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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 01-10-05, 09:03 PM   #1
mynameisnotdrew
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Biopace Chainrings on Singlespeed?

...actually on a 3speed road bike, but same difference. Will it work? For real? Anybody use one on a non-derailleur bike?
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Old 01-10-05, 09:08 PM   #2
HunterBee
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You would need a chain tensioner, I think. Other than that I don't see why it wouldn't work.
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Old 01-10-05, 09:21 PM   #3
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i got into a debate aobut this topic very recently. i think it would work, heres my reason:

because its an ellipse shape, you can break it into quadrants. the quadrants are of equal area, so the chainring is in contact with the same amount of chain as it rotates, maintaining equal tension.(aside from manufactoring deviations).

the fellow arguing with me compared it to an out-of-round chain ring and how you can see the chain pulling on the derailleur and whatnot from the tension changing.. but i say that is different because a perfect sphere will maintain constant tension, just as a perfect ellispe would..... it is the hi and lo spots that affect the chain tension.

so all in all i think that a biopace ring will work just as well as a round ring, it will have tight and loose spots, but no more than any ol' round ring.

but ive never tried it...so i dunno. i think you should try and lemme know how it goes
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Old 01-10-05, 09:33 PM   #4
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sheldon brown runs biopace on several fixies
and if it works on a fixie were you can't run a tensioner practically, you know it'll work fine on a 3 speed, if you wanna read about it, its here,
http://www.sheldonbrown.com/biopace.html
i would say give it a try at least and see if you like it
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Old 01-10-05, 09:37 PM   #5
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Biopace rings work GREAT for ss/fixed use. The rings are designed so that there is always equal chain tension. This is good for ss/fixed, as there is no chain tension weirdness from the rings. Biopace rings work GREAT for ss mtb, where you are grinding up hills in a big gear at VERY low rpm. biopcae rings don't work so great when you are trying to spin >90 RPM.
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Old 01-10-05, 09:53 PM   #6
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Quote:
Originally Posted by BostonFixed
Biopace rings work GREAT for ss/fixed use. The rings are designed so that there is always equal chain tension. This is good for ss/fixed, as there is no chain tension weirdness from the rings. Biopace rings work GREAT for ss mtb, where you are grinding up hills in a big gear at VERY low rpm. biopcae rings don't work so great when you are trying to spin >90 RPM.
That last bit contradicts what Sheldon says, and I have no problems over 100rpm -- especially if I remember or try hard to keep my hips steady and just use my legs -- the same for any type of ring, I suspect. From personal experience, I have fixed with a 38T Biopace ring, there are no significant issues with chain tension. But I was also was very careful to make sure the chainline was as straight as possible.
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Old 01-11-05, 10:11 AM   #7
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supposedly, the biopace is set at _X_ degrees off of true optimal. they will work for ss, but supposedly not at the true optimal. there is some physicist in brittain that cnc's custom biopace type sprockets set up for YOU. i have a friend who races bmx with them (Thomas "BATTLE CRUISER" Williams). he had to give the physicist a bunch of measurements like inseam, and desired gear inches and such, and the physicist dude figures out the optimal sprocket shape...and it works. you can feel it working.
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Old 01-11-05, 11:36 PM   #8
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I have been trying this same setup. Biopace on a raliegh 20 SA 3 speed. Over 25kph (do not know rpm) the whole bike starts to bounce. No problems with chain tension / skipping teeth.
S*cks bigtime to me. Sheldon must be much smoother than I am. Platform pedals though, so limited force direction.
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Old 01-12-05, 12:03 AM   #9
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I have clipless pedals, so it might be better. I find the bouncing really comes about for me because I am letting my upper body move, thus making the frame of the bike move. Once I settle my hips down in particular, things smooth out. <shrug>
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Old 06-16-05, 01:48 PM   #10
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Quote:
Originally Posted by pgringo69
supposedly, the biopace is set at _X_ degrees off of true optimal. they will work for ss, but supposedly not at the true optimal. there is some physicist in brittain that cnc's custom biopace type sprockets set up for YOU. i have a friend who races bmx with them (Thomas "BATTLE CRUISER" Williams). he had to give the physicist a bunch of measurements like inseam, and desired gear inches and such, and the physicist dude figures out the optimal sprocket shape...and it works. you can feel it working.
I rub magic pixie dust all over me and it makes me faster....and it works. you can feel it working.
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Old 06-16-05, 02:10 PM   #11
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I've done it, it works. Look at it this way, no matter what the CR orientation, exactly half of the teeth will have chain engaged all the time. So the total chain length doesn't need to change as you spin the cranks-no tensioner required. There is a very small change in length do to the angle that the chain makes from the ring to the cog, but it is very small change for biopace rings. In practice, it doesn't make much difference.
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Old 06-17-05, 10:42 AM   #12
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My brother just started running one on his single speed and he loves it. YMMV but it certainly seems to work without any problems.
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Old 06-17-05, 11:19 AM   #13
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When my derailer broke on my Rock Hopper with biopace on it, I shortened the chain and ran it as a singlespeed for a while. I had absolutely no problems with chain tension. I've got an extra biopace crank setup and the hankerin' to build another fixed gear, and I think the two may meet. It'll be setup for climbing, which is where biopace shines.
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Old 07-18-05, 02:07 PM   #14
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After running my (kinda/sorta) single speed for a month with a bio-pace oval chain ring, I switched to a round ring. My SS is a 1983 Trek road bike with the gear changers taken off. The chain tension is controlled only by the position of the rear wheel.

When back pedaling (such as when putting lube on the chain) it was obvious that the chain was very tight at certain positions, and rather slack at other positions. While pedaling, the chain tension seemed consistent, regardless of crank position. BUT, the rear wheel would tend to slip forward about 1/8th inch or 1/4th inch every few days. Then the chain would come off, or seem to have problems seating smoothly on the crank. Tightening the quick release on the rear hub to the (modest) limits of my arm muscles did not cure the problem.

Anyway, last week, I switched to an oval chainring. The chain tension is very consistent at all crank postions. The rear wheel no longer wants to drift forward. The bike is running very smoothly.

I don't think there is an logical reason an oval chainring did not work out for me. Maybe some sort of fluke, or other factors involved (the lack of any sort of chain tension device?). But, the modest cost of an oval ring makes my "low budget" SS run well, so I'm happy with the result.
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