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  1.  
    I have just lately started to get back on my bikes (vicariously atop my cinelli rollers). One bike is a road bike and one bike is a mountain bike; I knew, but never really thought about it much, that the crank arms are of different length. Is the length akin to that of piston length in internal combustion engines: i.e. longer length more lower and midrange power application as apposed to a shorter stroke to allow higher rpm's and more power application at higher rpm's? Thanks.
    • CommentAuthorgreg
    • CommentTimeJun 8th 2009
     
    Leonard Zinn is the man when it comes to crankarms: http://www.velonews.com/article/5257
  2.  
    Greg, thank you for the link. It was very interesting and informative. Again, thanks.
    • CommentAuthorj-dogg
    • CommentTimeJun 8th 2009
     
    I used to have a problem with 170's and climbing, I've noticed I can't climb well on 170's or 165's, but I can spin a lot higher than normal.

    I rode 170mm for the longest time and went to 175 and love it. I ride like "Big Mig" Miguel Indurain, I'd be perfectly comfortable with 200mm arms. Much like him I'm a high-torque low RPM rider. 60-80rpm is my happy spot. I max around 180rpm. To compensate for the lower RPM's I have sky-high gearing, 53-39 and a 23-11 9-speed cluster. Same setup as the Dodge Viper, low V10 engine RPM = high torque and .500:1 6th gear = 1200rpm at 60mph.

    My legs love it, I can ride all day now if I wanted to and my legs would be fine with it. When I'm cruising in the 53-11 at 16, 18mph I'm only barely turning 40rpm but because I make all my torque down low I rarely downshift to accelerate at all, only if I'm with a pack.

    I remember when I did MSBike 150 this year I rode the 53-11 for 14 miles straight. I dropped to the 12 and then 13 briefly to close the gap in our pack.

    Now my fixed gear is a 165mm 46-15 and it loves the high RPM it's nothing for me to touch 100 and 120rpm at the velodrome on it.
  3.  
    Longer crank arms do effectively gear you down (and shorter ones vice versa).

    Try Sheldon's gain ratio calculator. A 52/13 gear ratio on 700c wheels goes from a 8.9 gain ratio to a 7.0 between 150mm and 190mm of crank arm. Now, granted, I've never seen 150mm or 190mm cranks, but that difference is the same as between a 14 and 18 tooth cog on the back. That's a big difference.
    • CommentAuthorAlM
    • CommentTimeJun 22nd 2009
     
    165mm's are the stupidest trend.

    Crank lengths serve for people of different sizes/leg lengths. Most people don't know what the fuck they're doing.
    • CommentAuthorAaron C
    • CommentTimeJun 22nd 2009 edited
     
    Posted By: AlM165mm's are the stupidest trend.


    i didn't realize there was a trend around 165mm cranks...


    shit i must be missing the boat. i better swap out all my 170s
  4.  
    Posted By: AlM165mm's are the stupidest trend.

    Crank lengths serve for people of different sizes/leg lengths. Most people don't know what the fuck they're doing.


    I have 170s on most of my bikes, I think my road bikes are 175, but only because that's what I end up with. I wouldn't mind some 165s on my fixed gears, definitely for the trend, if you consider not wanting to eat shit when your pedal hits the ground in a turn trendy.
  5.  
    Yeah, short cranks for ground clearance is a real thing. Criterium bikes use short cranks because of their high speed, in-city tight turns. Fixie riders use them so, when they're cornering and can't position the pedal, they don't hit the ground and they don't overlap their toes with their tires. But it *does* effectively gear up the bike, which means your gear ratio isn't what it seems.
    • CommentAuthorLegislator
    • CommentTimeJun 23rd 2009
     
    Once you are used to your cranks and can spin them, there really isn't much of a difference between lengths, you can read up on most current fit studies and they will tell you the same thing. Power cranks are adjustable from 85mm to 220mm. My schwinn fastback currently has 130mm cranks and is geared at 58 in front and 13-14-15-16-17 in the back, I get full leg extension and can easily spin it up to high RPMs. conversely I have 3 bikes that have crankarm lengths of 180mm, 182.5mm and 195mm (that one is an old BMX) and though it feels different for the first few minutes when I jump on one of those bikes, I quickly get used to it and forget that the cranks are longer.

