Originally Posted by
rawly old
Correct, absolutely correct. However one offers considerably more leverage against the pedal
being more distant from the fulcrum.
Archimedes once said," Give me a place to stand, and I shall move the world," He was referring to leverage.
Think of your 170mm crank as the lever & the chainring as the fulcrum...
I'm no expert but I don't believe you have a proper handle on the physics. The crank arm is the lever; and, the bottom bracket is the fulcrum (axis or pivot). Your leg of course provides the turning force. Gearing does not change the length the lever arm, nor the amount of force (or power) that a cyclist is capable of generating.
Depending on the gear ratio of the bicycle, a (torque, rpm) input pair is converted to a (torque, rpm) output pair. By using a larger rear gear, or by switching to a lower gear in multi-speed bicycles, angular speed of the road wheels is decreased while the torque is increased, product of which (i.e. power) does not change. ~wiki
When looking at bicycle gearing, calculating the inches of travel makes sense because it takes into consideration the circumference of the wheel that is being turned-- all else being equal, just going to a smaller wheel will increase torque...