Michelin and American Honda Motor Company was filed by owners of PAX-equipped Honda Odyssey and Acura RL vehicles.[11] The suit, including consumers from Arizona, Florida, Illinois, and New York,[12] alleged that PAX tires had a significantly shorter lifespan than conventional tires, were vulnerable to increased wear and side punctures, could only be serviced by a limited number of facilities, and were prohibitively expensive to replace; and that the two companies misrepresented the cost and convenience of repairs and replacements to customers.[11][13][14] It was consolidated with three similar lawsuits in March 2008, and two other lawsuits against the companies were dismissed.[14]

A settlement was reached in December 2008.[15] The settlement stated that the PAX tire system should continue to be used with cars originally equipped with PAX system. The original warranty was extended to 36,000 miles, although it is unclear as to whether it is the materials and workmanship portion of the warranty or the hazard insurance portion of the warranty, or both. Also left unanswered was what happens to the trip interruption payments, and the guarantee to get a replacement tire delivered within one day if the car is stranded beyond the 125-mile flat tire driving limit since PAX-certified repair shops are not as plentiful as standard tire repair shops. In addition, a spare tire kit would be offered by Honda for those cars originally equipped with the PAX system tires since servicing may be impractical in certain geographic areas. If a spare had already been purchased, Honda would reimburse the owner approximately $110.00. The deadline for class claims was in January 2010. Affected owners were referred to the sfmslaw.com web site, the attorneys responsible for the class action suit.[16]

On December 20, 2010, the United States District Court for the District of Maryland granted final approval of the consumer class action.[17]