biopace on fixed
Jon_H
The reason I am asking is I can pick one up fairly cheaply as they don't
appear to be in fashion and the seller obviously has a few they want to get
rid of. Will this have an effect on the chain tension to any great extent,
especially downhill when the legs go into being dragged by the pedals mode..
cheers
Jon_H
Jon_H
"Jon_H" <jon...@mailthatishot.com> wrote in message
news:w47Xf.14359$Ph2....@newsfe4-gui.ntli.net...
I did find this http://sheldonbrown.com/biopace.html
if it's good enough for Sheldon Brown it's good enough for me.
cheers
Jon_H
Earl Bollinger
news:w47Xf.14359$Ph2....@newsfe4-gui.ntli.net...
No way on a fixed gear bike. The Biopace chainring os sort of a weird oval
shape, so there is no way to setup the proper chain tension.
Now if you are talking about a single speed with a freewheel for coasting.,
then yes you can do that, but you will need to use one of the many chain
tensioner devices that are available.
diann...@yahoo.com
I've used a 52 tooth BioPace chainring on a fixed gear bike. No
problems with the chain tension. It didn't get tight then loose as you
might imagine; there were still 52 teeth and the chain doesn't get
longer and shorter. Go for it, if you want to.
landotter
oval rings feel wierd at high rpms, but are pretty nice when you need
to "grind".
Simon Cooper
news:F_idnSL5879ivrDZ...@comcast.com...
That would be true if you contacted significantly more or less than half the
chain at once. It'd also mean the rear der moved back and forth all the
time on a geared bike, which it doesn't really. Essentially you have 2
large radius and 2 small radius parts of the chainring, and the chain wraps
about half way around it, so it's always encompassing 1 large radius and 1
small radius section - which takes the same length of chain.
Jon_H
"landotter" <land...@gmail.com> wrote in message
news:1143815142.0...@z34g2000cwc.googlegroups.com...
> I'd just go for a tooth or two higher on a Biopace equipped fixie, as
> oval rings feel wierd at high rpms, but are pretty nice when you need
> to "grind".
>
I'm currently running a 48T so I thought a 50T would be about right, I'm
looking at using a 90 inch gear for time trials.
cheers
Jon_H
Nate Knutson
I had a fixed gear set up with a Biopace ring for maybe 6 months that
was my only bike at the time. I asked Sheldon for tips (he has a bunch
of biopace fixies) when I set it up and he emphasized that chainline
was important when doing this.
Despite the obvious geek points, I never really liked it. The swing in
tension isn't as extreme as one might imagine (the number of teeth
being engaged at the same time doesn't change that dramatically) but
when you backpedal in most chainring positions there's still a huge
float, just like on a poorly set up fixed gear. That messes with the
"smoothness" of the ride a lot if you trackstand or push back on the
pedals to slow down or stop very much. More critically, I've wondered
whether having the chain be slack enogh when you push back might create
a risk of derailment. It seems like if there's even enough slack for
the chain to leave the cog and/or chainring even with some hand effort,
it could conceivably happen randomly when you're riding. What the
limits of this might be or if it even applies here I have no idea
about. I've kinda guessed it's why chainline is so important, though.
My setup was a 42t Biopace HP ring on a 70's Shimano steel disc brake
hub, which had track threading to secure a rotor and lockring, a cheap
stamped 17t cog, and 2 brakes. It worked for a while until I was riding
along, not sure whether I backpedaled or not, and a bunch of stuff
failed in some kind of sequence that left the chain derailed and
wrapped weirdly around the hub, both the cog and lockring threads
damaged, and the cog and lockring both bent and jammed oddly on the
hub. I never figured out exactly what happened but I'm pretty sure it
couldn't have had anything to do with the Biopacedness. I switched to a
freewheel on the other side of the same wheel with the same chainring
and rode the bike as a singlespeed (no tensioner) for a long time
without problems.
RonSonic
Counterintuitively, it isn't a problem. The chainring is lopsided, but
symmetrical, since a full half of it is covered by the chain at a time, it all
averages out.
Ron
meb
I have a pair of Biopace equiped recumbents in which the I do see a
return side tensioner oscilating premised upon chainring position.
However, unlike most upright fixies my chains encircle more than half
of the chainrings.
--
meb
RonSonic
Now that you mention it, so does the chain on a fixie. I guess by not enough for
it to become a problem.
Ron
Jon_H
"Nate Knutson" <bike...@riseup.net> wrote in message
news:1143827941.6...@v46g2000cwv.googlegroups.com...
Well the Biopace ring arrived today so I shall be fitting it and having a
quick spin around the block to see what happens.
cheers
Jon_H
>
amit....@gmail.com
Jon_H wrote:
> "Nate Knutson" <bike...@riseup.net> wrote in message
> news:1143827941.6...@v46g2000cwv.googlegroups.com...
> >
> > Jon_H wrote:
> > > Can anyone envisage any problems with a 50T biopace chainring on a
> fixed.
