A few fixed gear questions.

[RonSonic]

On Fri, 07 Jan 2005 12:56:30 -0600, A Muzi <[email protected]> wrote:

>> A. Muzi wrote:
>>>Good saddle and tire advice but your chain is way too tight.
>>>You're needlessly accelerating drivetrain wear.
>
>R15757 wrote:
>> My drivetrain components seem to last
>> about as long as anyone else's. The chain
>> might be a little tight although I can still
>> see a little droop in it. Like the OP I
>> prefer a tighter chain for improved
>> low speed response.
>
>Sorry. That was my response to your comment about levering
>the wheel into place. I assumed that if you needed a lever
>you were overtightening the chain. If you aren't exerting a
>lot of pressure, why use a lever?

Because it makes it very easy to hold it just so. I remember doing that in my
days with a SA 3s hub, just so easy to hold the wheel centered and right where
you want it.

>Try 'walking' the wheel into place by slacking one axle nut
>at a time - no lever needed.

Sure, but not as easy. Depending on whether you are willing to subject your bike
to the indignity of inversion.

There seems to be some controversy on that one.

Ron

 

[Tom Sherman]

A Muzi wrote:

> ...
> You'll learn to lift your butt off the saddle. No saddle will cushion a
> pothole with your full weight on it....

Even with a suspension seatpost?

--
Tom Sherman - Near Rock Island

 

[richard]

If you have the clearance (another argument for finding a road frame
from the 70's for conversion), try 32 or larger tires. You would not
believe the difference it makes on rough roads compared to 23's!

A Muzi wrote:
[SNIP}
>> 2. I ride in NYC where there are thousands of road obstacles (potholes,
>> manhole covers, etc.) and I'm finding the ride to be extremely harsh.
>> Any suggestions (e.g. a good fixed gear saddle)?
>>
> That sounds too tight.
> You'll feel lash no matter what when you reverse direction.
> http://www.yellowjersey.org/chainchk.html
>
> You'll learn to lift your butt off the saddle. No saddle will cushion a
> pothole with your full weight on it.
>

 

[Qui si parla Campagnolo]

Tom-<< In the past, Carl Fogel has posted links to pictures of motorcycles with

chain tensioners - a motorcycle is effectively fixed-geared when the
clutch is engaged. >><BR><BR>

OK, install a tensioner on a bicycle fixed gear and ride it and let me know
what happens.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

 

[Tom Sherman]

Peter Chisholm wrote:

[Dreadful AOL quoting format corrected]

> Tom Sherman wrote:
>>
>> In the past, Carl Fogel has posted links to pictures of motorcycles with
>> chain tensioners - a motorcycle is effectively fixed-geared when the
>> clutch is engaged.
>
> OK, install a tensioner on a bicycle fixed gear and ride it and let me know
> what happens.

I was merely attempting to preemptively post what Mr. Fogel's response
would be. The evidence [1] indicates that I did quite well.

[1]
<http://groups-beta.google.com/group/rec.bicycles.tech/msg/85f8f73c79d7a014?dmode=source>.

--
Tom Sherman - Near Rock Island

 

[[email protected]]

On 09 Jan 2005 14:24:58 GMT, [email protected] (Qui si parla
Campagnolo ) wrote:

>Tom-<< In the past, Carl Fogel has posted links to pictures of motorcycles with
>
>chain tensioners - a motorcycle is effectively fixed-geared when the
>clutch is engaged. >><BR><BR>
>
>OK, install a tensioner on a bicycle fixed gear and ride it and let me know
>what happens.
>
>Peter Chisholm
>Vecchio's Bicicletteria
>1833 Pearl St.
>Boulder, CO, 80302
>(303)440-3535
>http://www.vecchios.com
>"Ruote convenzionali costruite eccezionalmente bene"

Dear Peter,

During normal riding, a motorcycle's chain functions like a
fixed-gear bicycle's chain.

(The clutch can be used to freewheel, but massive engine
braking through the chain to the point of skidding the rear
tire is routine in trail riding.)

A motorcycle chain is much heavier and wider than the
bicycle chain.

A motorcycle chain moves much faster than the biycycle chain
(My trials machine has a fixed 14 x 52 front/rear ratio, as
opposed to say a 42 x 16 of a fixed gear bicycle.)

A motorcycle chain accelerates far more rapidly than the
bicycle chain and brakes far more heavily.

Single-pivot trailing-arm under-swing-arm chain tensioners
have been installed on all trials motorcycles since 1976.

front rear

chain-stay/swing-arm
bb---pivot-------------------------------axle
\\
\\
\\
------\\----------------------> lower chain run
\\_pad_

trailing arm and pad or idler gear
coil spring at pivot /
forces pad up and back /

I think that you're quite right about the strange tensioners
inexplicably sold for bicycles. The bicycle accessories
ignore common sense and use a leading arm that would indeed
be torn off by the slightest misalignment.

