Testing: Tire / Speedo / Differential Calculator - try it out!

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  1. #1
    CelicaSupra.com Member Deanfun's Avatar
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    Cool Testing: Tire / Speedo / Differential Calculator - try it out!

    Well, in a fit of boredom I rebuilt a spreadsheet I made a couple years ago and inadvertently deleted. Using data gleaned from the forum I have compiled a one-stop calculator for changing tire sizes, speedometer gears, and differentials.

    The excel sheet will tell you how far off your speedo is based on tire, differential, and speedometer gear combination. It will calculate and recommend the best speedo gear combination to use for your given tire/wheel/differential setup. While we aren't all changing tires and differentials all the time, it should be a nice thing to have around.

    Instructions are included in the spreadsheet, although it's pretty straightforward.

    Part numbers are good to go!

    I am looking for you guys to test it out and see if there are any questions or suggestions you guys have for improving the sheet. Have fun!

    Nov 7, 2016.
    Literally 10 years later, this thread has over 900,000 views. I should probably make something I'm a little more proud of.

    Now the file will live forever:
    https://drive.google.com/file/d/0B7I...ew?usp=sharing
    Last edited by Deanfun; 11-07-2016 at 07:48 PM.
    Dean L.
    1985 Toyota Supra - Hidden Content
    1987 Toyota Land Cruiser BJ73
    2007 Lexus LX470

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  3. #2
    CelicaSupra.com Member
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    Very nice Dean !!!!!!!

    Thanks !

  4. #3
    Awesome work Dean...stickied for now!!!

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  6. #4
    CelicaSupra.com Member Deanfun's Avatar
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    Spreadsheet has been updated to correct minor formula error.

    Thanks for the sticky!
    Dean L.
    1985 Toyota Supra - Hidden Content
    1987 Toyota Land Cruiser BJ73
    2007 Lexus LX470

  7. #5
    CelicaSupra.com Member charles q's Avatar
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    For those of us without Excel (just the viewer) what do we do?
    C.Q.
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  8. #6
    CelicaSupra.com Member Deanfun's Avatar
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    Quote Originally Posted by charles q
    For those of us without Excel (just the viewer) what do we do?
    The google spreadsheets are still pretty primitive, so I'd say you're just about out of luck. I'll take a look into it tomorrow and see what can be done.
    Dean L.
    1985 Toyota Supra - Hidden Content
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    2007 Lexus LX470

  9. #7
    CelicaSupra.com Member swank's Avatar
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    this is the coolest thing I've ever seen
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  10. #8
    CelicaSupra.com Member SupraFiend's Avatar
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    Yep, very cool. Super handy for anyone whos gone to a different tire diameter and rear end. It works too, it produces the right result for my 225/50-15 and 4.1 rear end combo, which is the stock 4.3 speedo gears.

    Dean forgot to mention that all of the part numbers are listed and up to date now too (Dean, edit your first post to fix that).
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  11. #9
    CelicaSupra.com Member charles q's Avatar
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    Could somebody post the results for my 245/50-16 and 3.73 diff? Don't have excel
    C.Q.
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  12. #10
    CelicaSupra.com Member Deanfun's Avatar
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    Quote Originally Posted by charles q
    Could somebody post the results for my 245/50-16 and 3.73 diff? Don't have excel
    The best combination for you is 11 tooth and 32 tooth. This puts you at 99.17% accuracy. Rigt now you are at ~89% accurate, meaning at 60mph your speed reads 53mph.

    11 33481-22020
    32 33403-19255

    Assuming you've got a 4.30 gear-set in their ('84 5-speeds came with 4.30's, right?) you'd have to change both gears out. From what I know, the 11-tooth gear requres pulling the tailshaft, but the 32-tooth does not.
    Dean L.
    1985 Toyota Supra - Hidden Content
    1987 Toyota Land Cruiser BJ73
    2007 Lexus LX470

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