Which is more reliable: the speedometer on your instrument cluster or the speedometer on your navigation system?

It is a common discussion among car enthusiasts. The speed you are currently driving is always displayed on a navigation system. Compare that number next to the speed displayed by the instrument cluster and you will notice that they (often) do not match. But which of the two is the most reliable? The speedometer on your instrument cluster, or the speedometer on your navigation system?

Do you recognize this situation? According to your speedometer you drive at 50 mph, but according to your navigation system you drive 55 mph. Speedcams are generally calibrated to perfection and still have a margin before you get a ticket. To be on the safe side, it is of course always good to keep the speedometer in this case. But it's actually pretty crazy and confusing. Therefore, students from the University of Luxembourg investigated this issue.

GPS speedometer of the navigation system

The big difference between the two speeds has everything to do with the way they are measured. The speedometer of your navigation system is (logically) controlled by GPS information. The navigation system calculates how many meters you are driving over a certain time unit at that moment. The only deviation in this is the positioning of the exact location of the vehicle. Depending on the device, this may differ by a meter or 2 from the actual position. The longer the distance over which the speed is measured, the more frequently the position is determined. This means that the deviation of position decreases as you drive faster.

Speedometer on your dashboard

Der Tacho im Auto ermittelt die Geschwindigkeit anhand von Reifendurchmesser, Temperatur, Verschleiß und Druck. Außerdem können durch Traktionsprobleme (Durchdrehen der Räder) auch Abweichungen auftreten und die Beschleunigungen wirken sich auf die angezeigte Geschwindigkeit aus. Mit anderen Worten: Es werden viel mehr Faktoren benötigt, um die genaue Geschwindigkeit zu bestimmen, was bedeutet, dass die Wahrscheinlichkeit von Abweichungen viel größer ist. Aus rechtlichen Gründen verwenden Autohersteller daher einen Sicherheitsabstand, um die Geschwindigkeit anzugeben. Bei einigen Autos können Abweichungen von bis zu 10 % auftreten. Mit anderen Worten, wenn Sie laut Tacho 80 km/h fahren, kann dies in einigen Fällen bedeuten, dass Sie tatsächlich 72 km/h fahren. Allerdings kann diese Abweichung für ein anderes Auto auf 1 % begrenzt werden.

But which speedometer should you pay attention to? Despite the fact that the speedometer of your instrument cluster is considerably less accurate than the GPS speedometer in your navigation system, the University of Luxembourg still advises to follow this. The safety margin is built in so that you never accidentally drive too fast.