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Thread: Crank Length Q

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    Default Crank Length Q

    Bear with me on this one . . .
    I've noticed a tiny, tiny pause at the top of my pedal stroke. I've been looked at a few times to adjust saddle height + fore/aft position. Raising my saddle helps reduce that pause but starts to irritate my hamstrings after an hour or so (I'm pretty This got me to wondering if a shorter crank would be helpful.

    Well, I finished up my track bike and popped some 167.5mm cranks on it. Same saddle height, setback and saddle-to-bar drop. Things feel smoother at the top of the stroke and all around better (especially at a higher output) but I'm left wondering if it feels better because I'm on a fixed gear and I'm being "forced" through the top of the pedal stroke.

    The obvious test would be to grab some 167.5 road cranks and throw them on my bike but they're hard to come by -- and I really don't want to throw down the $$$$$$ for DuraAce (or Sugino) cranks just to try it out.

    There's a bunch of cheaper cranks available in 165mm lengths. The question is whether its worth it to drop the cash on one of those options to test it out or if I'm thinking about this all wrong.

    Thanks
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    Could you swap the track cranks (with a road chainring) onto the road bike just as a test?
    DT

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    Default Re: Crank Length Q

    What length do you have on the road bike now?

    If you google crank length, there are many bike fit pundits talking about the benefits of shorter cranks. Some of them have nifty formulae to calculate what ought to be your ideal length.

    Anyway, I always had 170 road cranks (mainly because Campag's shortest until recently was 170) but, like you, felt that 165 track cranks were much better for me. A few of the calculation formulae proposed on the web put my ideal length at much less than 160 although I didn't bother remembering the actual numbers since they were not readily available. Long story short, I got 165 for my new road bike and can't be happier.

    Biomechanic theory apparently puts efficiency over power (leverage). I understand that shorter cranks give you better efficiency, and the benefits overweigh those of higher leverage / power per pedal stroke of longer cranks since one tends to deal with a few pedal strokes during a ride. Also, higher efficiency apparently makes you a better climber.

    When I used to race BMX, I had 172.5 and thought, at the time, was the right length compared to 170. I think I would not go any longer than 165 now, regardless of the type of bike.
    Chikashi Miyamoto

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    Default Re: Crank Length Q

    I'm 6'1" and have a 34" inseam. I use a 165 crank length on all my bikes. Knees have never been this happy. Go for it.
    Guy Washburn

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    Default Re: Crank Length Q

    @Chik I'm currently running 170mm Ultegra cranks (mid-compact). The formulas I've looked at put me right around 170mm.
    @david I'll try swapping the cranks but there's a big Q-factor difference between Ultegra and Miche (IIRC 146 vs 131) they might not fit but its worth a try huh?
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    The formula based on height yields 170 for me, but suggestions referenced here put me at about 159.
    CRANK LENGTH - Which one? - The Steve Hogg Bike Fitting Website
    Disclosure: I was fitted by a Hogg trained fitter on an older bike with 170 Campag cranks, but he did not say anything about crank length probably for practical reasons mentioned previously.
    Chikashi Miyamoto

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    Default Re: Crank Length Q

    Thanks Chik!
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    There's no formula that will determine your ideal crank length, and you're a perfect example of why. There's a theory (mostly just theory) of how a particular crank arm length gives you the most power translation, but more importantly is how well your joints (knee and hip in particular) accommodate a circle of rotation for a larger crank arm. If you have some limitation (whether bone impingement or muscle or tendon inflexibility or something else), you won't be able to power through the top or bottom of your stroke correctly and you'll have that coasting moment you describe. Second, if your thigh is hitting your pelvis or your stomach/chest at its high point, it may just coast through because it's being blocked from free rotation at that point.

    Yes, your fixed drive will push your foot through the top and bottom extremes of the pedal stroke, but you don't have to leave it that way. It's always likely to be much weaker than the mid-point power points in the crank rotation (and you may be feeling weakness, not inability to push at all). I'd look at your position to make sure you aren't so low that you are impinging on your legs' ability to power through the rotation. You don't have to go nuts about crank arm experiments -- you may well be having the same problem at shorter crank arm lengths as well, your sensation of smoothness notwithstanding (it's very hard to feel whether you are genuinely applying power at the top or bottom of the stroke).
    Lane DeCamp

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    Default Re: Crank Length Q

    Just a observation. When you kept your saddle height and set back and went to shorter cranks your distance from crank ctr to saddle top changed. Now....your femur is swinging in a new arc. Consider lowering your road saddle height and is that mo bettah?