But the chain constantly re-algins a common-sense trailing
arm design. Remember, on a fixie and on a motorcycle, the
chain is still going backward whether you're accelerating or
braking. It does not reverse direction unless you stop and
then roll backward, and at any normal backward speed the arm
still works fine.

Trailing-arm chain tensioners have been as reliable as
bricks on motorcycles for over thirty years. Whether such
tension is of any value on a bicycle is open to question,
but they simply wouldn't be ripped off by the chain--they
face the right way.

Carl Fogel

 

[Mark Janeba]

[email protected] wrote:
> Trailing-arm chain tensioners have been as reliable as
> bricks on motorcycles for over thirty years.

I must have missed something - why are bricks on motorcycles a good
standard for reliability? I'm pretty sure I've ridden motorcycles
unequipped with bricks. Or is it that these bricks are more reliable
than the ones in my house?

Mark "weird sense of humor" Janeba

(sorry if double posts; comcast's new mailserver is acting up)

 

[Sheldon Brown]

Several knowledgeable posters have reiterated that you can't/shouldn't
use a chain tensioner on a fixed gear bicycle.

Carl Fogel, comparing apples and locomotives, demurs based on irrelevant
motorcycle technology:

> During normal riding, a motorcycle's chain functions like a
> fixed-gear bicycle's chain.
>
> (The clutch can be used to freewheel, but massive engine
> braking through the chain to the point of skidding the rear
> tire is routine in trail riding.)
>
> A motorcycle chain is much heavier and wider than the
> bicycle chain.
>
> A motorcycle chain moves much faster than the biycycle chain
> (My trials machine has a fixed 14 x 52 front/rear ratio, as
> opposed to say a 42 x 16 of a fixed gear bicycle.)

So, assuming equal tire diameters, for equal accelleration forces, the
bicycle chain tension will be 3.25 (52/14) the tension for the
motorcycle's. To get the same amount of chain tension, the motorcycle
would need to be able to accellerate 3.25 times as fast as the bicycle.

In fairness, this does omit the fact that the motorcycle is heavier, so
the disparity is less.

> A motorcycle chain accelerates far more rapidly than the
> bicycle chain and brakes far more heavily.

Speed doesn't matter, only tension.

> Single-pivot trailing-arm under-swing-arm chain tensioners
> have been installed on all trials motorcycles since 1976.
>
> front rear
>
> chain-stay/swing-arm
> bb---pivot-------------------------------axle
> \\
> \\
> \\
> ------\\----------------------> lower chain run
> \\_pad_
>
> trailing arm and pad or idler gear
> coil spring at pivot /
> forces pad up and back /
>
> I think that you're quite right about the strange tensioners
> inexplicably sold for bicycles.

Let me explicate this for you. Motorcycles are _designed_ to have chain
tensioners, so their chainstays have suitable attachment fittments.

Bicycles are _not_ designed to have chain tensioners, other than
derailers. There have been bicycle chain tensioners designed to clamp
onto the chainstay, but these have not worked out well in practice.
Clamping to a tapered, elliptical tube securely without crushing it is
not so easy if any significant amount of load is to be withstood.

> The bicycle accessories
> ignore common sense and use a leading arm that would indeed
> be torn off by the slightest misalignment.

This is an imaginary problem. I've seen lots of singlespeed MTBs with
chain tensioners, but I've never seen nor heard of one getting torn off
in use.

> But the chain constantly re-algins a common-sense trailing
> arm design. Remember, on a fixie and on a motorcycle, the
> chain is still going backward whether you're accelerating or
> braking. It does not reverse direction unless you stop and
> then roll backward, and at any normal backward speed the arm
> still works fine.

Existing chain tensioners have provision for alignment of the pulley.
Once the pulley is aligned with the actual chainline, it stays there.
>
> Trailing-arm chain tensioners have been as reliable as
> bricks on motorcycles for over thirty years. Whether such
> tension is of any value on a bicycle is open to question,
> but they simply wouldn't be ripped off by the chain--they
> face the right way.

As mentioned above, having the chain tensioner ripped off is a
non-issue. The danger is having the chain derail from the chainring.

It is my impression (though I make no claim to motorcycle expertise)
that the front sprocket of a motorcycle chain is in an area of tight
clearance, where there's no room for it to derail.

Aside from the risk of derailment (and possible rear-wheel lockup) the
other reason not to use a chain tensioner on a fixed gear bike is the
excessive lash it would introduce to the drivetrain.

Sheldon "Bicycles Are Not Motorcycles" Brown
+-------------------------------------+
| Don't drink and drive: you might |
| hit a bump, and spill your drink! |
+-------------------------------------+
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

 

[Tom Sherman]

Sheldon Brown wrote:

> ...
> +-------------------------------------+
> | Don't drink and drive: you might |
> | hit a bump, and spill your drink! |
> +-------------------------------------+

Cyclists solved that problem a long time ago.

