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  1. #1
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    crank length effect?

    as per title that I've written
    I want to ask two things...
    what is the effect from crank length in cycling single speed/fixed gear bike?
    and what is the minimum length for crank arm should be? is it 165 or 150...
    thx...

  2. #2
    eye try itri's Avatar
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    Remember Physics from Grade School? 2nd class levers, load in the center, fulcrum and force on opposite ends? Same thing here. The further you move the force from the load the more efficient the lever becomes.

  3. #3
    * adriano's Avatar
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    good ones shorter than 165 are hard to find. putting everyone between 165 and 180 is ridiculous. i ride 160s.

  4. #4
    old legs
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    Quote Originally Posted by adriano View Post
    good ones shorter than 165 are hard to find. putting everyone between 165 and 180 is ridiculous. i ride 160s.
    just out of curiosity how tall are you and whats your inseam?

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    * adriano's Avatar
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    my inseam is 74cm.

  6. #6
    Mission Creep wmgreene85's Avatar
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    hes a tiny little boy

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    * adriano's Avatar
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    who said i was male?

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    Mission Creep wmgreene85's Avatar
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    your user name, and the way you try and be super clever is a big indicator. and now it all makes sense. its like reading the bible for the very first time.

  9. #9
    * adriano's Avatar
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    youre making me blush. at least buy a girl a drink first.

  10. #10
    ℞ ♥ squeegeesunny's Avatar
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    wm, if i were you, i'd stop arguing. adriano is clearly either a female or a homosexual male who likes to paint his nails and has a very petite physique.



    Quote Originally Posted by Johhny B View Post
    dude u need that trixie tool its the best tool ever it even comes with a bottle opener ! dude all the messengers reccomended it to me and evr since i got it im basically a mechaninc now and all the bike shops want me.

  11. #11
    dsh
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    Like a girl would ever use a lever actuated bell.

  12. #12
    * adriano's Avatar
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    Quote Originally Posted by maury View Post
    adriano...



    you are not the father!
    ..

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    Fresh Garbage hairnet's Avatar
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    i should be riding 200mm cranks but ive got 165s
    Quote Originally Posted by Scrodzilla View Post
    I'd rather ride a greasy bowling ball than one of those things.
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  14. #14
    Mission Creep wmgreene85's Avatar
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    sqeege, me and adriana go way back. stop interjecting: we almost have everything all worked out in court

    in all fairness, I think adriano has alot of good comments to bring to the table. And I appreciate the little sub community we all have in here. : )
    Last edited by wmgreene85; 08-01-10 at 02:48 PM.

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    * adriano's Avatar
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    why did you have to runaway to san francisco to find a yourself a new bear and a haro corporation coltello? ill never find a better bottom.

  16. #16
    The road less Taken Shortsocks's Avatar
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    I love how this thread went from crank length to finding better bottoms.......

    Socks
    The bicycle is a curious vehicle. *Its passenger is its engine. -John Howard

    When I see an adult on a bicycle, I do not despair for the future of the human race.- H.G Wells

    The bicycle, the bicycle surely, should always be the vehicle of novelists and poets. -Christopher Morley

  17. #17
    GONE~
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    Esotericism ftw!

  18. #18
    The road less Taken Shortsocks's Avatar
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    Mmmm
    Last edited by Shortsocks; 08-02-10 at 12:02 AM.
    The bicycle is a curious vehicle. *Its passenger is its engine. -John Howard

    When I see an adult on a bicycle, I do not despair for the future of the human race.- H.G Wells

    The bicycle, the bicycle surely, should always be the vehicle of novelists and poets. -Christopher Morley

  19. #19
    King of the Hipsters
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    Crank length corresponds to the radius of a circle.

    Longer crank arms make a larger circle.

    A larger circle means your feet travel farther every time around.

    Traveling farther takes more time.

    Therefore, longer cranks mean easier pedaling for a given gear, but at the price of a much slower spin and a less elegant spin.

    Mountain bikes traditionally have 175 mm cranks because they have gears and the longer cranks mean more torque for less effort.

    Dedicated track bikes tend towards the shorter 165 mm length because it means a faster more elegant spin.

    I ride both a 175 mm crank and a 170 mm crank on different bikes.

    I regret the 175 mm crank on a fixed gear bike because it severely restricts my spin.

    Go with 170 or below...and don't think 5 mm or 10 mm doesn't make a big difference.

    As for your leg length, if you fall within the 95th percentile, which 95 percent of us do, leg length or leg proportions have little to do with how your bike feels to you.

  20. #20
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    Quote Originally Posted by Ken Cox View Post
    Crank length corresponds to the radius of a circle.

    Longer crank arms make a larger circle.

    A larger circle means your feet travel farther every time around.

    Traveling farther takes more time.

    Therefore, longer cranks mean easier pedaling for a given gear, but at the price of a much slower spin and a less elegant spin.

