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How exactly do Tire-Pressure Monitoring Systems work?

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29/10/2018
 

Assistance systems help prevent accidents. In a new series on VisionZeroWorld we explain how ASB, ESP & Co. work. This time it’s the turn of the Tire-Pressure Monitoring System.


I just got quite a fright. Why’s my car suddenly veering to the left? Is something wrong with the steering? And then it occurred to me: Perhaps it’s the tire pressure, and at once my guilty conscience cut in – I couldn’t even remember when I’d last checked my tires. This kind of thing happens quite often with older vehicles. And if it’s a while since you took your driving test, you may recall how the instructors always used to say: “Don’t forget to check your tire pressures whenever you fill up!” Important advice – but few people took any notice.

 

Just ten years ago, accident research statistics showed that about two-thirds of cars on the roads in Germany had incorrect tire pressures – sometimes with fatal consequences. The state of the pressure in your tires affects both steering precision and directional stability, and it impacts on braking distances. Incorrect tire pressures can also lead to excessive fuel consumption and tire wear. But while these things have not changed over the years, fortunately there are now fewer cars on the road with the wrong tire pressures.

 

This is thanks to Tire-Pressure Monitoring Systems (TPMS), which have been mandatory in the EU for newly registered cars and recreational vehicles since 2014. A TPMS relieves the driver of having to check the tire pressures, that chore they were once expected to perform whenever they called in at a gas station. This is now carried out automatically and continuously.  And as soon as the pressure in any tire drops 0.2 bar below the preset value, a warning on the dashboard alerts the driver.

The Tire-Pressure Monitoring System from Continental also greatly enhances safety in trucks. Photo: Continental

 

There are two different types of TPMS, those with direct and those with indirect tire pressure measurement. With direct measurement systems, such as “ContiPressureCheck,” pressure and temperature sensors are integrated in the tires, normally directly on or near the valves. These sensors constantly transmit the pressure levels to a control device, which evaluates this data. If a deviation is detected, the driver sees a warning on the dashboard showing which wheel is affected and how much the pressure has dropped. A TPMS with direct measurement is more precise, since each tire has its own sensor – irrespective of whether summer or winter tires are fitted. The sensors are powered by tiny batteries, which need replacing after five to ten years.

Tire pressure loss is indicated by a warning on the dashboard. Photo: Continental

Correct tire pressures are crucial for achieving Vision Zero, a world without accidents. Photo: Continental

 

In a system with indirect measurement, the tires are not fitted with sensors; instead, the system makes use of the readings from the wheel-speed sensors that are transmitted to safety systems such as ABS and ESP. A loss of pressure affects a tire’s rolling radius, rolling behavior and rotational speed. Any such changes are detected by constantly comparing the data from all four wheel-speed sensors. A TPMS with indirect measurement reacts less precisely and more slowly to changes in tire pressure than with direct measurement. But since it uses sensors and control units that are already installed in the vehicle, it is cheaper – and drivers don’t face the extra cost of fitting new tires equipped with sensors.


But no matter which type of Tire-Pressure Monitoring System is used, if it is properly calibrated, it will bring a great increase in safety and convenience for drivers – always assuming, of course, that they react to the warnings that the system issues.

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