I. THE DEFINITION OF TPMS

A Tire Pressure Monitoring System (TPMS) is generally an electronic system designed to monitor the air pressure inside all the pneumatic tires on automobiles, aeroplane undercarriages, straddle lift carriers, forklifts and other vehicles.

II. TYPE OF TPMS

１．Direct Type Direct sensor TPMS : These systems employ physical pressure sensors inside each tire, and a means of processing and sending that information from inside the tire to the vehicle's instrument cluster. Direct sensor TPMS are specifically designed to cope with the effects of changes in tire pressure due to ambient temperature changes and road to tire friction based temperature changes. Friction between the tire and road surface heats up the tire and increases the pressure in the tire. The alarm activation threshold pressures are usually set according to the manufacturers recommended "cold placard inflation pressures". ２．Indirect Type Indirect TPMS do not use physical pressure sensors. Indirect TPMS measure the "apparent" air pressure, by monitoring individual wheel rotational speeds, and other signals available outside the tire itself. Most indirect TPMS use the fact that an under-inflated tire has a slightly smaller diameter than a correctly inflated tire and therefore has to rotate at a higher angular velocity to cover the same distance as a correctly inflated tire.

III. PERFORMANCE

A TPMS helps to improve vehicle safety, and aids drivers in maintaining their vehicle tire pressures. Properly maintained tires help with vehicle safety, performance and economy. In the US, the National Highway Traffic Safety Administration (NHTSA) has estimated that every year, 533 fatalities are caused by tire defects in road accidents[citation needed]. Adding TPMS to all vehicles could avoid 120 of the 533 yearly victims and spare as many as 8,400 injuries every year. The French Sécurité Routière (Road Safety organization) estimates that 9% of all road accidents involving fatalities are attributable to tire under-inflation[citation needed], and the German DEKRA estimated that 41% of accidents with physical injuries are linked to tire problems. For these safety and environmental reasons, the US Federal government has mandated the use of TPMS, and other countries should follow closely. The TPMS mandated by the US aw must warn the driver when a tire is under-inflated by as much as 25% {Ref: US DOT HTSA Docket No 2005-20586}. However, since the recommended tire pressures for most ehicles are more than 160 kPa (23 psi), a deflation of 40 kPa would be within the 25% allowance and would not trigger the TPMS warning mandated by the U.S. law. Therefore, the mandated TPMS is mainly designed for safety and is unlikely to deliver the bove benefits. Drivers are still advised to manually check their tire pressure often to maintain optimal performance.

V. How TPMS works