Biopace rings, which way around?

[jimo746]

I have a couple of biopace chainrings to fit to some cranks, which way around do they go? I assume there is an optimum position for the egg shaped ring?
Also, would there be any issues with mixing biopace rings with round rings on the same chainset?

 

[heavyhighsierra]

there is a small tab on the inside of the chain ring that should be aligned with the crank arm. I have mixed biopace rings with others rings on the same crank without any problems.

 

[yagamuffin]

Are they Biopace or Egg Rings?
I may be (probably am) wrong but I think Biopace rings are oval, whereas Egg Rings are, well, egg-shaped(!).
And I think (again, am probably wrong!) they fit differently with one having the longer length inline with the cranks and the others being perpendicular to the crank.

This isn't actually much help is it, I'm sure someone more knowledgeable will be along soon though

 

[velomaniac]

Biopace - Longitudonal axis inline with the crank arms.

 

[barry2017]

Velomaniac and Highsierra are right. But only on Shimano. All the non-Shimano oval rings I've encountered go on at 90 degrees to biopace ones.

Hope that makes sense.

 

[jimo746]

Thanks folks they are Shimano Biopace rings, so longitudinal axis in line with the cranks it is

 

[velomaniac]

Not entirely true, sakae rings designed to mimic biopace are also logitudonally aligned with the cranks. oval rings from the road bike world had different orientations. Biopace as the name implies was the result of bi- ergonomic studies carried out by shimano and is on paper quite clever. When the cranks are horizontal the gearing is reduced thus reducing the chance of traction loss off road and helping the rider when the cranks reach the position of least power transfer.
Personally I dont like them but only because of the strange pedal feedback not because they dont work, shimano trying to solve an issue that doesn't really cause anyone concern. :roll:

 

[heavyhighsierra]

the rings are intended to increase the crank speed on the down stroke by reducing the ring size at that point. Then the momentum built up carries you through the dead spot with less effort, while also pushing the larger portion of the ring. It is quite a ingenious concept, albeit a hotly debated one. On MTB's the biopace ring is said to help climbing by smoothing the power delivery.

 

[MisterGrizzly]

Biopace - Longitudonal axis inline with the crank arms.

Couldn't have put it better! Nicely done! And I concur

 

[pete_mcc]

To be factory correct you should align along the length of the crank BUT to make them work properly they should be turned through 90degrees (or as near as you can with a 5 arm crank).

Shimano were wrong, badly, with this one. The point at which you exert the most power is the bottom section of the down swing of each crank arm, it's where you really stamp down on the crank and so it makes sense that this is where the high inches and therefore the widest part of the ring should be. All other decent ring makers knew this:

Durham bullseye in the 80s:

Chris bell in the 90s:

Osymetry in the 00s:

Shimano f*cked it up so bad that it took an entire generation before racers were willing to try ovals out again! Get them the right way round and they feel great, put them the Shimano way and the oval effect will feel odd as their orientation will multiply the oval feel rather than it smoothing out the pedal stroke!

More info here:
http://www.highpath.net/highpath/cycles/ovals/02.html