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  1. #1
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    Gear inches/gain ration + rpm = mph/kph

    I've seen this before but for the life of me can't remember where. I've googled and searched here for it but still have not found it. Can someone please point me in the direction of the said chart?

    I'm interested in knowing that if I gear my bike at X and am pedalling at X rpm I should be able to go X mph (given the ground is flat and my pace is sustained).

    I've seen a chart laying this all out. Or is there an equation I could use to figure this generally?

  2. #2
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    Gi*rpm/1063=mph

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    Quote Originally Posted by dutret
    Gi*rpm/1063=mph
    What am I doing wrong?

    example:
    75.5*100/1063 = 6.4


    I know when I spin at 100rpm with that gear inch I am going well beyond 6.4mph.

  4. #4
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    Quote Originally Posted by obstacle
    What am I doing wrong?

    example:
    75.5*100/1063 = 6.4


    I know when I spin at 100rpm with that gear inch I am going well beyond 6.4mph.
    the only way i could get his formula to make sense was to multiply the GI number by 2.54 to convert to metric...i don't know though, i'm not looking at any formula thangs...just guessing.
    Quote Originally Posted by Malibu Police Chief
    I don't like your jerk-off name. I don't like your jerk-off face. I don't like your jerk-off behavior, and I don't like you, jerk-off.

  5. #5
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    Quote Originally Posted by piwonka
    the only way i could get his formula to make sense was to multiply the GI number by 2.54 to convert to metric...i don't know though, i'm not looking at any formula thangs...just guessing.
    That gives me 18.4 as a result, which is interestingly about 6.4 from where my computer says I should be. What's wrong here
    Last edited by obstacle; 06-18-07 at 03:27 PM.

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    yeah that needs a pi in there sorry.

  7. #7
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    Quote Originally Posted by dutret
    yeah that needs a pi in there sorry.

    huh?

  8. #8
    spinlikehell mickster's Avatar
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    Quote Originally Posted by obstacle
    huh?
    He means the formula is Gi*pi*rpm/1063=mph

    The gear inch figure (eg 75.5) is the nominal *diameter* of the wheel - need to mulitply by Pi to find the inches travelled in one pedal revolution.

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    park ranger
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    oh yeah...circumference...lol.
    Quote Originally Posted by Malibu Police Chief
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    Quote Originally Posted by mickster
    He means the formula is Gi*pi*rpm/1063=mph

    The gear inch figure (eg 75.5) is the nominal *diameter* of the wheel - need to mulitply by Pi to find the inches travelled in one pedal revolution.


    Got it, that does the trick...thanks.

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    Isn't it 1056 and not 1063??? 1/(60min/hr)/(12in/ft)*(5280ft/mile) = 1056 (inch*hr/min*mile) Divide Gi*pi*rpm by this to get mile/hr?!?!

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    Senior Member CafeRacer's Avatar
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    There used to be a wicked website that had a calculater for that sorta thing. Miles and Kilos.......

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    Senior Member barba's Avatar
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    I made a little Excel chart that calculates rpm-->speed (and the other way around) for any given gear combo. PM me if you want a copy.

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    R900Campagnolo marcelinyc's Avatar
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    Senior Member Gomez308's Avatar
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    sheldon brown has a calculater that will figure this out for you.

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    Senior Member CafeRacer's Avatar
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    The prob with some of the charts already made is they dont go high enough into the RPMs.......

  17. #17
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    Quote Originally Posted by CafeRacer
    There used to be a wicked website that had a calculater for that sorta thing. Miles and Kilos.......
    maybe this? good to 160rpm.

    http://software.bareknucklebrigade.c...it.applet.html

  18. #18
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    sheldons works well

    http://www.sheldonbrown.com/gears/

    also, if you ever forget, just type in "bicycle gear calculator" into google and its the first one that comes up

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