Burton, I owned a crankset with Biopace rings, not an earlier version. There was an attempt to market to professional riders as well but almost none cared for them. The exception was Bobby Julich who continued to time trial with them but rode standard rings otherwise. But yes, they weren't accepted by the general public and were discontinued for many reasons I'm sure.

Its worth noting there were a few variations to Biopace over the years... it started out pretty oval shaped and gradually got less-so. On my '92 MTB, I honestly don't notice a difference in the pedal stroke at all.

With me, i am not sure if Biospace is a problem for me, but from trial and error i know 175mm (instead of 170mm) is a problem for me. On a non Biospace 170mm I am fine, that is all i know right now.

this thread's been helpful - I built a winter bike this year and used 175mm cranks (what I had in the garage), my road bike has 165's and I'm 5'3". I don't notice any knee pain but have found that I have to the seat up really high. I'm used to spinning much faster and I don't like this languid spinning pace, plus my quads are getting tired! So here's my question - I just want to replace the cranks and don't know what will fit. The current ones are old Alivio. Will any Shimano crankset work? Anything else fit? Cheap is the ultimate goal here!!

The seat is higher with 175's? This doesn't make sense as extension is measured at the bottom of the pedal stroke.

A difference in saddle height is more a function of difference in BB height. All other things equal, longer cranks require a LOWER saddle height to maintain proper leg extension at the bottom of the stroke without rocking the hips.

ok to clarify, I upped the seat because I get more leverage - it feels like I'm sitting higher though I'm not sure I'm actually any higher than on road bike. Either way, I want to drop crank length, will any Shimano crankset work? Anything else fit?

I swap among Sugino, Shimano, and SR pretty regularly.

Most cranksets will work but often you will have to change out the bottom bracket to accommodate the new crankset due to length or design.

cool, thanks! turns out I think they're sugino anyway - I assumed since everything else was alivio so were the crank (yeah I know assuming...)