"This is a common misunderstanding. The "leverage" of a bicycle drive train, also known as "gain ratio" depends on the crank length, wheel diameter and the sizes of both sprockets."
May not be leverage, but if I'm in a 39x26 gear with no lower gear, then that 172.5 crank sure feels better on a steep hill to me than a 170. If you don't change gears, then I just believe that if the lever arm is longer, then the force being applied at the pedals will create 'leverage'. At least that is the way the physics works for me. Lou Deeter, Orlando FL