I found an almost complete peugeot hybrid in the trash under a foot of
snow. so i brought it home and started building it into a fixed gear. I
set the clainline very carefully and everything, but everytime i
cranked the pedals the chain would derail. i almost went insane and
then i saw it had biopace rings.
i could not get it to work at all. i was using the middle position and
i know smaller biopace rings had more eccentricity than the larger
ones, so maybe sheldon's page is not a sick gag and it only works with
the bigger rings, who knows.
since the rings are riveted to the spider i decided to make it a single
speed and use the rear dr. as a chain tensioner.
John Thompson
No can do. You cannot use a chain tensioning device on a fixed gear bike
(it will be destroyed as soon as you try to resist the motion of the
pedals), and a non-round chainring requires a chain tensioner in order to
prevent the chain from falling off the ring as the effective ring radius
changes during pedalling.
--
John (jo...@os2.dhs.org)
John Thompson
> Counterintuitively, it isn't a problem. The chainring is lopsided, but
> symmetrical, since a full half of it is covered by the chain at a time, it all
> averages out.
Ah, but it *IS* a problem. The issue isn't that half the ring isn't always
wrapped by chain, but rather that the effective radius of the ring changes
as the pedals move. This in turn changes the angular distance between the
last tooth on the rear cog and the first tooth on the ring, which means
the chain continually slackens and tightens as you pedal. This isn't too
much of an issue provided you can keep contant tension on the chain by
pedalling, but becomes problematic at high rpms -- such as experienced on
high-speed downhill runs, and precisely the situation where you DON'T want
to worry about your chain coming off!
I have an ostensibly round ring (but in fact about 2mm out of round) I've
used on a fixed gear and had considerable trouble setting the chain
tension such that it is loose enough to freely move but tight enough to
prevent derailment. Biopace rings are MUCH further out of round than that.
--
John (jo...@os2.dhs.org)
SYJ
Jon_H wrote:
>
> I did find this http://sheldonbrown.com/biopace.html
> if it's good enough for Sheldon Brown it's good enough for me.
>
> cheers
> Jon_H
Say, where is Cap'n Bike? I haven't seen him post in awhile...
SYJ
Nate Knutson
Do you know if it was a regular Biopace ring or a Biopace HP? (Regular
ones are perfectly ovular, HP's have a less extreme oval to them and
have a more complicated shape to try and make the design work better at
high RPM). I could see regular BP rings not working as well because the
tension change will be more extreme.
Sheldon Brown
>
>>Counterintuitively, it isn't a problem. The chainring is lopsided, but
>>symmetrical, since a full half of it is covered by the chain at a time, it all
>>averages out.
>
>
> Ah, but it *IS* a problem. The issue isn't that half the ring isn't always
> wrapped by chain, but rather that the effective radius of the ring changes
> as the pedals move. This in turn changes the angular distance between the
> last tooth on the rear cog and the first tooth on the ring, which means
> the chain continually slackens and tightens as you pedal. This isn't too
> much of an issue provided you can keep contant tension on the chain by
> pedalling, but becomes problematic at high rpms -- such as experienced on
> high-speed downhill runs, and precisely the situation where you DON'T want
> to worry about your chain coming off!
Actually the radius has nothing to do with it, the issue is concentricity.
A properly centered chainring, whether round, biopace or elliptical will
always have half of the teeth on either side of its "equator."
A 42 tooth chainring (what I mostly use on my fixed gears) will engage
21 rollers with 21 teeth.
There is a _slight_ tension variance due to the fact that the angle
between two straight chain sections varies slightly with the orientation
of the chainring.
I can assure you, John, that this _does_ work. I have Biopace
chainrings on several of my fixed gear bikes, including my fixed gear
tandem (which has three of them!) and also on a couple of bikes with
internal gear hubs. No chain tensioner is needed, and my chains do not
fall off.
> I have an ostensibly round ring (but in fact about 2mm out of round)
> I've used on a fixed gear and had considerable trouble setting the
> chain tension such that it is loose enough to freely move but tight
> enough to prevent derailment. Biopace rings are MUCH further out of
> round than that.
They may not be round, but they are well made and tend to be pretty
concentric.
For your eccentric setup, there is a technique that often helps to
correct this problem. I explain it at:
http://sheldonbrown.com/fixed-conversion.html#tension
Sheldon "Biopace" Brown
+----------------------------------------+
| All theory, dear friend, is grey, |
| but the golden tree of actual life |
| springs ever green. --Goethe |
+----------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
Ted Bennett
Would you include a Bio-Pace ring in the "non-round" category? If so,
you are wrong. My fixie has *never* thrown its chain in many miles of
use, with a 42T Biopace ring. And I'm far from from the only one.
You are right about a chain tensioner not working on a fixed gear. The
post you replied to did not mention a chain tensioner.
Ted
--
Ted Bennett
Jon_H
"Ted Bennett" <tedbe...@earthlink.net> wrote in message
news:tedbennett-24BCB...@news.west.earthlink.net...
10 Mile TT on the fixie tomorrow night so I should know more. A quick blast
around the block has not produced any problems so far.
cheers
Jon_H
Jon_H
followed by 10 miles at my modest TT pace. then 2 miles back to the HQ. it
didn't seem to make it any easier though.
cheers
Jon_H
Peter
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