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Thread: biopace rings

  1. #1
    surly old man jgedwa's Avatar
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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

  2. #2
    Sheldon Brown's posse shogun17's Avatar
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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.

  3. #3
    Paste Taster Retem's Avatar
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    yeah why not page capitan bikee him self mr. sheldon brown and get his explaintion for you
    I am dyslexic so bear with my posts.... [SIGPIC][/SIGPIC]

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    live free or die trying humancongereel's Avatar
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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.
    have:ea50 flats, black, light, stiff.
    144 bcd 3/32" 49t sugino track chainring, possibly 75.

    want: risers, light, stiff, 1", black if that can be
    144 bcd 46t or 47t chainring any kind or width

  5. #5
    Spelling Snob Hobartlemagne's Avatar
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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.

    The first rule of flats is You don't talk about flats!

  6. #6
    jack of one or two trades Aeroplane's Avatar
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    Ken Cox did a huge biopace experiment himself, he's got some epic posts about it on here.
    Quote Originally Posted by Dr Irwin Goldstein
    Men should never ride bicycles. Riding should be banned and outlawed. It is
    the most irrational form of exercise I could ever bring to discussion.

  7. #7
    legalize bikes
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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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    TRUED 'TIL DEATH DerekRI's Avatar
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    Just curious, but why would you want to use a biopace?

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    Crapzeit! mcatano's Avatar
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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.

  10. #10
    legalize bikes
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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!

  11. #11
    elite
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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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    Ho-Jahm Hocam's Avatar
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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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    legalize bikes
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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.

  14. #14
    surly old man jgedwa's Avatar
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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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    Ho-Jahm Hocam's Avatar
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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"

  16. #16
    Gone, but not forgotten Sheldon Brown's Avatar
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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

    Sheldon "Flying In The Face Of Conventional Wisdom" Brown
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    |    explanation.  --H.H.Munro ("Saki")(1870-1916)   |
    +----------------------------------------------------+
    [COLOR=blue][CENTER][b]Harris Cyclery, West Newton, Massachusetts[/b]
    Phone 617-244-9772, FAX 617-244-1041
    [URL= http://harriscyclery.com] http://harriscyclery.com[/URL]
    Hard-to-find parts shipped Worldwide
    [URL=http://captainbike.com]http://captainbike.com[/URL]
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  17. #17
    Ho-Jahm Hocam's Avatar
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    Just once I want to see 'Sheldon "Droppin the knowledge" Brown'

  18. #18
    Paste Taster Retem's Avatar
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    Quote 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
    I am dyslexic so bear with my posts.... [SIGPIC][/SIGPIC]

  19. #19
    legalize bikes
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    welly well well well....i stand corrected. see, its not that hard...

  20. #20
    King of the Hipsters
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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.

    They make chocolate and strawberry ice cream for a reason.

  21. #21
    na975
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    ee

    wouldn't the chain get mad tight on the high spot of that biopace ring??

  22. #22
    You know you want to. Eatadonut's Avatar
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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.
    Weather today: Hot. Humid. Potholes.

  23. #23
    King of the Hipsters
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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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