Originally Posted by
Moisture
...According to the nubs on the biopace chainrings - should I orient the rings 90 degrees backwards? Or 180 degrees forwards?
Try them for a couple of weeks or a month in factory standard orientation. Takes awhile to feel comfortable with Biopace.
I tried every possible orientation of both Biopace rings on a road bike double 52/42 set, and always returned to the standard orientation.
The 52 ring is barely non-round, so reorienting it won't make a big difference.
The smaller 42 Biopace ring is much more eccentric and you'll feel a noticeable difference in every possible position with a typical 5-bolt crank spider. Some of those alternative position will feel very wrong, with less felt effort on the downstroke and more "resistance" on the upstroke. When you find that position you won't want to ride it that way more than once.
The only alternative position that felt okay to me was advanced one position clockwise from standard. But I returned to the standard position after a month or two.