Those of us who were riding in the mid eighties probably remember when Shimano introduced their revolutionary Biopace chain rings and while many of us really liked them they did not gain widespread acceptance in the competitive world, Shimano's marketing was poor, and there were more than a few skeptics and critics.
I once thought Sheldon Brown and I were the only two people on the face of the earth who shared an appreciation for Biopace and actually joked with him about this on a few occasions.
The Biopace design is not an oval crank but rather, a computer designed egg shaped curve which in practice engages the smallest radius during the horizontal power stroke and engages the larger radius when the cranks are vertical.
This causes the leg to accelerate during the power stroke by lowering the gearing a little and when the load on the leg is highest and then slows the leg as it comes back up at which point the opposite leg will be beginning it's power stroke. This reduces stress when the leg changes direction which i also beneficial.
I have a left leg that is not "all there" and a right leg that does about 80% of the work so it can get highly stressed when one has to ride into the wind or climb.
I have been using Biopace cranks since they stopped making them and had a set on my extracycle as the design is quite good for low rpm climbing but is also good for those who can maintain a higher steady cadence and can actually smooth out a less than perfect pedaling technique.
Before the accident I was looking at competing at a master's level so knew how to spin and could spin some monster gears while now I usually run a lower gear and still spin like a gerbil on crack, albeit with one good leg.
As a bicycle mechanic I have encouraged those with knee issues to keep their Biopace cranks when other folks have told them to remove them and have been thanked for this as they are easier on knees.
I ruptured the bursa in my left knee 5 years ago and the first bike I rode afterwards was my Biopace equipped touring bike as running the same gearing on my mountain bike was far too painful.
I recently installed a Biopace crank on my commuter, which is the sister to my touring bike as I had been developing knee pain and was having problems maintaining a smooth cadence as my left leg would either stall or sometimes have powerful muscle spasms.
It has made an amazing difference in reducing that knee pain and smoothed things out a great deal so thought anyone with a similar imbalance issue or anyone who is really pedaling one legged might appreciate this information.
You cannot buy these chain rings new but there are lots of them on the second hand market and many shops will just give them away.
I am sure I have enough spares here to give some away to anyone that might want to try this.