Speedo gear

Discussion in 'The "Juice Box"' started by 70buickboy, Nov 20, 2016.

  1. 70buickboy

    70buickboy Well-Known Member

    I'm changing tire sizes, 14's to 15's. What tooth# would I need to compensate for the taller tire's ?
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    Not possible to give you an answer, not enough information. You need exact rear tire size, rear gear ratio, and the number of teeth on the DRIVE gear(located on output shaft of transmission)
     
  3. 70buickboy

    70buickboy Well-Known Member

    OK, i'll work on getting that info.

    Thanks
     
  4. LouV

    LouV Silver Level contributor

  5. 70buickboy

    70buickboy Well-Known Member

  6. BRUCE ROE

    BRUCE ROE Well-Known Member

    You don't need to get all that info. Just use your GPS or measured mile & stopwatch or
    whatever, and measure your speedo error. Then pull the speedo cable out of the trans to
    see what ratio the teeth on your gears have. Adjust that ratio by the error to see what it
    should be. Select a new set of gears close to that ratio, oh and check operation. It will
    more accurate than a calculated gear set (even if you didn't make an error), because it
    takes into account the exact rolling diameter of your tires. Bruce Roe
     

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