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    The Novak Guide to
    Jeep Speedometer Gears, 1980-2006

    Measure your tire on the vehicle. Don't go by the size on the sidewall. The tire sizes across the top of this chart are loaded heights, taken from the ground to the top of the tread with the vehicle's weight on the tire. A loaded tire flattens where it meets the road and turns more times per mile than its full height suggests, and it's that loaded height the speedometer responds to. Figure it at about 3 to 4% under the sidewall size. A tire sold as a 37 usually measures near 35½. Go by the sidewall number and you'll land one to two gears too small, and your speedometer will read high. If you can't get a measurement, use 270.29 × axle ratio ÷ sidewall size.

    This guide is useful for calibrating and sourcing speedometer gears for your Jeep transfer cases, ranging from the early New Process units (starting in 1980), the Dana 300 (starting in 1981) through the later New Process units made until 2006. The tooth counts are applicable whether its a cable-drive speedometer, or a Vehicle Speed Sensor (starting in 1992) style assembly. RockTrak NP241OR's do not apply since they are natively and directly electronic speed sensing.

    The output shaft drive gears are all spiral-type, featuring 13 (effective) teeth. Dana 300's may feature fewer drive teeth, but have the same pitch as a 13. The chart below show the mating driven gears. As a quick reminder, if you choose a smaller driven gear, the speedometer will be driven faster. If you choose a larger driven gear, the speedometer will be driven slower.

    In 1992, Jeep began to use Vehicle Speed Sensors, and essentially used the same color coding and calibration system as the cable drive speedometers. However, VSS style driven gears have a shorter shank and are only compatible with VSS style senders.

    Long shank speedometer gear

    Long style shank for cable drive speedometers

    Short shank speedometer gear

    Short style shank for VSS applications

    We stock all of the gears in this chart. Click any tooth count number to view the matching gear and add it to your cart.

    Swipe the chart sideways to see larger tire sizes →

    Tire Dia. /
    Axle Gears    		 27" 28" 29" 30" 31" 32" 33" 34" 35" 36" 37" 38" 40" 42" 44"
    3.07 30 29 28 27 26 - - - - - - - - - -
    3.55 34 33 32 31 30 29 28 27 27 26 - - - - -
    3.73 36 35 34 33 32 31 30 29 28 27 26 26 - - -
    4.10 40 38 37 36 35 34 33 32 31 30 29 28 27 26 -
    4.56 - 43 41 40 39 37 36 35 34 33 32 31 30 28 27
    4.88 - - - 43 41 40 39 38 37 36 35 34 32 30 29
    5.13 - - - - 43 42 41 40 38 37 36 35 34 32 31
    5.38 - - - - - - 43 41 40 39 38 37 35 34 32
    5.71 - - - - - - - - 43 42 40 39 37 36 34
    6.17 - - - - - - - - - - - 43 40 39 37
    6.50 - - - - - - - - - - - - 43 41 39
    6.72 - - - - - - - - - - - - - 42 40

    ↗ Select a tooth count in the chart above to view the available gear.



    Accuracy

    A good many of the charts on the web are wrong. We calculated every figure above individually from the standard formula instead of estimating or stepping them, so the chart holds up across its whole range:

    Driven gear teeth = 262.19 × axle ratio ÷ tire diameter

    The constant comes out of the hardware. The output shaft drive gear has 13 effective teeth and the speedometer is driven at 1,000 cable revolutions per mile: 13 × 63,360 ÷ (π × 1,000) = 262.19.

    The tire column headings are loaded height, not the size printed on the sidewall. What drives the speedometer is how many times the tire turns in a mile. A tire carrying the weight of a vehicle flattens where it meets the road and turns about 3 to 4% more often than its full standing height implies. Measuring from the ground to the top of the tread with the vehicle's weight on the tire accounts for that, and this chart is built on it.

    If you'd rather work from the sidewall size, run the same formula with a constant of 270.29, which builds that 3 to 4% in for you:

    Driven gear teeth = 270.29 × axle ratio ÷ sidewall tire size

    Both forms are the same calculation with a different measurement fed into it, and they agree. The factory pairing of 3.55 gears with 225/75R15 tires calls for a 34 tooth gear, and either form returns 34.

    Be wary of charts that step by a flat two teeth for every two inches of tire. Tooth count varies with the inverse of tire diameter, not in a straight line, so a chart built that way can only be right in one spot. It drifts at the ends, by three teeth or more on tall tires with deep gears.

    Some sources wrongly list these gears as compatible with 1955-1979 Jeeps. This is inaccurate, unless an earlier Jeep has received a later transfer case.

    The colors below represent the typical colors for these driven gears. Note that different tooth counts can have the same colors.