For a range of crank lengths far wider than the narrow 165-180 range usually offered/used, there is no significant difference in biomechanical efficiency if gain ratio is held constant. See here for the most recent mainstream discussion of the matter.
cheers i checked an explanation on sheldon but this is much clearer. saves me spending on a 175mm crank now
cheers i checked an explanation on sheldon but this is much clearer. saves me spending on a 175mm crank now