Tire Pressure Monitoring Systems (TPMS)

As part of the effort to increase awareness of the need to maintain proper tire pressure, the U.S. government has taken steps to make it easier for drivers to be aware of potentially unsafe low pressure in their tires. As of the 2008 model year, the National Highway Traffic Safety Administration (NHTSA) now requires that all passenger cars and light trucks feature the Tire Pressure Monitoring System (TPMS).

TPMS is an automated system that monitors the air pressure in a vehicle's tires. When air pressure in one or more tires drops 25 percent or more below the correct pressure, a warning indicator alerts the driver. TPMS typically delivers these alerts to the driver through one of two types of warning lights on the dashboard.

	1. The first uses the official TPMS symbol, which is a cross-section of a tire with an exclamation mark in the center.
	2. The second is a top-view graphic image of a car that indicates which tires are low.

DIRECT VS. INDIRECT

Tire pressure is monitored through one of two methods: direct or indirect. Direct TPMS monitors the actual air pressure inside each tire via a sensor mounted within the tire. Indirect TPMS measures tire pressure by monitoring the speed and rotation of each individual wheel. When a significant variation in speed and rotation is detected in one or more wheels when compared with the others, it is often an indication of underinflation. This information is then transmitted to the vehicle's on-board computer, and the driver is alerted.

Even though TPMS has only recently become standard for all vehicles, a number of older models already have them installed. Approximately 20 percent of 2006 vehicle models came pre-equipped with TPMS, and that number increased to 70 percent in the 2007 model year. If you are unaware if your vehicle has TPMS installed, check your vehicle owner's manual.
 

TMPS does not eliminate the need of checking your air pressure!

Due to the percentage of air loss that is required to trigger the TPMS warning system air pressure maintenance remains critical.  For example, The driver of a passenger car that calls for 35 psi may not be warned about tire pressure loss until it drops to 26 psi depending on the type of monitoring system used. Under the same circumstances, a driver of a light truck that calls for 80 psi won't be warned until just 60 psi remains. In both of these cases, significant load capacity has been sacrificed before the driver is warned. 

The TPMS system is there to warn the driver only in the case of a significant drop in air pressure.  Only by checking your vehicle's cold tire pressure with a pressure gauge at least once a month and before long trips can you be assured that your tires are properly inflated and that they will perform as designed.

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