TPMS Basics

A Tire Pressure Monitoring System or TPMS is an electronic system designed to monitor the air pressure inside the tire. In the Industrial and Mining sectors, the systems also monitor the air chamber temperature of each tire along with a host of other features which vary by manufacturer.

A typical TPMS consists of the following components: battery based wireless sensor/transmitter device, high frequency antenna module, and a central receiver. The sensors are directly mounted inside the tires and they are responsible for measuring the tire pressure and temperature which is then wirelessly transmitted to the server and optionally to an in-cab receiver in the vehicle. The receiver analyzes every piece of data sent from the sensors and issues warnings whenever there are abnormalities in pressure and temperature levels.

TPMS does not replace manual pressure checks, however relying on manual checks alone is not sufficient to ensure tires are operating within optimum pressure levels. The following is a list of manual pressure check limitations:

• Pressure can only be checked when the vehicle is parked.
• Possibility of inaccurate readings due to human error.
• Temperature is not monitored during manual pressure checks.

Each tire manufacturer offers load/inflation tables. The tables base their cold inflation pressure calculations on the anticipated maximum weight of the load for the tire size/ply rating. Unfortunately, the pressure of a tire can change dramatically with the ambient temperature, and using a static calculation does not account for this. Some TPMS automatically formulate the calculated cold inflation pressure by taking the tire chamber air pressure and temperature into account. Click here to find out more about cold inflation.

The following image demonstrates the pressures a tire will reach when the temperature rises to 75°C / 167°F. In this example, all three tires were inflated to 110psi at 0°C (left), 20°C (middle), and 40°C (right).

TKPH versus TPMS

Ton kilometer per hour (TKPH) is the calculation based on the weight and speed a tire can handle without overheating and causing damage. When a tire reaches its TKPH rating under operation, it should theoretically be at its maximum operating temperature (critical temperature). The critical temperature for a radial tire is approximately 105°C / 221°F and this temperature is typically found in the tread. To date, the only way to determine the actual tread temperature is by drilling tires and measuring the temperature. This is called a heat study.

A heat study, to compare actual belt temperature levels to the suggested TKPH and to internal sensor readings, was undertaken by an Australian mine. Four Komatsu 930E trucks which were fitted with 53/80R63 XDR2 B Michelin tires were used. The purpose of the study was to determine whether the correlation between TKPH and tread readings or tread readings and internal sensor readings are more accurate. At the conclusion of the study, it was determined that internal sensor readings offer a better estimation, and fluctuate closer to the actual tire tread temperature than TKPH readings do.