It is rare for me to drive without any assistance.With Android Auto or when the mobile phone is placed on a stand. And I am usually helped by apps like Waze or Google Maps (usually the first one, because I like it better integrated into the Google infotainment system or as a navigation app on its own).

So the normal thing is that the car control panel is equipped with this little help to better reach my destination. Over the years I have observed something that has always caught my attention: My car’s speedometer shows a different speed than Google Maps and Waze And the faster I go, the bigger the difference.

Although there are differences between some cars and others, the trend is the same as it is subject to a regulation that aims to keep you sticking to road speed. so you avoid risking your integrity and penalties.

Speed ​​of Google Maps and Waze speed vs speedometer

In fact, the essence of the matter, on the one hand, how to achieve this speed, on the other hand, is contained in UN ECE Regulation 39. This regulation means the approval of the speedometer and the odometer, and it is implemented. In Europe, but similar rules apply elsewhere. In any case, it requires it’Indicated speed (editor’s note: from vehicle speedometer) cannot be less than the actual speed of the vehicle‘.

Or, in the same way, the speedometer should show a speed that either corresponds to the actual speed or is slightly higher. But never inferior. Logically, Like every instrument, it has a margin of error.So in this case, manufacturers are clear that this margin of failure has to go upwards.

In fact, there is an equation in the regulations that relates the speed indicated by the speedometer (V1) to the actual speed (V2):

0 ≤ (V1 – V2) ≤ 0.1 V2 + 4 km/h

For example, if your actual speed is 100 km/h, your speedometer may show up to 14 km/h faster. So, if you are driving on a minor road with a good shoulder and you see on the speedometer that you are exceeding the legal speed (100 km/h), common sense will tell you that: Reduce your speed to adhere to the road conditions and avoid being penalized.

If the previous equation is difficult for you to understand, it is simpler to put it in words: In Europe The maximum error margin of the vehicle speedometer compared to the actual speed is 10% + 4 km/h..

But if you’re running Android Auto or just have a navigation app open, you’ll be surprised to see a different speed. Which speed is good? What speed should I pay attention to? Adhere to.

Navigation applications show a speed that they determine thanks to the relationship between our geographical position (data received with GPS) and the change in unit time. Although there are errors and inaccuracies in GPS (approximate accuracy varies between 1% and 3%), In general, the displayed speed will be closer to the actual speed.

As information, it is good to have the actual speed in practice and if both are below the speed prescribed by law for that road, it means there is still room to press the gas pedal. However If we are on the verge of the limit set by law, be careful because there is an oversight This can mean going faster than you should, with less room for maneuverability, and can also mean penalties (there’s another melon to unpack here: radars’ margin of error).

Cover | Own photo and photo montage

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