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Wheels: Transmission: Rear Axle: Speed-Ratio-RPM Calculation

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  • Other: Wheels: Transmission: Rear Axle: Speed-Ratio-RPM Calculation

    I've made an update to my Excel spreadsheet.

    The link below will allow you to download the .xls file from my Google Drive.

    https://drive.google.com/open?id=0B_...WZIUVdhODFsNUU

    If not IM me with your email..

    Once again you can enter your tire size (metric) and 4 rear-end gear ratios and two transmission ratios (up to 5 speeds).

    Before it just had MPH that would give you engine RPM per Transmission Gear per Diff Ratio per Transmission

    Now you can enter an RPM and it will give you the MPH per Transmission Gear per Diff Ratio per Transmission

    The work sheet is locked except Grey cells so you can enter your data,



    Click image for larger version

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  • #2
    Speedometer Pinon Gear Tooth Calculation

    I've updated my spread sheet once again.

    My Google Drive link...

    Click here ==>> https://drive.google.com/open?id=0B_...WZIUVdhODFsNUU

    I have added a more detailed calculation for the speedometer pinion tooth calculation..

    Previously I had fixed values of 10 and 11. Unfortunately Studebaker's use 7 or 8 spline speedometer gears on the tail shaft

    Now you can enter your own values of the number of splines that are on your Speedo drive on the tail shaft..



    Speedo pinion teeth calculation is based on
    • Tire size
    • Differential gear ratio
    • Speedometer gear on the tail shaft ...


    Enter your tire size on A2, B2 and C2
    Enter your Differential gear ratios on E2 to E5
    Enter your tail shaft speedo spline count on G6 or G7




    Read your pinion tooth count for option 1 on M3 to M6
    Read your pinion tooth count for option 2 on N3 to N6

    Round up...



    for 205/60/15 tire with a 3.31 differential and 7 spline tail gear, you would use a 18.9 (19 rounded up) cable pinion gear.

    If you are still reading this and want a bit of knowledge, read ahead..

    All speedometers are calibrated at 60MPH for a speedometer cable speed of 1000 RPM. The speedometer should read 60MPH and the Odometer will register 1 mile every 60 seconds.

    Don't use your drill to test this out. The drive in the speedometer is magnetic and your drill electrical field as it spins at 1000RPM will effect the reading.

    Click image for larger version

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    Last edited by SScopelli; 06-10-2019, 07:16 PM.

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    • #3
      Here's a good tire size calculator to play with...

      Click here ==> https://tiresize.com/calculator/

      For Numeric; Alpha numeric; Euro; P-Metric; Euro-Metric or PMetric conversion..

      Click here ==> https://www.tirerack.com/tires/tiret...rsionchart.jsp

      I've uploaded the images of the parts book for the pinion and drive gear teeth count.




      You can see that they did change the drive gear tooth count (5, 7, 8) based on the rear gear ratio.




      Click image for larger version

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      Last edited by SScopelli; 06-26-2019, 02:38 PM.

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