Biopace chainring. Would Fixed be possible? Don't think so, but could you have just enough slack in chain that it doesn't bind up on the high point, but not slip off on the low?

They were no damn good when they first came out. They're still no damn good for anything. And no, they won't work.

Do yourself a big favor, and bury anything you have with the word "Biopace" on it as deep as you can dig, then forget about it.

https://www.sheldonbrown.com/biopace.html
it was good enough for Sheldon.

Let us know how you make out then. They were, and still are, ****.

I have 42 on my converted centurion that was on the 600 cranks I used. It works fine but chain tension varies much more than I'd like. I never had a problem but I'm looking for a round ring.

I rode biopace chainrings on my good weather fixed gear bike for two years, and I liked it; especially on hills.

I adusted my chain tension to the tiniest amount of slack that felt comfortable to me, at the chain's two tightest positions, and this gave me about 1/2" slack at the loosest positions.

From memory, I think I did this with the two extreme's of biopace rings, a 53t ring and a 39t ring; one of which gave me 82 gear inches with a 17t cog; and the other of which gave me 60 gear inches with a 17t cog.

Shimano tuned or shaped these two rings for maximum efficiency or comfort at two different rpm's, and I can't remember the details.

In the end, it takes the same amount of energy to do the same amount of work, regardless of the shape of the chainring.
However, the biopace chainrings did feel more comfortable.
Suprisingly, initially, I could spin faster with the biopace; and the non-round biopace actually felt more round than a conventional round chainring.

I don't remember why I abandoned the biopace chainrings.
I still have several of them hanging on my garage wall.

I do remember that I couldn't get the biopace chainrings to run as quietly/silently as my round chainrings (I like a dead silent chain), as the chain would make a little noise, twice per crank revolution, as the chain went "up" the ramp of the increasing portion of the biopace ring.

One can buy a biopace ring for less than$30, and, it makes a worthy and fun experiment.

To some extent, they work.
Subjectively, it feels easier to spin, due to the distribution of the effort, even though we know the laws of physics tell us it takes the same amount of energy to do the same amount of work.

Can you please explain what you don't like about them and if you have experience in this application?

It was designed to run at 90, IIRC. I still run Biospace on my road bike, I like it

What Sheldon Brown said.

I've been using them for a while and they work fine as long as your chainline is straight. It's true that they are noisier and the slack varies a bit through the rotation. I get them from the LBS for 0-50 cents each.

Thanks for the input. I have a nishiki frame that I am thinking of converting, and I put them on it when it was "shifty." I always felt like it felt more "round" then normal chainrings, just wanted to see what it would be like fixed. Here is the bike I'm thinking of converting for the fun of it.




mind the paneling. Old pic form out building at old house

Sure they will work fine but a round chainring would be better suited for a fixed gear application. Why risk your safety to prove a point that something works on a bike where chain tension is such an important safety issue.

Its not to prove anything, just something to try. Gonna give it a try, and I'll post my results here later. In the process of the conversion now, with the biopace chainring.

There is no safety issue with Biopace chain rings... again...Sheldon Brown provides some of the best info on this.

There's no safety issue, it just depends whether or not you like the way Biopace rings feel. IIRC, Sheldon's point was that the same number of teeth are engaged at any given time, so the tension does not vary if the ring is centered correctly. My dad has a custom Davidson from the late 80's with full Shimano 600 group, including Biopace chainrings, which I assume he put on because of his knee problems. I don't like the way those rings feel, personally. I'm just used to round chainrings and cannot perceive any real benefit from using Biopace. Different, to be sure, but not better for me.

Try it and see if you like it. Worst thing that could happen is you don't and you get a new chainring.

Just be sure to keep your shovel handy in the probable event that you will want to take my earlier advice.

And yes, I have experience with them. They feel horrible, and when trying to stop on a fixed gear, you may or may not feel a huge backlash in the system, depending on where the pedals are when you start. Also, your chainline must be perfect. If not, the chain will be far more prone to coming off.

BTW, the basic idea has been around since the 1800s, and every once in a while, someone tries to resurrect it. With equal frequency, they fail. Shimano's attempt in the 80s was an attempt to market biking more broadly, as they were touting the easier feel to the pedaling. The dead spot they attempt to correct doesn't exist on a fixed gear.

I dislike them intensely, as you may have gathered, but Sheldon did, in fact, like the feel of them. You may too, just be aware of the possible issues, and make sure your chainline is correct first. BTW, the Biopace HP rings are better than the MTB version.

Thank you for your input. I will keep this in consideration. These are the HP rings. Just need to go to LBS to get shorter bolts and I'm gonna give it a try.

I have a biopace crank w/ 2 rings.
If someone is interested, PM me!

Carlos Sastre used an elliptical chainring in the most recent Tour de France.

Yes, but it's an entirely different animal to the old Biopace, and he wasn't riding a fixed gear. His could be tuned through very small increments to find the precise optimal mounting position to even out any issues he has with his pedal stroke. Biopace was very limited, and the recommended mounting position was to make pedaling seem easier for the couch potato masses, not optimized for spin, power, etc.

The reason most pros don't use them is that they don't feel they have issues to resolve. I doubt they have all taken the time to perform the exhaustive testing necessary to determine whether they actually could benefit or not. However, the companies currently promoting these pieces don't have the promotions budget necessary to make serious inroads into the pro peloton.

You would see more pros on them if someone with them started consistently running away from everyone. On a road bike, I would be curious to play with the new Rotor rings. On fixed, no.

Can't have it both ways, krusty.