Michelin PAX System - Michelin PAX System Run Flat Tires

Michelin PAX System Run Flat Tires

Michelin developed the PAX system in the late 1995, first calling it PAV, but introduced the system as the PAX system in late 2000. 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 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, plus 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 $1200 USD 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). The inner support ring is also coated with a gel that is required to lubricate the rotating flat PAX tire.

A PAX tire may be patched from the inside as a conventional tire. If the tire is replaced, and the inner support ring is undamaged, the inner support ring need not be replaced. A new gel pack is generally applied when the tires are demounted and repaired or replaced.

PAX tires are measured in the metric system exclusively unlike the mixed English and metric measurements prevalent in conventional tires. For example a conventional passenger car tire might have the designation 245/45-18, indicating a tread section 245 mm wide, with an aspect ratio of 45% (i.e., the sidewall height is 45% the width of the tread section), mounted on an 18 inch conventional wheel. The similarly sized PAX tire would designated 245-680R460A, indicating the same 245 mm tread section, but a 680 mm overall diameter (a specification not in the conventional passenger car tire nomenclature), the R, meaning radial construction, a 460 mm wheel seat diameter (approximately 18.1 inches) and A for asymmetric, meaning that the wheel is asymmetric, or PAX system.

Special machinery and training is required to service the PAX tires. Michelin was confident enough in its service network that it guaranteed a replacement within 12 hours, if the Michelin dealer could not repair the original tire, or did not stock the replacement. Michelin also worked with Honda (for the Odyssey minivan) and Acura (for the RL luxury sedan) to ensure each dealer carried a full set of replacements wheel tire combinations in inventory. However, Canadian models of Odyssey did not offer PAX tires.

In theory, the PAX tire would not have the same proprietary issues that plagued the Michelin TRX tire that was introduced in the mid-1970s but died out in the 1980s. By licensing the PAX technology to other companies, Michelin would ensure that the consumer would not be locked into a single supplier as with the TRX. Pirelli, Goodyear, Toyo and Sumitomo have licensed the technology from Michelin, but these companies never came out with PAX system tires. So in reality, the consumer was still left with a single supplier solution.