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rolling radius.... yes i'm bored

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

  1. dummi

    dummi smoking a6

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    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
     
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  3. AndyMac

    AndyMac Moderator
    Staff Member Moderator

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    It's more to do with the gearing rather than speedo accuracy
     
  4. [ 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...
     
  5. dummi

    dummi smoking a6

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    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
     
  6. /ubbthreads/images/graemlins/laugh_roll.gif

    Absolute nutter!

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

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