The United States was required to equip light passenger vehicles with TPM systems after September 1, 2007, and is now a standard feature on the newest vehicles. The maximum importance of TPMS has its place in the automotive manufacturing industry in regard to several factors. Aftermarket TPMS systems are also available for older vehicles.
There are two configurations of Tire Pressure Monitoring Systems:
- Indirect TPMS - Indirect TPMS does not require the use of pressure sensor hardware per se. It relies on using sensors to monitor the rotational speed of individual tires and other signals exterior to the physical tire. The earliest generation of indirect TPM systems worked on the theory that an under-inflated tire has a reduced diameter and lesser velocity, thus it can be read and reported through the wheel speed sensors as abnormal in relation to the other tire's performance parameters. The second generation TPMS devices use spectrum analysis of each each wheel to detect under-inflation. The system reads minute oscillations caused by under-inflation speed signals that are designed to work with ABS/ESC sensor units. Both indirect TPM systems do not report physical pressure values, giving a true reading. While less accurate than a direct system, indirect TPM systems are more user-friendly and able to be configured with ease.
- Direct TPMS - The direct version of TPMS uses direct sensors on each tire by either an external or internal sensing component. They receive direct tire pressure data (sometimes tire temperature) in real time whether the vehicle is parked or moving. In one example, data is sent to the instrument panel from a sensor located on the interior side of the valve stem, reporting under-inflation in any tire combination. Internal sensors that are mounted to the wheel rim do not provide easy service access and those mounted externally on the wheel are subject to theft and physical damage via the environment and road hazards. The sensors require a battery which must have an adequate charge to send accurate data. Some of the components included with the direct TPMS are a pressure sensor, micro and system controller, analog digital converter, RF or radio frequency controller, low frequency receiver and voltage regulator. Some direct TPMS that are internally mounted to the rim underside must have the sensors replaced when the batteries are dead. Direct TPMS can be used on everything from motorcycles to big rig trucks that have dozens of wheels.
The importance of TPMS
- Tire performance is closely related to inflation pressure. Under-inflated tires cause increased braking distance and change the car’s center of gravity, oftentimes causing directional swerving or lateral instability resulting in a rollover or out-of-control maneuver during a tight turn. Driving with under-inflated tires causes damage to components such as wheel adapters, rims, braking systems, and more.
- Under-inflated tires put more tread on the road's surface, increasing drag and friction. Drag and friction produces excessive heat, especially at high sustained speeds. Tires that become overheated can blow and separate from the rims. Excessive tire friction puts additional stress on the engine and reduces RPM, leading to increased fuel consumption which can be significant if the under-inflation problem goes unchecked for an extended length of time. This causes additional stress on both tires and engine components, leading to costly repairs.
- Under-inflated tires lower the chassis profile (frame) of a vehicle. A frame that is significantly lower than its regular curb height can lead to bottoming out on speed bumps, driveways and other road obstructions. Bottoming out can cause damage to expensive suspension parts in the driving linkages as well as damage to the oil pan, transmission, drive line and underside of the radiator.