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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 01-16-07, 12:09 AM   #1
jgedwa
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biopace rings

Somewhere in Sheldon Brown's stuff on-line he says that contrary to what one might guess, biopace rings are perfectly useable for fixed gear.

I have a junky MTB that I converted and put on a 42 tooth biopace just to see. At least with this set up, there is no way to get the chain to be acceptably tight throughout the rotation of the front ring. With it as tight as possible at one point, it will have far too much slack at another.

Anyone else play with this? Is it perhaps less of a problem with a larger chainring?

jim
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Old 01-16-07, 12:13 AM   #2
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I used a 42t biopace on my ultra-crap conversion. It was 42-17 gearing (lazy, I know. Its 52-18 now) with very long chainstays. I think a bigger rear cog & longer chainstays make the sag less important. It worked fine. Acceptable tensions all the way through a rotation. Makes bugger all difference though, run a normal ring.
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Old 01-16-07, 12:22 AM   #3
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yeah why not page capitan bikee him self mr. sheldon brown and get his explaintion for you
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Old 01-16-07, 12:30 AM   #4
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no idea, but that post looks like you've been drinking, retem.

for what it's worth, i'm starting to get drunk myself. you have no idea how long it's taking me to make this post without spelling, punctuation, etc. errors.
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Old 01-16-07, 07:03 AM   #5
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I rode at the velodrome in frisco a while back with a biopace. Everyone there
was going on and on about how bad it was to ride a fixed gear with it since
the chain tension was always changing.
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Old 01-16-07, 07:43 AM   #6
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Ken Cox did a huge biopace experiment himself, he's got some epic posts about it on here.
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Old 01-16-07, 10:04 AM   #7
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Quote:
Originally Posted by Hobartlemagne
I rode at the velodrome in frisco a while back with a biopace. Everyone there
was going on and on about how bad it was to ride a fixed gear with it since
the chain tension was always changing.
theoretically the chain tension shouldnt change any more than your average quality round ring. a little math proves the point but i dont wanna get into that. but due to manufacturing quality, in practice round or elliptical rings have tight and loose spots.
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Old 01-16-07, 10:10 AM   #8
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Just curious, but why would you want to use a biopace?
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Old 01-16-07, 10:12 AM   #9
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I think the argument about whether or not Biopace on a fixed gear works or not basically boils down to whether you equate "working" with "feeling exactly the same as a round ring." Will you notice a difference? Probably - I did. Will you be any more likely to break/through chains? Not in my experience or in the experience of the other people who have tried it. Will you experience any sort of performance benefits? Debatable.

There's no real reason to do it, and no real reason not to. Follow your bliss, I guess.
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Old 01-16-07, 10:31 AM   #10
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Quote:
Originally Posted by DerekRI
Just curious, but why would you want to use a biopace?
so he doesnt have to spend $17 on a rocket ring, duh!
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Old 01-16-07, 11:06 AM   #11
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biopace works fine for a fixed gear. even normal chainrings have differences, nothing's perfectly shaped. a biopace ring will give you same chain tension all the way around if it is perfectly elliptical, however 99.99999 of all chainrings arent, so there you go.
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Old 01-16-07, 12:04 PM   #12
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Quote:
Originally Posted by trackstar10
biopace works fine for a fixed gear. even normal chainrings have differences, nothing's perfectly shaped. a biopace ring will give you same chain tension all the way around if it is perfectly elliptical, however 99.99999 of all chainrings arent, so there you go.
Same chain tension all the way around?

Uhhh what?
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Old 01-16-07, 12:18 PM   #13
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Quote:
Originally Posted by Hocam
Same chain tension all the way around?

Uhhh what?
as already stated, in theory yes. in practice about as good as any round ring.

now, the problem arises with the positioning on the biopace. they are only supposed to be mounted in one position (i guess you could rotate it 180* also). they tend to wear a lot on the power portion of the pedal stroke, whereas you can rotate a round ring so it wears more evenly. so a lot of old biopace are already heavily worn, exagerrating tight/loose spots. but this happens with any ring that has not been rotated occasionally.
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Old 01-16-07, 12:42 PM   #14
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No way. Sheldon claims that a circular or elliptical ring will engage the same number of teeth. But even if this is true, the angle of the chain coming off the top and bottom of the ring will be different. Therefore creating a different distance to the cog. Therefore more chain required sometimes than others. Therefore different tension through the rotation.

