Originally Posted by
Kimmo
And they're too close to round to make much difference. Useful amounts of ellipticality (?) start to cause problems with the FD.
Interestingly, Biopace rings are made so the ratio's lower during the power phase of the stroke, and almost all the rest are the other way around... IMO the latter makes more sense.
Idk about that. I was just comparing a 53T Biopace to a 52 and 53 round ring, putting them back to back. The Biopace ring got "smaller" than the 52 ring in some spots, and larger than the 53 in others. So I'd say it has a range of maybe 51-54 teeth. And that's on the largest ring, which are the roundest looking. I don't have any little round rings for comparison, but the little 26 and 28T Biopace rings are really elliptical as seen in the photo above of the Sugino ring. They probably change several teeth in each direction.
Sheldon's article on Biopace explains why the power stroke has the lower ratio.
Whether Biopace is a marvel of engineering or an unsightly blemish on Shimano's history, some will never agree on. But I like my Biopace.