Classic & Vintage - Is this the right way to put Biopace rings on

Actually I'm not sure if they are even biopace. They are from a Suntour XCM gruppo. SR crank, Sakae rings.
I know, I should have taken the picture BEFORE I took them apart but I was planning to put them right back together. Poop happens.
I can't find any alignment marks on them.
http://i291.photobucket.com/albums/ll299/sailorbenjamin/IMG_1678.jpg

doesn't look like biopace...

I believe you should set it up how you want to. either the tall section at 90, or the tall section at 180

here's biopace compared to a black round chainring.
http://i199.photobucket.com/albums/aa131/AEObikes/misc/biopace3.jpg

Nope. Not Biopace. I have Biopace and those ain't they. They look like an attempted copy that were made shortly after Biopace came out. I don't remember the company that pulled that trick.

They look like SR's version of Biopace rings. Regardless, the 'hump' or high part should be in-line with the arm.

There are 2 versions of Biopace rings...a more severe version like in post 1 and a more mellow version like in post 2.

Those are oval rings, not Biopace.

Biopace = good
Oval = notsomuch

Is there not an arrow on the ring?

Thanks for the input. No arrow or any mark other than the brand name.
They aren't exactly oval, they have a parralelegramness to them. I pulled them off a dumpster bike cause I wanted smaller rings than what I currently have but maybe I should have just hunted down some larger cogs.
I suppose I should just slap them on and go for a ride.
Thanks again.

Why does relative mounted position make any difference at 90 rpm?

I don't get this bike up to 90 RPM. This is the bike I tow the 2 little girls in a trailer up the hill to the park with. It's grunt work.
I'm also kinda interested in the theory of it all. Patially so I can wow the other dads at the park. I suppose with these it's all marketing theory.

Why does relative mounted position make any difference at 90 rpm?

Biopace or out of round rings provide extra torque on the downstroke ye lenghtening the radius of the ring. It the ring isnt properly oriented the reduced radius part of the ring will be on the downstroke decreasing torque.

Early biopace rings were very exaggerated and many riders would 'bounce' in the saddle at high rpms. Shimano developed a not so aggresive biopace ring that worked better for higher rpm riding.

I have a pair of genuine Biopace rings on a Sakae crank. As an "approaching 50" kind of guy, I need every advantage I can get when riding with the younger group. I've found that the Biopace rings give me a little extra umpf every revoultion. Those little umpf's add up. Doing identical twenty mile rides with only different chainrings, I've gone from coming in last to staying with the group. Not bad!
The large ring has a pin that lines up with the crankarm, the small ring has a nub. Since you don't have those, here's a rough estimate:
Look at the crank from the drive side. With the crankarm at 12 o'clock, one of the high spots will be at 1 o'clock. The "flat" spots will be on the sides. The 3 o'clock flat will have one of the 5 ring support arms aiming right at it - the opposite flat at 9 o'clock will in between two support arms.
From your photo, rotate the rings one hole counterclockwise (as viewed from the inside). That looks like it will do it. Hope this helps!

I have always liked Biopace rings at all speeds but find them especially good for utilitarian applications... my longbike runs a 28/38 Biopace 2 setup and I love it.

I have also run them on ss and fixed gear bikes where I tend to spin at very high rpms.

I would think they would work a little behind TDC on the downside crank, but I've never been a big fan of the idea anyway. My mountain bike has biopace small chainrings. They seem like a good idea for people like me that tend to use too high of a gear. The original Biopace chainrings were very eccentric, it was only later Shimano wised up and went with a very small change in diameter.

The large ring has a pin that lines up with the crankarm, the small ring has a nub. Since you don't have those, here's a rough estimate:
Look at the crank from the drive side. With the crankarm at 12 o'clock, one of the high spots will be at 1 o'clock. The "flat" spots will be on the sides. The 3 o'clock flat will have one of the 5 ring support arms aiming right at it - the opposite flat at 9 o'clock will in between two support arms.
From your photo, rotate the rings one hole counterclockwise (as viewed from the inside). That looks like it will do it. Hope this helps!

One of my few direct e-mail correspondences with Sheldon Brown concerned this very issue, as v 1.0 of his Biopace article didn't cover how to index the rings.
Love Biopace, but never used the SR version.
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Very helpful, Jim, thanks. I've got a set I plan to try.


Biopace or out of round rings provide extra torque on the downstroke ye lenghtening the radius of the ring. It the ring isnt properly oriented the reduced radius part of the ring will be on the downstroke decreasing torque.

Early biopace rings were very exaggerated and many riders would 'bounce' in the saddle at high rpms. Shimano developed a not so aggresive biopace ring that worked better for higher rpm riding.

http://sheldonbrown.com/biopace.html