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  1. #1
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    what crank length is right? 170mm, 175mm, or 190mm???

    I ride my bike for commuting, a single speed road bike. I am currently using 165mm cranks that came with my bike. I took a look at this site here: http://www.nettally.com/palmk/Crankset.html

    So measuring my inseam with that method and plugging it into the forumula i get 190mm, this is with a 34.75 inseam. i am slightly over 6 feet 1 and i find 190mm a bit much, is the site correct? i was considering between 170mm or 175mm but this 190mm is ridiculous, or are they right? what are your thoughts?

  2. #2
    Senior Member oldbobcat's Avatar
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    Crank length calculators should be taken with a grain of skepticism. They are usually based on the model that people with average-length legs (whatever that is) should be turning average-length cranks (170 mm), and everyone else should use the same proportion.

    Truth is, riders with shorter legs ride on cranks that tend to be longer in proportion to their legs than riders with longer legs. And the crazy thing is, as mathematically improbable as it seems, it works for most riders.

    190s are an expensive custom shop item, anyway. 170s or 175s would work fine; for single speed I'd favor 170s.

  3. #3
    coprolite fietsbob's Avatar
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    165 is good for spinning a fairly low gear ratio at a higher rpm..
    and not putting a pedal hit into a banked corner on the velodrome ,
    and becoming an airborne projectile..

    long legged, low cadence big ratio may favor the longer crankarm

    for added leverage.

    if you want 190, then contact Lennard Zinn, CO based custom builder
    and a series of bikes, to the Tall Rider..

    He got someone to make longer than 180 cranks ..
    Last edited by fietsbob; 08-28-11 at 02:37 PM.

  4. #4
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Bullseye made custom cranks up to 225mm length, and I've heard of tests done with cranks as short as 110mm. As Old Bob said, testing shows that there's very little difference in power production among different length cranks.

    Here's a good start on the "real" answers:
    http://velonews.competitor.com/2011/...answers_178528

    To take advantage of radically different length cranks, you'd have to have custom frame made to keep the pedals at the right height off the ground. FWIW: I'm 6-foot-4 and I'm quite comfortable spinning 175mm cranks.
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  5. #5
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    The length of the crank is dependent upon the height of the rider but when it comes down to it, it doesn't matter much. The shorter the crank, the faster you have to turn your legs. They assume the taller person has bigger muscles thus the crank is longer as you have the muscle power to turn it. With a shorter or longer crank length, you would adjust the seat height accordingly. A person may have an aggressive frame but don't like the positioning. One could put a higher angled stem on to reduce the aggressiveness, or the more expensive option, shorten the crank length. With the latter, he will lower the saddle/seat post to compensate for the shorter crank length thus reducing the aggressiveness of the frame, the position of the difference between the handlebars to the seat height.

  6. #6
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    As Jeff noted, crank length has very little to no effect on power and speed when measured objectively but some riders have a strong personal preference and can tell small differences so the subjective part can be important. I'm 5'9" and have 170's on most of my bikes However, I'm pretty unfussy about crank length and have switched from bikes with 170's to another with 175's and never noticed any change. Others think a 2.5 mm length difference is a big deal.

    The calculator that recommended 190 mm cranks for someone 6'1" seems WAY out of line with conventional recommendations and probably should be ignored. I expect you will be happy with 175's.

  7. #7
    bike whisperer Kimmo's Avatar
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    This table I found here seems to make more sense.

    60 to 65cm 150mm
    66 to 70cm 155mm
    72 to 75cm 160mm
    75 to 78cm 162.5mm
    79 to 81cm 165mm
    82 to 83cm 167.5mm
    83 to 86cm 170mm to 172.5mm
    87 to 90cm 175mm to 177.5mm
    91 to 94cm 180mm
    94cm plus 185mm

    It says you should prolly be on 175s, but who knows?

