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  1. #1
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    correct crank length?

    I've looked at different formulas for determining proper crank length but how do you guys figure it? And please list your inseam and favorite crank length (did that sound dirty? ) and why . thanx
    "I won't sell these for a penny less than $60.00. I'd rather put 'em back on the shelf and keep 'em! "

  2. #2
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    30 +/- 1/2 inch inseam. I use a 170mm crank because when I bought it there was a 165mm, 170mm, and a 175 mm, and I didn't know which one to choose, so I took the middle one.

    Hey, it works for me...

    Actually, I use a 170mm crank because, even though 5mm doesn't sound like much, a 175mm made contact with more rocks that I would like. Whether it's an illusion or not, the 170s make me feel as if I'm not hitting as many things on my downstroke...

    Probably not the answer you're looking for....

    Tim
    I wish I didn't know now what I didn't know then.

  3. #3
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    Zinn has a formula on his website for sizing his cranksets.

    Crank length (mm) = Inseam (mm) X 0.216

    I ride what feels right after all these years. 175 is about max on a road frame for clearance, but I have as long as 187s (I think thats how long the bullseyes are) on my mountain bikes.
    Quote Originally Posted by banks
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  4. #4
    i am, therefore, i ride
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    This topic was just discussed a few days ago under " Everything Drivetrain" ..... crankarm length sub-topic.

  5. #5
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    exactly what I'm looking for!

    Quote Originally Posted by tibug
    30 +/- 1/2 inch inseam. I use a 170mm crank because when I bought it there was a 165mm, 170mm, and a 175 mm, and I didn't know which one to choose, so I took the middle one.

    Hey, it works for me...

    Actually, I use a 170mm crank because, even though 5mm doesn't sound like much, a 175mm made contact with more rocks that I would like. Whether it's an illusion or not, the 170s make me feel as if I'm not hitting as many things on my downstroke...

    Probably not the answer you're looking for....

    Tim
    you go by feel and actual conditions, not a formula. Thats what I want, random reasons
    "I won't sell these for a penny less than $60.00. I'd rather put 'em back on the shelf and keep 'em! "

  6. #6
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    thanx, missed it. I'll check it out.
    "I won't sell these for a penny less than $60.00. I'd rather put 'em back on the shelf and keep 'em! "

  7. #7
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    Quote Originally Posted by IF52
    Zinn has a formula on his website for sizing his cranksets.

    Crank length (mm) = Inseam (mm) X 0.216

    I ride what feels right after all these years. 175 is about max on a road frame for clearance, but I have as long as 187s (I think thats how long the bullseyes are) on my mountain bikes.
    if you don't mind, whats your inseam?
    "I won't sell these for a penny less than $60.00. I'd rather put 'em back on the shelf and keep 'em! "

  8. #8
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    3 most ridden bikes have 175s because that is what they came with. SS built out of parts laying around the house has 170s because that is what was lying around when I built it. How is that for scientific? 5'10" and I wear pants with a 32 inseam.

  9. #9
    i also unicycle
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    i prefer 180s for mtb, but i'm 6'4 and have a 36 in or so inseam. i ride 175s on the road, but only because i'm too poor at the moment to upgrade to 177.5 cranks.
    mtbr says you should know: i work in a bike shop.
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  10. #10
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    Quote Originally Posted by stan4bikes
    if you don't mind, whats your inseam?
    A little north of 35".

    Back when I started riding I don't recall that there was much other than 170mm or maybe 172.5mm cranks on off the shelf bikes, even on bikes big enough for me. So I started out on short cranks. Then around 87 I was Fit Kitted and the recommended crank length was 175. So when I built up my Gianni Motta it got 175mm Chorus cranks. By that time I was also into mtn bikes, and just about everything for offroad came with 175mm cranks. Then a pal of mine got a IRD Stroker and Rod talked him into really long cranks. And he was a little guy compared to me. So I figured if he could ride 190 something millimeter cranks then I could surely ride 187s, or whatever they are, on my Avalanche. Turns out I actually liked the length even regarding clearance, so when I built the IF I went with another set of long ass Bullseyes. Since Bullseye is no more, I scrounge 180s whenever I can afford to.
    Quote Originally Posted by banks
    That is one big f'n dude!
    Yes I am!

