Advertise on Bikeforums.net



User Tag List

Results 1 to 25 of 25
  1. #1
    Senior Member
    Join Date
    Jul 2011
    Location
    Merry Land
    My Bikes
    Guru Evolo R, Colnago Pista, Look AL 464P SS, various frankenbikes
    Posts
    433
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)

    What crank arm length on your fixed? Your SS?

    I have a Sugino 75 170mm on my fixed, which I feel is a great compromise for road routes, and recently put a 172.5 on my SS for that added leverage on the slightly longer, hilly routes I cover with it. I recently read an article promoting the virtues of very short arms, like below 150, citing a supposed mechanical advantage with all kinds of anecdotal evidence utilized as supportive data. Seemed at least compelling.

    To be honest, I rode with 165's for years but always felt they were too short and feel better with longer arms, but being the curious (and actually open minded…..sometimes…) sort that I am, I wanted to hear some of your perspectives on this issue. BTW, I'm 6 ft. with a fairly long 34 in. inseam, if that matters.
    Last edited by stilltooslow; 11-13-13 at 06:51 PM.

  2. #2
    pro in someone's theory prooftheory's Avatar
    Join Date
    Jul 2011
    Location
    Las Cruces, NM
    My Bikes
    FTP
    Posts
    2,258
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    The track guys in here (TT and carleton) always say that optimal crankarm length is different for each individual and can't even be predicted based on body geometry. TT is very short and uses 175s for instance. If you are more comfortable at 172.5 then use that. I use 165s and I feel like I'm pretty efficient with those but I don't notice it much if I go up to 170. The only real argument for shorter on fixed is pedal strike. It may be worth a couple millimeters less than optimum to avoid crashing.

  3. #3
    Veteran Racer TejanoTrackie's Avatar
    Join Date
    Jul 2009
    Location
    Ciudad de Vacas, Tejas
    My Bikes
    28 frames + 73 wheels
    Posts
    7,734
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by prooftheory View Post
    TT is very short and uses 175s for instance.
    Huh ? The longest cranks I have on any of my bikes are 170mm, and all my fixed gear type bikes have 165mm. However, I can hardly tell the difference unless I'm spinning really fast or racing. Far more important is getting your seat position dialed in and having a smooth efficient pedal stroke. As to pedal strike, BB height is just as significant a factor as crankarm length, and some SS bikes are based on road frames, which have low BB's.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  4. #4
    pro in someone's theory prooftheory's Avatar
    Join Date
    Jul 2011
    Location
    Las Cruces, NM
    My Bikes
    FTP
    Posts
    2,258
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    It is weird that I have a distinct memory of you posting that you had ordered longer cranks because they were going to help you spin faster. I must have dreamed it.

  5. #5
    Senior Member seau grateau's Avatar
    Join Date
    Sep 2009
    Location
    LA
    My Bikes
    Shogun Selectra (geared), Affinity Lo Pro (fixed)
    Posts
    5,525
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I rock the 170s for no reason other than they came stock on the bike or the cranks I wanted were most readily available in 170. Never saw any reason to change. I don't imagine it's an issue I'll have have to consider seriously.
    Quote Originally Posted by adriano View Post
    thanckx.
    Quote Originally Posted by Nagrom_ View Post
    "I made love to your mother dozens of times last week, and she doesnt know what a worn chain ring looks like"

  6. #6
    Senior Member gregjones's Avatar
    Join Date
    Aug 2012
    Location
    West Georgia
    My Bikes
    K2 Mod 5.0 Roadie, Fuji Commuter
    Posts
    2,173
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Some folks say 165, some say 170.

    Mine are 167.5. That's how to decide.

