Speedo testing and adjustment?
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  1. #1
    Fellow Frogger! DJ-Studd's Avatar
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    Apr 2003
    Victoria, Australia

    Speedo testing and adjustment?

    I was just wondering where one would go to have the accuracy of their speedo checked and, if incorrect, have it adjusted.


    -- DJ

  2. #2
    1000+ Posts Damien Gardner's Avatar
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    Jan 2001
    Wendouree Vic. Aust
    Unfortunately accuracy is relative, to the specifications of componentry used, coupled with outside variables like tyre pressure, (heat of tyre at time of test a big factor here), tyre wear (changes to diameter) etc.
    Any Dyno shop, can state a comparison figure, compared to your speedo, after testing your car on his machine.
    Said machine, brand new is probably accurate to within 5-10%. ADR's allow 10% variations in our speedo manufacture.
    VDO used to have a plant in KYNETON Vic, & closed down mid 90's, went offshore i think.
    I haven't heard of anyother Speedo repair/calibration shops other may know.

    Ps buy a GPS they're within 1% (for internal componentry) & as stated else where the longer it's turned on the better the accuracy, in any reading provided.
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  3. #3
    Gone Fishin' Ray Bell's Avatar
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    Jun 2001
    Burpengary and Murrumburrah, Qld and NSW
    Originally posted by DJ-Studd
    I was just wondering where one would go to have the accuracy of their speedo checked and, if incorrect, have it adjusted.
    We covered this in the last week or so... but here goes again.

    Find one of those 'speedo check' stretches with km posts each km.

    Sit on a set speed (with no variance) for each km and carefully time each km for the distance.

    Divide the result (in seconds) into 3600 for each km and that's your speed.

    There is no more accurate method, but it's not acceptable in a court... only the hit and miss method of using a dyno approved by the RACV will be acceptable there.

    And if you don't understand this, check out a dyno some time and tell me you believe that there's never any slippage between the tyres and the rollers, and that the rollers don't compress the contact point of the tyres more than the road does.

    There is no remedy other than knowing how much to allow as you read the speedo at different speeds. Well, not within reason. Getting someone to adjust the speedo would be a dodgy busines, I reckon.

  4. #4
    Member Freddie's Avatar
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    Apr 2002
    Torquay, Victoria
    The local (Geelong) instrumentation place no longer use rollers or distance measuring and instead they set a GPS unit to speed mode and take a drive at steady speed down the road - they then have a small gearbox (compound train) with variable gear ratios available that they mount in the speedo cable

    Works well and cost was about $200 2 years ago

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