biopace on fixed

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

Quoted message said:

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..

Quoted message said:

cheers
Jon_H

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

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

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.

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

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.

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".

"Earl Bollinger" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can anyone envisage any problems with a 50T biopace chainring on a

fixed.

Quoted message said:

Quoted message said:

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,

Quoted message said:

Quoted message said:

especially downhill when the legs go into being dragged by the pedals
mode..

cheers
Jon_H

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.,

Quoted message said:

then yes you can do that, but you will need to use one of the many chain
tensioner devices that are available.

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.

"landotter" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

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.

Earl Bollinger said:

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

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.

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

RonSonic said:

On Fri, 31 Mar 2006 06:43:46 -0600, "Earl Bollinger"

Quoted message said:

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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

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.

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

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 said:

RonSonic said:

Earl Bollinger said:

"Jon_H" <[email hidden]> wrote in message
news:[email hidden]...
> Can anyone envisage any problems with a 50T biopace chainring on a

fixed.

Quoted message said:

> The reason I am asking is I can pick one up fairly cheaply as they

don't

Quoted message said:

> appear to be in fashion and the seller obviously has a few they want

to

Quoted message said:

> get
> rid of. Will this have an effect on the chain tension to any great

extent,

Quoted message said:

> especially downhill when the legs go into being dragged by the

pedals

Quoted message said:

> mode..
>
> cheers
> Jon_H
>
>

No way on a fixed gear bike. The Biopace chainring os sort of a weird

oval

Quoted message said:

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.,

Quoted message said:

then yes you can do that, but you will need to use one of the many

chain

Quoted message said:

tensioner devices that are available.

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

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.

Now that you mention it, so does the chain on a fixie. I guess by not enough for
it to become a problem.

Ron

"Nate Knutson" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a

fixed.

Quoted message said:

Quoted message said:

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

Quoted message said:

Quoted message said:

rid of. Will this have an effect on the chain tension to any great

extent,

Quoted message said:

Quoted message said:

especially downhill when the legs go into being dragged by the pedals

mode..

Quoted message said:

Quoted message said:

cheers
Jon_H

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.

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

Quoted message said:

Jon_H said:

"Nate Knutson" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Jon_H said:

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.

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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..

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 ([email hidden])

RonSonic said:

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 ([email hidden])

Jon_H said:

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

Quoted message said:

Jon_H said:

"Nate Knutson" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

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.

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.

Someone said:

Quoted message said:

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.

John Thompson said:

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.

Quoted message said:

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

John Thompson said:

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a fixed.
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..

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.

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

"Ted Bennett" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

John Thompson said:

Jon_H said:

Can anyone envisage any problems with a 50T biopace chainring on a

fixed.

Quoted message said:

Quoted message said:

Quoted message said:

The reason I am asking is I can pick one up fairly cheaply as they

don't

Quoted message said:

Quoted message said:

Quoted message said:

appear to be in fashion and the seller obviously has a few they want

to get

Quoted message said:

Quoted message said:

Quoted message said:

rid of. Will this have an effect on the chain tension to any great

extent,

Quoted message said:

Quoted message said:

Quoted message said:

especially downhill when the legs go into being dragged by the pedals

mode..

Quoted message said:

Quoted message said:

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

Quoted message said:

Quoted message said:

prevent the chain from falling off the ring as the effective ring radius
changes during pedalling.

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

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