thoughts on DH/FR crankarm length?

[Dennis]

ok, so now that I am going to build this DH/FR bike, any thoughts on how long my crankarms should be?
I know they need (should) to be shorter than XC type riding, but am unsure about how much shorter.
165 or 170 for a not quite 5'8" tall person?
thanks for the input
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[Matno]

I'm no crank-length expert, but the "experts" all disagree anyhow. My two cents says to get the shortest crank arms you can. Hitting cranks on the ground is about as annoying as anything (except maybe snapping a stem or handlebar) and can be dangerous in a high-speed DH setting. Since you don't really need the cranks all that much on a DH rig, I shouldn't think it would matter. Besides, you can always adjust your gearing to compensate for the slight loss of leverage.

Personally, I think crank-length debates are overdone - especially in MTB settings. The actual differences are really small.  5mm is not something I think most people would even notice. Heck, I didn't even notice the difference on my road bike. (Now I've got 172.5's on the road bike and 175's on the K2, but I've tried others and only settled on those sizes because they were what was available...)

Suspension design is probably just as important if not more so. I rode a Jekyll last year with the geometry slacked out (i.e. lowest BB setting) and the cranks hit just about every rock I came near. It was almost bad enough to turn me off to the bike (but I still think it's the best bike I've ever ridden. Shhhh....)  

[Carbon_Angus]

i think they make a difference, if i was going to ride a DH bike and ride it like it was meant to be ridden, i'd go with a shorter crank, especially for your size.  

besides ...it looks better, Dennis!  [smiley=laughing.gif]

i've ridden 177.5 and now have 175's on all my bikes and i could tell the difference pedaling and also found a few new rocks on my trail with the 177.5's

it's only 2.5 mm in length diff. but the circumfrence can be felt...both ways

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[Simon]

Have a look at http://www.middleburn.co.uk/cranklengths.htm also has a link to a crank length discussions.Simon