    IMO you really need to try different lengths and give yourself a chance to get used to it before making a call on your preferred length; I'm 175cm with an 82cm inseam and only ever ridden 170s, but after getting hold of some 175s, there's no turning back - I have more power with em; it feels like my chainring is 1t smaller. They took a bit of getting used to (I chose not to lower my seat as well, which seemed to work), but I found I could still spin them pretty quick. Maybe I could even go to 177.5s before it puts a meaningful dent in my redline (which, come to think of it, I have pretty much no reason to hit anyway).

  8. #8
    we be rollin' hybridbkrdr's Avatar
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    Thanks for the table. I'm used to 170mm but keep on wondering whether I'd feel more "liberated" with 175mm. But, my inseam is only 83.5cm.

  9. #9
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    hule, My road bike's crankarms ranged from 165 mm to 175 mm (I'm 6', ~33.5" inseam). My max cadence is down slightly with the 175 mm crankarms when compared to 170 mm crankarms, but with either when I approach max cadence, I upshift.

    Barring a physical issue I think cyclists are quite adaptable to crankarm length.

    Brad
    Last edited by bradtx; 08-29-11 at 06:11 AM. Reason: corr

  10. #10
    Map maker cbchess's Avatar
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    +1 for 175mm cranks I am 6'2 with 33 pants inseam and they feel fine.

  11. #11
    coprolite fietsbob's Avatar
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    well at least it's not a Fixie, so you can corner with the inside pedal up.

  12. #12
    bike whisperer Kimmo's Avatar
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    Quote Originally Posted by hybridbkrdr View Post
    Thanks for the table. I'm used to 170mm but keep on wondering whether I'd feel more "liberated" with 175mm. But, my inseam is only 83.5cm.
    And mine is only 82cm, but as I said, there's no turning back.

    If you have a good spin, it's win - the extra 5mm is no big deal next to the extra leverage.

    170mm is generally treated as a default size too often, IMO. Thus way too many 170mm cranks exist, making it hard to experience anything else. Definitely worth trying a different size, but I had to find a set of cranks on a junk bike before it was practical for me.

  13. #13
    Subjectively Insane MilitantPotato's Avatar
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    I'm 6'8" with a 101cm inseam and I have 210mm cranks on one of my bikes. Due to a biomechanical issue (janky hip joint) they're a touch long.
    After a few hours on my bicycle with 175mm cranks I'm noticeably more worn out (leg muscle wise) than on my bicycle with 210mm cranks.

    The 175mm cranks feel like a child's bike, they feel very small. Though there's no night and day change in power output, my body is MUCH happier with longer cranks.

    The only downsides are pedal strike, heel strike on panniers, and toe over-lap with shorter top tubes.

    Though this forum shoots down the prospect of longer cranks, from my personal experience they're very much a boon for us giants.

    I purchased mine from HS Cycles which also make Zinn's cranks, but cost significantly less.
    Last edited by MilitantPotato; 08-31-11 at 12:24 AM. Reason: Grammar strength I have not.
    You've got a bike, so you gotta move.

  14. #14
    bike whisperer Kimmo's Avatar
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    Wow, can you show us a pic of your bike?

  15. #15
    Constant tinkerer FastJake's Avatar
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    After reading Sheldon's article on crank length, I got the idea in my head that longer can be bad but there's no downside to shorter arms. http://sheldonbrown.com/cranks.html

    On that note, all my road bikes have 170s (I'm 5' 9") and all my mountain bikes have 170s or 175s. Honestly, I don't think it's a huge deal because I've never been able to tell the difference from one bike to the next. I would like to try some 165s though for my next fixed gear build...
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  16. #16
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    Quote Originally Posted by FastJake View Post
    On that note, all my road bikes have 170s (I'm 5' 9") and all my mountain bikes have 170s or 175s. Honestly, I don't think it's a huge deal because I've never been able to tell the difference from one bike to the next. I would like to try some 165s though for my next fixed gear build...
    I'm your height and that's my experience exactly. Going from my road bikes, all with 170 mm cranks, to my MTB with 175 mm cranks was seamless. However, I've talked to other riders who make a big deal about crank length and claim they can feel minor differances.

