Tyre Pressure Monitoring System (TPMS)

The Tyre Pressure Monitoring System (TPMS) is an active safety system fitted to vehicle tyres to monitor tyre pressure and temperature in real time, alerting the driver when abnormalities occur (such as under-inflation, over-inflation, or excessive tyre temperatures). Alongside airbags and Anti-lock Braking Systems (ABS), TPMS is regarded as one of the three core automotive safety systems.

Working Principles and Technical Classifications

Based on the monitoring method used, TPMS is primarily categorised into two types: direct and indirect.

Direct TPMS (Mainstream Solution)
Direct TPMS features a dedicated sensor module comprising a pressure sensor, temperature sensor, and wireless transmitter installed inside each tyre (typically mounted at the valve stem position or strapped onto the wheel rim). The sensor measures tyre pressure and temperature in real time at preset intervals (such as every few seconds) and transmits the data via radio frequency (RF) signals to an on-board receiver, displaying accurate pressure and temperature readings for each tyre on the instrument cluster.

• Advantages: Precise monitoring with real-time numerical readings.

• Cost: Relatively higher; built-in sensor batteries require replacement over time (typical lifespan of 5 to 10 years).

• Classifications: Based on how the sensors are mounted, direct TPMS is subdivided into internal sensors (fitted inside the tyre, offering greater reliability and accuracy) and external sensors (screwed onto the valve stem, easy to install but prone to damage and theft).

Indirect TPMS (Cost-Effective Solution)
Indirect TPMS does not measure air pressure directly; instead, it monitors tyre behaviour using the wheel speed sensors from the Anti-lock Braking System (ABS). When a tyre loses pressure, its rolling radius decreases, causing it to rotate at a different speed compared to properly inflated tyres. The system detects this rotational speed difference to infer that a tyre is under-inflated.

• Advantages: Lower cost, requiring no additional dedicated hardware.

• Limitations: Cannot display exact pressure figures; unable to detect simultaneous, uniform pressure loss across all four tyres; prone to false alerts during cornering, on wet and slippery roads, or under aggressive driving.

Core Benefits and Regulations

The primary value of TPMS lies in prevention. Incorrect tyre pressure is a major cause of tyre blowouts, uneven tread wear, and higher fuel consumption. According to data from the US National Highway Traffic Safety Administration (NHTSA), when tyre pressure is 25% below the recommended level, the risk of a blowout increases threefold. Maintaining proper tyre pressure not only enhances driving safety, but also improves fuel economy.

Due to its critical safety benefits, TPMS has been made mandatory standard equipment in numerous markets:

• United States: Mandatory on all new passenger vehicles since 2007.

• European Union: Mandatory for new vehicle type approvals since 2012, and across all newly registered vehicles since 2014.

• China: Mandatory on all newly produced passenger cars since 1 January 2020.

Key Precautions and Maintenance Tips

• Sensor Care: When replacing tyres or rims on vehicles equipped with direct TPMS, always inform the workshop technician to avoid damaging the sensors. After replacement, a sensor re-pairing or relearning procedure must be carried out for the system to display readings correctly.

• Temperature Effects: Tyre pressures are naturally lower when cold, and will rise as the tyres heat up during high-speed driving—this is normal thermal expansion. It is recommended to check and adjust tyre pressures when tyres are cold (after the vehicle has been parked for at least 3 hours or driven for less than 2 km). If a TPMS warning is triggered, always inspect and adjust tyre pressures based on the manufacturer's recommended cold tyre pressure specifications.