TPMS Basic Notions
WHAT IS TPMS?
TPMS – Tire Pressure Monitoring System are integrated vehicle systems, which continuously monitors tire pressure. There are two types of such systems; the direct system (measuring tire pressure via a sensor from inside the the wheel) and the indirect system (which measures pressure indirectly through the vehicle’s ABS sensor). A display from inside the the vehicle informs the driver if one or more tires lose pressure.
TPMS fulfills three functions:
- Increased safety while driving
- Avoiding increse fuel consumption due to wrong tire pressure
- Avoiding tire wear caused by its reduced pressure
For the system to work, all wheels have to be fitted with pressure sensors, all tyres have to be inflated to the specified air pressure and the system has to be initialised.
What are the differences between direct and indirect system?A direct system measures tire pressure via a sensor integrated in the wheel. This information is transferred wirelessly to a control unit located inside the car. Various displays from different cars manufacturers allow the driver to always read the actual values of pressure or to receive a warning message only when the pressure in one or more tires is too low. Such systems are very accurate because monitors the pressure of the individual wheels.
How it works indirect TPMS?In an indirect system, ABS and traction sensors, integrated in the car, monitors the rotational speed of each wheel. In situations of low tire pressure appear differences in the speed of rotation. In addition, are measured and oscillations that are pressure-dependent of the wheels through advanced processing of signals from sensors. A change in these parameters will be considered a further indication of the pressure loss.
What are the advantages and disadvantages of these systems?A direct TPMS enables very accurate collection of data and provides additional functions such as recognizing the wheel position, detecting pressure loss when the car is stopped and also monitors pressure for the spare tire.
A direct TPMS requires extra effort and expense considerably higher when replacing tires and during maintenance. All tires (summer, winter, spare) of an automobile must be equipped with a functional sensor.An indirect TPMS is not so precise in functioning because it does not measure neither pressure and neither temperature from the tires. It also does not detect loss of pressure from the tires when the car is stationary. However, the system is much easier to maintain and less expensive because they are not using dedicated sensors in each wheel. All of the tires shows pressure drops every few months as a result of the diffusion. The tire pressure monitor warns the driver to correct in time tire pressure through a corresponding message. In the case of a significant drop in tire pressure when driving a yellow warning lamp lights up and a warning message („check tyre pressure”) will be displayed on the screen to allow the driver to take appropriate measures. In this case when lights a control witness, then recommends to inflate the wheel.
Starting from 1 November 2014: according to EU Directive all new cars should be fitted with TPMS by carmakers. However, EU Directive does not stipulates what pressure monitoring system should be used (direct or indirect – dTPMS and iTPMS).