But, the real question is whether or not there is enough difference to matter.

All I know is that if I have my chain at max tension when the ring is at one point in its rotation, I can still slip it off by hand when it is at another.
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Old 01-16-07, 12:46 PM   #15
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Quote:
Originally Posted by jgedwa
No way. Sheldon claims that a circular or elliptical ring will engage the same number of teeth. But even if this is true, the angle of the chain coming off the top and bottom of the ring will be different. Therefore creating a different distance to the cog. Therefore more chain required sometimes than others. Therefore different tension through the rotation.

But, the real question is whether or not there is enough difference to matter.

All I know is that if I have my chain at max tension when the ring is at one point in its rotation, I can still slip it off by hand when it is at another.
Much more convincing than "as already stated"
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Old 01-16-07, 02:35 PM   #16
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Quote:
Originally Posted by DerekRI
Just curious, but why would you want to use a biopace?
Because it's easier on the knees, and permits you to spin faster.

See: http://sheldonbrown.com/biopace

Quote:
Originally Posted by jgedwa
No way. Sheldon claims that a circular or elliptical ring will engage the same number of teeth. But even if this is true, the angle of the chain coming off the top and bottom of the ring will be different. Therefore creating a different distance to the cog. Therefore more chain required sometimes than others. Therefore different tension through the rotation.
That's actually true.

Quote:
Originally Posted by jgedwa
But, the real question is whether or not there is enough difference to matter.
In my experience (and I have a LOT of experience with this!) it isn't enough to matter if you have good chainline. I've got Biopace rings on several of my fixed gear bikes, including my fixed gear tandem (all 3 rings on that are Biopace.) http://sheldonbrown.com/picchio

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Old 01-16-07, 02:48 PM   #17
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Just once I want to see 'Sheldon "Droppin the knowledge" Brown'
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Old 01-16-07, 03:05 PM   #18
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Originally Posted by humancongereel
no idea, but that post looks like you've been drinking, retem.

for what it's worth, i'm starting to get drunk myself. you have no idea how long it's taking me to make this post without spelling, punctuation, etc. errors.

nah nasty bike wreck friday night I wish I was drunk
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Old 01-16-07, 08:18 PM   #19
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welly well well well....i stand corrected. see, its not that hard...
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Old 01-17-07, 01:09 AM   #20
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I ride 53 X 19 with a biopace ring, for 73 gear inches.

Subjectively, the biopace feels like two gear inches lower.

So, I go as fast or faster than a normal 73 gear inch setup but it feels like 71 gear inches.

Spins faster and easier.

The ring actually feels rounder than a round ring.

When I ride a round ring, now, it feels like a vertical ellipse compared to a biopace.

I adjust my chain tension to about 1/8" slack at the tightest point, and that gives me about 3/8's or a half inch at the loosest point.

I play around with rings and cogs a lot, and periodically I put on a round ring.

I prefer the biopace.

Purely subjective.

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Old 01-17-07, 02:28 PM   #21
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ee

wouldn't the chain get mad tight on the high spot of that biopace ring??
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Old 01-17-07, 02:33 PM   #22
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I ran biopace for a little while, and loved it, but when I started doing a lot of traffic riding, I found that sprinting was harder on a biopace ring - and considering how much sprinting one does dodging through traffic, it was worth it to me to switch to round. I plan on putting the biopace on my next build.

It's not going to work with every ring or every bike though. Just like with a round ring, if it's worn badly, or if you don't have a magic gear ratio (since you said you're on a mountain bike I assume vertical or near-vertical dropouts), you might not get lucky.
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Old 01-17-07, 03:57 PM   #23
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Quote:
Originally Posted by Eatadonut
I found that sprinting was harder on a biopace ring...
I found everything easier, including sprinting.

Hills and anything out of saddle got much easier.

Quote:
Originally Posted by na975
wouldn't the chain get mad tight on the high spot of that biopace ring??
I adjusted my chain tension so that I had 1/8" play at the high spot, which gave me 3/8" to 1/2" play at the low spot.
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