It’s rare that I drive without any assistance, either with Android Auto or by placing the phone in a holder. And what helps me is usually apps like Waze or Google Maps (usually the former, as I like it better integrated into Google’s infotainment system or as a navigation app in its own right). So the normal thing is that the car dashboard coexists with this little help to better achieve my goal. Over the years I have observed something that has always stood out to me: My car’s speedometer reads a different speed than Google Maps and Waze, and the faster I go, the bigger the difference..

While there may be differences between some cars and others, the trend is the same as they are subject to regulation aimed at ensuring you stick to road speed. so you avoid risking your integrity and penalties.

Speed ​​of Google Maps and Waze vs speed of speedometer

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

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

In fact, the regulations include an equation 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 more speed. Therefore, if you are driving on a secondary 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: Reduce your speed to adhere to the characteristics of the road and also avoid getting fines.

If the previous equation is difficult for you to understand, it is simpler to put it in words: In Europe The maximum margin of error 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 the change of our geographical location (data received via GPS) per unit time. Although GPS also has errors and inaccuracies (its 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 the law for that road, it means there is still room to press the accelerator pedal. However If we are on the verge of the law, be careful because there is an oversight. This could mean having less room for maneuverability by going faster than you should, and could also mean penalties (there’s another melon to unpack here: the radars’ margin of error).

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