Originally Posted by
Trakhak
The reason it disappeared:
When Biopace first appeared (on sport-touring bikes but not racing bikes), reviewers in bike magazines praised it to the skies.
Then Shimano got greedy and added Biopace to their racing bike component groups. Racers disliked the feel in general and when pedaling at high cadences and sprinting in particular and bad-mouthed it. The reviewers then did a 180 and damned it.
In response, Shimano introduced Biopace II, with much-reduced eccentricity (and some further, almost-round version whose name I've forgotten). But the damage was done, and Shimano soon gave up and dropped Biopace.
Ironically, Biopace made/makes perfect sense for the original target market.
....
Thanks for the explanation. I never rode or worked on a biopace bike, so I assumed that the eccentricity of the chainrings mucked up shifting or something simple like that. Looks like my guess was wrong.