Tire Pressure Monitoring System

A tyre pressure monitoring system, universally abbreviated to TPMS, alerts the driver when one or more tyres falls significantly below its correct inflation pressure. It exists because under-inflation is both common and insidious: tyres lose pressure naturally over time and through tiny punctures, the loss is hard to detect by eye, and many drivers rarely check their tyres manually. Yet even modest under-inflation degrades safety and efficiency, so an automatic warning fills an important gap in routine vehicle care.

There are two fundamentally different approaches. Direct TPMS places a battery-powered sensor inside each wheel, usually integrated with the valve stem, which measures the actual air pressure (and often temperature) and transmits the reading by radio to a receiver in the car. It reports each tyre's pressure individually and accurately, but the sensors have finite battery lives of several years and must be re-registered when wheels are swapped. Indirect TPMS uses no dedicated sensors at all; instead it borrows wheel-speed data from the anti-lock braking system, exploiting the fact that an under-inflated tyre has a slightly smaller rolling radius and therefore turns marginally faster than its correctly inflated neighbours. It is cheaper and maintenance-free but less precise, cannot give an absolute pressure value, and must be reset after any inflation or tyre change.

The consequences of running on soft tyres explain why the technology matters. Under-inflation increases the contact patch and flexes the sidewalls excessively, generating heat that can lead to sudden tread separation or a blowout at speed. It lengthens braking distances, blunts steering response and reduces cornering grip, all of which compromise safety. It also accelerates and unevenly distributes tread wear, shortening tyre life, and raises rolling resistance, which measurably increases fuel consumption and carbon emissions — a tyre running well below specification can add several per cent to a car's fuel bill.

These safety stakes prompted regulation. Following a series of fatal rollover crashes linked to tyre failures, the United States mandated TPMS on new passenger vehicles from the mid-2000s, and the European Union followed, requiring the systems on new car types from 2012 and all new cars from late 2014. As a result, the warning light depicting a cross-section of a tyre with an exclamation mark is now a familiar feature of virtually every modern dashboard.

Drivers should understand what the warning does and does not mean. A TPMS is a safety net that flags a low tyre, but in most systems it only illuminates once pressure has already dropped well below the recommended figure, so it is no substitute for periodic manual checks with a gauge, ideally when the tyres are cold. Cold weather can trigger the light through natural pressure contraction, and a slow puncture may need professional attention. TPMS is closely related to the anti-lock braking system, whose sensors indirect versions depend upon, and to electronic stability control, both of which rely on tyres being properly inflated to perform as intended.