What crank length are you running?- Mtbr.com
Results 1 to 23 of 23
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    637

    What crank length are you running?

    Due to ergonomic reasons (having short legs), and reading that it could help with lower back pain issues, I decided to try shorter cranks on my bikes:

    From 172.5 to 165mm on my Road bike and from 175 to 170mm on my geared MTB. Been on this setup for around 6 months and like how my pedal stroke seems more fluid and less lumpy than it was before. I also found that my speed increased in some areas. Of note I was pushing similar gears to before - which I was surprised about, since I thought the lower torque generated by the shorter crank would make the gears harder to push.

    However I still had 175mm cranks on my singlespeed, which after getting used to the shorter cranks on other bikes, felt very odd for the first 10 mins of a ride.

    So on the weekend, I finally got around to trying the 170mm cranks on my Singlespeed (without changing my gear range). Immediately I noticed that climbing felt harder, though as I've noticed on my other bikes, spinning the gear up on flat sections was much easier.

    I felt like my ride was much slower, due to the extra resistance in climbing (kinda like when I first started riding a singlespeed). However, checking strava after the ride, I'd found that I'd set PRs on alot of climbing sections, and even got a KOM on one 5 min trail, beating my previous PR by 30 seconds.

    Honestly, before I'd uploaded my ride, I'd convinced myself to go back to the 175 cranks, but now I'm not sure. The climbing certainlty wasn't comfortable - but maybe its something I'll get used to.

    I'm considering tryign a lower gear. currently I'm running 34:21, but will try a 22 and see how that goes.

    I'm interested to hear if anyone else is running shorter cranks, and how they compared to longer ones.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
    Planet X Dirty Harry
    Chiner 29er SS

  2. #2
    mtbr member
    Reputation:
    Join Date
    Apr 2008
    Posts
    634
    I tend to go the opposite route, and run longer cranks. On road, where everyone my height would say 172.5, I run 175's, and can't stand the feeling of 172.5. I notice it instantly. Mtb, I usually run a 175, but I have a bike put together by a buddy and he has freakishly long legs for his height, and it has 180's, and I don't even notice a difference, in a good way. But if your feeling says go short and you notice a better pedal stroke, and if you are hitting PR's (despite how you feel), I would say stick with the short! Whatever works.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Sep 2011
    Posts
    321
    Switched to 165mm on my cross bike after a fitting last year, then put 170mm on both my ss mtbs. Never felt better!

    I feel like peformace gains are better all around as I'm in a more powerful position thoughout the stroke. I run 30/19 on my 29er and 30/20 on my 29+ for central Texas trails.

    I did use Sheldon Brown's gain ratio calculator when I switched so you might want to play with that. But I'm a firm believer now in using the right size crank for your leg proportions. YMMV
    Pedal through it!

  4. #4
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    637
    Thanks, that's interesting. I just tried the the gain ratio calculator (didn't know it existed)

    With 175 cranks and 34:21 I get 3.2
    and with 170 cranks 34:22 I get 3.2

    So looks like thats what I need to do. I did try the 22 sprocket when I first started singlespeeding, but found my speed on the flats suffered, hopefully with the shorter cranks I'll be able to spin this gear better.

    Did the shorter cranks affect your riding at all. I find I'm faster on the flat, but as I said climbing feels harder - though not necessarily slower.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
    Planet X Dirty Harry
    Chiner 29er SS

  5. #5
    Armature speller
    Reputation:
    Join Date
    Sep 2004
    Posts
    3,022
    I dropped from 180 to 175 on my Unit as I can't spin the 180's comfortably at high revs. Everywhere else they were fine.

    My leg length indicates I should be using 180-185.

    I'm tempted to try them again and see what it feels like now after 6 months on the shorter cranks.

  6. #6
    mtbr member
    Reputation:
    Join Date
    May 2015
    Posts
    50
    I have always been a spinner and preferred lower gears, so I tried some short cranks when I did my SS conversion, I think these are 152mm, so far I like them a lot, and I get a bit more ground clearance as I built this for my local single track.

