Why sometimes speedometers show incorrectly

Deviations in the speedometer can have different causes. If you fit smaller tires on your car, the speedometer will show a different value. This is especially the case when the speedometer is connected to the hub by a shaft.

In modern cars, the speed is read electronically and the speedometer is connected to the gearbox. This allows for more accurate readings. However, speed deviations are not completely ruled out. For example, for cars registered in Germany, the speedometer does not show more than 5% of the actual speed.

Drivers usually do not notice deviations at all. When you get behind the wheel, you cannot tell if you are going 10 km / h faster or slower. If you are being photographed by an overspeeding camera, it may be due to, for example, a tire change.

In these cases, the speedometer in the car shows a moderate speed, but in fact it is overestimated. You were driving faster than allowed without even noticing it.

Always use the correct size tires to avoid deviations in the speedometer reading. Check your vehicle's documentation to find out what it is and what replacements are allowed.

Speedometer drift is most common in older cars. One of the reasons is that the deviations in the respective percentage were different. This is especially true for vehicles manufactured before 1991. Tolerances were up to 10 percent.

Up to a speed of 50 km / h, the speedometer should not show any deviations. Above 50 km / h, a tolerance of 4 km / h is allowed. Thus, at a speed of 130 km / h, the deviation can reach 17 km / h.