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rolling radius.... yes i'm bored

Discussion in 'General Technical / How To' started by dummi, Apr 15, 2006.

  1. dummi
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    dummi smoking a6

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    [Apr 15, 2006]
    just trying to work out errors for the speedo if they would be significant finding the following

    1741.7 mm rolling radius @ 225/40/18
    1791.96mm rolling radius @ 245/40/18
    1714.99mm rolling radius @ 245/35/18

    225/40/18 said to be commonly used as stock, use 245/40/18 as an upgrade


    100 kph @ + 50mm

    + 3.1mph @ 62mph

    + 3.49 mph @ 70mph

    not sure if thats correct but if it is not a lot in it
    #1
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  3. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Apr 29, 2006]
    It's more to do with the gearing rather than speedo accuracy
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  4. imported_VaulterTim
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    imported_VaulterTim Guest

    [May 7, 2006]
    [ QUOTE ]
    just trying to work out errors for the speedo if they would be significant finding the following

    1741.7 mm rolling radius @ 225/40/18
    1791.96mm rolling radius @ 245/40/18
    1714.99mm rolling radius @ 245/35/18

    225/40/18 said to be commonly used as stock, use 245/40/18 as an upgrade


    100 kph @ + 50mm

    + 3.1mph @ 62mph

    + 3.49 mph @ 70mph

    not sure if thats correct but if it is not a lot in it

    [/ QUOTE ]


    How did you you work out those rolling radii Dummi?

    I make them as follows...

    225/40 x 18" rolling radius - 637.2mm or 63.72cm or 24.88"
    245/40 x 18" rolling radius - 653.2mm or 65.32cm or 25.72"
    245/35 x 18 rolling radius - 628.7mm or 62.87cm or 24.75"

    Maybe I'm wrong there but I can't see how an 18" wheel could have a rolling radius of 170-odd cm... or 60+ inches... that's 5 feet! /ubbthreads/images/graemlins/confused.gif

    Are the wheels on a monster truck? /ubbthreads/images/graemlins/wink.gif

    T

    P.S. Those figures are actually rolling 'diameter' since it is the total of two tyre sidewalls plus the height of the wheel... radii would obviously be half those figures...
    #3
  5. dummi
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    dummi smoking a6

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    [May 7, 2006]
    lol yer that would be a bit silly, i think thats the circumference i worked out distance covered in 1 rotation then worked out % difference at 70mph in rotated distance at those rolling radii, i think, forget why i did it now though lol
    #4
  6. imported_VaulterTim
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    imported_VaulterTim Guest

    [May 7, 2006]
    /ubbthreads/images/graemlins/laugh_roll.gif

    Absolute nutter!

    I love it /ubbthreads/images/graemlins/grin.gif
    #5

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