Originally Posted by
robow
If I remember correctly, it was mid to late 80's that Shimano brought out the Biopace chainrings. Those rings are not round like almost all chain rings are but rather slightly elliptical which was supposed to give the rider a more efficient peddling motion. They did not go over well and were dropped only a few years later. Some people really liked them but I developed some knee pain that I had never experienced before and changed them out to standard round rings, and my discomfort went away almost immediately. But as I said, some including yourself may luv em'
robow and Op James guy-- Biopace was still around in 91 when I bought my first nice bike, it had a 50/40/28 Biopace crankset on it, and I too developed knee issues that probably were connected to the oval rings, so I too got rid of them and have had a distrust of non round rings ever since.
I'm fairly sure my issues were related to the hoppity hoppity thing that would happen to your pedal stroke at higher cadences. I'm a skinny guy and naturally prefer slightly faster cadence, or rather, my knees and legs do not like slow cadence, and I have clear memories of how annoying the uneven pedal stroke motion was as you got going faster cadence wise.
downtube shifters really didnt help as we tended to put off shifting sometimes with them, especially in urban settings etc
I do recall that oval rings changed a lot since 35-40 years ago, so the modern non round stuff that some top racers use (still use I think) have a different design, but Im not sure.
bottom line, ride them and see how they are for you. Probably depends on how much you ride, your preferred cadence and other stuff.
Biopace did disappear for a reason though.
figure out the bolt pattern , the bcd, of the crankset and look into replacement possiblities--some chain rings are super expensive, others not so much, but you're probably limited to what is available nowadays anyway. Not a big market for it probably.
I'd regrease everything, all bearing points.