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  1. #1
    Senior Member Drummerboy1975's Avatar
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    The cranks too short?

    I'm looking at a vintage bike for sale locally and the guys telling me that the crank is too short for him and that's why he's selling. What does he mean? Or do cranks actually come in different sizes?

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    They certainly do. Most manufacturers provide adult crankests in a range of 165mm-175mm, in 2.5mm increments. Some manufacturers offer as high as 180mm. Older cranksets, offered in imperial measurements, usually range from 6-1/2" to 7" in 1/4" increments, The size is measured from the center of the spindle hole to the center of the pedal hole and is typically stamped on the back of the arm.

    Length of crankarm is usually established based on the length of the thigh, however personal preference and discipline also play big parts. Cyclists who like to spin typically choose a slightly shorter crankarm than what eould be considered normal while low cadence and high torque riders often prefer a slightly longer crankarm. Track cyclists typically favour slightly shorter arms while TT riders and ATB riders generally go slightly longer.
    Last edited by T-Mar; 01-24-12 at 09:04 AM. Reason: added 2nd paragraph

  3. #3
    rhm
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    Yes, cranks come in a narrow range of sizes. You are unlikely to find anything shorter than 165 mm or longer than 175 mm. The range of cranks available is much too narrow to allow most riders to chose crank arms proportional to some body measurement, so don't worry about that. In my opinion, shorter is better for all road riding. Serious off-road riding sometimes requires a longer crank arm.

    Other forum members will chime in to say longer is better. Don't listen to them.

  4. #4
    Senior Member ColonelJLloyd's Avatar
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  5. #5
    Senior Member KOBE's Avatar
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    Longer is better.

    An easy change, sounds like he is rationalizing a new bike.

  6. #6
    Senior Member miamijim's Avatar
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    He probably means the frames to small....
    WWW.CYCLESPEUGEOT.COM 2005 Pinarello Dogma; 1991 Paramount PDG 70 Mtb; 1976? AD Vent Noir; 1989 LeMond Maillot Juane F&F; 1993? Basso GAP F&F; 1989 Terry Symmetry; 2003 Trek 4700 Mtb; 1983 Vitus 979

  7. #7
    incazzare. lostarchitect's Avatar
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    He's saying that when he smokes crank, it doesn't do as much for him as it used to. He was probably trying to find out if you have a lab in your basement.
    1964 JRJ (Bob Jackson) San Remo Plus, 1989 Trek 520, 2000ish Colian (Colin Laing), 2013 Velo Orange Pass Hunter

  8. #8
    Senior Member Drummerboy1975's Avatar
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    Ok.

    Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?

  9. #9
    Wookie Jesus inspires me. Puget Pounder's Avatar
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    Quote Originally Posted by Drummerboy1975 View Post
    Ok.

    Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
    Not following here. What do you mean?

  10. #10
    rhm
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    Quote Originally Posted by KOBE View Post
    Longer is better.
    told you! Don't listen to him!

    Quote Originally Posted by Drummerboy1975 View Post
    Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
    No to the first, yes to the second.

    No, with shorter crank arms you have (a tiny bit) less leverage, so turning a big gear is (a tiny bit) harder but your feet travel (a tiny bit) slower at a given cadence; so when you speed your feet up to their normal speed you increase your cadence and the bike's speed. In other words, shorter crank arms are better for a higher cadence.

    Yes, assuming a standard BB height you will want your seat higher if you use shorter crank arms. Shorten your crank arms by 5 mm, raise your seat by the same amount.

  11. #11
    incazzare. lostarchitect's Avatar
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    Quote Originally Posted by Drummerboy1975 View Post
    Ok.

    Wouldn't it be easier to just ride on the big gear of your crank and raise ones seats?
    Not understanding you. We're not referring to the size of the chainring, it's the length of the crank we're talking about. The crankarm is the thing that attaches the pedal to the bottom bracket. The chainring is the ring of teeth around the bottom bracket that the chain rides on.

    1964 JRJ (Bob Jackson) San Remo Plus, 1989 Trek 520, 2000ish Colian (Colin Laing), 2013 Velo Orange Pass Hunter

  12. #12
    Senior Member Drummerboy1975's Avatar
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    Yes we are all talking about the same thing. But going to thwarting larger chainring changes cadence.

  13. #13
    incazzare. lostarchitect's Avatar
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    Thwarting? I dunno man.
    1964 JRJ (Bob Jackson) San Remo Plus, 1989 Trek 520, 2000ish Colian (Colin Laing), 2013 Velo Orange Pass Hunter

  14. #14
    Senior Member ColonelJLloyd's Avatar
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  15. #15
    rhm
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    Quote Originally Posted by lostarchitect View Post
    Thwarting? I dunno man.
    You just don't get it, man. Probably just over your head.

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    2.5mm=0.098425" Not really as big a deal as some would make it out to be.

  17. #17
    Senior Member Grand Bois's Avatar
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    Quote Originally Posted by Drummerboy1975 View Post
    Yes we are all talking about the same thing. But going to thwarting larger chainring changes cadence.
    What?

  18. #18
    Senior Member Drummerboy1975's Avatar
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    Quote Originally Posted by Grand Bois View Post
    What?
    Auto correct on my phone Guys.

    Replace the word "thwarting" with "the".

  19. #19
    rhm
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    This might be a good time to hit that button that says "Edit Post." Your call.

  20. #20
    aka Tom Reingold noglider's Avatar
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    You don't read my signature anyway, do you?

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  21. #21
    Wookie Jesus inspires me. Puget Pounder's Avatar
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    It's a circus in here.

  22. #22
    Rolling along fas2c's Avatar
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    I am thinking that crank length has the most effect to long distance riders who spend hours at a time in the saddle. What may seem as a minor inconvience to those riding for an hour or less becomes a very painful problem to LD riders. A small change of a few cm.s can have a dramatic result.

    I have read discussions too concerning the need of LD riders to pedal in concentric circles and fine tuning the crank length can help with this. I am sure some of this can be mental but I am sure some of it may hold a bit of truth to it as well.

    To me the guy is justifying the purchase of a new bike. Cranks are easy to swap.

  23. #23
    rhm
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    Quote Originally Posted by fas2c View Post
    I am thinking that crank length has the most effect to long distance riders who spend hours at a time in the saddle.
    Yes, I think that is true. Riding a century on 170's definitely seems to leave my legs sorer than a century on 165's.

    But there's also a matter of getting used to something. I could get used to 170's or longer ones, and I'm sure it would do me no harm; but now that I'm used to 165's and shorter the 170's do make me sore on long rides. Commuting on 170's is not a problem, though.

    Quote Originally Posted by fas2c View Post
    To me the guy is justifying the purchase of a new bike. Cranks are easy to swap.
    You're probably right about that.

    Frankly, Drummerboy, crank arm probably doesn't matter enough to think about it this much. Whatever crank arms are on the bike in question, if you like it, you will not have a problem with the crank arms.

  24. #24
    Senior Member JReade's Avatar
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    How often do you type "thwarting " so it trumps "the"on autocorrect?

    Or you are typing that bad ...
    Jesse

  25. #25
    Senior Member Bill Kapaun's Avatar
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    Quote Originally Posted by crazyb View Post
    2.5mm=0.098425" Not really as big a deal as some would make it out to be.
    It can be if you have bad knees. I don't have full range of motion in my R knee, and the difference between 170 & 165 is simply amazing.

    Since you raise the seat up 2.5mm, the bottom pedal is 5mm further away.

    One can do too much of a "good thing" however. My cadence actually slowed a couple RPM when I went to 160's.

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