Crank arm length, and benifits of.- Mtbr.com
Results 1 to 19 of 19
  1. #1
    A plain old rider
    Reputation: The Tree's Avatar
    Join Date
    Feb 2004
    Posts
    50

    Crank arm length, and benifits of.

    I have looked in a lot of different places and haven't gotten a straight answers on crank length for a trail/DH bike. I realize that inseam length and height plays into it (I'm 5'6" with an inseam of 29"). I have usually used cranks that are 175mm in length and was thinking of going to 170mm, because I realized a lot more people of below average height run slightly shorter cranks. What do you think about running shorter cranks or what length cranks do you run? I checked for previous posts but didn't find any.
    Last edited by The Tree; 02-18-2004 at 09:29 AM.
    The greatest gift you ever give is your honest self.

    Fred Rogers

  2. #2
    Former Noob Herder
    Reputation: zedro's Avatar
    Join Date
    Jan 2004
    Posts
    5,261
    another factor to consider is ground clearance. Alot of people despite their height will run shorter cranks so they can avoid clipping rocks. I use 165's and i'm 6'2", however this is for a DH bike that i dont use for alot of pedalling, at least not uphill or long periods at a time.

  3. #3
    Too Close To The Hill
    Reputation:
    Join Date
    Jun 2007
    Posts
    208
    Current thoughts on this?

    For non-DH where one is pedaling seated, shorter cranks would raise the seat post and therefor the center of gravity. I don't think that applies to DH... so any disadvantage to the ground clearance?
    Lacerations through intact armor are a mark of talent... or stupid... or both...

  4. #4
    Glad to Be Alive
    Reputation: SHIVER ME TIMBERS's Avatar
    Join Date
    Jan 2004
    Posts
    42,929
    if you are getting by with 175's then keep on using them...in theory and reality more torque because of more leverage...but take a ruler out and look at 5mm...(not much)...I run 170's....I watch the clearance (don't pedal in rocky sections)...but all in all...if you get by with 175's on the terrain you ride then keep using them...I pedal strike in the terrain I ride to much..even with 170mm
    the trick is ENJOYING YOUR LIFE EACH DAY, don't waste them away wishing for better days

  5. #5
    Too Close To The Hill
    Reputation:
    Join Date
    Jun 2007
    Posts
    208
    I pedal strike a fair amount... blowing several Prerunner pins every half dozen runs is eventually going to get as expensive as a new pair of crank arms...
    Lacerations through intact armor are a mark of talent... or stupid... or both...

  6. #6
    wuss
    Reputation: dropadrop's Avatar
    Join Date
    Sep 2005
    Posts
    2,362
    I have a lot of pedal strikes with my 175's, but I'm scared to test 170 as the terrain I ride also has a lot of short technical climbs where I really need as much torque as I can get...

  7. #7
    mtbr member
    Reputation: Brando-99's Avatar
    Join Date
    May 2009
    Posts
    54

    More power

    I don't remember where I read it, but I seem to remember an article stating that each additional 5mm in length yields an additional 3% increase in power transmission to the rear wheel. Food for thought...
    Anything worth doing is worth overdoing.

  8. #8
    RTM
    RTM is offline
    #1 Latex Salesman
    Reputation: RTM's Avatar
    Join Date
    Sep 2005
    Posts
    1,846
    I also go with the shortest I can find, 165MM. Slightly less power is not nearly as annoying, dangerous and expensive as hard pedal strikes.

  9. #9
    wuss
    Reputation: dropadrop's Avatar
    Join Date
    Sep 2005
    Posts
    2,362
    Quote Originally Posted by Brando-99 View Post
    I don't remember where I read it, but I seem to remember an article stating that each additional 5mm in length yields an additional 3% increase in power transmission to the rear wheel. Food for thought...
    I think the 3% is torque, so downhill or flats won't be affected as much as uphill?

  10. #10
    mtbr member
    Reputation: 2clue's Avatar
    Join Date
    Jun 2007
    Posts
    1,391
    You have to also account the fact that it is more difficult to spin properly on longer crank arms then it is on shorter.

    Sure, 180mm with give you more Torque when mashing through a 100 yard technical section where it is beneficial. However it is also a lot more difficult to spin/ride efficiently with such long crank arms. 165mm on contrast will allow you to spin more easily resulting in a more efficient use of your energy on long sustain climbs and flats.

    Pedal strikes and clearance issues are easily addressed by simply adapting your riding style to the terrain. It's a very common practice amongst lots of riders to time their strokes through technical sections to avoid and pedal strike (especially eggbeater users as they dismount from their pedals if struck a certain way).

    The choice as to which direction you should head in, really should be dependent on what you feel will increase your efficiency the most.

