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changing crank arm length

Old 01-07-06, 10:20 PM
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trekking_TW
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changing crank arm length

Is there any advantage or disadvantage to changing the crankarm length?

I'm changing my cranks and currently have 170mm length 105. I'll be changing to DA 172.5mm unless this would cause major problems for me. I've heard that shorter cranksarms cater more to the spinners and longer cranks are preferred more by the mashers. Is this the case?
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Old 01-07-06, 10:53 PM
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You generally have the idea right, but height, or more accurately leg length, plays a big factor as well. If you are taller than average a longer crank arm may suit you better, but in my opinion, 2.5 mm isn't going to make a huge difference anyway.
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Old 01-07-06, 11:11 PM
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Originally Posted by trekking_TW
Is there any advantage or disadvantage to changing the crankarm length?
?
Some people claim that the longer cranks provide extra leverage (I think I'm one of them
), but some of the 'physicists' say it's impossible when gears are involved -- either way, 2.5mm difference will be barely noticeable.

What you should notice is the drop in relative saddle height. You'll most likely lower the saddle ~2.5mm (assuming it's currently in the right position for you), which means the seat will be ~5mm lower, relative to your knees, through the top secion of the pedal stoke.

Others claim that different crank lengths can improve the biomechancis of the quads once the correct length for the individual has been found, but....yada yada..... The whole topic is inconclusive and complicated, especially when muscle firing preferences and biomechanics are involved
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Old 01-07-06, 11:17 PM
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I think it might be more important than manufacturers sale for.

170mm for all.
I need around 168.
The stresses would be reduced in the skeletal. Building a bike i'd order the right length.
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Old 01-08-06, 04:06 AM
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See, http://www.cranklength.info for all you ever wanted to know on the subject. If 170mm is the right length for you in the first place then 2.5mm is neither here nor there however if your legs are on the shorter side them moving longer may be detrimental. Going longer may make it harder to be comfortable in an aerodynamic tuck which will wipe out any benifit you may beleive that you will gain.

Regards, Anthony
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Old 01-08-06, 05:36 AM
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Everybody has a slightly different view of crank length. For kicks I switched from 175 this last summer to 172.5 and didn't like the change so switched back. I have long legs and I thought I may prefer the ability to spin the 172.5mm cranks at a bit higher RPM while being in a slightly shorter gear...wasn't the case for me. Some say that 2.5mm is not noticeable but to me it is. A further argument as to why 2.5mm is noticeable is to consider that cranks are available in only 2.5mm increments = 5mm in circle diameter and crank arms are typically available as std. within a very narrow band width i.e. 170-175 for most cranksets...there are exceptions. The other intangible for me was KOPS and overall balance on the bike. I like the longer cranks for standing as I felt I had a bit more balance and could push a slightly bigger gear with lower cadence with longer crank arms.
Personal preference again weighs heavily for most and like frame size, in spite of what you measure I believe trial and error is still the best teacher.
HTH,
George
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