    They go round and round and so follows the rear wheel. No problem.
    Updated K2 pics 9/10/14
    Click PR Logo
    PedalRoom

  7. #7
    Veteran Racer TejanoTrackie's Avatar
    Join Date
    Jul 2009
    Location
    Ciudad de Vacas, Tejas
    My Bikes
    28 frames + 73 wheels
    Posts
    7,734
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by prooftheory View Post
    It is weird that I have a distinct memory of you posting that you had ordered longer cranks because they were going to help you spin faster. I must have dreamed it.
    Longer cranks definitely do NOT help you spin faster. Think of high revving engines, that have less crankshaft offset for the same reason to keep piston speeds under control.
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  8. #8
    pro in someone's theory prooftheory's Avatar
    Join Date
    Jul 2011
    Location
    Las Cruces, NM
    My Bikes
    FTP
    Posts
    2,258
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by TejanoTrackie View Post
    Longer cranks definitely do NOT help you spin faster. Think of high revving engines, that have less crankshaft offset for the same reason to keep piston speeds under control.
    That is definitely the conventional wisdom as passed down from sheldon but my memory is that you were actually bucking the said wisdom and pointing out that leg length didn't necessarily have an impact on optimal spinning. Again, some weird bfssfg acid trip I had.

  9. #9
    Veteran Racer TejanoTrackie's Avatar
    Join Date
    Jul 2009
    Location
    Ciudad de Vacas, Tejas
    My Bikes
    28 frames + 73 wheels
    Posts
    7,734
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by prooftheory View Post
    That is definitely the conventional wisdom as passed down from sheldon but my memory is that you were actually bucking the said wisdom and pointing out that leg length didn't necessarily have an impact on optimal spinning. Again, some weird bfssfg acid trip I had.
    Leg length =/= crank length
    What, Me Worry? - Alfred E. Neuman

    Quote Originally Posted by Dcv View Post
    I'd like to think i have as much money as brains.

  10. #10
    pro in someone's theory prooftheory's Avatar
    Join Date
    Jul 2011
    Location
    Las Cruces, NM
    My Bikes
    FTP
    Posts
    2,258
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    Obviously. What I meant was that the leg-length to crank-arm length ratio wasn't predictive of optimal spinning. At this point, I can find @carleton posting similar claims but I thought you had joined with him in these assertions and I can't find it, so it is simply a false memory. Idiots sometimes get those.

  11. #11
    Senior Member
    Join Date
    May 2010
    Location
    Medford, MA
    Posts
    268
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    For another perspective on crank length, gearing, and mechanical advantage, read here: http://sheldonbrown.com/gain.html
    The basic point is that if you talk about leverage, you should talk about the leverage of the entire drivetrain together, meaning the total mechanical advantage from the gearing and the cranks combined. So in theory, if you want to keep everything the same but change your crank length, you would have to change your gear as well to wind up putting the same amount of force on the pedals for the same power output (but at a different cadence).

    Aside from that, I think ideal crank length has more to do with the mechanics of your body, and what you're used to (and what you need to prevent pedal strike). If you have longer legs, you're more likely to want longer cranks. Short legs, short cranks.

    But here's another reason you might want to go shorter on a fixed gear: If you change crank lengths *without moving your seatpost*, two things happen. One is that your leg extension at the bottom of the pedal stroke changes. Shorter cranks mean your leg is extended less, longer cranks mean it's extended more. The other is that the angle of your knee at the top of your pedal stroke changes. Shorter cranks mean your knee is bent less at the top, longer cranks mean it is bent farther. You put more strain on your knee joint when you put pressure on it when it's bent farther, and less strain when it is closer to straight. That's why riding a bike with the saddle too low will make your knees sore in short order. (Not to say that you can't or shouldn't move your seat height - just describing the geometry of the situation)
    On a fixed gear, you wind up grinding in too high of a gear a lot of the time, because you only have one. So using shorter cranks means that at least you aren't putting the pressure on your knees at as much of an angle. At the same time, it is easier to spin fast more smoothly without bouncing if you have a little slack at the bottom of the pedal stroke. Shorter cranks get you both of those things simultaneously.

