Tire pressure monitoring

Objective

Tire pressure monitoring systems (TPMS) check that the manufacturer’s recommended pressure is maintained.

How it works

There are two types of TPMS systems:

• Direct System: the pressure is measured through a sensor located in the wheel valve.
• Indirect system: in this case, the pressure is measured by comparing the rotation speed of a tire with that of another tire that has not suffered any loss of pressure. This is because a tire that has less pressure has a smaller diameter and therefore rotates faster.

The system must be reset, to log the new values, once we have checked and adjusted the tire pressure. In this way, the system will consider this pressure to be the correct one and it will serve as a reference for the comparisons. Depending on the manufacturer, the system can be reset in one of two ways:

• through the customizable menu on the instrument panel or center console.
• by means of a push button located on the center console.

Components

• Direct control system. This tire pressure control system has 3 different elements:
• Four sensor-emitter modules, installed on the wheel valves (some manufacturers also include another on the spare wheel). Each module incorporates a pressure-temperature sensor and an inertial switch activated by wheel rotation to determine that the vehicle is in motion. The sensor-emitter module is powered by a lithium battery with a life of approximately 10 years.
• The system control unit.
• A high-frequency antenna under the bodywork, which is called the receiver. Some manufacturers integrate this into the control unit.

• Indirect control system.

The pressure control system makes use of the rotational speed sensor already incorporated into the wheels of the vehicle to operate the ABS/ESP system. This system does not calculate or know the pressure, but simply estimates that a tire is less inflated by comparing its angular velocity with that of the diagonally opposite tire.

When a tire loses pressure, as mentioned above, the diameter of the tire is reduced. As a result, to travel the same distance in a straight line as another, it will have to rotate more often.

The system’s calculator is in charge of detecting this difference using the indications from the sensors of each tire; it then warns the driver of the loss of tire pressure.

Collisions avoided

• Possible blowouts due to poor tire pressure.
• Loss of control in difficult situations.
• Tire skidding on a curve.
• Aquaplaning due to lower than recommended tire pressure.
• It also avoids irregular tire wear due to too little or too much pressure.

Effectiveness

Economic and Eco-friendly.

If the tire pressure is too low, it can increase fuel consumption by 20% in the case of passenger cars and 30% in buses and trucks.

According to a study carried out by the TRL in March 2018 for the European Commission, it is estimated that there are 30% fewer traffic accidents thanks to the tire pressure control system.

Use and limitations

The direct TPMS system, has an important advantage in that it knows the exact pressure of the tires at all times and is able to detect variations of 0.2 bar, while with the indirect system you can detect a difference of more than 30% between two tires.

The direct system is more expensive because it requires the installation of several elements while this is not necessary with the indirect system because it uses the sensors of other systems such as the ABS and ESP.

Cost

The TPMS system has been standard on vehicles since November 1, 2012, prior to which the cost ranged from 100 and 700 euros.

Mandatory

Since November 1, 2012, in new approvals and in new passenger cars registered since November 1, 2014.

From July 2022 it will be mandatory on new trucks, vans and buses.