    The 165 mm cranks on a fixed gear make sense since you have to pedal through corners and the additional ground clearance can be beneficial.

  17. #17
    bike whisperer Kimmo's Avatar
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    The only corners fixed-gear bikes should be turning on are banked anyway : p

  18. #18
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    Quote Originally Posted by Kimmo View Post
    The only corners fixed-gear bikes should be turning on are banked anyway : p
    Haven't seen the hipsters and messengers much huh?

  19. #19
    bike whisperer Kimmo's Avatar
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    *should*

    ; )

  20. #20
    Senior Member Drakonchik's Avatar
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    Suspect the preponderance of people poo-pooing long cranks is because 95% of people are not very tall. Therefore they've always easily found available crank sizes that are about right. They can't imagine a crank length that just feels way too short.

    To reverse the situation, what if the only generally available crank sizes were say 180mm to 195mm. And yet all you fair-average sized persons were forced to ride them. See how you'd like it on fast road rides. "But crank length doesn't make much difference." :-)

    I'm 6'1" with 35" inseam. When I changed from 175mm to 180mm cranks in 2002 I never looked back. The immediate subjective feeling of riding 180mm was so "right" . . . . but more to the point I was able to sprint faster, sustain standing climbs 2-3 times longer, and keep my cadence in 90-110 (whereas on 175mm I was spinning 110-140mm in competitive rides) with ultimately less fatigue.

    Now when I get on a bike with less than 175mm it feels like a silly circus bike. Really.

    So to the OP I say: get a set of 180s. Truvative and SRAM have some double road sets that can be had for a reasonable door fee.

  21. #21
    Senior Member oldbobcat's Avatar
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    Quote Originally Posted by MilitantPotato View Post
    Though this forum shoots down the prospect of longer cranks, from my personal experience they're very much a boon for us giants.
    .
    Didn't mean to shoot down the idea of long cranks for giants, just the model that would put the original poster on 190s. Interpolating from your model, the original poster should be on 173.9 cm cranks. That's right in the ballpark of every one of our suggestions.

  22. #22
    bike whisperer Kimmo's Avatar
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    Quote Originally Posted by oldbobcat View Post
    Interpolating from your model, the original poster should be on 173.9 cm cranks. That's right in the ballpark of every one of our suggestions.
    LOL, 1,739mm is so not in the ballpark : p

  23. #23
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Quote Originally Posted by Jeff Wills View Post
    Bullseye made custom cranks up to 225mm length, and I've heard of tests done with cranks as short as 110mm. As Old Bob said, testing shows that there's very little difference in power production among different length cranks.

    Here's a good start on the "real" answers:
    http://velonews.competitor.com/2011/...answers_178528

    To take advantage of radically different length cranks, you'd have to have custom frame made to keep the pedals at the right height off the ground. FWIW: I'm 6-foot-4 and I'm quite comfortable spinning 175mm cranks.
    Five foot nine and have a 33 inch riding inseam... I too prefer 175's which might be a function of my femur length in relation to total leg length.

    we build custom bikes for extremely tall riders and for some of them who might have a 40 inch inseam, a 190mm crank makes sense when that is built into a custom frame that also accounts for unusual dimensions.

  24. #24
    Student of the Billy styl badbikemechanic's Avatar
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    This is the current breakdown for manufacturers. There isn't a 190 out there.

    175 for mountain bikes
    172.5 for road bikes
    167.5 or 170mm for track bikes.

    Take your pick
    "I can't learn ya if you don't want to be learned" - Billy
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  25. #25
    bike whisperer Kimmo's Avatar
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    Hey Mondrian, that's no breakdown for manufacturers, that's someone's idea of what size cranks belong on what type of bike for one rider. It doesn't exactly explain the existence of 175mm road cranks, for example...

    Also, http://zinncycles.com/Zinn/index.php.../custom-cranks http://www.hscycle.com/Pages/customcrankset.html

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