Originally Posted by
canklecat
Biopace worked for some of us. I used a 52/42 set almost exclusively throughout 2019 on one road bike. It needed only a few tweaks to suit me.
With 33" inseam I can handle cranks up to 175, but Biopace rings felt best to me with 170 cranks. I felt knee twinges with longer cranks. Even 172.5, my usual preference, wasn't quite right with Biopace. Switching back to 170 immediately felt better.
And it worked better for me with slower cadence. I usually spin around 90 rpm but with Biopace it felt better to crank around 60-75 rpm, tops, and push harder gears. I got so accustomed to it that when I switched another bike back to round rings and longer cranks this year I had to relearn to spin. (Which isn't necessarily more efficient for everyone anyway. It was mostly a thing to promote quicker recovery between stages on long tours.)
The more oval/eccentric smaller 42T Biopace ring felt more like my other bike's 38 or 39T round ring. It can fee a bit surge-y at first, but I got accustomed to it.
I tried the trick of re-orienting the Biopace rings to other positions -- very limited with the typical 5-bolt spider -- but eventually returned to the Shimano factory standard positions. There may be some benefit to re-orienting other oval/eccentric chainrings that offer more bolt hole positions. But Shimano's theory seemed to be about right for some folks.
I also tried mixing 50 and 52T round rings with the Biopace 42T, and vice versa, but resumed using the full 52/42 Biopace setup. It shifted better. And the 52T Biopace is only slightly eccentric so it didn't feel dramatically different from round rings. The smaller chainring felt different, and worked well for me on climbs after I changed my cadence to push harder gears slower. My legs got stronger over 2019 and carried over to 2020 even now that I've resumed using mostly round rings and spinning more.
I'd consider newer types of oval/eccentric rings, at least for one of my bikes just to experiment a bit.
This is what I find really helpful about these cranks.
First off, they naturally change the way you apply power to the cranks. They require you to be smooth and work more precisely with the power curve to get the most of then. Plus, they are rather strict with ensuring that you maintain this certain cadence which just so happens to be the most efficient RPM when it comes to cycling. They don't seem to feel too bad spinning at a relatively higher cadence, but their particularly unhappy with going too low which seems to cause this lumpiness.
I find myself wanting to find the right cadence which really smooths out that power delivery and optimizes the efficiency. I think it's really helpful with making you a better biker.