What difference does crank length make?

Do you take crank length into account when working out gear inch? Or power transmission? I need to know what for.

it’s a lever innit

From time to time crank length is a topic of much debate, from the “doesn’t make a difference” camp to the “proportionate to leg length” camp at the other extreme (some of the extremists in this mob would have me riding 187.5s, if such a thing existed). See if you can figure it out. On my bikes I have variously 165mm, 170mm, 172.5 and 175mm cranks.

As to gear inch, crank length isn’t a variable. Sheldon Brown has an alternative measure called “Gain Ratio” which factors in crank length - see http://sheldonbrown.com/gain.html

in a form of bike racing that is all about acceleration like bmx, yes
for riding on the street, no

For power transmission I would say yeah, because longer crank = more torque, though of course the actual velocity of your feet is higher when spinning (though the angular velocity stays the same), which (don’t quote me on this) might be the argument for 165 at the track (plus clearance)?

from what I understand, short cranks are better for your health. Longer cranks give you a bit more power but are worse for you ankles/achilles/knees as there’s more pressure through those joints.

You know - that makes sense, to me.