    There are specific applications for differing lengths of cranks, be it clearance, rider leg length or style of riding, but don't get too hung up on it because unless you're a cat 1 racer, it doesn't really matter all that much.
    • CommentAuthorAlM
    • CommentTimeJul 12th 2009 edited
     
    Posted By: AlM

    Most people don't know what the fuck they're doing.


    Unless you're riding a conversion with 175's, you're not gonna hit your pedals on the ground... well, maybe if you have one of these popular cheap fixed gear frames with road geometry. I can cut a straight corner as fast as I want and stay in the same lane on my 175's and come nowhere near clipping my pedals.

    And yes, 165mm's are a huge trend around here at least, I just bought 175mm Suntour superbes for $125 because nobody wants cranks that long. USED sugino 75's are selling for $200 in 165, 167.5 lengths. 175mm pairs are selling for $120-150 because nobody wants them. If you actually get daring and start cutting corners you'll realize that crank length isn't much of a big deal because the BB height of your TRACK BIKE saves you.
  6.  
    I have 170's on my track pro, and I have 177.5 or something like that on my road bike. I want to try much much longer cranks on my track pro for SWEET FIXIE time trials, as while they're great for a good spin, I wanna push bigger gears.
    • CommentAuthorlatron
    • CommentTimeJul 12th 2009
     
    I'm looking for some 180s -- D.A. or Campy.
  7.  
    Posted By: AlM165mm's are the stupidest trend.

    Crank lengths serve for people of different sizes/leg lengths. Most people don't know what the fuck they're doing.


    Trend eh? So like the fact that 5mm makes the difference between having toe overlap and not having toe overlap on a lot of bikes is somehow a trend now?
    Dude blanket statements just plain old suck, get your head outta your ass. :P
    • CommentAuthorcloud
    • CommentTimeJul 31st 2009
     
    agreed^... my inseam length must also be super trendy because my 165's are appropriate for my track bike
    • CommentAuthorcloud
    • CommentTimeAug 2nd 2009
     
    as far as i know less leg extension on a road bike is appropriate compared to a track bike, i could be wrong.
    • CommentAuthorSkidMark
    • CommentTimeAug 3rd 2009 edited
     
    From what I've been told shorter cranks help you with keeping a consistent high cadence (spinning). You do lose a little leverage with shorter crank arms.

    I've also been told that traditionally track bikes have 165mm cranks, so it's not really trendy.

    I have 165 mm cranks on my track bike AND toe overlap.

    On steeply banked velodromes longer cranks could be a hazard at low speed.
    • CommentAuthoreaglerock
    • CommentTimeAug 3rd 2009
     
    Posted By: SkidMarkOn steeply banked velodromes longer cranks could be a hazard at low speed.

    Bikes are a hazard at low speed. Why would anyone ride slow (0-5mph?) on a banked track, anyway?
    • CommentAuthorscruggle
    • CommentTimeAug 3rd 2009
     
    Posted By: eaglerock
    Posted By: SkidMarkOn steeply banked velodromes longer cranks could be a hazard at low speed.

    Bikesare a hazard at low speed. Why would anyone ride slow (0-5mph?) on a banked track, anyway?


    Are you serious? Someone might ride slow for tactical reasons.
    • CommentAuthorthe rabbi
    • CommentTimeAug 3rd 2009 edited
     
    Posted By: scruggle
    Posted By: eaglerock
    Posted By: SkidMarkOn steeply banked velodromes longer cranks could be a hazard at low speed.

    Bikesare a hazard at low speed. Why would anyone ride slow (0-5mph?) on a banked track, anyway?


    Are you serious? Someone might ride slow for tactical reasons.
    only in match sprints. but even then, any steep banked track, you still need to keep a certain speed (in the turns) or you're gonna fall.

    but even then, below 5mph in the straights is ridiculous.

    at adt, i have to keep up at ~17mph around the turns or i'm gonna slide out. haven't tried with my new tubulars, but i imagine i can go just a bit slower.
 
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