I was blessed that Biking Yogini bought me a brand, spanking new bike last month, vintage 1990 from Arlington’s Old Bike Shop. It was a replacement for a bike stolen from in front of her office on my previous visit. Truth to tell, I never really felt good on it, and was not sorry to see it go. But I liked the new old bike from the first. It’s a city bike, straight handle bars and glass-resistant tires, as is my wont.
The next day I took it on the Capital Crescent trail, ten miles up to Bethesda. It felt faster, easier to pedal than the bike I’m used to at home in Philadelphia. I was surpised how zippy it was, but thought it unlikely that that extra energy could come from being on Day 4 of a water fast.
Riding to the train station the following day, I noticed a wobble in the front chainring. not left-to-right, but forward and backward. Looking down, I could see the chain moves slightly out and in with each rotation. An elliptical chain ring! Maybe that’s why it felt so zippy.
After I got home, I googled “elliptical chain ring” to see what I could learn. Here’s the story:
Early in the history of velo-sport, enthusiasts had the idea that the portion of the pedal cycle where feet are at top and bottom is a dead zone where it’s not possible to exert much pressure. Wouldn’t it be more efficient to design the chain ring to move quickly and easily through that part of the cycle, and provide extra resistance for the downward thrust? Thus was born the elliptical chain ring. The long diameter of the ellipse is perpendicular to the pedal arms.
But in practice, cyclists never liked them very much. They felt harder to pedal, not easier. In time trials, they didn’t seem to improve pedaling efficiency. And, worst of all, they seemed to be associated with injuries. There was a characteristic whiplash of the knee that came from the quick reversal of direction at the bottom of each pedal stroke.
Through the years, the elliptical rings were brought back by different companies in different variations. Later models were less extreme, closer to circular, but they never caught on. The old knee problems persisted.
The late 1980s were the dawn of computer-aided design, and innovative engineers at Shimano in Japan took up the problem and determined to do it right. Their curiosity was sparked by the persistent finding that cyclists preferred round chain rings to elliptical, and they thought: maybe a reversed ellipse would be even better. What would happen if we rotated the ellipse 90 degrees, so there is increased resistance in the “dead zone”?
The best thing they did was to keep an open mind. They tried lots of different ring shapes with lots of different cyclists. They asked for subjective impressions, and also measured performance in long rides and in sprints. Out of their research came the Biopace chain ring. The widest part of the ellipse is almost aligned with the pedal arms, rotated about 80o compared to the version that had failed repeatedly.
The Biopace was an engineering success, but a marketing fiasco. The literature was over-hyped and over-explained. Too much information. There were no knee injuries, but Biopace never caught on, and in 1994, Shimano stopped producing them.
I was home in Philadelphia, away from my beloved new bike, but I emailed Yogini and asked her whether the wide part of the ellipse was aligned with the pedal arms or perpendicular. She sent me a photo that confirmed my suspicion that I had been riding Biopace.
I wondered if I could retrofit my Philadelphia bike?
Though Biopace hasn’t been manuractured in 20 years, there is an aftermarket on Ebay. I counted the teeth of the large and middle chain rings on my Astral 700. 52-40. I found a set of chain rings that matched close enough at 52-42, and from the picture, the 5-point mounting looked to be compatible with what I had. I lost the first bid, but I was the only one bidding on the second. They arrived a few days later, $16 included postage.
I have never monkeyed with a front chain ring before, but I thought I’d try to install it myself. It took an hour and got me thoroughly greasy. 5 Allen lugs for each of the two rings. The hard part was that the Allen lugs fit just barely between the teeth of the next smaller chain ring, and each one took some wiggling and jiggling to get it into the hole. The front derailleur had to be moved ¼" higher because it rubbed against the chain when the ring reached its widest point. I attempted this on my own, but must confess I took the bike into the shop for final adjustment, to keep the derailleur from rubbing.
It works. I have two zippy bikes, with brand spanking new 20-year-old chain rings.