Originally Posted by Trakhak

The design of earlier iterations of oval rings was based on the assumptions that racers would benefit from increasing the gear ratio in the section of the pedaling circle used for applying power and decreasing the ratio in the other sections and that the sky's the limit for the eccentricity of the chain ring.

Shimano's marketing department (I'm guessing here about the origin of their approach, but it was someone pretty smart), having noticed that the vast majority of riders buying racing-style bikes in the early '80s were sport riders, asked Shimano's engineers to come up with an improved design for non-racing riders, who tend to use lower cadences than racers. Thus, the egg-shaped oval chain rings with two focus points.

They failed in the marketplace for one primary reason: Shimano proceeded to spec BioPace rings throughout their component groups, and while the sport riders were generally happy with them, racers hated them for their lumpy feel at high cadences. Guys writing for bike magazines heard their racer friends complaining and damned the rings to the depths (having praised them to the skies when they were first introduced).

Originally Posted by dsaul

Biopace and modern oval chainrings are not the same thing. Biopace had the clocking of the "oval" wrong and made the gearing lower in the strongest portion of the pedal stroke and higher in the weakest part of the stroke. This put more stress on your legs and joints at the point where they were least prepared to deal with that stress. https://absoluteblack.cc/home/menu-1...20rings%20work.