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DerAmpelmann

Did you know that car speedometers lie?

Did you know that car speedometers lie?  

10 members have voted

  1. 1. Have you noticed or heard before that car speedometers usually show slightly faster speed than the real speed?

    • Yes, I was aware of this.
      6
    • No, I hadn't heard of this before.
      4
    • No, and I don't think this is true.
      0


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Hey peeps!

 

I was discussing speeding and fines with a friend when this thought popped up in my head. How many people are aware that their car speedometers do not quite show the real speed? They're designed to show speed slightly faster than the speed you're actually driving to stay on the safer side, so to say. It would be very questionable situation, if you ended up getting a speeding ticket because of the inaccuracy of your car's speedometer, and hence they are rather made inaccurate by making them show faster speed than real speed.

 

How inaccurate the speedometer is varies between car models and brands, some speedometers have next to no difference to real speed, some can lie as much as 5 km/h (~3 mph) or more. While two cars are driving the speed limit according to their speedometer, one may be going a little faster than the other. Due to this it's beneficial that you check how inaccurate your speedometer is. It can be done using a GPS device, for example your phone or satnav. Just make sure the signal is good, so you can get trustworthy readings. Once you memorize how inaccurate your speedometer is, you can easily compensate that. You may argue that you wouldn't trust GPS, but modern day global positioning system and devices that use it are very accurate, frighteningly so.

 

I'm sure many of you had heard of this before, given that people reading these forums have an interest in vehicles. This is just to satisfy my seemingly endless curiosity. Do you think that this is an utter lie or conspiracy to get you a speeding fine? Are you frustrated that people can't even drive as fast as allowed? Be my guest and discuss it!

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Besides the model of the car/truck/bus it is mostly dependend on the method that is used for measuring the speed.

Is it measured electronical or mechnical

Where is the sensor placed

If it is an electronic sensor: what kind of polling (data) rate does it have and what kind of tolerance

 

But as long as your real speed (compared to the shwon speed) is not too slow, it's fine. But you should also not be able to get a speeding ticket for driving 1 unit above speed limit, because the tolerance for the speed-o-meter is too low.

 

And a fact that you forgot to mention:

Many (western) countries do have a law that precisely describes what tolerences are allowed/mandatory (max and min values). And this law is usually getting tested with type/model approval of the respective car

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Hello There;

 

As your topic has been inactive for over 14 days, we are archiving your topic. Due to the fact our forums are a busy place, we archive topics that are inactive for 2 weeks to help keep just those topics that are truly active for our community.

 

If you have any further questions or comments, or wish for your topic to be unarchived don't be afraid to contact me.  :wub:

 

//Moved to Archive

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