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  1. #1
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    Long but light cranks: What route?

    I started a new "AM" build today.
    The bike is currently completely rideable and rides great. 29lbs for a 6" travel bike isn't too bad but I need to start putting the parts on that I really want.

    I need longer cranks. I have a 36" inseem. I'm 150lbs. I'm generally a very smooth rider.

    I've been rocking K-Force Light carbon cranks on my Foes ProLite with great success.
    I also have a few pairs of Gravity Lights, 1 pair of Race Lite SS, Race Face Ride XC, Shimano Deore, Hussefelt and LX cranks on my bikes and none of them are really what I'm after.
    I need something 175 or 180. External bearing. 104mm BCD. Light. 9spd compatible.

    Current considerations are:
    2010 XTR
    Stylo OCT
    Noir
    Six C

    What do you recommend? What are you against?

  2. #2
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    I'm with that cranks: http://www.chainreactioncycles.com/M...?ModelID=20679 - 180mm
    260lbs rider, no so smooth. I have feeling that I don't need anymore granny ring on climbs, but I didn't test them for long.

  3. #3
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    Quote Originally Posted by bmxconvert
    Current considerations are:
    2010 XTR
    Stylo OCT
    Noir
    Six C
    What do you recommend? What are you against?
    For easy (if a little boring life) Shimano XTR or XT, both come in 180mm lengths and both are (objectively at least) almost perfect. Light, reliable, easy to work with.

    Ignoring that Six C cranks and Profile Race cranks are lovely, very lovely. But profiles are a bit heavier than you're looking for.

  4. #4
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    I've got the option to get a set of Noir cranks for about $230 cranks in 175mm.
    XT cranks come in pretty similar in price but also come in at 180mm.

    I'm not sure I really need the 180mm arms. I ran 170's on my bikes for the last few years. I finally bumped to 175 this year and it's great for longer rides.
    I'm concerned that 180 is going to end up adversely effecting the maneuverability of my bike. It's easy to toss around now... will a longer separation help?

    As mentioned I'm 5'11, 150lbs with a 36-36.5" inseem. My height is in my rather lanky legs.

  5. #5
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    Quote Originally Posted by bmxconvert
    I'm not sure I really need the 180mm arms. I ran 170's on my bikes for the last few years. I finally bumped to 175 this year and it's great for longer rides.
    I'm concerned that 180 is going to end up adversely effecting the maneuverability of my bike. It's easy to toss around now... will a longer separation help?
    If you don't know what longer cranks will do, why do you think you need them? What about 175 makes them great for "longer rides" compared to 170?

  6. #6
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    Quote Originally Posted by craigsj
    If you don't know what longer cranks will do, why do you think you need them? What about 175 makes them great for "longer rides" compared to 170?
    170's feel fine on bikes that I spend most my time staning, such as on my Demo, Chase, or EMD SS.
    However, on bikes I sit for most the rides such as my Canaan or ProLite, I feel like my legs are moving in too short of a circle. Like I'm not maximizing the minimal power that I make. I find that my legs fatigue quicker. Once I swapped the 175 XT's(octolink) onto my Canaan I found that it felt far more natural. I felt less like I was on a circus bike.

  7. #7
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    Quote Originally Posted by bmxconvert
    I'm concerned that 180 is going to end up adversely effecting the maneuverability of my bike. It's easy to toss around now... will a longer separation help?
    IMO the biggest reasons to switch crank lengths on a mtb are ground clearance and fit, fit being the more important.

    Longer cranks give you a little more leg extension for a given seat height, which could be helpful to you as you've got long legs. The wider circle might let you use your back and thigh muscles better.
    With one crank down it also lowers your centre of gravity very (very) slightly. Not enough to worry about though.

    At cranks level the difference is negligible. You're talking having your feet an extra 2cm apart, it doesn't make much difference.

