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Thread: Speedo calibration help

  1. #1
    Potential Tuner
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    Speedo calibration help

    I have changed the speedometer calibration 5 times but it does not seem to change. I'm comparing speedometer to gps using track addict and it seems to 5 to 7 mph off each time. Am i missing something ? The buggy is a 16 RGR900 with 32s and 13 % reduction in trans

  2. #2
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    Apr 2019
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    Did you figure it out?

    My 2016 Ranger is almost the same. 32 Terminators, with Highlifter Reverse chain and reduction in transmission.
    I am sure there is a formula for this I just have not had the time to figure it out. I was able to get it real close by switching Override Cal to Calibration and Cal Value to 150ft.

    It probably has to due with tire rollout and the number of teeth on the tone ring.
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  3. #3
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    Still have not been able to get it but currently have 155in. And I swear it doesn't seem like it's changed anything . I will try your suggestion and see what happens.

  4. #4
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    Tried the 150 ft and it was almost dead on . Thanks for the suggestion!

  5. #5
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    Happy to help.

    I think this is how it works but, I have not swapped tires to verify and maybe someone else can confirm.

    The spur gear has 53 teeth and the sensor picks up on that. So there is 53 pulses per tire rotation or the distance traveled for 1 pulse is the tire circumference/53. It looked to me that this number was off by a factor of 1000 so I came up with this.

    Diameter*PI/53*1000/12 = cal factor in feet.


    I suspect that 158.06755 feet is the theoretical number for 32 inch tires. I say theoretical because tires usually don't measure advertised size and then add a little squat to them with weight and the roll out (the distance traveled for one revolution) is shorter.

  6. #6
    Tuner in Training jaz|TUNING's Avatar
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    May 2022
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    I have bigger tires and can possibly test here soon. Waiting for the logging issue to be fixed, so it's currently back on DynoJet, but I can swap over to test.