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Old 2008-09-14, 11:53 PM   #1
pdc
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Crank Length VS. Height and Weight or Does Size Really Matter?

Ok, lets talk about the size of our cranks. Seriously...

I was wondering how the height and weight of a rider would effect what the optimum crank length would be. I've heard some distance riders saying that a 125mm or shorter length is optimal even for climbing fairly significant grades. I wonder if this would remain true for a rider like myself who is 6'3" and 200 lbs. For me when I was road riding daily I still felt more comfortable with 150mm cranks (I ride a fairly hilly course). The length helped me both acending and decending. A guy who was say 150 lbs might benefit from short cranks as he has less weight to push up the hill and less weight to hold back decending. I think the same would hold true for Muni.

Please add your thoughts.

-Phil
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Old 2008-09-14, 11:57 PM   #2
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I think if your going weight:length then it may be the opposite, with more weight you have more pressure so you don't need additional leverage from longer cranks. I like cruising around town on 150s on my 36er but for going fast I like short cranks (125) because its easier for my stubby legs to spin.
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Old 2008-09-15, 12:44 AM   #3
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I think rider strength and technique are of far more significance than rider weight and height when it comes to optimum crank length, which also might changes over time as strength and technique develop.

Last edited by lunicycle; 2008-09-15 at 12:45 AM.
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Old 2008-09-15, 01:30 AM   #4
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I think technique is the more important of the two, especially if you ride with a brake as I do. Because of my injuries my muscles tend to be out of shape, but I can still do great riding because of my technique. Muscles are good for climbing (ewww), and slowing down (which I have a break for (why would you want to slow down)).
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Old 2008-09-15, 02:23 AM   #5
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Quote:
Originally Posted by pdc
Ok, lets talk about the size of our cranks. Seriously...

I was wondering how the height and weight of a rider would effect what the optimum crank length would be. I've heard some distance riders saying that a 125mm or shorter length is optimal even for climbing fairly significant grades. I wonder if this would remain true for a rider like myself who is 6'3" and 200 lbs. For me when I was road riding daily I still felt more comfortable with 150mm cranks (I ride a fairly hilly course). The length helped me both acending and decending. A guy who was say 150 lbs might benefit from short cranks as he has less weight to push up the hill and less weight to hold back decending. I think the same would hold true for Muni.

Please add your thoughts.

-Phil
In the bike world, taller riders use slightly longer cranks and smaller riders use shorter cranks. The length only varies by about 5mm though. It is obviously a bit different in the unicycling world, but I think that smaller/lighter riders will have an easier time with shorter cranks.

Your area is indeed hilly, and for the climbing the 150s are going to feel easier for you. I would stick with that length knowing your terrain and experience. You might want to try some 140mm cranks out though. I have some Schlumpf 140mm aluminum cranks to use specifically for the Shenandoah region. I think that is the ideal size for Skyline Drive, even though I have yet to try them out! I am not sure if there are other 140mm squar taper cranks out there that are lightweight and of decent quality, but it may be worth it to order a pair of the schlumpf 140s.

EDIT: It looks like you can also get some of the steel United 140mm cranks on UDC for 12 dollars. I personally hate the heavy steel cranks, but that is a much cheap option.
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Last edited by siafirede; 2008-09-15 at 02:26 AM.
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Old 2008-09-15, 03:22 AM   #6
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The torque/weight ratio is constant for all riders using any one crank length as long as the weight of the unicycle is insignificant. Torque advantage comes with increasing crank length and decreasing wheel diameter for all riders. I like long cranks because I have long legs and don't have as much of an exaggerated pump stroke when I pedal as someone with stumps. That is, I can get away with it so why not go with the torque advantage? I even put 170's on Blue Shift...but Phil already knows this.
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Old 2008-09-15, 07:14 AM   #7
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I came here to say what Harper said.

If you're a tall person with long legs you'll have an easier time with longer cranks. Your knees won't move up as high or be as exaggerated compared to a shorter person.

If you're tall and can get away with it, take advantage of it. Use longish cranks if you can spin them smoothly and still "dance" on them while climbing.

I have long legs for my height. I have been comfortable on longer cranks than other people. I like the advantages I have with longer cranks for the riding that I do and riding the way I like to ride. That's all that matters.

If you have poor spinning technique then climbing with cranks that are too long can actually hinder you. Poor technique can cause you to get stuck and lose momentum at the bottom of the stroke, especially when standing out of the saddle while climbing. The comment about "dancing" on the pedals was a reference to that. If you can dance and keep the pedals going without dwelling at the bottom of the stroke then you're good. If you can dance on the pedals without causing your whole body to bob up and down excessively you're good.

Shorter people (or people with shorter legs) will have a more difficult time dancing on the pedals with longer cranks. When the cranks get so long that you can't dance properly then the long cranks become a hindrance rather than a benefit.
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Old 2008-09-15, 08:40 AM   #8
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I really can't get on with short cranks on my coker. I tried 125s for a bit before unicon, because it was "the thing to do" for flat riding (Denmark), but after 100 miles or so I went back to the trusty 145s. I'm not a huge spinner (my max speed is usually about 16mph), so perhaps longer cranks suit me better. The 125s just made freemounting more difficult and didn't seem to have any advantage for me - my top speed was actually slower because of lack of control. Perhaps I didn't stick at it for long enough. Also, the short stroke of the 125s just feels very inefficient to me, wasting muscle range and putting needless extra pressure on the knees. Most other people seem to think they're fantastic though, and all the fastest riders favour small cranks, so presumably it's not just "emperor's new clothes".

I'm just under 6' 2", and weigh 12st (168lbs).

BTW: I think my top speed on the coker is limited more by lack of guts than ability to spin. I can spin faster on the 26" muni with 150s, but obviously at a lower speed so it doesn't feel so dangerous.

Rob
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Old 2008-09-15, 04:17 PM   #9
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I don't know that there's any correlation between height and preferred crank length. I've seen riders of a wide range of heights with a range of cranks lengths on 36ers around here, on the road and off the road, up and down hills.
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