crank arm length
 

How do you know what length is best/most comfortable/most efficient for you and your style of riding?

There are some crank length calculators out there based on your leg length but honestly, the only way you'll know what cranks work the best for you will be to ride them and see. The calculator I tried said 171 for me. I ride two bikes with 175's and one with 172.5's. I feel slightly better on the 172.5's but it's very subtle and could be all in my head for all I know. The bikes are all very different so it's tough to compare too. Many guys run cranks way longer or shorter than a calculator says and they do just fine.

I did a search through some old threads for the perfect discussion for you to read, but I couldn't find one that doesn't go off track :p (here's one: http://www.bikeforums.net/showthread...74#post1218974) so,.....shall we start yet ANOTHER one? :D Sorry, but I care about people's knees :)


Firstly, measure your inseam like this. You've obviously gotta be in bare feet and you've gotta shove the clipboard right up your crotch, mark the wall, then take the measurement.
http://www.bsn.com/Cycling/inseam.gifhttp://www.myra-simon.com/bike/images/inseam.jpg

The very general rule is to use a crank which is ~19 to 20% of your inseam, or follow charts like these

Leg Length.. Crank Length
60 to 65cm..... 150mm
66 to 70cm .....155mm
72 to 75cm .....160mm
75 to 78cm .....162.5mm
79 to 81cm..... 165mm
82 to 83cm..... 167.5mm
83 to 86cm..... 170mm to 172.5mm
87 to 90cm..... 175mm to 177.5mm
91 to 94cm .....180mm
94cm plus....... 185mm

or, this is a more conservative, traditional guide:

..Height......Inseam.....Crank length
under 5'.......70 cm.......165
5' to 5'2"......74 cm.......167.5
5'2" to 5'7"...80 cm........170
5'7" to 6'......86 cm.......172.5
6' to 6'5"......93 cm.......175
over 6'5"......99 cm.......177.5 - 180.0

How tall are you?

It seems as though shorter riders can handle using a crank which is around 21% of their inseam (probably just because that's what came with the first bike they bought), yet many taller riders (over 6'2") don't like to go over ~19%.

As far as style goes, if you're a fast-twitch, sprinter type, a slightly shorter crank would be preferable, but if you're grinder, aerobic type of rider, you might prefer a slightly longer crank