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Custom Length Cranks Help!
Hey,
I have standard length Cranks (175mm i think) and always have trouble with pedaling at speed... i can pedal in a high gear, but if i have to climb i just can't get the rotation speed.... (cadence)
i have been doing some research and i have found custom length cranks might be the way to go...
i did a quick calculation on the ZINN website and it looks like i might benefit from 206 - 210mm Cranks
My question (after all that babble) is can anyone who has custom cranks please comment on their personal results???
Thanks 
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Longer cranks will have you spinning slower, so wont help your cadence.
Although I know you are a tall dude, 210mm cranks are ridiculously long. You would strike every last little root or rock on the trail.
Sure - run a 180mm crank (which is plenty long on an MTB), but better to practice your technique using drills. That will help your cadence much more than long cranks.
I havent answered your question I'm afraid, but if it helps, I run 180's on my road bike, and 175's on my MTB and notice the shorter ones are more 'spinny'.
Bloodyhell you'd be smacking them on every pebble and dip on the path...
As Antsonline says the longer the crank generally the slower your cadence
I'm 6 ft 7 and have a custom Zinn 29'er. It's important to remember I have 29" wheels, not 26", which makes a big difference in pedal ground clearance. If you go longer cranks you also have to check the clearance between your shoe and the front wheel when turning. Don't forget that one.
OK so I have 3 sets of custom cranks (long story).
Specialites TA Carmina 185mms I use on my commuter 26" hardtail. These were my first custom cranks (well they're not actually custom but they are rare as hen's teeth) and they felt great until I got my next set of longer cranks.
Next I bought the Zinn and I was advised by Lennard that size wise I need 210mm cranks, so that's what I got. They give you massive torque so you can get more force through the pedal, but you can't spin as quickly as with shorter pedals. Because of the size, they're also heavier than shorter pedals so there's more rotating mass to move (same principle as wheels). They are also loooooong, and apart from confirming I had the pedal grounding issue that others mention (and that's with 29" wheels), it feels like you're pushing a massive circle, which I found more obvious when I stood up (oh, you'll also have to watch your knees don't hit your shifters on the upstroke when you're standing, as I found out when I changed from riser to flat bars).
I have now moved to a set of 195mm cranks from http://www.hscycle.com/Pages/customcrankset.html and they are the dogs nads. Great compromise, they spin well (for me) and have more clearance, plus they're half the price of Zinn cranks.
One more problem you'll come across. All 3 firms I've bought custom(ish) canks from only make cranks for square taper BBs. I don't have a problem with that as my bikes are built around them, but if you're thinking you can just go and order a set of cranks for your external BB you'll have to hunt harder than I did.
All up if you're tall, go for custom cranks. And a 29er.
Hope that helps.
PS - I have a used but very useable set of Zinn 210mm cranks sitting in my garage, for square taper BBs, if you're interested!!
When you change crank length you're also going to have to look at your seating and cleat positions - when you lengthen the cranks your foot will be further forward, so you'll have to move yout seat and /or your cleats further forward to retain your normal riding position. This in turn will affect your forward/aft balance (seat), and/or your foot position on the pedal (cleat), as well as your reach to the bars. If you're going up in crank length by an inch, this is more important than it might seem otherwise if you're already at your seat forward/cleat forward limit.
Morgan,
I am also 6'7" so it is good to see i am not alone...
I am actually looking at getting a StumpJumper 29er, unfortunately they ZINN bikes are just out of my price bracket which sucks as they look like a nice bike.
i know NOTHING about crank length to be honest, which is why i dropped the question out here as i know the ZINN has a higher BB clearance than the StumpJumper, about 50mm more...
anyway i think i might get the bike first and then worry about custom cranks afterwards, i think if anything perhaps 5 or 10mm longer might be a better bet...say 180 or 185mm cranks
oh i don't need to worry about cleats (don't use them yet) still stick with flat pedal's although i starting to hate them...keep slipping off them and getting the teeth into the shin...
oh and my seat position at the moment is set far back but this will all change perhaps with the dualie (currently a hardtail)
Cheers for the help Morgan