Do you know how accurate your car’s speedometer really is?

Home Forums Blogs Do you know how accurate your car’s speedometer really is?

This topic contains 2 replies, has 2 voices, and was last updated by Stuart Masson Stuart Masson 4 years, 6 months ago.

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  • #3056 Reply
    Stuart Masson
    Stuart Masson
    Keymaster

    Have you noticed that your car speedometer often reads faster than what your satnav says? Which is correct and what sort of margin of error should you get?
    Find out here…

    http://thecarexpert.co.uk/how-accurate-is-a-car-speedometer/

    Join the discussion on speedometer accuracy here!

  • #3698 Reply
    sackedstig
    sackedstig
    Participant

    Good article although its important to point out that your average GPS (Tom Tom/smartphone) don’t have masses of processing power in the GPS chip and these chips are prone to making errors when converting the satellite signal into something the device understands.

    to get around the errors that these chips make, the units predict to a point where you are and how fast your going, ever turned off and noticed the arrow stays on the original road for a second or two?

    Also satellite signals will bounce off objects – buildings/motorway bridges/lorries etc which again adds errors that the device uses software to ensure the little arrow doesn’t jump all over the place.

    When car mags use GPS to measure speed its mainly used to remove the inconsistency between speedos of the different cars on test and these devices are a lot better quality (hence often needing an additional aerial on the roof of the car) but this technology would be overkill on a Tom Tom and make it bulky.

    When GPS info is needed to be very accurate (cruise missile etc) the GPS unit is worth tens of thousands of pounds, there are multiple units that compare data as a failsafe incase one goes faulty and the unit is the size of football at a minimum.

    Going my own way since 1982, not sure where I'll end up but you're welcome to come along for the ride.

  • #4449 Reply
    Stuart Masson
    Stuart Masson
    Keymaster

    Interestingly this blog is getting literally hundreds of hits today from the BBC website, as someone referenced it in a comment relating to today’s news that the Government intends to crack down on middle-lane hoggers.

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