    Ground clearance depends on the frame. On a 6inch fs frame it's probably not much of an issue. Even at sag you're only looking at 20mm or so bb drop, so plenty of space under the cranks.

    Just take a set off a customer's bike and give it a go...

  8. #8
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    Shimano simply works

    If price is no issue - XTR works great. The XT crankset saves bling dollars and maintains strength. Shimano has never let me down and lasts awhile too.

  9. #9
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    Quote Originally Posted by Fix the Spade
    IMO the biggest reasons to switch crank lengths on a mtb are ground clearance and fit, fit being the more important.

    Longer cranks give you a little more leg extension for a given seat height, which could be helpful to you as you've got long legs. The wider circle might let you use your back and thigh muscles better.
    With one crank down it also lowers your centre of gravity very (very) slightly. Not enough to worry about though.

    At cranks level the difference is negligible. You're talking having your feet an extra 2cm apart, it doesn't make much difference.

    Ground clearance depends on the frame. On a 6inch fs frame it's probably not much of an issue. Even at sag you're only looking at 20mm or so bb drop, so plenty of space under the cranks.

    Just take a set off a customer's bike and give it a go...
    Thank you. That pretty much confirms everything I believed.
    I'm not concerned about crank strikes at all. My Demo, Chase, Session10 all have really low bottom brackets and I rarely strike pedals.
    Unfortunately, none of my local guys are running 180's except on singlespeeds and even then it's only 1 or 2.
    I'll see what I can dig up.

  10. #10
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    Quote Originally Posted by Fix the Spade
    IMO the biggest reasons to switch crank lengths on a mtb are ground clearance and fit, fit being the more important.
    This is right. A longer crank also moves your more forward on your seat in addition to lowering your saddle.

    Any differences in power are imaginary. There's a whole lot of confirmation bias with people who think longer is better.

    You cadence will be naturally higher on a shorter crank but the difference between 170 and 175 is only 3% so it's not something to worry about. The best reason to lengthen a crank is if your BB is higher than you like or if you'd like to shorten your reach/move your weight forward. Basically it's about fit.

  11. #11
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    With my saddle centered on the rails of a straight post and the post at proper height(slight bend in the knee) the ball of my knee sits approximately 10mm in front of my pedal spindle on my current 175's.

    Apparently I have freakishly long femurs..? I have no desire to push the saddle backwards, but I think that 180's are by far my best bet.

    Now if only there were a 180mm carbon crank.

  12. #12
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    Is that knee position a problem? Is you weight too far back?

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    The knee position doesn't seem to be a problem.
    I was run over by a car a year ago which blew out my knee so my right knee is finicky but it doesn't seem to bother it.

    Although... when fitting road bikes the knee position over the pedal spindle is used to determine crank arm length. Shouldn't it be similar on a mountain bike?

    My weight is pretty evenly distributed.

  14. #14
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    There's a lot of opinions on fit, road and MTB both. If it's not bothering you, it feels comfortable, and you are happy with your weight distribution, it doesn't seem like there's a problem to solve. I don't know or concern myself with that particular measurement. I have the same inseam as you and use cranks from 165 to 180mm depending on frame. 175 is the longest I have tried on MTB, but 170mm would be my natural choice. Depends on BB drop and CS length.

  15. #15
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    I think either way I go: 175 or 180 will be sufficient.

  16. #16
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    I rode my 180s for the first time yesterday for a longer time and I felt more fatigue, probably because I tried unwittingly to spin with the same cadence like my previous 175.
    It seems to me also that weighting and unweighting the cranckarms from side to side during descend cause much time because the larger circle. I felt shorter reach to the bar with 180s too.

  17. #17
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    Interesting. I had never thought about the cornering reaction time due to longer cranks. I have a hard time believing that I would notice it.

    I run 180mm cranks on my bmx bike and have no issues dropping cranks to lean into ramp transitions and set up for tricks and such.

    Right now the cranks at the top of my list are Race Face Turbine SL's.

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