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    Default Re: Crank Length Q

    Quote Originally Posted by Too Tall View Post
    Just a observation. When you kept your saddle height and set back and went to shorter cranks your distance from crank ctr to saddle top changed. Now....your femur is swinging in a new arc. Consider lowering your road saddle height and is that mo bettah?
    Yes, but there are a couple theories to this. One is that you lower the saddle when you lengthen the cranks, so that the bottom point is at a constant distance when pedaling; similarly, raise the saddle when going to shorter cranks.

    The other theory (which I subscribe to) is that your legs don't necessarily know the bottom point (maximum stretch point) of the pedal stroke but rather know the circle they rotate in. If it's a slightly smaller or larger circle, it doesn't matter much unless it's unreasonable or it's causing impingement somewhere. In this theory, you don't change your saddle height because the center of the pedaling circle didn't change. If you go significantly shorter in crank arm length, you will slightly increase your knee angle at 3 pm which in turn creates a totally catastrophic change in your knee-over-pedal-spindle alignment, which we all know is what drives any kind of positioning on the bike. Ahem. But if you're changing your crank arms by 5 mm, you aren't likely to notice the horizontal translation in knee to pedal relationship. You also are benefiting from the foot not having to travel quite as far back at 9 pm (which some very astute orthopedists think is more of a problem for a cyclist than the 3 pm position is anyway).

    You know which one I think is correct, and I'm never wrong. Try it out. It's always dependent on your personal physiology and morphology. What works for one person won't work for another and you shouldn't be looking to anyone except your own measurements and experience. I tend to diss many fitters because they use generic formulas and we are not, as individual riders, generic. I know I'm being grossly unfair, but don't create a problem for yourself that doesn't exist. You'll find you always, until the end of time, will encounter eccentricities in your pedal stroke and be working to iron one out or another. As soon as one gets better, there's another. It's part of cycling and anyone who suggests there's a static fit solution doesn't know what they're talking about.
    Lane DeCamp

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    Default Re: Crank Length Q

    i really struggle with crank length theories, but its a rainy day so ill at least add a data point or two that could prompt a useful thought.

    i ride mid foot cleats and am 1.88m (6'2" or thats what i've been saying...) with a measured inseam of 89.5cm, i ride various saddles at about 76-77 cm measured up the seat tube, with the noses, offset between 5 and 7cm from the bb-vertical line, ariones', antares', a selle SMP, ect..

    ive been stretching my hamstrings for 1-2mins a day for the last three months in an effort to make them longer and get a little lower on my pursuit bike ( season quite rapidly approaching! ). previously, since going mid-foot when by saddles all dropped 2-2.5cm, any increase in saddle height would make them hurt, as you describe, or give my quads a hard time and quickly cause knee trouble. but i've gone up 5mm two weeks ago on my everyday road riding and commuting bike without any worry. and track will follow suit shortly, though the bikes have different saddles and bar positions.

    ive ridden 175's on the road for ever, trying 172's and 170's made no real difference. however on the track, early season, i find im often far more comfortable on shorter cranks; that 165's or 170's make a massive difference over the 175's i always end up on.

    our season runs over our summer here, november- march and by about christmas time i'm feeling strong/fit/limber/whatever you want to call being-in-good-shape enough to put the 175's back on, i always finish the season winning alot more than at the start, so either, its simple and long cranks = winning, or (far less likely ) if im feeling capable of pushing longer cranks, im feeling capable of winning.

    be aware of the change in gearing that crank length can cause, and in note to what tootall mentioned and lane explained, my saddle usually moves up or down with a crank length change, but somewhat bizarrely not the full amount; i find changing from 170 to 175 might need a 3.5mm-ish increase, why this isn't 5mm i haven't quite got pinned down yet, but im convinced its hamstring-at-the-front-and-back-of-the-stroke related. ( 3 and 9 o'clock )

    id be interested to see you experiment with some simple but consistent hamstring-stretching, followed by a small saddle height increase, than to buy shorter cranks.
    Last edited by Crowemagnon; 10-26-2018 at 08:43 PM. Reason: always grammar, and imperial units.

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    Default Re: Crank Length Q

    There's some very good information in this thread, even if the advice is not entirely consistent.

    One thing I'll add is that you shouldn't sweat small changes in crankarm length. Think of motions in other sports, could they even be measured to a precision of 2.5 mm?

    And I've always found it a good practice to split my time among a few bikes with slightly different positions (road, mountain, TT when I was competing) and thought this gave me a measure of flexibility, adaptability, and resilience.

