We are new to tandem riding and know practically nothing about it, but while we were climbing a hill a guy who was passing us on a single suggested that we move the pedals out of synch in order to have at least one of us on the power stroke more of the time. Later that day the timing chain broke, so when I replaced it (with bombproof single speed chain) I decided to give it a try. I didn't want to go too far for fear of losing cornering clearance or making standing too awkward, but I did offset the pedals by 10 or 20 degrees. It didn't seem to affect our ability to stand smoothly and we both felt like our stroke became smoother and more powerful all the way around (although this is, obviously, pretty subjective). Even if we were imagining it, at least it made us FEEL stronger and smoother -- and we didn't seem to pay any penalty for it.