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Thread: crank length

  1. #1
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    crank length

    I've always ridden a 175 (both road and mtn) but now I'm reading that 180 is the preferred length for SS set up. Does it really make a difference? I ride a 29er SS and do quite a bit of climbing and some long flats as well. Is this something to worry about when selecting a new crank?

  2. #2
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    I'm interested in where you found info about 180's being the preferred length? I've heard people talk about benefits but haven't been able to find any articles or testing results. FWIW I have 175 on one ss and 180 on another ss I just bought. I did notice a difference between the two lengths in effort required (the 180 required more perceived effort), but that could just be my legs getting used to the new length plus about 100 other things so don't know exactly how much it affected my ride but I did notice a difference.

    I was thinking about selling the 180 and getting 175 so would like to see what people say here myself.

  3. #3
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    I haven't read any official report but when I've inquired with online stores regarding ss cranks they say "everyone's going with 180's now". And my LBS also told me the way to go is 180...but nobody has told me why. I don't want more effort...I would prefer it to be the other way around.

  4. #4
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    180s give you a longer leverage arm... you put in less force, but have to spin a larger circle...
    I went with 180s from 175s. Gearing obviously is more important, but I was looking for an extra bit of help on the climbs.... I dig it big time.

    I'll let the physics/engineer-types weigh in here (the whole torque thing)

    I do find it easier to climb, but the 15 min. road ride to and from the trailhead is more of a PITA... you also get more pedal strikes (barely).

  5. #5
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    To me it's about proper fit / ergonomics.

    If you're body is bigger, you get a larger frame. For example no one 6' tall would ride a 15" frame. Same thing for cranks. Got long legs? Get long cranks.

    This is MY OPINION. I've been riding 195mm cranks (not a typo) for the past 16 years and love them. I have a 36" inseam. If you have short legs, don't get long cranks.

    Any adjustment in the circle your legs spin will need to be adapted to. At first, long cranks will absolutely feel wrong, at least they did in my case. But after riding them for a couple months (way back in '94), I found I could climb things that none of my riding buddies could climb. I felt like I was cheating.

    --sParty

    P.S. Re: pedal strikes... if your crank length is correct for your leg length but you suffer too many pedal strikes, then your bottom bracket is too low. Don't confuse a frame not being designed for you with correct crank length. Two different issues. Yes, it's expensive to have a custom frame designed to employ long cranks, but regardless, this is the "right way." Again, my opinion.
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  6. #6
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    Quote Originally Posted by sprocket47
    ... they say "everyone's going with 180's now"...
    Just because the cool kids are doing it... I heard that speech about wagon wheels, too.

    I do suspect those of larger physical stature might enjoy a bit more leverage cranking one gear, though.

  7. #7
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    I have short legs for my height (30 inch inseam) and I ride 175s. Would not want any bigger.

    My wife is short, and she prefers 170s.

    Sure, bigger cranks give you a little more leverage, but when you're spinning half the length of your leg it's slightly uncomfortable.

  8. #8
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    Ride more!

  9. #9
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    Here's a slide show covering crank length studies. It summarizes research involving power, cadence, efficiency, fatigue, and pedaling technique. The short version for ADD types is that crank length has very little effect and that you can choose your desired length for whatever reason you prefer. You will not produce more power with a longer crank as is popularly believed. You do need to understand the gearing and cadence ramifications. There is plenty of misunderstanding there as well.

    The popular belief that cranks should be proportional to body size is a myth. It doesn't hurt, provided it doesn't cause pain or injury, but it doesn't help either.

  10. #10
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    Quote Originally Posted by craigsj
    The popular belief that cranks should be proportional to body size is a myth. It doesn't hurt, provided it doesn't cause pain or injury, but it doesn't help either.
    Actually, there is new research that indicates a shorter crank arm length might be beneficial for mtb applications. I posted on this before -- link is here. The bottom line is that while peak power was not affected by crank arm length, the time to generation of peak power was faster with a shorter crank arm length, translating to a performance advantage for shorter crank arm lengths. Follow the links and have a read if you're so inclined -- certainly interesting and seems to be a well controlled study -- well, as much as human performance experiments can be.
    "The plural of anecdote is not data." -- Attributed to various people in a variety of forms, but always worth remembering...

  11. #11
    dwt
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    Their are two basic theories:

    The Sheldon Brown theory that crank length makes no difference on a geared bike, only on a single speed.

    http://www.sheldonbrown.com/cranks.html

    And the theory that it makes a difference on any bike and should be proportional to leg length.

    http://bicyclecranklength.blogspot.com/
    http://www.nettally.com/palmk/crankset.html

    Who knows? I don't race anymore, have ridden 175mm cranks on 26" wheel bikes for close to 20 years, and have little inclination to change either.
    Old enough to know better. And old enough not to care. Best age to be.

  12. #12
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    I switch between 170, 175, and 180mm cranks depending on what bike I am riding. Personally, I'd just stick with 175mm if I were building a new single speed. 180mm cranks feel different, but it's not like it will get you to the top of the hill any easier. Another reason is if you have mulitple bikes or like to swap parts - I wouldn't want the 180mm cranks on my full suspension bike (a Niner WFO).

  13. #13
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    I really, really want to try longer crank arms. I've only ridden two lengths and only one size offroad. I'm six foot-ish with a 33ish inseam. 175s feel perfect offroad, but that is just ignorance talking.

    I do know that I much prefer 170s for SSing on road. It is so much easier to spin faster that I can ride faster without much effort. Of course, this reasoning is why I want to try 180s. Spinning isn't quite as important offroad, but I do rely on spinning bursts on a regular basis. Longer cranks might interfere with that, but they also might help me clear things.

    I do think it is fair to say that this would be difficult prove either way, as both will have some performance pros and cons in addition to personal experiences, which is probably the biggest hurdle to clear.

  14. #14
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    Quote Originally Posted by PeT
    Actually, there is new research that indicates a shorter crank arm length might be beneficial for mtb applications. I posted on this before -- link is here. The bottom line is that while peak power was not affected by crank arm length, the time to generation of peak power was faster with a shorter crank arm length, translating to a performance advantage for shorter crank arm lengths. Follow the links and have a read if you're so inclined -- certainly interesting and seems to be a well controlled study -- well, as much as human performance experiments can be.
    Interesting. The article you linked to referred to two research studies, the first by Martin that wrote the slides I linked to earlier, and a newer study by Macdermid. I haven't been able to get the Macdermid paper yet. I have read that cyclists that greatly value fast times to maximum power tend toward shorter cranks. I'm interested in how reliable their 27.8% figure is and how they value it in the context of overall MTB performance.

    Quote Originally Posted by dwt
    The Sheldon Brown theory that crank length makes no difference on a geared bike, only on a single speed.
    Sheldon Brown did not say that crank length makes a difference on single speed. Quite the contrary, he said:
    Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.
    Single speed bikes have gearing too!

    As for who knows, researchers know and Lennard Zinn doesn't.

    Quote Originally Posted by umarth
    Longer cranks might interfere with that, but they also might help me clear things.
    I think of crank length in technical situations as a zero sum game. It doesn't improve power but it does change the amount of foot travel between dead spots. That will improve some situations but hurt others IMO. A longer crank will lower the saddle which is probably good, but it will move the foot forward which may not be especially on a long chainstay bike. I think of crank length as another fit variable; the right choice may vary from frame to frame and with intended use.

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