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  1. #1
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    Crank arms - 175 versus 180

    As if the BB thread isn't enough of a long shot.....

    I'm debating if i'd really notice a difference between the two lengths. Nevermind weight difference (it's only 10 grams - I can live with that) or the rock clearance (bike has a BB height of 14.25" - "I ain't skeered"). I'm concerned only with that of efficiency/leverage gains and possibly better ergonomics.

    I've used 175 all my MTBing life as that's pretty much the industry standard (except maybe small bike sizes???) and what's come with all my bike's so far. I've never noticed and pain in my knees or any other leg joints that weren't explainable for other momentary reason (ie, my knees hurt... it's friggin' cold. My knees hurt.... because that was a BIG hill. My knees hurt.... because I just fell down. You get the picture, i'm sure).

    I've always heard and read that someone with long legs like mine (36" inseam) should use 180 mm cranks "for obvious reasons of ergonomics and mechanics" (longer legs = longer cranks) - is this truth or myth? What are the facts and most importantly - the gains? Would there be any reason(s) one would switch between the two for reason's of training/racing?

    If anyone out there has "stepped up" in crank length i'd reeeeeeally like to hear what you have to say on a comparison basis.

    PATIA!

    p.s. - yes, I searched but there's nothing with "180" in this section that relates.
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  2. #2
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    I like my 180's

    I use 180's for MTB and road, I used to use 175 but stepped up, on the road I noticed I was going about 1.5 KPH faster average for the same heart rate, I can spin them to 160rpm no probs too.
    On the MTB I do need to be a bit more careful smacking a pedal but it isn't a big deal. I had to wait about 3 months to get my XTR Hollowtech 2 cranks to come from Japan though, they are a bit hard to come by.
    My inseam is about 34" I think, but I wouldn't go back to shorter cranks, the 180's feel just right for me.
    See if you can get a used pair somewhere cheap to try it out, I had a friend who used them so I could try before I buy.
    I does take a while to get the extra flexibility in the hip flexor, do lots of streching.

    Good luck

  3. #3
    I should be studying...
    Reputation: frank daleview's Avatar
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    It's been a while since I've studied any biomechanics so I'll spare you my half assed explanation (if you're really interested, I could whip out my old text book...). I think it's safe to say that your inseam, longer cranks may be a worthwhile experiement. I have a 33.5 inseam (actual, not pant inseam) and have played around with the idea. Your flexibility also has a lot to do with it.
    Formerly known as iceaxe

  4. #4
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    Hey Andrew-
    try a search of the singlespeed board, there's been some big discussions on going with longer cranks. Some even to 190.
    It can take a while to get used to (ie over a month). remember to move saddle forward & down if you try longer cranks.
    my puny 31" inseam prolly wouldn't benefit from going with longer cranks, so I'm sticking with 'em. I'd say you're a good candidate for longer cranks with that inseam.

    Quote Originally Posted by AndrewTO
    As if the BB thread isn't enough of a long shot.....

    I'm debating if i'd really notice a difference between the two lengths. Nevermind weight difference (it's only 10 grams - I can live with that) or the rock clearance (bike has a BB height of 14.25" - "I ain't skeered"). I'm concerned only with that of efficiency/leverage gains and possibly better ergonomics.

    I've used 175 all my MTBing life as that's pretty much the industry standard (except maybe small bike sizes???) and what's come with all my bike's so far. I've never noticed and pain in my knees or any other leg joints that weren't explainable for other momentary reason (ie, my knees hurt... it's friggin' cold. My knees hurt.... because that was a BIG hill. My knees hurt.... because I just fell down. You get the picture, i'm sure).

    I've always heard and read that someone with long legs like mine (36" inseam) should use 180 mm cranks "for obvious reasons of ergonomics and mechanics" (longer legs = longer cranks) - is this truth or myth? What are the facts and most importantly - the gains? Would there be any reason(s) one would switch between the two for reason's of training/racing?

