Direct TPMS vs Indirect TPMS - What's the Difference?

Tyre Pressure Monitoring Systems (TPMS) are safety devices that measure and monitor tyre pressure in real time. By continuously tracking the air pressure inside each tyre, a TPMS alerts drivers when one or more tyres become underinflated hence helping them take corrective action before a minor issue turns into a serious safety risk.

There are 2 main types of TPMS - indirect and direct.

Indirect TPMS

Indirect TPMS relies on the vehicle's existing Anti-Lock Braking System (ABS) wheel speed sensors to estimate tyre pressure levels. When a tyre loses pressure, its rolling diameter becomes slightly smaller, causing it to rotate faster than the other tyres. The vehicle's computer detects these changes in wheel speed and uses them to estimate tyre pressure.

One of the main advantages of indirect TPMS is its simplicity. Because it uses hardware already installed in the vehicle, there are no additional tyre pressure sensors, batteries or wireless components to maintain or replace. This can reduce maintenance requirements and eliminate the need for sensor servicing over the life of the vehicle.

However, indirect TPMS is less accurate and less consistent than direct TPMS. Since it estimates tyre pressure rather than measuring it directly, it cannot display actual pressure readings and may struggle to detect certain pressure changes. Factors such as tyre wear, tyre rotations, uneven loading, road conditions and changes in tyre size affect the system's accuracy.

Direct TPMS

Direct TPMS is the tyre pressure monitoring technology used by Promata. Rather than estimating tyre pressure, direct TPMS uses dedicated pressure sensors fitted to each wheel to measure tyre pressure in real time. These sensors can either be mounted externally on the valve stem or installed internally inside the tyre - depending on the system and application.

Close-up of a car wheel with Promata external TPMS car sensor.

The sensors continuously collect pressure data from the tyre itself and transmit this information wirelessly to a display monitor mounted inside the vehicle. The monitor allows drivers to view the pressure of each tyre at a glance and receive instant alerts if pressure levels move outside the preset safe range.

Because direct TPMS measures actual tyre pressure rather than relying on calculations, it is significantly more accurate than indirect TPMS systems. On top of this, direct TPMS can also monitor tyre temperature in addition to tyre pressure. Doing both provides a more complete picture of tyre health and helps drivers make more informed decisions on the road.