Auto tire pressure monitoring systems are used to provide information on an automobile's tire pressure to the vehicle's driver. The two types of tire pressure monitoring systems are direct monitoring and indirect monitoring, with indirect monitoring being more common.
Depending on the vehicle model, the tire pressure monitoring system may constantly report the tire pressure or may simply trigger a warning indicator if a tire becomes dangerously low. Beginning with the 2008 model year, the National Highway Traffic Safety Administration requires all cars and trucks provide warning when the tire pressure is more than 25 percent below the recommended level.
Direct monitoring systems work by use of a sensor placed inside the vehicle's wheel. The sensor is placed in the tire in various ways, including being attached to the inside of the valve stem or simply strapped to the wheel. The sensor detects the pressure in the tire then transmits the level to a receiver via radio signal.
Indirect monitoring systems determine tire inflation levels by using information from the wheel speed sensor that is part of the anti-lock brake system. Low tires are detected as underinflated tires, smaller in circumference than properly inflated tires, making them spin faster than the other wheels.
