SpeedofLite 

This post contains two short articles.
The first is focused on Shimano Biopace.
The second is a brief review of other non-circular designs and the author's experience with Thetic, Bridgestone, and Durham,

bikemig 

Chris Froome uses oval chainrings so it's not like this idea has completely gone out of style.

stardognine

I haven’t read that whole article yet, but definitely will. Thanks for posting it. 👍😎

Velo Mule

This is an enjoyable read since we are looking at this decades later. It sure seems that Shimano put great effort into the design. I haven't tried Biopace, however, I had a bike only briefly that had a SunTour version of BioPace. I didn't get enough time on it to get a feel if it would be better for me. I also have chondromalisia, so I would, at some point like to try it out.

"Chris Froome uses oval chainrings so it's not like this idea has completely gone out of style." Is this perhaps why people have commented that he pedals like a washing machine? bikemig

I think athletes work to accommodate the equipment they use. Maybe BioPace is the domain of amateurs and tourists.

top506

My experience concurs that they are easier on the knees.

Top

Standalone 

I think I’ve read this one before. For some reason I have always loved vintage magazine writing and advertising.

I like biopace on a road touring triple for the large and middle chainring, but being a 6’4” Clyde, the granny is going to be for mashing to some extent, and Biopace just saps my torque.

I recently switched out the inner for a circular chainring on my Trek 620 when replacing the BB ahead of a tour. My son rode it 160 miles and seemed to do great!

sheddle

I don't know if this is my bad pedaling form, but i have them on my old MTB and can't tell

scarlson 

SpeedofLite Thanks for posting this article! I'm a Biopace devotee.

You could have one of the "milder" flavors of Biopace, possibly Biopace II and Biopace HP. HP was "high performance" oriented toward people who liked to spin, and II was just a general mellowing-out as far as I have read.
I find that the most immediately noticeable difference for me occurs when switching back from Biopace to round rings. I end up coasting a click or two of the freehub at the top of each stroke!

Me too! I have joint hypermobility - everything dislocates - so my knees dislocate a little at the top of the stroke (painless in the moment, but quickly leading to overuse) if I use too high a cadence or if my cranks are too long. I needed to switch to 165 cranks to stop this happening with round rings. Retrofitting Biopace rings allowed me to keep using my 172.5 TA Zephyr and TopLine Speed Stick cranks which have sentimental value to me on their respective bikes. I really went all-in for nice cranks thinking I was a 172.5 man, but turning 31 was a doozy for my knees. Biopace saved my bike parts investment.

His chainrings are clocked such that the high gear is in the middle of the stroke, the opposite of Biopace. But he's an animal. I can't imagine my knees lasting five miles on a bike like that. This stuff is all so personal and quite possibly a lot of it is subjective! But I think there's real tangible benefit in them continuing to exist for people with joint problems.

canklecat

I used a set of Biopace 52/42 chainrings on a 1993 Trek 5900 road bike most of 2019 and part of this year before disassembling that bike for an overhaul (still waiting for some parts). I liked 'em, although it required some adaptation.

I found Biopace worked best for me with shorter cranks (170mm, which was short for me) and slower cadence. Before 2019 I was a spinner, usually 90 rpm like clockwork, sometimes 100 rpm on climbs, 130+ rpm on fast downhills without coasting. But Biopace felt better to me with a slower cadence. I gradually adjusted by pushing harder gears around 75 rpm. Seemed to improve my stamina as well, so I rarely spin anymore even with my other bikes using conventional round chainrings.

The one quirk I experienced was trying those Biopace 52/42 rings with a 172.5mm crankset. Within a couple of weeks I had some knee twinges. Switching back to the 170 cranks resolved that problem. I usually prefer 172.5 and 175 cranks on my bikes with round chainrings.

I suspect that when some cyclists experience knee pain with Biopace, they may have encountered a similar quirk and didn't experiment with different crank lengths to see if it helped.

Some folks also report better results by reorienting the Biopace rings on the crank spider. The options are pretty limited. I tried that and it worked okay on the big ring but felt odd on the smaller ring. Probably because the big Biopace ring eccentric shape isn't as oblong as the smaller rings. Eventually I switched back to factory orientation and that felt fine to me.

Changing the orientation of the big Biopace ring can also lead to some chain drops on shifting because the chain catch doodad is on the chainring rather than on the crank. But I was able to minimize chain drops by carefully tweaking the front derailleur so it wasn't a big problem.

Newer style eccentric chainrings offer more variations in orientation, so those might work better for some folks.