    If anyone out there has "stepped up" in crank length i'd reeeeeeally like to hear what you have to say on a comparison basis.

    PATIA!

    p.s. - yes, I searched but there's nothing with "180" in this section that relates.
    [SIZE=1][/SIZE]

  5. #5
    Weird huh?
    Reputation: cmdrpiffle's Avatar
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    I always used to use 180's. Still would except I cannot find them. Downhillers,trail riders,etc won't get much advantage. If you love to climb like me......the longer length is an advantage. (I'm not talking about climbing in those 20 something chainrings with your butt on the saddle) I'm talking climbing!! I know Shimano makes them for XTR, but the other manufacturers who claim to.....never have them.

    Cheers,
    Mike

  6. #6
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    Well, it looks like it's an easy decision based on what you guys are sayin'. Good point made with the climbing, cmdrpiffle. (what's wrong with the granny ring and seat? )

    loosch - hip flexor? Ummm, wuzzat?

    iceaxe - flexibility - can you be a little more specific? You mean as in my physical flexibility? How would that come into play?

    Someone tell me about this hip thing. Y'all freaking me out here. How does longer crank length relate to this? Still going around in a circle, yes/no?

    logbiter - noted on the SS Section. Great tip, thanks!
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  7. #7
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    -loosch - hip flexor? Ummm, wuzzat?

    -iceaxe - flexibility - can you be a little more specific? You mean as in my physical flexibility? How would that come into play?

    -Someone tell me about this hip thing. Y'all freaking me out here. How does longer crank length relate to this? Still going around in a circle, yes/no?


    The hip flexor group of muscles are located at (you guessed it) the hip, they affect they way you lift your leg. With longer cranks the leg goes thru a bigger circle, hence you lift it more. You need to be a bit more flexible in the hip because the angle from the leg to the body closes in a bit more if you keep your handlebars the same.

    Hope this helps.

  8. #8
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    Quote Originally Posted by loosch
    The hip flexor group of muscles are located at (you guessed it) the hip, they affect they way you lift your leg. With longer cranks the leg goes thru a bigger circle, hence you lift it more. You need to be a bit more flexible in the hip because the angle from the leg to the body closes in a bit more if you keep your handlebars the same.

    Hope this helps.
    Yes, got it, it helps immensly, thanks!

    The hip bone is connected to the back bone. The back bone is connected to the...

    Good, now all I need is 110/74 BCD chainrings. And winter to go away.
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  9. #9
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    AndrewTO you sound like the perfect candidate for 180 cranks IMHO - you have long legs and a bike with a very high BB - so going to 180 cranks you wouldn't be bashing the pedals on rocks all the time. I would try it myself except my bike's BB is only 12.5" and I constantly smack the poedals on obstacles on the trail. Advatages would be very great, better leverage (for your leg length) more torque for less power excerted. Will prob be quite hard to find a set though since most everythings either 170 or 175 these days.
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  10. #10
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    I have 180mm XT cranks on my 5 Spot that are working out ok. The pedals do seem to hit more often and that makes me second guess the 180s. However with the XXL frame size and 180 cranks I do feel very comfy on the bike. I get some knee/joint pain at times and have taken glucosamine+chondroitin+MSM with good results.
    I would say go with the 180s unless you need more pedal clearance.

  11. #11
    viva la v-brakes!
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    proportional crank length

    do a Google search for "proportional crank length". You may decide you want something significantly longer then 180.
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  12. #12
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    Quote Originally Posted by FishMan473
    do a Google search for "proportional crank length". You may decide you want something significantly longer then 180.
    I don't know. I've been doing some snooping on the SS section here on MTBR and found that "20% of inseam measurement" formula and found that i'm at 183.

    That and I wouldn't knnow where to begin looking for anything over that (never even knew they existed untill readin the SS section).

    Gonna pick up some chainrings and try it out. Won't happen untill next year probably. (shrug) At least not on anything but a trainer.

    I'll do the search you recommend as it's an interesting new thing to check out and learn.

    Thanks!
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