  7. #7
    Downcountry AF
    Reputation: *OneSpeed*'s Avatar
    Join Date
    Oct 2013
    Posts
    6,136
    good question, i've been thinking about this lately. I'm 6'3" on 175 cranks. lately, every time i get on the bike the cranks have this felling of being too short. I'm curious to try 180mm cranks but i feel like the BB on my Unit is already lower than my other bikes and i have more pedal/foot strikes. I'm very aware of it and it affects the way i ride. i wish my BB was higher.

    I'm not sure on the science behind it, i did some reading a while back, but in my head i feel like i want longer cranks for the additional torque. I get the same short crank feeling on my Krampus, which has 780mm handlebars that i love. same with the fat bike, wide bars give better leverage. seems like a similar concept.

    longer cranks would give better torque, effectively a lower gear ratio, but make it harder to spin a high cadence on the flats. so if you change your gear ratio to offset a change in your crank length is it all a wash in the end on a SS?

    on a geared bike the change in gear ratio is far less important/noticeable. that seems it would just be more about what your comfortable with, and i don't think it's uncommon to run shorter cranks on a road bike.
    Rigid SS 29er
    SS 29+
    Fat Lefty
    SS cyclocross
    Full Sus 29er (Yuck)

    Stop asking how much it weighs and just go ride it.

  8. #8
    mtbr member
    Reputation:
    Join Date
    Jan 2012
    Posts
    12,756
    Quote Originally Posted by xcbarny View Post
    Thanks, that's interesting. I just tried the the gain ratio calculator (didn't know it existed)

    With 175 cranks and 34:21 I get 3.2
    and with 170 cranks 34:22 I get 3.2

    So looks like thats what I need to do. I did try the 22 sprocket when I first started singlespeeding, but found my speed on the flats suffered, hopefully with the shorter cranks I'll be able to spin this gear better.

    Did the shorter cranks affect your riding at all. I find I'm faster on the flat, but as I said climbing feels harder - though not necessarily slower.
    Looks like from your strava you're getting a pretty good performance gain now. I'd stick with that and see how it pans out for awhile as you get acclimated to the climbing. Faster is faster.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    268
    Quote Originally Posted by *OneSpeed* View Post
    longer cranks would give better torque, effectively a lower gear ratio, but make it harder to spin a high cadence on the flats. so if you change your gear ratio to offset a change in your crank length is it all a wash in the end on a SS?
    This is the fundamental trade-off of any gear reduction system: torque multiplication vs speed. Longer crankarms will provide more torque, but reduced top speed. Increasing the gear-inches to get back the speed, will also eliminate the torque advantage.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Sep 2011
    Posts
    321
    Quote Originally Posted by xcbarny View Post
    Thanks, that's interesting. I just tried the the gain ratio calculator (didn't know it existed)

    With 175 cranks and 34:21 I get 3.2
    and with 170 cranks 34:22 I get 3.2

    So looks like thats what I need to do. I did try the 22 sprocket when I first started singlespeeding, but found my speed on the flats suffered, hopefully with the shorter cranks I'll be able to spin this gear better.

    Did the shorter cranks affect your riding at all. I find I'm faster on the flat, but as I said climbing feels harder - though not necessarily slower.
    Yep, think I went down one tooth based on similar calculations.

    Just for background, when I had 175mm cranks and saddle height was adjusted for proper leg extension at the bottom, my knees were always too high at the top of the stroke. This was of course uncomfortable and led to hip pain. I always struggled chasing a comfortable position on the bike and did not realize the crank issue was the root of the problem until i got a fitting. The fitter called it out immediately and listed out all the problems I was feeling without me saying a word.

    In my opinion, the old notion of leverage from a longer crank should only be considered after efficiency and ergonomics are looked at first.
    Pedal through it!

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    637
    Here's a link to a few methods for working out your optimal crank length, though its probably more applicable to road bikes:

    BikeDynamics - Bike Fitting Specialists - Crank Arm Lengths

    My optimal length is 167.5mm, but since its hard to get this size in mtb cranks, I stuck to 170mm.
    Its possible that since with Singlespeeding, we spend more time out of the saddle, we can get away with longer cranks. And the extra leverage is beneficial for getting up pinch / technical climbs ?

