I'm 6'3", with a 37" inseam. According to Lennard Zinn (framebuilder, exponent of proportional crank arm sizing, and all around tall guy), I should be riding 195 mm cranks. Yes, one NINETY fives. On my upright bikes, I ride 175s because they're readily available and work well for me. Tried 180s a few times over the years and had nothing but trouble, mostly sore knees all the time. It may have to do with the fact that I've always cultivated a smooth, fast (100+ rpm) spin, but whatever. The moral of the story being you shouldn't blindly accept what you're given, be it advice or equipment. Experiment, and find out what works best for YOU.

BTW, Bill, you'd probably be well served by working to increase your pedal speed. 65rpm is AWFUL slow. A higher cadence is easier on the legs and knees, and gives you a better cardio workout.

Scott P
Bend, OR