Changing crank arm length
 

Can anyone explain the benefits or detriments of changing crank arm length? I currently use a 172.5 double with 53/39 and want to change to a compact 50/34. The available crankset is 175. Will this do any thing to my biomechanics--knees,seat height etc
Thanks

Longer cranks are for longer legs, so it depends on your body size and type, but it really just comes down to rider preference. Some like the extra torque you get with longer cranks, others say you can't spin 'em as fast or that they will hurt your knees. There is a lot of discussion on this in the road bike forum, you might want to check it out.

Yes, a longer crank arm will require a slight saddle adjustment down, because the pedal will now be farther away in the down stroke.

http://www.sheldonbrown.com/cranks.html