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Re-Gear Calculation

Discussion in '2nd Gen. Tacomas (2005-2015)' started by Bodedillon, Aug 7, 2020.

  1. Aug 7, 2020 at 5:32 PM
    #1
    Bodedillon

    Bodedillon [OP] Active Member

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    Hey TW, supposedly my truck was re-geared by the previous owner. It's on 35's and does 2100 rpm at 60mph. Can anyone point me towards a gearing calculator or explain how to do the calculations?
     
  2. Aug 7, 2020 at 5:42 PM
    #2
    3JOH22A

    3JOH22A Cunning Linguist

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    You didn't give the specific tire brand/model, so let's assume a common 35x12.5-17" BFG AT KO2, which per Tire Rack does 602 revs per mile. 60 miles per hour is 1 mile per minute, so the tire is spinning at 602 rpm while the engine does 2100 rpm.

    You're in 5th gear with the 5-speed auto? The 5th gear is 0.72:1. So 2100 / 0.72 / 602 = 4.84. Your axle ratio is probably 4.88... if 60 mph is by GPS and not by speedometer.
     
  3. Aug 7, 2020 at 5:51 PM
    #3
    Marshall R

    Marshall R Well-Known Member

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  4. Aug 7, 2020 at 5:52 PM
    #4
    tacotroy17

    tacotroy17 Well-Known Member

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  5. Aug 7, 2020 at 6:41 PM
    #5
    gotoman1969

    gotoman1969 Well-Known Member

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    Or old school. Tape a piece string to the driveshaft so it’s hanging straight down. Jack up the rear wheels off the ground and spin one tire a complete revolution. Count how many wraps of string around the driveshaft. Close to 5(488) about 4 1/2(456) barely over 4(410)
     
    Island Cruiser and maxtherat like this.
  6. Aug 7, 2020 at 6:46 PM
    #6
    kodiakisland

    kodiakisland Well-Known Member

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  7. Aug 7, 2020 at 7:33 PM
    #7
    3JOH22A

    3JOH22A Cunning Linguist

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    Since it's an open diff, I think you need to either chock one of the wheels or have the locker engaged.
     

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