This is the second comment in this thread criticizing the biopace, what exactly was the problem with it? It seems to me that the oval chainring is seeing a resurgence lately (in the MTB community at least).
A couple bikes in my family's fleet have Biopace rings, both having been made around the same time period. What I recall at the time was that they were greeted by a collective yawn because they weren't eccentric enough to have much of an effect.
I just measured a 48T Biopace ring that was in my spare parts bin, and the ratio of major to minor diameter is about 3 percent.
The only annoyance I can think of is that you can't use those rings with a single-speed or gearhub without a chain tensioner.
If they're wrecking your knees, don't push such long gears. Or, rotate the ring by 72 degrees on the crank to pretty much negate the effect.
I just measured a 48T Biopace ring that was in my spare parts bin, and the ratio of major to minor diameter is about 3 percent.
The only annoyance I can think of is that you can't use those rings with a single-speed or gearhub without a chain tensioner.
If they're wrecking your knees, don't push such long gears. Or, rotate the ring by 72 degrees on the crank to pretty much negate the effect.