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Discussion Starter · #1 ·
I've been riding my 5 spot for 3 1/2 years on stock RF X type evolves, but never even thought about crank length.

The cranks are going to be put on my hard tail, so am wandering about whether a new XT set should be bought at 175 or 170 length.

I'm 5' 7'' with a 29 inside leg, so thought that the shorter crank arm might be better for reducing the amount of bend in my leg at top position.

Any thoughts?

Cheers
 

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GUIDANCE COUNSELOR
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I think I read somewhere that the rule of thumb for mountain bikes is:

170mm for those under 5'10"
175mm for those over

There are alot of theories, but I think this rule is pretty good. If you are really short, or really tall, obviously this doesn't apply. People used to say that optimum crank length is equal to your inseam x 5.48. I'm not sure that really applies to mountain biking as much as road riding, as mountain biking is pretty much a whole different technique. Some singlespeeders use 180's to get extra leverage and some DH/freeriders use shorter cranks for more clearance.
 

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Natl. Champ DH Poser/Hack
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me? not thinkin so noah. off road requires alot more on/off torque than road. im 5'9' and rode 170's on a mtb and it pretty much sucked. felt like i was on a childs bike. 170's for more like 5'5" and less with a reasonably comparitive inseam. not sure if theres a good off road rule for this or not. funny, as there should be. with the diff types of ridin these days the answers are sure to be all over the place. longer for xc, shorter for fr and dh, down right tiny for trials. maybe someones got somethin that makes more sense than this.

i think ya gave it a good try though noah and i see where ya were commin from but i run a 172.5 on a dbl and a 175 on a tpl for the road. i think most my size do.

edit: i guess in the end its about makin the custy happy. lets say its a production bike. if they buy the right sized frame and its speced with the right sized parts and THEN theyre not happy, ya swap it out. simple cs. if its a custom build, ya give yer best advice and work with em the best ya can. sometimes that may mean swappin parts that arent trashed.
 

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involuntary dismounter
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dscot420 said:
I have heard it isn't the length of your crank, but how you spin it that's important ;)
Some girls, er homers may tell ya different though :p
um...that's a cute idea :lol:...and i hate to ruin it for ya...but the length of the crank is important, as is your endurance and skill at spinning it! :D
 

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glutes said:
Any thoughts?
Zinn has got an interesting take on crank length. Check it here. Pretty interesting read.

According to the formula...

Crank length (mm) = Inseam (mm) X 0.216​
...I should be using 180mm cranks (I'm 5' 11" with a ~33" inseam).
 

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PCinSC said:
Zinn has got an interesting take on crank length. Check it here. Pretty interesting read.

According to the formula...

Crank length (mm) = Inseam (mm) X 0.216​
...I should be using 180mm cranks (I'm 5' 11" with a ~33" inseam).
That's the exact same formula that NoahColorado gave, above.... ceptin his formula was in inches. .216*25.4 (mm/in)= 5.48. I wonder if he read it in Zinn's book too:D
 

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Am not, had mine removed.
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Spinner or Masher...

That's pretty technical; all I ever got when I asked the same question was, if you are a spinner go with the shorter of your choice and if you are a masher go with the longer. I stuck with it since I can't spin a top and feel pretty good on 175-180's. Placebo effect?
 

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Blue Shorts said:
That's the exact same formula that NoahColorado gave, above.... ceptin his formula was in inches. .216*25.4 (mm/in)= 5.48. I wonder if he read it in Zinn's book too:D
Yeah thats where I read it!
 

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Discussion Starter · #12 ·
thanks folks, for the thoughts. I tend to pedal slowly in high gear rather than spin in a low gear, so I guess I'll stick with 175 or whatever my current ones are. Might help if I knew heh?
 
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