Crank length downsizing?- Mtbr.com
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  1. #1
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    Crank length downsizing?

    Anyone gone from a longer to a shorter SS crank and found it better/easier/zoomier etc? I have been on 180mm cranks since before the dawn of time so naturally that is what I ran on the SS as I got onto one.

    But as I get test bikes rotating through, none of them have 180s on 'em. I noticed less torque when I am 'under the gear' with a 175mm crank, but I got used to it on the geared bikes.

    Going back to the SS with the 180s always felt like coming home. Then I got this SS test bike and it is 175s. 10 hours or so of riding and back to a spin on my friends Selma with 180s (he is 6'4"...I am 6'2"). I was very surprised how much I felt it was taking out of my legs to turn the 180s. I could feel the advantage every so often when I was in the downstroke, but a good part of the time I felt like I was giving up some snappiness in the overall performance, even in climbing.

    I can see the advantage if I am spinning higher RPMs...heck even a 170 crank would be better there...but this felt...not really slower...but more like I was working harder even at lower r's. Can it be that much harder to get that 5mm extra around the circle? I can see where it may be that I am simply getting in tune with a 175 and now I would need to adapt back to the 180s....however, my buddy was on the test bike (we swapped bikes to compare it to the Selma) and he felt like the climbing was less work too, like he was getting the cranks around better compared to the 180s he rides.

    I was very surprised. I need to work on this some more to make sure it was not just a dream, but it sure has me questioning my future in crank lengths.

    Just wondering...I have seen lots of threads on going bigger/longer, but seldom any for the other way.
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  2. #2
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    Reputation: ionsmuse's Avatar
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    I've been using 165s on my Karate Monkey for a few years now. IMO the higher turnover is better in the long run. Less pedal strike on the low BB bike is also big benefit.

  3. #3
    Ovaries on the Outside
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    I'm six foot. On the road I try for 170s and on the mtb, 175. The difference in crank arms, even 5mm is a lot of work to get around in a circle. I'm a spinner, and when I want to tear up singletrack, I want to be able to fly through the twisties and climb the long hills. 175s help me nail high RPMs for a long time, and still get up the climbs. I have a fairly wide handlebar, and I feel that really helps to increase the torque.

  4. #4
    PSYCHOLUST
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    IN MY PERSONAL OPINION ..... I find it hard to imagine such incredibly small increments make a difference.

    My girlfriend has a bike with 175's and another with 165 and says she can feel no difference..... When I hold a 5mm allen in my hand and imagine a crank 5mm longer or shorter............ I could move the cleat on my shoe and get the same mechanical advantage that 5mm in crank length can make

  5. #5
    I don't huck.
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    Quote Originally Posted by scyule
    IN MY PERSONAL OPINION ..... I find it hard to imagine such incredibly small increments make a difference.

    My girlfriend has a bike with 175's and another with 165 and says she can feel no difference..... When I hold a 5mm allen in my hand and imagine a crank 5mm longer or shorter............ I could move the cleat on my shoe and get the same mechanical advantage that 5mm in crank length can make
    I hear ya, but I can tell right away when I swap between bikes. Not even remotely hard to tell the diff.
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  6. #6
    Really I am that slow
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    170 fan here and I can tell a 5mm diff for sure...
    Read my BLOG!

    just a guy who loves bikes and exploring

  7. #7
    Out spokin'
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    Quote Originally Posted by scyule
    IN MY PERSONAL OPINION ..... I find it hard to imagine such incredibly small increments make a difference.

    My girlfriend has a bike with 175's and another with 165 and says she can feel no difference..... When I hold a 5mm allen in my hand and imagine a crank 5mm longer or shorter............ I could move the cleat on my shoe and get the same mechanical advantage that 5mm in crank length can make
    The more you ride, the easier it is to tell.

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  8. #8
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    I can tell 5mm for sure. I just put 170s on one of my fixed gears because they were lying around. It sucks.

  9. #9
    A crunchy treat
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    Circumference of-

    180mm crank rotation: 1131mm

    175mm: 1099.6mm

    170mm: 1068.1mm

    165mm: 1036.7mm

    So there you go, 5mm crank arm difference makes about 31mm difference to the circumference of your pedal stroke. Whether you notice it or not is very dependent on how long your legs/feet are and how long you've been riding a certain length and got used to it.

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