Originally Posted by
genejockey
We were simplifying the example to make it clearer, based on the diagram that njkayaker, which claimed the pedal top didn't travel in a circle because the distance from the BB center changes. His diagram showed a pedal parallel to the ground at all crank angles, so I have been making the point that in this situation, the pedal top does in fact travel in a circle but that circle - and therefore the center of that circle - is offset from circle traveled by the pedal spindle by the stack height, i.e. if the pedal top is ALWAYS displaced from the pedal spindle at the same angle and distance, and the pedal spindle travels in a circle, the pedal top MUST travel in a circle.
You raise a DIFFERENT question, which is the degree to which ankling changes the path of the pedal top. On average (I found) riders' foot angle changes 24 degrees from minimum to maximum deflection. Look Keos have a stack height to the top of the pedal of about 11.5mm. You can determine how much this would move a point on the pedal top with some simple geometry that I can't be arsed to bother doing. Knock yourself out.