Tire wear, European law: find out why your car speedometer does not display the exact speed

A European standard requires car manufacturers to ensure that the displayed speed is lower than the actual speed on your speedometer.

You may have already asked yourself this question: does my car speedometer display the exact speed when I am driving? ? Well no, the actual speed is very different from the one displayed in front of you.

Indeed, all car manufacturers are required to adhere to strict standards regarding the display of your car, according to France Live. As detailed in Regulation No. 39 of the United Nations Economic Commission for Europe, the speed displayed must under no circumstances be lower than the actual speed.

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Up to 10%

The regulation explains that a speedometer is allowed to display a speed up to 10% + 4 km/h higher than the actual speed. For example, if the speedometer indicates a speed of 100 km/h, the real speed is probably 94 km/h, depending on the margin applied by your speedometer.

The precise objective of this regulation is to prevent drivers from driving faster than they think. To measure your real speed, you can use GPS or applications on your mobile such as Waze or Coyote.

Tire wear

Your speed display can also be distorted if your tire is too worn. A tire of the wrong size can also alter the data transmitted by the magnetic sensors.

These are the sensors that measure the rotation of the wheels using optical or magnetic devices. A bad adjustment can therefore create a speed difference.