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How accurate is the A3 speedo

Discussion in 'A3/S3/Sportback (8P Chassis)' started by Steve-L, Aug 3, 2006.

  1. Steve-L
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    Steve-L Member

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    [Aug 3, 2006]
    As the title says, I know most speedo's read under but curious to know if anyone has tested the accuaracy at varying speeds primarily 60, 70 & 100mph ?
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  3. jdp1962
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    jdp1962 Grumpy Old Moderator Staff Member Moderator

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    [Aug 3, 2006]
    If you have a Road Angel or sat-nav, or anything with GPS functionality, you should be able to display your real speed, & compare it with the speedo. They usually update around every three seconds, so there's alway a bit of lag when accelerating, but once your speed is steady, you can compare directly. When my GPS is showing a steady 70mph, the car speedo is reading 73.
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  4. Vertigo1
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    Vertigo1 Well-Known Member

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    [Aug 3, 2006]
    Speedos always over-read, never under. Mine is about 10% out, so 100mph indicated is 91 actual and 127 actual is 140 indicated.
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  5. bobtooke
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    bobtooke New Member

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    [Aug 4, 2006]
    Mine is about 5 to 6 % out from my GPS (ie at an actual 70mph shows 73/74-ish). This is about average for most modern cars.
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  6. dmaudi
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    dmaudi Member

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    [Aug 5, 2006]
    my understanding is that legally speedo's have to read over, I think it is 6%, totally agree with the numbers, I've seen mine go past 160 yet my SatNav says max attained is 143 or 146, can't remember exactly from my desk,

    does that also mean the odometer reads over or is that accurate? otherwise we're all getting less miles out of our cars than we think....

    anyone know if the speed limiter's based on speedo speed or true speed?
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  7. C_Audiboy
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    C_Audiboy Vroom Vroom

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    [Aug 5, 2006]
    In mine, speedo reads 70MPH when sat-nav displays 68MPH so approx 3% over-read here.......
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  8. Eeef
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    Eeef Lord of War

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    [Aug 6, 2006]
    mine is exactly 5% over.
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  9. RobB
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    RobB Member

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    [Aug 7, 2006]
    Mine seems almost spot on at lower speeds, using those speed warning radar signs that flash your speed when you go past.

    Also, I read that the 3.2 does 24.7mph / 1,000rpm in 6th, which makes my 100mph at 4,000rpm seem pretty accurate. Same for top speed - 159mph in Germany - still creeping up slowly then a noticeable stop at about 6,300rpm, which means only about 3mph out compared to the limiter's supposed 250kph / 156mph.
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  10. adamhill
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    adamhill New Member

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    [Aug 8, 2006]
    Mine is about 10% and consistent with slow and fast speeds. I am shocked by this tolerance and questioned it with Audi UK - they simply said that 10% was within their acceptable range.
    I told them that 10% tolerance is historical from the old cable driven speedos and that I do not consider it to be acceptable on a modern car where the speedo is electronic.

    We agreed to disagree in the end
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  11. marriedblonde
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    marriedblonde Moderator

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    [Aug 8, 2006]
    I'm sure there was another thread about this not so long ago...
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  12. marriedblonde
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    marriedblonde Moderator

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    [Aug 8, 2006]
    We do not know our car's true spped. We can get pretty close with a sat nav unit (accurate to approx 0.1%)

    There's lots of variables to consider regarding our speedo's. New compared to old worn tyres will have an effect. Under/over inflation will obviously effect the speedo reading. The theres the plethora of tyre manufacturers out there. Although the tyres same they are the same size the circumference is different from make to make.

    To give an example of the difference of a new compared to old tyre:

    If a new 225/40/18 tyre has a diameter of 637mm the circumference is 2000mm (I am using pi at 3.14 for these exmaples so not 100% accurate but will give you an idea)

    So that tyre has 8mm of tread say. When worn to the legal limit the tread will be 1.6mm so the diameter is now only 622.2mm and therefore the circumference is now 1953.7

    The difference as a % between old and new is 2% thats without taking into account for tyre inflation. So if your speedo is overreading by 10% with a new tyre it will be over reading less with a worn one.

    J.
    #11

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