    Personally, I always had 165's on my fixed. I used to have 170's on my geared bike, but at a certain point I realized that since I rode it so little, I wasn't really used to the 170's anymore and sort of felt like I was pedaling squares... plus I kept scraping my pedal in corners because the road bike doesn't have the clearance the fixie has. So I put 165's on everything now, and it's much more comfortable that way. I'm 5'6" with a 30" inseam, FWIW.

    One last little aside about crank length - have you ever noticed how many bikes that come in really small sizes still come with 170 cranks, because no one wants to bother with more than like two crank sizes? (170mm cranks on frames smaller than maybe 56cm and 175's on everything bigger) And then all the really short riders keep asking why they always feel like their knees are hitting their chest when they ride and the bike shop dudes don't have any idea?

  12. #12
    Senior Member
    Join Date
    Apr 2013
    Location
    North Attleboro, MA
    My Bikes
    Surly Steamroller
    Posts
    264
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    What kind of riding were they doing with these 150 and shorter cranks?

    I'm just curious, because in my experience there is a balance (equilibrium?) that is reached at somepoint between the crank legnth and the speed produced from spinning. To me too short a crank arm just means you'll spin out sooner in certain circumstances.

    The only benefit to the short cranks would be for a brief burst of speed, like when doing BMX tricks.

  13. #13
    Morton Nagrom_'s Avatar
    Join Date
    Dec 2011
    Location
    East Bay
    My Bikes
    Kilo TT, CAAD10
    Posts
    9,712
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by OneGoodLeg View Post
    The only benefit to the short cranks would be for a brief burst of speed, like when doing BMX tricks.

    Quite the opposite actually.
    Shorter crank arms give you less leverage, meaning less torque for the same amount of power input. This means you have less of an ability to accelerate.

    Theoretically, using shorter crank arms will give you a higher top end speed if you can produce the same foot speed as you can on longer crank arms. Not in terms of revolutions per minute, but rather distance per minute.

    Carleton and I did the math a couple years ago in another thread, but it turns out its pretty linear. We used a base crank arm length of 170mm. For every 5mm increase/decrease in arm length there is a ~3% increase/decrease in leverage and a ~3% decrease/increase in in cadence given the same foot speed, respectively.



    Remember:
    This is all physics on paper. We aren't robots riding bicycles in vacuums. Physiology dominates nearly all the physics in this case. Just because it's better on paper doesn't mean it's better in real life, and in particular, it doesn't mean it's better for YOU.
    Quote Originally Posted by seau grateau View Post
    No offense but you're an idiot.
    PedalRoom

  14. #14
    old legs
    Join Date
    Aug 2009
    Posts
    956
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    When I rode fixed used 165mm cranks mostly because I live in a small town with lots of little maze like streets where I had to turn while riding. Since I switched to SS I use 175mm cranks because the big arms make climbing easier

  15. #15
    Senior Member
    Join Date
    Jul 2011
    Location
    Merry Land
    My Bikes
    Guru Evolo R, Colnago Pista, Look AL 464P SS, various frankenbikes
    Posts
    433
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by OneGoodLeg View Post
    What kind of riding were they doing with these 150 and shorter cranks?
    I wish I could find the article, although it was actually more of a sales pitch for the company that made the extra short cranks. If I recall correctly, the main subject of the 'case study' was a triathlete type who greatly improved his time after making the switch. Again, it was all sales-y, but still quite compelling. The author went on to mention others who are moving to shorter arms, where he brought up Lance Armstrong as well.

    I'll try to find it, but if anyone else does, feel free to post the link.

  16. #16
    A little North of Hell
    Join Date
    Mar 2006
    Posts
    4,374
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    [SIGPIC][/SIGPIC]
    XXXI

  17. #17
    ÖöÖöÖöÖöÖö Dannihilator's Avatar
    Join Date
    Oct 2002
    Location
    Annandale, NJ.
    My Bikes
    2014 Surly Steamroller, 1977 Puch Pathfinder
    Posts
    18,924
    Mentioned
    22 Post(s)
    Tagged
    1 Thread(s)
    170mm here.
    Strike like an eagle and sacrifice the dove.
    Words and Stuff.

