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  1. #1
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    Crank length Funtime

    https://youtu.be/bjrNuPjACnU

    So I'm trying to figure out what crank length to use on my next bike. After much research it seems there's no good answer. I'm sure I'll get the "have a pro fit you" , but everything I've read says that doesn't necessarily work either. Or really does anything?

    I'm on 170mm now. Sometimes I feel I'd like to go longer. Not really sure why. I think it dates back to bmx days when a short crank wasn't good. Of course there were no gears.

    So I'd like some opinions as I've read many different ones from pro riders. For instance Sagan used 172.5 and so does Quintana, despite their height and I presume leg differences. Many others don't fit the traditional mold and many ametuers are the same.

    Different articles mention different terrain as a factor as well.
    I'm 5"10" and ride flats and climbs about equally.
    Last edited by greatestalltime; 2 Weeks Ago at 02:25 PM.

  2. #2
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    To quote the great Lennard Zinn:

    Quote Originally Posted by Lennard Zinn
    I could go on for hours about how no decent crank length test has ever been done by anyone and why it is actually virtually impossible to do a definitive one. Rider adaptation to the crank over time is required for each crank length to ensure optimal performance, but, if adaptation is allowed, it then becomes impossible to ensure that the subjects have exactly the same fitness level for the testing of each crank length. And a proper scientific test is double-blind, so the subject doesn’t know what they are testing. But with crank length, the subjects can feel the difference, and the bike has to be set up differently and the cadences used have to be adjusted for the different crank lengths. So the test riders are tipped off, which can also skew the results and make it not stand up to scientific scrutiny.

    So a clearly-explained logical examination of crank length and its relation to rider size may actually be about as good as can be done. There simply will never be a definitive test that will tell riders exactly what crank length will make them fastest.
    Technical FAQ with Lennard Zinn: When it come to crankarm length - no easy answers | VeloNews.com


    This is one of those topics where the answer you hear tells you more about the fitter/builder/speaker than about the equipment "best" for you.
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  3. #3
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    Quote Originally Posted by Marc View Post
    To quote the great Lennard Zinn:



    Technical FAQ with Lennard Zinn: When it come to crankarm length - no easy answers | VeloNews.com


    This is one of those topics where the answer you hear tells you more about the fitter/builder/speaker than about the equipment "best" for you.
    Thanks. That's kind of what I've gathered as well. Despite the fact some seem confident shorter is better and one pro, who I can't reminder, uses 180mm and swears by them and he wasn't overly tall.

    I think I'm moving up. The question is 175 or 172.5
    Last edited by greatestalltime; 2 Weeks Ago at 06:37 AM.

  4. #4
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    You didn't say what size frame you ride, but if you're 5'10", I'll assume you ride a road size 56 or maybe a 54. That would be around a 17 mountain bike size.

    Most road bikes in this size category come with 172.5 crank arms. Some touring bikes in this same size category come with 170 due to a lower BB. Mountain and some hybrids come with 175.

    Personally, I think there are better ways of separating yourself from extra cash than to change the length of your crank arms. If you really feel compelled to get longer crank arms, I wouldn't go any longer than 172.5. Longer may work for the pros. For the rest of us, it would probably only result in knee problems due to a sharper bend on the upstroke.
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  5. #5
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    My generalized rule of thumb is the more you spin, the shorter you want your cranks to be. Longer crank arms allow you to apply more force to the pedals, which is generally done at lower RPMs. YMMV
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    Quote Originally Posted by Lombard View Post
    You didn't say what size frame you ride, but if you're 5'10", I'll assume you ride a road size 56 or maybe a 54. That would be around a 17 mountain bike size.

    Most road bikes in this size category come with 172.5 crank arms. Some touring bikes in this same size category come with 170 due to a lower BB. Mountain and some hybrids come with 175.

    Personally, I think there are better ways of separating yourself from extra cash than to change the length of your crank arms. If you really feel compelled to get longer crank arms, I wouldn't go any longer than 172.5. Longer may work for the pros. For the rest of us, it would probably only result in knee problems due to a sharper bend on the upstroke.
    This will be for my new bike which is a 54. My current is a Giant tcr advanced sl in a medium. That's the one with the 170's.

    I'm more of a masher not a spinner so that's why I'm thinking of moving up a little in length.

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    Quote Originally Posted by Lombard View Post
    Personally, I think there are better ways of separating yourself from extra cash than to change the length of your crank arms.
    This is a perfectly excellent summary! Crank length is totally personal and very adaptable, with the "spinners like shorter" being just about the only "fact" that holds up to scrutiny.

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    Quote Originally Posted by Lombard View Post

    I wouldn't go any longer than 172.5. Longer may work for the pros. For the rest of us, it would probably only result in knee problems due to a sharper bend on the upstroke.
    Unless you are one of those guys can easily touch your butt with your heel I would be careful going with longer cranks. I am 6'5 with long legs and recently went down to 170's due to lack of range of motion from multiple surgeries.

  9. #9
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    there's a reason track cranks are 165.

    i like pedaling through turns too. so no longer than 172.5 for me.
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    I have 172.5's on my road bike and 165's on my TT bike. The put the 165's on to move the seat up a touch and keep the hip angle open. When in position and going hard breathing is easier which is awesome! Due to the stoic pacing of ITT's the shorter length was easy to get used to. Honestly I don't recall having to get used to anything save maybe slightly different gearing.

