Originally Posted by canklecat

I'm not sure that Shimano ever published its research or rationale for Biopace. The theory is well known -- generally, to compensate for human imperfections in pedaling -- and predates Biopace. But Biopace also predates power meters and methods for analyzing and quantifying theories and impressions.

My hunch is that Biopace rings shift pretty well because they're barely out of round. The effect is mild, offering a little difference in leverage that varies according to rider. As I described above, I found a sweet spot in the big ring by reorienting it 72 degrees clockwise/forward of the standard position; while the little ring felt better in standard orientation.

Some users of more extreme ovals and oblongs report some shifting challenges, especially on rougher roads, gravel and off roads, which may be why some folks converted to single chainring setups with more cogs in the back to compensate.

Other makers of more extreme non-round chainrings offer more mounting positions so we aren't limited to the 72 degree changes in orientation available to 5-bolt cranks.

I don't know whether makers of other non-round chainrings have done thorough lab tests or published their results. I wasn't particularly interested in the topic until I got a bike with Biopace earlier this year and decided to give it a fair shake before offering an opinion. In my limited experience it seems to offer some advantages, but I had to modify my pedaling style a bit to make it work well for me.