  11. #11
    Custom Wheelbuilder
    Reputation: Zen Cyclery's Avatar
    Join Date
    Mar 2009
    Posts
    533
    I have jumped around on a ton of different crank lengths. I ran 175mms, 170mms, 165mms, and 172.5 mm.
    With regards to increased leverage, I did not notice anything (all though I'm sure on paper it makes a difference). I did notice significant advantages with rock clearance though, particularly in the 165mm length.
    Overall, I would say that my favorite length is 170mm. At your height, I think a 165 or 170 would be a good call.
    Check out www.zencyclery.com for fully customizable, handbuilt wheels.

    www.facebook.com/zencyclerywheels

  12. #12
    mtbr member
    Reputation: monkei's Avatar
    Join Date
    Apr 2007
    Posts
    545
    Quote Originally Posted by SummitAP View Post
    I pedal strike a fair amount... blowing several Prerunner pins every half dozen runs is eventually going to get as expensive as a new pair of crank arms...
    The Ti pins are well worth the extra $ if you go through the alumnium ones too fast, seem to hold up much better.
    My bike video YT channel: biiiiiiiiiiiikiiiiiiiinnnnnnng

  13. #13
    mtbr member
    Reputation: Gman086's Avatar
    Join Date
    Jul 2004
    Posts
    4,571
    Quote Originally Posted by monkei View Post
    The Ti pins are well worth the extra $ if you go through the alumnium ones too fast, seem to hold up much better.
    Where do you get Ti pins?

    Thanks,

    G
    "There's two shuttles, one to the top and one to the hospital" I LOVE this place!!!

  14. #14
    mtbr member
    Reputation: monkei's Avatar
    Join Date
    Apr 2007
    Posts
    545
    Where do you get Ti pins?
    I've gotten 'em both times direct from Twenty6, once for a set of Prerunners, and more recently for my Predators.
    My bike video YT channel: biiiiiiiiiiiikiiiiiiiinnnnnnng

  15. #15
    mtbr member
    Reputation:
    Join Date
    May 2006
    Posts
    1,631
    I'm 5'9 and been using 165 mm since early spring. I've used both 1780 and 175mm in the past. I prefere the 165mm. advantages as noted in other post, spinninng effience, less pedal strikes... The trade off spinning v/s tourgue. With the shorter cranks you start pedaling sooner out of courners and through rocksections. The only disadvantage with less tourge would be coming out of a tight turn from nearl a dead start and having to crank up a steep hill. Other than that I haven't had any problems with loss of tourque, that hasn't been compensated for by spinning earlier. I also tend to pedal alot more than I used to because less worry about pedal strike.
    The guy yo' momma "act" like she don't know!

  16. #16
    Registered text offender
    Reputation:
    Join Date
    Dec 2011
    Posts
    1,137
    I'm 6' 1" and run 165mm cranks. I like the cadence, the clearance, and I don't have to raise and drop the seat as far or as often. My knees are happier as well.

    If I were a single speed masher I would go with 175's.

  17. #17
    7MGTE
    Reputation: supramk388's Avatar
    Join Date
    Mar 2007
    Posts
    1,704
    160 FTW, its all about clearance in DH. Once you get up speed its all about the bike and the rider (mostly rider) to maintain that speed.

    I saw pros riding chain less in 2010 putting down times better that pros/cat 1 riders with full drive trains (cranks, chain, gears, etc...)

    Worry about crank length on your XC, bmx, SS, and AM bikes.

  18. #18
    mtbr member
    Reputation:
    Join Date
    Mar 2012
    Posts
    2
    I think shorter cranks should also help on DH/FR type stuff because your stance will be more neutral when the cranks are parallel to the ground i.e. both your feet are on the same level. To take an example to extremes if you were able to mount some pedals straight to your BB your feet would be side by side, if you were to run 300mm cranks it would be like taking a long stride or a lunge to get the cranks parallel to the ground, this will mean that one foot would be very far forward and one very far back, making handling quite difficult.

    For what it's worth my current bike has 175mm cranks but I'm building up a new bike and will put on 170mm. As my old bike is a 9 speed and the new will be a 10 speed I should be able to offset any loss of torque, I'm going with 170mm mainly to reduce pedal strikes, though you do wonder how much can 5mm difference make.

  19. #19
    Too Close To The Hill
    Reputation:
    Join Date
    Jun 2007
    Posts
    208
    I think your argument is technically correct, and realistic for clips. Not being clipped in, sometimes my feet end up on the pedals with a lot more variance than 5-10mm
    Lacerations through intact armor are a mark of talent... or stupid... or both...

Members who have read this thread: 0

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.