  18. #18
    Senior Member
    Join Date
    Apr 2013
    Location
    Glendale, CA
    My Bikes
    2013 Giant TCR Advanced SL4, 1989 Centurion Ironman Master Dave Scott
    Posts
    2,446
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    165 because I thought it was an understood standard on a fixie/track bike. But I am riding a frame with proper track geo and bottom bracket height. My road bike has 172.5 and they feel pretty damn comfortable to me
    http://www.pedalroom.com/members/rms13

  19. #19
    Senior Member
    Join Date
    Jul 2011
    Location
    Merry Land
    My Bikes
    Guru Evolo R, Colnago Pista, Look AL 464P SS, various frankenbikes
    Posts
    433
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Soil_Sampler View Post
    Thanks SS….that be the one.

    Soooo…….hype and sales propaganda, or is there some element of truth in there??

  20. #20
    Grumpy Old Bugga europa's Avatar
    Join Date
    Oct 2006
    Location
    Adelaide, AUSTRALIA
    My Bikes
    Europa, Hillbrick, Road Chief, Repco Superlite (Ol' Rusty)
    Posts
    3,114
    Mentioned
    12 Post(s)
    Tagged
    0 Thread(s)
    You're only going to notice the difference in crank length if you ride lots of different bikes and to honest, I don't think it makes any difference on the street. The track is different of course.

    My Hillbrick is running 170s but she was built as a fg bike and has the higher bottom bracket to suit. I have never suffered pedal strike despite using relatively wide pedals.

    My Europa was built as a road bike. When she was fixed, I started with 170s and got the occasional pedal strike. When I upgraded the cranks, I went for 165s and I never suffered pedal strike. She's now geared again and is using 170s. Thanks to all my fg riding, I keep forgetting I can coast through corners and quite often have pedal strike.
    I had a good bike ... so I FIXED it

  21. #21
    Old fart JohnDThompson's Avatar
    Join Date
    Nov 2004
    Location
    Appleton WI
    My Bikes
    Several, mostly not name brands.
    Posts
    12,818
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    I have 165mm arms on both my fixed gear bikes (for clearance) and 170mm arms on my road bikes. I don't notice any real difference beyond less pedal strike with the shorter arms on the fixed gear bikes.

  22. #22
    I just wanna ride stryper's Avatar
    Join Date
    Oct 2008
    Location
    Chico Califo
    My Bikes
    2013 BMC Impec
    Posts
    1,059
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Soil_Sampler View Post

    wow. much photoshop. such excellence.

  23. #23
    Not actually Tmonk TMonk's Avatar
    Join Date
    Jun 2007
    Location
    San Diego, CA
    My Bikes
    caad9, capo (fixed), centurion dave scott 10sp, dolan pre cursa (track)
    Posts
    6,282
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    172.5 on all road bikes, fixed gear roadie

    165 on track bike
    "Your beauty is an aeroplane;
    so high, my heart cannot bear the strain." -A.C. Jobim, Triste

  24. #24
    7-speed doomsday prepper ThermionicScott's Avatar
    Join Date
    Aug 2011
    Location
    CID
    My Bikes
    1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX
    Posts
    8,500
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    165mm on mine. No reason but peer pressure, but it works well enough that I have no reason to switch.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
    RUSA #7498

  25. #25
    THE STUFFED Leukybear's Avatar
    Join Date
    Oct 2009
    Location
    Sandy Eggo, CA
    My Bikes
    Sworks Venge; Kona Paddywagon; Ibis Mojo SL-R
    Posts
    10,387
    Mentioned
    10 Post(s)
    Tagged
    1 Thread(s)
    165mm track
    170mm road

Posting Permissions

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