Bicycle peoples: this may be the end of round chainrings.

Fausto

Elite Member
Nov 29, 2000
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"Osymetric" chainrings won the bronze in the Olympic TT this year.

When Bobby Julich crossed the finish line just 26.45 seconds behind teammate Tyler Hamilton in Wednesday's Olympic individual time trial, it wasn't just a victory for a man and his country-technology also won in the streets of Athens.

Helping to power Julich's bike were two very unusual chainrings that could very well transform the way we propel our bicycles in the future. Julich was riding a pair of French made, out-of-round, "Osymetric" chainrings which Julich claims have helped him all season.

Now before you say, "Biopace," think again. In a phone interview with VeloNews from France designer Jean-Louis Talo was clear to point out that his patented out-of-round chainrings are considerably different that Shimano's original Biopace and Biopace II chainrings.

"Biopace did very little to address the dead-spot in a rider's pedaling stroke," Talo asserted. "My chainrings are designed to optimize the power portion of the stroke while minimizing the dead-spot. If you look closely, you can see my chainrings aren't just oval or elliptical as others have been, but shaped entirely to take advantage of a rider's leg musculature. The geometry we use is two successive curves having a unique symmetry, both with a central point of rotation. When the pedal is up [at 90 degrees] a rider's strength is minimal so the ring radius is small as well. When the pedal comes near to horizontal, the rider's strength is more, so the chainring is bigger to take advantage of that. Unlike Biopace, my rings constantly change radius to take full advantage of the complete power stroke of a rider. This is the first time this has been accomplished in a chainring."

Should be interesting to see if these catch on or end up in the bargain bin like Biopace rings.
 

oboeguy

Diamond Member
Dec 7, 1999
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Oh noes! not teh Biopace!!!11

<shudder>

The first road bike I actually owned (as opposed to borrowed for a summer here or there) was a used Ironman Centurion... which had Biopace rings. They were... weird. I changed them before long. I might still have them around somewhere...

Anyway, it sounds interesting. Did any pros ever endorse Biopace? It sounds like Jullich has basically endorsed this new thingie. Too bad they won't be out in time for the NYC Century. At "5 secs every km", that could save me like 13 minutes. :D (as if I ride fast enough for that to be true hahahaha)
 

Electric Amish

Elite Member
Oct 11, 1999
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Originally posted by: Shockwave
Whats a riders dead spot?

On something like an oval chainring, there would be a deadspot on the long axis where it would require extra force from the rider to turn the wheel.


(AFAIK)
 

Chu

Banned
Jan 2, 2001
2,911
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Originally posted by: oboeguy
Oh noes! not teh Biopace!!!11

<shudder>

The first road bike I actually owned (as opposed to borrowed for a summer here or there) was a used Ironman Centurion... which had Biopace rings. They were... weird. I changed them before long. I might still have them around somewhere...

Anyway, it sounds interesting. Did any pros ever endorse Biopace? It sounds like Jullich has basically endorsed this new thingie. Too bad they won't be out in time for the NYC Century. At "5 secs every km", that could save me like 13 minutes. :D (as if I ride fast enough for that to be true hahahaha)

What is biopace?
 

3chordcharlie

Diamond Member
Mar 30, 2004
9,859
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Originally posted by: Electric Amish
Originally posted by: Shockwave
Whats a riders dead spot?

On something like an oval chainring, there would be a deadspot on the long axis where it would require extra force from the rider to turn the wheel.


(AFAIK)

Actually I would guess the oval is designed to help you past that point by changing the torque for part of your stroke. When one leg is all the way up and one all the way down (or thereabouts) you're torque output will be at a minimum. Even if you work hard to spin smoothly, there will still be strong and weak parts of your pedal movement; this could be a neat way to solve that and let you spin even more smoothly.
 
Feb 10, 2000
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Originally posted by: Chu

What is biopace?

Biopace was a stupid "innovation" by Shimano that originated in the late '80s. SR/Suntour made a competing product called Ovaltech. Basically, both were elliptically-shaped chainrings. IIRC the theory was that they would eliminate (or at least alleviate the effects of) the flat spot in the pedal stroke when the rider's leg is fully extended or fully compressed, when he is making much less power/torque. I gather the new "osymetric" chainrings are supposed to do the same thing.

In practice, Ovaltech/Biopace seems to have been a snake-oil product, and it tended to accentuate ergonomic pedal/cleat problems to the detriment of many riders' knees. I believe the lab testing showed no positive advantage from these elliptical chainrings.
 

Armitage

Banned
Feb 23, 2001
8,086
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Originally posted by: DonVito
Originally posted by: Chu

What is biopace?

Biopace was a stupid "innovation" by Shimano that originated in the late '80s. SR/Suntour made a competing product called Ovaltech. Basically, both were elliptically-shaped chainrings. IIRC the theory was that they would eliminate (or at least alleviate the effects of) the flat spot in the pedal stroke when the rider's leg is fully extended or fully compressed, when he is making much less power/torque. I gather the new "osymetric" chainrings are supposed to do the same thing.

In practice, Ovaltech/Biopace seems to have been a snake-oil product, and it tended to accentuate ergonomic pedal/cleat problems to the detriment of many riders' knees. I believe the lab testing showed no positive advantage from these elliptical chainrings.

Shrug ... I like mine, especially for climbing &amp; long distance touring. They're no good for spinning, but when I'm touring I'm ussually in the low 80s anyway. In fact, I still have em on the small and middle ring. Switched to a round 52 on the outer ring now that I'm not doing much/any touring.

edit ... just looked at the link ... those are alot more asymetric then the biopace rings. Bet that takes alot of getting used to!