    PS Once I started riding on 175's on a mountain bike, I put them on all my bikes (inseam 87 cm).
    Tee Aitch

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    Default Re: Crank Length Q

    Quote Originally Posted by thollandpe View Post
    Think of motions in other sports, could they even be measured to a precision of 2.5 mm?
    idk if it's a fair comparison; most other sports don't have repetitive motion that is limited mechanically.

    i kinda wish there'd be more/cheaper cranks similar to look's, with their adjustable q factor (the pedal is threaded into a wedge, that could be rotated to provide 170, 172.5 or 175mm).
     

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    Default Re: Crank Length Q

    Quote Originally Posted by 11.4 View Post
    There's no formula that will determine your ideal crank length, and you're a perfect example of why. There's a theory (mostly just theory) of how a particular crank arm length gives you the most power translation, but more importantly is how well your joints (knee and hip in particular) accommodate a circle of rotation for a larger crank arm. If you have some limitation (whether bone impingement or muscle or tendon inflexibility or something else), you won't be able to power through the top or bottom of your stroke correctly and you'll have that coasting moment you describe. Second, if your thigh is hitting your pelvis or your stomach/chest at its high point, it may just coast through because it's being blocked from free rotation at that point.

    Yes, your fixed drive will push your foot through the top and bottom extremes of the pedal stroke, but you don't have to leave it that way. It's always likely to be much weaker than the mid-point power points in the crank rotation (and you may be feeling weakness, not inability to push at all). I'd look at your position to make sure you aren't so low that you are impinging on your legs' ability to power through the rotation. You don't have to go nuts about crank arm experiments -- you may well be having the same problem at shorter crank arm lengths as well, your sensation of smoothness notwithstanding (it's very hard to feel whether you are genuinely applying power at the top or bottom of the stroke).
    Hey Lane,

    Thanks for this. When you suggest looking at my position do you think it's easy enough to compare riding in the drops vs on the tops or do I need to go beyond that to adjusting spacers? The hip issue exists in the drops and on the tops -- more of an issue in the drops.

    Well, I guess I'll give the 165mm cranks a go and see if it works for me. If not, no big deal . . . I just wish Shimano had R7000 or R8000 in stock somewhere.
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    Quote Originally Posted by false_aesthetic View Post
    Hey Lane,

    Thanks for this. When you suggest looking at my position do you think it's easy enough to compare riding in the drops vs on the tops or do I need to go beyond that to adjusting spacers? The hip issue exists in the drops and on the tops -- more of an issue in the drops.

    Well, I guess I'll give the 165mm cranks a go and see if it works for me. If not, no big deal . . . I just wish Shimano had R7000 or R8000 in stock somewhere.
    Can you borrow a power meter that measures force applied around the entire pedal revolution on both sides? Here's why that could help you: You could be having problems for several reasons. First, an actual impingement or limitation on range of motion due to the orientation of your hip socket(s) or injury or scarring that limits the range of motion. Second, simple interference of your thigh with your chest or abdomen. Third, a weakness in your pedal stroke. That weakness can often be a matter of glutei that don't activate in your pedal stroke -- this is a very common problem among cyclists and can affect your entire pedal stroke without your realizing it. There's also having a basically flawed position, but you need to work these issues out first to know whether your position is in fact flawed. If you can evaluate your pedal stroke with power data, you can figure out whether you have a weakness in your pedal stroke or whether you have the strength and coordination to push through the top of your pedal stroke but don't achieve it because of physical constraints (impingement, your torso interfering with your thigh movement, etc.). You're a good example of a rider who would benefit from an appointment with a real kinesiology-trained fitter. There aren't many good ones around, but it's worth even a trip to see someone good who can diagnose such issues.

    That you have the problem in the drops or sitting up, or that it's more of an issue in the drops, doesn't necessarily tell you much. You could display those patterns in any of the options listed above. Also, note that because of the potential for any of these problems, you likely change your position substantially as you go from drops to tops -- you may not rotate your hips when going to the tops but instead arch your lower back more, or when going into the drops you may do so by rotating your hips severely so as to avoid an impingement but thereby depriving yourself of glutei strength because you now have a back that's destabilized and can't support the glutei. It's a bit of a chain of issues and you have to walk back down the line and be prepared to experiment to see which are the originating issues and which are simply responses to another problem. Make sense? I'd suggest making an experiment of yourself for a season, make changes, document everything, and only make one change at a time and give it a few weeks each time so your body fully adapts to it. It can sound tedious but it can teach you an enormous amount about how your body works and where the weaknesses lie.
    Lane DeCamp

