Originally Posted by
smontanaro
Understood, but my knee will also be in greater flexion at the top of the pedal rotation. There is probably a happy middle somewhere.
Skip, it looks like you face a trade off between "tighter" knee closure angle due to higher TDC foot position with the longer crank arm, and more rocking of your hips on the seat as your leg stretches down an extra few mm to reach the pedal and finish a good power stroke. I doubt there's a generic solution to that dilemma. In my self-fitting I strive for ust enough pedal extenstion that I'm not driving my foot into the pedal at BDC. Usually this results in low hip rocking with 172.5s or 170s. I find 170s a little more comfortable overall.
Another question is, which choice makes it easier to pull your foot back at bottom, and to (perhaps more affected) push your foot over the top for a little earlier start at the power stroke. I could see the longer arm and tightened knee angle affecting how the start of the downstroke works.