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Thread: Need help working out final drive ratios

  1. #1
    Senior Member schrickvr6's Avatar
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    Need help working out final drive ratios

    Ok where do i start, basically i want to lower my gearing to something reasonable but i want to get an idea of what sort of speeds it would do in each gear with a different ring and pinion.

    The car currently has a 3:39:1 fd ratio and will do ....

    1st - 47mph
    2nd - 74mph
    3rd - 106mph
    4th - 131mph
    5th - 174mph

    The ratios available to me are 3:66:1, 3:94:1 and 4.24:1, i'm guessing the higher the number the lower the gearing but by how much?

    TIA

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    Theres a formula around somewhere to work this out.
    You will need the gearbox ratio and (I think) the rolling radius of your driven wheels.
    Will have a hunt around for you

    This might work - not the one I was looking for though
    http://www.xse.com/leres/ss/calculator.html
    Last edited by IainB; 17-01-2005 at 01:46 PM.

  3. #3
    Senior Member schrickvr6's Avatar
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    Nice one Eazi that was spot on, although i had the speeds a little out before, i didn't realise i can do almost 140 in 4th

    So the choices are 160mph, 150mph and 140mph, i'll probably go for 150mph unless i decide i don't need to use motorways again

    3.39 fd ratio Standard

    Gear Ratio Final M@R R@80MPH
    1 11.19 43.7 12803
    2 6.58 74.4 7527
    3 4.41 111.0 5044
    4 3.53 138.8 4035
    5 2.81 173.9 3220

    3.66 fd ratio

    Gear Ratio Final M@R R@80MPH

    1 12.08 40.5 13823
    2 7.10 68.9 8126
    3 4.76 102.8 5446
    4 3.81 128.5 4356
    5 3.04 161.1 3477

    3.94 fd ratio

    Gear Ratio Final M@R R@80MPH

    1 13.00 37.6 14881
    2 7.64 64.0 8748
    3 5.12 95.5 5862
    4 4.10 119.4 4690
    5 3.27 149.6 3743

    4.24 fd ratio

    Gear Ratio Final M@R R@80MPH

    1 13.99 35.0 16014
    2 8.23 59.5 9414
    3 5.51 88.8 6308
    4 4.41 111.0 5047
    5 3.52 139.0 4028

  4. #4
    F.A.S.T. Butuz's Avatar
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    • Butuz's system
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    Youve got a really long 5th gear havent you! My 4th to 5th change only drops about 500rpm.

    Butuz

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    Senior Member schrickvr6's Avatar
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    All of the gears are stupidly big tbh although i would love to keep 1st the way it is and drop everything else down. It can be a royal pain in the arse sometimes,e.g having to drop down to 2nd for a 60mph corner just to keep it in the power band.

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