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    Default Re: Crank Length Q

    Quote Originally Posted by 11.4 View Post
    It's always dependent on your personal physiology and morphology. What works for one person won't work for another and you shouldn't be looking to anyone except your own measurements and experience. I tend to diss many fitters because they use generic formulas and we are not, as individual riders, generic. I know I'm being grossly unfair, but don't create a problem for yourself that doesn't exist. You'll find you always, until the end of time, will encounter eccentricities in your pedal stroke and be working to iron one out or another. As soon as one gets better, there's another. It's part of cycling and anyone who suggests there's a static fit solution doesn't know what they're talking about.
    Steve Hogg would agree with you.

    The first fitter I saw was trained by Serotta and was into numbers and formulas as answers rather than merely as reference points. He created problems I didn't have before the fitting. He previously used Retul hardware and software, so that probably tells you all you need to know. He ditched Retul after noticing that the system has no consistency, giving completely different analyses for the same person even on the same day. (Retul reps from Germany came to look at what he had been telling them, took the hardware back and never got back to him.) When I went to see him, he was using a different system, but the methodology was still the same.
    Chikashi Miyamoto

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    Default Re: Crank Length Q

    Quote Originally Posted by 11.4 View Post
    You're a good example of a rider who would benefit from an appointment with a real kinesiology-trained fitter. There aren't many good ones around, but it's worth even a trip to see someone good who can diagnose such issues.
    Lane, do you have a line on someone worth visiting in the SoCal area? I've had bad experiences with the "best" folks on the west side of Los Angeles.

    In the mean time I'll see if I can find a PM. I'm pretty sure most of my buds only have Stages or 4IIII meters which I don't think fit the bill.
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    formulae are useless other than to state the obvious: that long-legged folks do better with a longer cranks and stubby-legged people have little business on 180s, but even that is subject to exceptions. We've had a few decent threads on the topic, which won't stop me from re-stating my take on it. Basically it comes down to personal preference, influenced by the type of riding one does and one's range of motion.

    The one myth that I am always trying to bust is the leverage argument. Nothing magical happens when you put on longer cranks that allows you to put out more power. That's not to say there is no effect, but you have effectively changed the gear ratio. But wait! say the naysayers, you have more torque. Well, yeah, but you also have more torque if you drop a gear. Actually, I don't even think torque is the right term; isn't it mechanical advantage? Maybe one of our engineers should drop in. No matter. It is easier to turn over a 52x16 with a longer crank, but it's also easier with a smaller wheel (650 wheels need taller gearing than 700 to go the same speed). Likewise for the same foot speed, it's easier to spin a 165 100 rpm than a 180 (the latter has to travel farther faster to keep up with the same angular velocity of the shorter diameter). So at some point you trade the ability to grind a bigger gear with the ability to maintain a nice cadence, which is why we use gears in the first place: match the load to the engine. I'm a spinner. Couldn't stay on top of the 11 if I had to. Good friend is the opposite; going 18mph he's in the 53x13 and probably barely cracks 110 rpm when he sprints but he can turn that damned 11.

    Anyway, there's also range of motion and for sure everyone has a point where they can't bring their knee any higher without power falling off massively. Even if you have the flexibility to do so, you just don't generate power; it's like placing your foot on the kitchen table and trying to step up. Almost impossible unless you have the limbs of an NBA center. (Another good though imperfect analogy is stair climbing. Which is faster: taking 3 steps at a time or 3 quick, short steps? Either extreme becomes inefficient, but you're basically doing the same work.)

    I'll stop there. It does sound like you (OP) might be flirting with the limits of your range of motion with your knee coming up higher, and a shorter crank might do you some good. I've ridden 165s for years, though the recent new Foil came stock with 170s and I'm fine on those too. But never liked 172.5; they just feel ponderous (again, spinner with short 30" inseam) and 175s are an absolute no go, except grinding and log hopping on a mountain bike .
     

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    Default Re: Crank Length Q

    I appreciate the feedback ya'll. Shimano just got in a handful of R8000 cranks so I ordered one yesterday. Unfortunately it's shipping from the east coast.

    Now I get to find out if the crank is gonna affect my FTP
    elysian
    Tom Tolhurst

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    Default Re: Crank Length Q

    Something that I have been asking myself: The dichotomy of spinner vs masher (is that the right term?) - does it have any relation to the muscular setup of an individual? What I mean is a predominance of fast-twitch or slow-twitch muscle fibers.
     

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