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Gearing vs. tire sizing

Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by iceman, Jan 2, 2010.

  1. iceman

    iceman New Member

    Joined:
    Jan 2, 2010
    Messages:
    24
    Hey, great site. I found the gearing and tire calculator and would llike to know the difference between using larger tires vs. the 5th gear swap to lower rpm. I know that the 5th gear will only change 5th gear but how is rpm affected when using larger tires? Your calculator doesn't have a slot for that.
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  2. BillK

    BillK New Member

    Joined:
    Aug 29, 2007
    Messages:
    78
    Larger tire will lower rpm regardless of the gear. Every gear will go down the same percent.
  3. iceman

    iceman New Member

    Joined:
    Jan 2, 2010
    Messages:
    24
    What I mean is what is the gearing for every gear so I can put it into the calculator. This is for a '98 jetta.
  4. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    20,907
    Car:
    2006 Jetta TDI
    Location:
    CT
    Here is what you want:

    gear - ratio
    1 -----3.777
    2 -----2.117
    3 -----1.360
    4 -----0.971
    5 -----0.755

    final drive - 3.157

    This is for a 02a CTN 5 speed transmission for the 1Z AHU engines. I didn't put it up because 5th gear is the most relevant to a 5th gear swap. You will also want to change the speed input field to see what engine rpm the engine will be at. Here is the link to the tire, wheel, gearing, and engine rpm calculator - http://www.myturbodiesel.com/1000q/tirewheelCalc.htm
    Last edited by a moderator: Jan 3, 2010
  5. iceman

    iceman New Member

    Joined:
    Jan 2, 2010
    Messages:
    24
    I think you reversed 1st and 2nd gear, I put in the numbers and they don't match up with what I see.
  6. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    20,907
    Car:
    2006 Jetta TDI
    Location:
    CT
    Whopps! I read the manual too fast, 1st is actually final drive. The listing is now fixed and should be correct.
  7. iceman

    iceman New Member

    Joined:
    Jan 2, 2010
    Messages:
    24
    Great, these new numbers seem correct. 1st gear is so low that I wanted to raise it too, not just 5th.

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