  11. #11
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    I don't know where I got this info, but I've had it for years. It's worked well sizing cranks to my kid's bike and, in almost all cases, the crank lengths suggested here are shorter than what is usually available. Shorter cranks will make a bike feel easier to pedal.

    Inseam followed by crank length:
    15" = 135mm
    15" - 16" = 140mm
    16" - 17" = 145mm
    17" - 18" = 150mm
    18" - 20" = 155mm
    20" - 24" = 160mm
    24" - 28" = 165mm
    28" - 32" = 170mm
    32" + = 175mm

    According to Zinn's formula, I should be on 205mm cranks with a 37.5" inseam.

  12. #12
    Witty McWitterson
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    180's for mountain. 177.5 for road/cross. 34"-35" inseam. And I've got a stash of both lengths - just in case.
    Just a regular guy.

  13. #13
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    Quote Originally Posted by ssmike
    I don't know where I got this info, but I've had it for years. It's worked well sizing cranks to my kid's bike and, in almost all cases, the crank lengths suggested here are shorter than what is usually available. Shorter cranks will make a bike feel easier to pedal.

    Inseam followed by crank length:
    15" = 135mm
    15" - 16" = 140mm
    16" - 17" = 145mm
    17" - 18" = 150mm
    18" - 20" = 155mm
    20" - 24" = 160mm
    24" - 28" = 165mm
    28" - 32" = 170mm
    32" + = 175mm

    According to Zinn's formula, I should be on 205mm cranks with a 37.5" inseam.
    Yeah, that Zinn formula is kind of crazy. He seems to really be into long cransk though. He has another formula for really tall people. It is basically the same formula, except you use 0.21 instead of 0.216. Using either factor for my inseam produces about a 6mm difference between the two.
    Quote Originally Posted by banks
    That is one big f'n dude!
    Yes I am!

  14. #14
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    Good thread

    29" - 170mm road and mtn., 175mm on SS
    Canadian Parts on Canadian Bikes in Canada

  15. #15
    All 26.5" all the time!
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    Quote Originally Posted by ssmike
    I don't know where I got this info, but I've had it for years. It's worked well sizing cranks to my kid's bike and, in almost all cases, the crank lengths suggested here are shorter than what is usually available. Shorter cranks will make a bike feel easier to pedal.

    Inseam followed by crank length:
    15" = 135mm
    15" - 16" = 140mm
    16" - 17" = 145mm
    17" - 18" = 150mm
    18" - 20" = 155mm
    20" - 24" = 160mm
    24" - 28" = 165mm
    28" - 32" = 170mm
    32" + = 175mm

    According to Zinn's formula, I should be on 205mm cranks with a 37.5" inseam.
    Here's another crank length chart, this one for BMX. The differences are interesting.

    http://www.danscomp.com/serve.php?se...crankchart.htm

  16. #16
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    So how do you measure your inseam.
    Quote Originally Posted by banks
    That is one big f'n dude!
    Yes I am!

  17. #17
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    Quote Originally Posted by IF52
    So how do you measure your inseam.
    Stand back to the wall, straight posture, on flat surface (latter is a bit of a problem in my house ).

    Put a book, spine facing up, nice and tight up against your crotch (don't make it hurt ). Use a tape measure to measure from the floor to the top of the spine and that's your inseam.

    That's how I do it...
    Tim
    I wish I didn't know now what I didn't know then.

  18. #18
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    Excellent. Exactly how I do it. I've seen in some places that you just use your pant length, or measure up to the pile of seams in the crotch of your jeans while standing on a level surface. Both of those can be way off.
    Quote Originally Posted by banks
    That is one big f'n dude!
    Yes I am!

  19. #19
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    I'm 5'10, inseam, who knows, ask my wife.
    Have been using 175 on mountain bikes and my road bike for years. I like the same crank length on everything I ride.

    Can I "spin" the175 on a road bike? Hey, it works for me, but i'm not road racing in France.

  20. #20
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    Quote Originally Posted by IF52
    Excellent. Exactly how I do it. I've seen in some places that you just use your pant length, or measure up to the pile of seams in the crotch of your jeans while standing on a level surface. Both of those can be way off.
    Here's good info on measuring your PBH

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