Driving a vehicle with underinflated tyres can create unsafe driving conditions for both you and others on the road that can cause accidents.

What is Tyre Pressure Monitoring System?

TPMS or tyre pressure monitoring system is a warning system that alerts the driver of a vehicle that the tyres are significantly underinflated. Many cars use a symbol on the dashboard (below). It looks like a horseshoe with an exclamation mark. However, we should note that many newer car models may also present the information on the central display.

What Came Before TPMS?

Proper tyre maintenance with the assistance of a TPMS system can help prevent accidents, injuries and even deaths in cases of blowouts that can cause the driver to lose control of the vehicle.

However, this hasn’t always been the case. Before tyre pressure monitoring systems became commonplace, drivers had to get out of their vehicle, crouch down and check their tyres with a tyre gauge.

As a result, legislation now requires a TPMS system on new cars sold in the UK. A more recent law change states that any TPMS sensor that no longer works correctly will result in an immediate MOT failure.

Indirect versus Direct TPMS – What’s the Difference?

Although mandatory, not every TPMS is the same. There are two types of TPMS – indirect and direct. The tyre pressure warning light discussed above is only the final step of the procedure.

What is Indirect TPMS?

Indirect TPMS will typically but not always rely on the same wheel-speed sensors that the anti-lock brake system use. This means an indirect TPMS doesn’t measure tyre pressure like a tyre gauge would but tries to derive a figure through other means.

It works by measuring the rate of revolutions each wheel makes and can be incorporated with embedded computer systems to compare with other data like speed.

Further, it can interpret the size of the tyres on a vehicle. When a wheel is spinning faster than expected values, the computer can conclude that the tyre is underinflated and alert the driver to act.

Pros of Indirect TPMS

• Requires less installation maintenance than direct TPMS
• Cheaper compared to direct TPMS

Cons of Indirect TPMS

• It can be inaccurate and unreliable if using different sized tyres or unevenly worn
• Needs to be rest after tyre rotation
• Resetting the sensor is required after inflation

What is Direct TPMS?

Direct TPMS will use more than wheel revolution data from the anti-lock brake system by using a pressure monitoring sensor in each tyre to produce specific pressure levels. It may also include, though not always temperature readings.

Each sensor has a distinctive serial number that makes it easy to separate from other tyres and systems on other vehicles.

This data is sent central control module, usually wirelessly, where the data is analysed and interpreted. Should the tyre pressure be lower than a safe level, it would alert the driver to take action.

The technology is often proprietary, which means that when replacing a TPMS sensor, it should be done by a professionally trained technician who will have the required tools to complete the replacement.

Pros of Direct TPMS

• Provides genuine tyre pressure readings
• Unlike indirect TPMS, not prone to inaccuracies
• Re-synchronisation after tyre rotation or replacement is simple
• Batteries inside sensors usually last around ten years

Cons of Direct TPMS

• More expensive overall than indirect TPMS
• Batteries usually can’t be replaced, requiring the whole sensor to be replaced
• While re-synchronisation is simple, it can require expensive tools
• Proprietary systems can be confusing to install and service for consumers
• Sensors can often take damage during mounting or demounting

Tyre Safety

Maintaining your TPMS sensors can help ensure tyre pressure readings are accurate, whether indirect or direct. However, it shouldn’t be considered a substitute for checking your air pressure but an additional tool.

It’s always recommended to also keep an eye on slow punctures. We discuss this in detail in one of other posts here.

Please have a look at our TPMS sensors in our shop that will help ensure your car remains safely on the road, protecting you and other road users. Our search function will help you find a suitable TPMS sensor for your car’s manufacturer and model.