    Anyway, I'll stick with the 170s for a while. I'm keen for them to work for me, since my pedalling is definitely better with them.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
    Planet X Dirty Harry
    Chiner 29er SS

  12. #12
    Armature speller
    Reputation:
    Join Date
    Sep 2004
    Posts
    3,022
    Extra leverage is cool, but shorter cranks and lowering the gearing is usually more efficient.

  13. #13
    psycho cyclo addict
    Reputation: edubfromktown's Avatar
    Join Date
    Sep 2010
    Posts
    2,609
    I am somewhat tall (over 6'1" with 32" inseam) and run 175mm on all my MTB's other than a Niner SIR 9 single speed at the moment.

    I run more stout gearing (36x18 with a 3.0" tire on the front is about optimal for local trails in my area). I notice the difference with 180mm cranks on slow mash climbs more than anything else.

    I'd also say that the bike geometry is a factor to consider with longer cranks. I've ridden SS rides of up to ~70 miles on different bikes (closer to 100 mi on geared) and some are less comfortable than others with longer cranks. I can ride the Niner anywhere from urban assault (with a lot of hill climbs) to all singe track and it is quite comfortable where other frames leave me feeling too leggy or my knees may bother me for a few days.
    【ツ】 eDub 【ツ】

  14. #14
    Occasionally engagedů
    Reputation: Ptor's Avatar
    Join Date
    Jan 2004
    Posts
    1,640
    Quote Originally Posted by xcbarny View Post
    I was getting ready to make fun of "optimized" crank lengths based on a magic formula, but this discussion and your link are really good. Unfortunately it's expensive, time consuming, and potentially physically damaging to do much individual testing of crank length. But many of us have been riding a long time and by virtue of evolving "standards" and riding different bikes we can make some educated guesses (I've ridden many miles on all sizes (2.5 mm increments) from 170 to 180. And I think your (xcbarny's) opening statement to this thread -- "due to ergonomic reasons..." -- is the key. If you have a good fit you can put more power to the pedals and go faster. The "longer crank arm gives more leverage" is a red herring -- leverage on a bike is a function of crank arm length, chain ring size, rear cog size, and wheel size. Change any of those and you change leverage. Get the optimum fit for your legs and body with the right crank arm length, then worry about how much leverage you need and adjust accordingly with the other three variables.
    "The plural of anecdote is not data." -- Attributed to various people in a variety of forms, but always worth remembering...

  15. #15
    mtbr member
    Reputation:
    Join Date
    Sep 2011
    Posts
    321
    Ptor - precisely!
    Pedal through it!

  16. #16
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    637
    Quote Originally Posted by Ptor View Post
    I was getting ready to make fun of "optimized" crank lengths based on a magic formula, but this discussion and your link are really good. Unfortunately it's expensive, time consuming, and potentially physically damaging to do much individual testing of crank length. But many of us have been riding a long time and by virtue of evolving "standards" and riding different bikes we can make some educated guesses (I've ridden many miles on all sizes (2.5 mm increments) from 170 to 180. And I think your (xcbarny's) opening statement to this thread -- "due to ergonomic reasons..." -- is the key. If you have a good fit you can put more power to the pedals and go faster. The "longer crank arm gives more leverage" is a red herring -- leverage on a bike is a function of crank arm length, chain ring size, rear cog size, and wheel size. Change any of those and you change leverage. Get the optimum fit for your legs and body with the right crank arm length, then worry about how much leverage you need and adjust accordingly with the other three variables.
    This Gain Ratio Calculator seems like it allows you to take all these variable into account to get a good comparison:

    Sheldon Brown's Bicycle Gear Calculator

    Hopefully I can try a bigger sprocket this weekend, and see how I go.

    Yes It can be very expensive to change this. So far I've converted 4 of my 5 bikes to shorter cranks. it has taken a while to save up the $$.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
    Planet X Dirty Harry
    Chiner 29er SS

  17. #17
    mtbr member
    Reputation: Stopbreakindown's Avatar
    Join Date
    Jun 2011
    Posts
    868
    I accidentally stumbled upon shorter cranks. I recently built up a B+ Canfield EPO w/ 165mm cranks in anticipation of more pedal strikes due to the BB drop caused by the 2.8 tires. It turns out that it feels as if my circles are more fluid and my legs are less tired after longer rides. (6' w/ short legs) I wish I had figured this out sooner.

