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Which Speedo Gear


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  • Which Speedo Gear

    I just got done lifting my ZJ and installing bigger tires.

    I have 3.73 gears
    Old tires 225/70/16s diam 28.4
    New tires 245/75/16s diam 30.5
    Current speedo gear is 35 tooth (removed and counted 3X to be certain)

    3 different charts say to use a 33 tooth speedo gear

    Math: new gear = old gear X old tires / new tires
    Unk = 35 X 28.4 / 30.5 = 32.6 teeth so use a 33 tooth gear

    Someone on JU says they used a 34 tooth with same setup and was verified with GPS to be accurate.

    So my question is, which gear 33 or 34 tooth.

    Thanks in advance

    1 Jeep dealer says that a 33 tooth is not avail for a 98 ZJ and a 33 won't fit, smallest available is 34 teeth. 2nd Jeep dealer says same thing, 34 is the smallest, but the p/n I got from the Grand tech section is a good part and will fit.

    I be confused :confused:
    It's a Jeep thing, my wife doesn't understand.

  • #2
    I am running 3.73 gears and 31's with a 33 tooth gear and mine is almost right. The chart over on NAGCA is where I got my info. I assume that you looked there because you posted their too. Most people that run 30's don't even change their speedo.
    Just your avearge Grand Cherokee.....right?
    "looks over function....yeah, right"


    • #3
      It looks to me like a 33 tooth is for 31's and a 34 tooth is for 30's. That was my findings. And seeing as how when you drive, the tires get smaller, a 34 tooth might be better.
      Ya Savvy?

      Motech Performance


      • #4
        I ordered the 33 tooth earlier today. Will put in tomorrow and give it a try. I will take it up on the highway and time it from mile post to mile post @ 60MPH.

        Yes the tire will get smaller as you wear them in but even at a loss of 1/2 of the tread, the math still says to use a 33 tooth. Thanks for the info. I will post up the road results after I do them.
        It's a Jeep thing, my wife doesn't understand.