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Sat Nav vs Speedo

Dubplate Aug 20, 2007

  1. Dubplate

    Dubplate Member

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    on the way down to southampton this weekend i noticed that my speedo was showing a speed of 85mph but my sat nav was showing a speed of 78mph, i have heard that the sat nav would be a more precise reading, is this true ?
     
  2. Ess_Three

    Ess_Three Active Member

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    Yes. The Sat Nav is more accurate.
     
  3. mitch78

    mitch78 Active Member

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    :thumbsup:
     
  4. Rocko

    Rocko A5 TSFI

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    If you're running larger than standard alloys this can offset your car speedo so your sat nav would be more accurate. Also depends on what sat nav you've got also.
     
  5. Dubplate

    Dubplate Member

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    Its a standard S3 and a pogodrive sat nav..... i was pretty shocked with the difference as it is quite a gap in the two values....
     
  6. Rocko

    Rocko A5 TSFI

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    Well thats my reason out the window.

    That is pretty scary, difference between 3 points and not.
     
  7. james0808

    james0808 Active Member

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    Going from the original 16's to the 18's on the A4 made the speedo more accurate.
    Didnt change going from 18's to 19's.
     
  8. Rocko

    Rocko A5 TSFI

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    Sure I never speed anyway James:noway:
     
  9. Dubplate

    Dubplate Member

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    perish the thought.................:ohmy:
     
  10. craigynett

    craigynett Member

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    When I 1st got my Road Angel in my old CRX I noticed a big difference. It only had 15" alloys, they're usually 14" standard.

    Even at low speeds there was a difference. 30mph on the Road Angel was 33 on my car speedo. 65mph Road Angel, 70mph speedo. 162mph on my Road Angel & off the clock on my speedo:rockwoot:

    When going through speed cameras i'd go through using Road Angel to check my speed.


    Craig :cool:
     
  11. AndyMac

    AndyMac Moderator Staff Member Moderator

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    On the stock wheels/tyres speedo's have to over read your speed (show a faster speed than your actual speed), it's some EU directive. As they are running an analogue meter then there will always be room for error, so manufacturers have to ensure even with a 10% error, you are still not going faster than the speedo says.
    So most speedos over-read between 5-10%. Your sat nav speed is your actual speed. Since owning an RA2 I never even look at the speedo anymore.
     
  12. jcs356

    jcs356 Brum brum

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    OK, I'm ready to be shot down on this one, but if you are going up or down a steep hill, then doesn't the satnav become marginally less accurate?
    I always thought the unit assumes you are travelling along a flat piece of land to come up with your speed between pings with the satellite using longitude/latitude. If you are actually going up a steep hill then your relative position (longitude/lattitude) will vary less between pings than if you were on a flat road, so the unit thinks you haven't travelled as far so it adjusts your speed down. Actually, you have still covered the same 'distance', just some of it has been vertical ascent?
    I guess it depends upon how often the pings between the unit and receiver are as to how much margin for error there could be?
    Does that make any sort of sense, or am I talking drivel as usual???
     
  13. shineydave

    shineydave Member

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    just use the speed indication built into the diagnostic function on the air-con controller, that's pretty accurate
     
  14. fingermouse

    fingermouse thats me

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    you think yours are bad the mk5 golf is terrible when it reads 90 on the clock its only doing 78 on the sat nav.

    as for my S3 on 19`s its fairly close up to 90 mph


    note to all all test results done on private roads or track :p
     

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