  18. #18
    Always in the wrong gear
    Reputation: Impetus's Avatar
    Join Date
    Aug 2014
    Posts
    2,368
    5'9"
    standard XT 175s on my MTB (SS geared AB oval 32x22)
    DuraAce 170s on my road bike.
    both were purchased more for quality/condition/availability (2ndhand) than fitment nuances.
    I'd probably be happy with 170's on my SS. I'm definitely a spinner not a masher.

  19. #19
    mtbr member
    Reputation:
    Join Date
    Jun 2016
    Posts
    73
    Im from the oldschool and run 180's on anything that needs them. Have been for 30+ years, since my bmx days.

    It works well enough for my 5' 9" frame, 30" inseem to strike fear into my gear head friends when I show up on my oney. They know who they'll be chasing for the day...
    Attached Thumbnails Attached Thumbnails What crank length are you running?-20160620_234001.jpg  


  20. #20
    No known cure
    Reputation: Vader's Avatar
    Join Date
    Feb 2004
    Posts
    2,986
    180mm crank arms
    34X20
    31.5 inseam
    26" wheel
    3.2 gain ratio
    Ripping trails and tipping ales

  21. #21
    I Tried Them ALL... SuperModerator
    Reputation: Cayenne_Pepa's Avatar
    Join Date
    Dec 2007
    Posts
    6,434
    I'm short-legged, but runs 175mm simply because I like the added leverage.
    "This is a male-dominated forum... there will be lots of Testosterone sword-shaming here" ~ Kenfucius

  22. #22
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    637
    I got to try a 22t sprocket yesterday, to replace the 21 that I had on, giving me 34:22 ratio.

    This changed the bike back to feeling how it did with 175 cranks and 34:21. Effort at the cranks felt the same, and I felt that I could get ontop of the gear if I needed to, without feeling like was going to stall. Yet I aslo got the benefit of the shorter cranks such as smoother pedal stroke and better spinning.

    I also didn't ever feel like I was under geared (whilst riding single track), like I had done when I'd previously tried the 22T cog with 175mm cranks.

    So seems like the Gain ratio calculator works.
    Lapierre XR29ei, Chris King LB Carbon, XTR 1 X 10
    Planet X Dirty Harry
    Chiner 29er SS

  23. #23
    mtbr member
    Reputation: Flat Ark's Avatar
    Join Date
    Oct 2006
    Posts
    1,646
    I am 5'8" and have been on 170's for the last 3-4 years. Stumbled onto them by chance when I bought a beater bike. I just noticed that I always felt more hooked-up/engaged all the way around my pedal stroke when on that bike. Decided to upgrade the cranks and that is when I saw 170mm stamped on them. I now have 170's on all of my bikes. As a bonus the knee issues that had plagued me for several years disappeared seemingly overnight.

    It did take some getting used to though. For a while I had the sensation of running with my shoes tied together. Like I wanted to take bigger strides but just couldn't. That all went away though and now it feels as though it takes much more effort to run 175's. I'll never go back.

    Sent from my LG-D850 using Tapatalk

Similar Threads

  1. Replies: 2
    Last Post: 03-01-2015, 06:48 AM
  2. What bar width and stem length are you running?
    By petey15 in forum Women's Lounge
    Replies: 13
    Last Post: 01-14-2015, 08:11 PM
  3. Replies: 40
    Last Post: 02-06-2014, 04:28 PM
  4. BB shell length / crank spindle length for HiFi 29?
    By bisicklay in forum Gary Fisher
    Replies: 1
    Last Post: 01-11-2014, 04:41 PM
  5. What length stem are you running on your Tallboy?
    By Jarlaxle in forum Santa Cruz
    Replies: 13
    Last Post: 06-12-2012, 05:06 PM

Members who have read this thread: 6

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.