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Gear Ratio Calculation

Discussion in 'Technical Q&A' started by Tifosi15, Sep 30, 2010.

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  1. Tifosi15

    Tifosi15 Formula 3

    Jul 15, 2009
    2,125
    Austin
    Full Name:
    Bryan
    #1 Tifosi15, Sep 30, 2010
    I guess this is a bit of a stupid question but does anyone know the formula to calculate gear ratios? I believe I have the correct one but have ended up with the wrong numbers in whatever I'm trying to find. Thanks in advance
     
  2. beast

    beast F1 World Champ

    May 31, 2003
    11,479
    Lewisville, TX
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    Rob Guess
    #2 beast, Sep 30, 2010
    Take the number of teeth on the driven gear (Output) and divide the number of the teeth on the drive gear (Input) to get the gear ratio.

    IE drive gear 25 teeth driven gear 45 teeth 45/25 = 1.8:1 ratio
     
  3. Fast_ian

    Fast_ian Two Time F1 World Champ

    Sep 25, 2006
    23,397
    Campbell, CA
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    Ian Anderson
    #3 Fast_ian, Sep 30, 2010
    What are you trying to find?

    Don't forget the final-drive ratio if you're after wheel speed...

    Cheers,
    Ian
     
  4. Tifosi15

    Tifosi15 Formula 3

    Jul 15, 2009
    2,125
    Austin
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    Bryan
    #4 Tifosi15, Sep 30, 2010
    My equation, (it would be easier to display if I could actually put up the equation)


    in finding velocity=60mph:

    (tire diameter)(RPM)(2pi)(60)
    divided by
    (2)(ratio of gear)(final drive)(60)(88)


    Technically the 60s can cancel
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,931
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #5 Steve Magnusson, Sep 30, 2010
    Last edited: Sep 30, 2010
    +1 (and, for some F, you would need to include the transfer gear ratio in your equation too)

    If it's something related to Ferrari, they have a lot of confusing "specs" in their documentation (that sometimes include the transfer gears and sometimes don't, etc.)

    I'd also add that while Rob describes a perfectly valid (and probably the clearest) convention, sometimes driver/driven gets used. For example, a 10-tooth pinion gear driving a 43-tooth ring gear could show up in the documentation as:

    43/10
    10/43
    43:10
    10:43
    4.30:1
    0.23256

    and all would technically be Okish.
     
  6. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,741
    #6 Mitch Alsup, Sep 30, 2010
    For a F355:

    Tire RPM=engine RPM/drop gear/crown gear/ratio gear/output gear

    Drop gear*crown gear*output gear ~= 4.441 Or what many would call the Differential ratio.
     
  7. Tifosi15

    Tifosi15 Formula 3

    Jul 15, 2009
    2,125
    Austin
    Full Name:
    Bryan
    #7 Tifosi15, Sep 30, 2010
    I would like to find engine speed
     

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