    Mountain bikes traditionally have 175 mm cranks because they have gears and the longer cranks mean more torque for less effort.

    Dedicated track bikes tend towards the shorter 165 mm length because it means a faster more elegant spin.

    I ride both a 175 mm crank and a 170 mm crank on different bikes.

    I regret the 175 mm crank on a fixed gear bike because it severely restricts my spin.

    Go with 170 or below...and don't think 5 mm or 10 mm doesn't make a big difference.

    As for your leg length, if you fall within the 95th percentile, which 95 percent of us do, leg length or leg proportions have little to do with how your bike feels to you.
    Pretty much how I understand it too. It has to do with more leverage, a longer duration on each power stroke. What I'm not thoroughly convinced of is that a longer crank arm length is more power, because I also think a cyclists leg strength and fitness come into play, add that there might be a gear where the cyclist just isn't strong enough or fit enough to get an optimal power stroke ? It also has to do with matching each individuals pace/cadence with the optimal gearing and crank arm length. Unfortunately we don't have the equipment to measure this, all we can do is play around and find what we think to be the best setup. Another thing too, is bottom bracket ground clearance. not all frames have the same clearances from the ground and that might even apply to frame size in the same model bike as it may also apply to bike brands & models. 5 mm differences in crank arm length is .2 inches, so a bike with a 10 1/2" bottom bracket road clearance might only be able to accommodate 165 mm crank arms, while a bottom bracket road clearance of 11+ inches would allow for longer crank arm length & choices.

  21. #21
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    as I know in riding fixed gear bike, the crank length is quite important, right? especially for those who using straight fork.
    the shorter crank length will avoid us from pedal strike to the wheel or maybe the pedestrian... am I right...
    actually, now I want to try to shorten my broken threadless 175 crank arm into 160mm or maybe 150mm
    right now I'm riding 170mm crank arm

  22. #22
    Senior Member Johnny Nemo's Avatar
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    There is an argument that shorter is better for a fixed gear as it's less prone to pedal strike when cornering, and gives you better spin. I ride 160 on fixed and 170 on road bike.

  23. #23
    Disgruntled Grad Student seejohnbike's Avatar
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    proper crank arm length? long story short: it depends.

    Are you a lanky giant, or a the size of a jockey? The proportions of your leg will determine how you pedal, and what dimension of crank will allow you put the most power down.

    do you spin? do you mash? Do you keep a cadence somewhere in the middle? Regardless of whether shorter cranks are good for spinning, if spinning isn't your style, then they will do you little good. Vice-versa...

    Do you plan on riding on the track? do you plan on riding on the street? Both?

    What kind of bike is it going on, and will you specifically have to compensate for a low bottom bracket?

    My suggestion: Unless you're specifically compensating for one or more of these criteria, get cranks that fit your body. Off the peg track bikes come with varrying crank lengths, in accordance with frame size, and these bikes are already designed to have high bottom brackets to avoid pedal strike, and to accommodate some degree of spinning.

    On toe overlap: work around it/learn to deal with it. For some frames, it's practically unavoidable. Adjusting your timing/re-evaluating your pedal/clip/shoe combo seems like an easy enough fix, and allows you to maintain optimal crank setup.

    Pedal-strike: Again, unless your bike is at significant risk, or you're riding on a steep velodrome, don't worry about it. I wish I had more specific data to present, but I have semi-anecdotal/semi-empirical data that suits me just fine. I ride a 58cm, with a 58mm bb drop/overall bb height of 292 mm. I have only experienced pedal-strike once, at speed, in a race/crit, taking a tight corner. It wasn't enough to bring me down, but it was enough that I definitely noticed the pedal tap the pavement, and I knew to back off a bit.

    Why this matters: This was over the course of several laps (20 in all, iirc), all of which at similar speed, on the same problematic corner, continually pushing to see how fast/tight I could take the turn. It wasn't exactly scientific, but it was approaching something like it, repeat trials and all. The lean angles I was achieving were definitely more extreme than most of the other riding I do, ever. I'm not completely blasť about pedal-strike, but now what kind of turns I truly need to worry about...

    I don't mean to discount others' accounts of (or of avoiding) pedal-strike, but in most of the other stories I've heard, pedal-strike occurs on a one-off sharp turn, or evasive maneuver. Although every little bit of clearance helps, at the end of the day, the difference between cranks people are considering is usually only down to half a centimeter. At some point, if you take a one-off sharp turn, you could be going down no matter what.
    If we knew what we were doing, it wouldn't be called research.

  24. #24
    Senior Member
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    Seems there are a lot of theories that are grounded in sound logic.

  25. #25
    To be continued Dannihilator's Avatar
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    170 on the mtb, 170 on the pista and 165's on the 930, though I would like to find 170's of the same type of crank.

    Also have to remember one's knee tract.
    Strike like an eagle and sacrifice the dove.
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