Biopace chain rings are not a true oval and overcome the deficiencies of oval chain wheels and Shimano described them as a "point-symmetric egg curve".

When you are in the power phase of the pedaling stroke and the cranks are horizontal you engage the smaller radius which allows you to accelerate your foot and then when the pedals are vertical and in the dead spot you are engaging the higher radius which smooths the transition speed as your legs changes direction.

Like Sheldon I agree that this was a great design that should have had broader acceptance among general cyclists and they are particularly nice when you use them on certain bicycles like tourers, mountain bikes, and utility bicycles.

You can spin them at high cadences just as easily and they can smooth things out for some but they really shine at lower cadence when you want to be able to lay down consistent smooth power.

This design has seen a rebirth as other companies are now offered similar designs and these have shown themselves to be quite successful in racing applications.

I suffer from neuropathy in my left leg and this causes some issues with maintaining a smooth cadence and can increase the stress to my right leg which does much more of the pedaling work under high loads. I recently installed a Biopace triple on my commuter / utility bike and also have one on my extracycle and can really notice the benefits this brings.

I have a nice collection of Biopace rings here and plan to retrofit my touring bike as besides the climbing advantage it will allow me to spin higher gears in a smoother fashion as this is where I have the most issues.

I have used Biopace on ss and fixed gear bicycles with no issues and have a Biopace single set up to install on my new winter bike as I think this will be a very suitable application.