    With that said the 165's on the road bike would be a total disaster (for me at least). Sprinting or continuous hard accelerations would be a difficult to generate power so the 172.5's are staying. I'd say stay with what you're used to. I've borrowed 170's and 175's from friends and once you adjust saddle height and setback the difference was not noticeable. Again maybe slight gearing selection but that's it.

  11. #11
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    >>I'm more of a masher not a spinner so that's why I'm thinking of moving up a little in length.

    If that's the case, and you find 170 is inadequate, then perhaps you should consider 175 instead of 172.5. You may not notice 5mm, but will definitely notice 1cm.

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    too bad there isn't 5 million other crank length threads all over the internet to read up on.

  13. #13
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    But there are plenty of non-contributing posters.

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  14. #14
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    I have several bikes with crank lengths of 170 to 175 and while ere might be a difference in the ride quality/characteristics introduced by those differences between bikes, I'm not sure what they are and I couldn't tell you what the length of the crank is when I'm on the bike. Remember, 2.5 mm = 1/10 inch; not that much. Crank lengths < 180 and > 165 only matter to me for cornering clearance.

  15. #15
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    I'm 5'11" and I run 165. More aero and can corner harder. May not be relevant to most.

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    Quote Originally Posted by Kerry Irons View Post
    This is a perfectly excellent summary! Crank length is totally personal and very adaptable, with the "spinners like shorter" being just about the only "fact" that holds up to scrutiny.
    I'm not a spinner.

    More and more triathletes and time trialists are moving to shorter cranks because it allows you to get more aero without decreasing hip angle.

    That's the primary reason for the big push to shorter.

    That and relative measurements for shorter riders would mean many people riding 49 and 52s would be on 160s and the like.

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    Quote Originally Posted by woodys737 View Post

    With that said the 165's on the road bike would be a total disaster (for me at least). Sprinting or continuous hard accelerations would be a difficult to generate power so the 172.5's are staying.
    That makes no sense, not from a physiological perspective nor a physics perspective.

  18. #18
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    5'10 with a 31" inseam checking in. One bike came with 170 crank arms, my other 2 has 172.5. For me the 172.5 felt like I was slogging. I switched one of my 172.5's for 170 cranks and am much happier.

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    Quote Originally Posted by jason124 View Post
    5'10 with a 31" inseam checking in. One bike came with 170 crank arms, my other 2 has 172.5. For me the 172.5 felt like I was slogging. I switched one of my 172.5's for 170 cranks and am much happier.
    Are you a spinner or gear masher?

  20. #20
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    Quote Originally Posted by pedalbiker View Post
    That makes no sense, not from a physiological perspective nor a physics perspective.
    I have no coherent rebuttal. Just a short amount of time experience. I love them on the tt bike but, perhaps I just need to be in a higher gear on the road bike while sprinting etc...higher foot speed v. higher torque type thing.

  21. #21
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    Quote Originally Posted by pedalbiker View Post
    More and more triathletes and time trialists are moving to shorter cranks because it allows you to get more aero without decreasing hip angle.

    That's the primary reason for the big push to shorter.

    That and relative measurements for shorter riders would mean many people riding 49 and 52s would be on 160s and the like.
    Since only a small fraction of cyclists are triathletes and time trialists, it is unlikely that's "the primary reason for the big push to shorter." There was a "everybody should go longer" thinking that came along with the MTB use of longer cranks, and now many have realized it didn't translate to the road that well.

    Not sure what your "relative measurement" comment is based on. Once again: there is no valid research showing the benefit of longer or shorter cranks associated with body measurements.

  22. #22
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    Quote Originally Posted by bvber View Post
    Are you a spinner or gear masher?
    I am a spinner.

  23. #23
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    Quote Originally Posted by jason124 View Post
    I am a spinner.
    Spinner on uphills, somewhere in between spinner and masher on flats.
    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein

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  24. #24
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    Between the range of widely available cranks it doesn't matter what you run when you're an average size man. Pick the ones on sale.


    I find the really short cranks, like the modified ones, cobb or rotor really appealing. Using the 9.7% formula <5'4 riders should be on ~145mm cranks. A frame built around those proportional cranks (and proportional wheels) can have a ~240mm BB height, over an inch lower, with the same lean angle as a 56cm 700c bike. Sweet!

  25. #25
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    Quote Originally Posted by Kerry Irons View Post
    Since only a small fraction of cyclists are triathletes and time trialists, it is unlikely that's "the primary reason for the big push to shorter." There was a "everybody should go longer" thinking that came along with the MTB use of longer cranks, and now many have realized it didn't translate to the road that well.

    Not sure what your "relative measurement" comment is based on. Once again: there is no valid research showing the benefit of longer or shorter cranks associated with body measurements.
    Nah, pretty sure that the vast majority of posts I've read over the last few years about shorter crank arms center on that very reason. So yes, in terms of public perception and knowledge about the subject, it's a valid assertion.

    And relative meaning relative. A 5'2" rider will be on a significantly smaller bike than a 5'11" rider, yet said bikes likely come stock with 170 and 172.5mm cranks, respectively. It's completely disproportional.

    I don't know why you're going all fallacious about valid research. It's pretty cut and dry that crank length is a bike position issue, the same as stem length and top tube length and everything else.

    But if you want to argue about valid research concerning position, well, a wall would be a more interested audience.

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