I'm planning to try a newer design oval, eccentric or asymmetrical chain ring setup this year. Hadn't planned to but last year I bought an older Trek 5900 carbon fiber road bike frame from a friend and he remembered that I'd mentioned being curious about Biopace. So he brought the bike set up to ride with good older Shimano 600 and comparable components taken off an Ironman.
Turns out I actually liked Biopace. But only with 170 cranks -- more about that below.
Before the nitpicking begins, Biopace are technically eccentric or oblong, sort of a squashed square in the smaller rings. The larger 52T ring is just slightly asymmetric and doesn't feel much different from round. But the 42T smaller ring feels different.
I rode that bike about 2,500 miles last year, no problems. The smaller ring felt a bit pulse-y or surge-y on climbs, but I adapted quickly. And, just as Shimano suggested years ago, I found it worked better for me with a slower cadence. With round rings I usually spin at 90 rpm like clockwork. With Biopace I experimented with mashing bigger gears and found my sweet spot was closer to 75 rpm average, as slow as 60 rpm on seated climbs, and in the 40-50 rpm range when standing to stomp the pedals. There was a slight sensation of improved leverage. And slowing down smoothed out my sometimes raggedy cadence.
The main advantage I noticed was my heart rate didn't peg so quickly. At 90 rpm on climbs my HR would jump to 160 or higher. At my age (62) that's pretty close to redlining. With Biopace and a slower cadence my heart rate stayed in a sustainable range at the same perceived effort and average speed.
My climbing improved a bit, although that may have been due in part to the lighter carbon frame. The bike weighed about 20 lbs total, including pedals and tires, compared with 25 lbs for my steel bike. Made a difference on climbs. And I set the carbon bike up slightly more aggressively so the lower, more aero position was probably a factor too.
And some folks prefer to change the factory orientation of the elongated lobes. I tried both ways and didn't notice much difference on the big ring, but the smaller ring felt weird in any position but the original orientation. With only 5 bolt holes re-orienting is limited. Some newer oval, eccentric, etc., chainrings have multiple bolt holes to finesse the orientation and where the down stroke engages the elongated lobes.
The only problem I had occurred when I took that Trek 5900 out of service to repair the headset, and decided to move the Biopace rings over to my Centurion Ironman. Within a week I was feeling knee twinges and slight aches -- unusual for me. After a couple of weeks I was really concerned. I made several tweaks -- saddle height and fore/aft position, stem height, chainring re-orientation -- but nothing helped.
And my cadence felt more raggedy than ever. The pulsing, surging sensation with Biopace was exaggerated and distracting.
The only remaining difference was the cranks. Instead of moving the entire Shimano 600 crankset with 170 cranks over to the Ironman, I put the Biopace rings on the Ironman's Suntour GPX crankset with 172.5 cranks.
So I swapped the entire Shimano 600 crankset -- 170 cranks, Biopace rings in factory orientation -- over to the Ironman. Problem solved. The knee twinges cleared up and I felt that forgiving sensation of my raggedy pedal pressure. I tend to stomp and have never really mastered the pedaling in circles technique. Non-round rings seem forgiving of that quirk, for me at least.
Surprisingly, for me at least, Biopace was very sensitive to crank length.
I'm not sure whether that would translate to other non-round chain rings, but it's worth considering.
My bike cranks range from 170 to 172.5 to 175. But I'm seriously considering switching them all to 170. FWIW, I'm 5'11" with 33" inseam and thigh length a bit longer than normally proportional. That might be a factor in optimal crank length, at least with non-round rings.