--
Tom Sherman - Near Rock Island

 

[[email protected]]

On Sun, 09 Jan 2005 15:12:11 -0500, Sheldon Brown
<[email protected]> wrote:

>Several knowledgeable posters have reiterated that you can't/shouldn't
>use a chain tensioner on a fixed gear bicycle.
>
>Carl Fogel, comparing apples and locomotives, demurs based on irrelevant
>motorcycle technology:
>
>> During normal riding, a motorcycle's chain functions like a
>> fixed-gear bicycle's chain.
>>
>> (The clutch can be used to freewheel, but massive engine
>> braking through the chain to the point of skidding the rear
>> tire is routine in trail riding.)
>>
>> A motorcycle chain is much heavier and wider than the
>> bicycle chain.
>>
>> A motorcycle chain moves much faster than the biycycle chain
>> (My trials machine has a fixed 14 x 52 front/rear ratio, as
>> opposed to say a 42 x 16 of a fixed gear bicycle.)
>
>So, assuming equal tire diameters, for equal accelleration forces, the
>bicycle chain tension will be 3.25 (52/14) the tension for the
>motorcycle's. To get the same amount of chain tension, the motorcycle
>would need to be able to accellerate 3.25 times as fast as the bicycle.
>
>In fairness, this does omit the fact that the motorcycle is heavier, so
>the disparity is less.
>
>> A motorcycle chain accelerates far more rapidly than the
>> bicycle chain and brakes far more heavily.
>
>Speed doesn't matter, only tension.
>
>> Single-pivot trailing-arm under-swing-arm chain tensioners
>> have been installed on all trials motorcycles since 1976.
>>
>> front rear
>>
>> chain-stay/swing-arm
>> bb---pivot-------------------------------axle
>> \\
>> \\
>> \\
>> ------\\----------------------> lower chain run
>> \\_pad_
>>
>> trailing arm and pad or idler gear
>> coil spring at pivot /
>> forces pad up and back /
>>
>> I think that you're quite right about the strange tensioners
>> inexplicably sold for bicycles.
>
>Let me explicate this for you. Motorcycles are _designed_ to have chain
>tensioners, so their chainstays have suitable attachment fittments.
>
>Bicycles are _not_ designed to have chain tensioners, other than
>derailers. There have been bicycle chain tensioners designed to clamp
>onto the chainstay, but these have not worked out well in practice.
>Clamping to a tapered, elliptical tube securely without crushing it is
>not so easy if any significant amount of load is to be withstood.
>
>> The bicycle accessories
>> ignore common sense and use a leading arm that would indeed
>> be torn off by the slightest misalignment.
>
>This is an imaginary problem. I've seen lots of singlespeed MTBs with
>chain tensioners, but I've never seen nor heard of one getting torn off
>in use.
>
>> But the chain constantly re-algins a common-sense trailing
>> arm design. Remember, on a fixie and on a motorcycle, the
>> chain is still going backward whether you're accelerating or
>> braking. It does not reverse direction unless you stop and
>> then roll backward, and at any normal backward speed the arm
>> still works fine.
>
>Existing chain tensioners have provision for alignment of the pulley.
>Once the pulley is aligned with the actual chainline, it stays there.
>>
>> Trailing-arm chain tensioners have been as reliable as
>> bricks on motorcycles for over thirty years. Whether such
>> tension is of any value on a bicycle is open to question,
>> but they simply wouldn't be ripped off by the chain--they
>> face the right way.
>
>As mentioned above, having the chain tensioner ripped off is a
>non-issue. The danger is having the chain derail from the chainring.
>
>It is my impression (though I make no claim to motorcycle expertise)
>that the front sprocket of a motorcycle chain is in an area of tight
>clearance, where there's no room for it to derail.
>
>Aside from the risk of derailment (and possible rear-wheel lockup) the
>other reason not to use a chain tensioner on a fixed gear bike is the
>excessive lash it would introduce to the drivetrain.
>
>Sheldon "Bicycles Are Not Motorcycles" Brown
>+-------------------------------------+
>| Don't drink and drive: you might |
>| hit a bump, and spill your drink! |
>+-------------------------------------+
> 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

Dear Sheldon,

I'm simply pointing out that trials machines have had
trailing-arm chain tensioners for over 30 years.

Motorcycles function pretty much as fixed gear bicycles,
only with considerably greater forces and speeds.

They don't rip off trailing arm chain tensioners as Peter
insists will happen.

I have no idea what forces Peter thinks will rip trailing
arm chain tensioners off--presumably speed, weight, tension,
or the good fairies of legend, since the tension itself
merely moves the arm a little further outward against the
coil spring.

And yes, motorcycles rather easily accelerate more than 3.25
times as fast as bicycles. I keep getting the feeling that a
number of bicycle dealers have never even looked at a
motorycle, much less ridden one.

Consider that practically any 250cc 200+ pound motorcycle
can spin its 4-inch wide rear tire with a 200-pound rider
from a dead stop.

Peter has not mentioned any fear of the chain flying off the
chain ring (he talks about the bicycle ripping the tensioner
off, a perfectly natural consequence of the strange bicycle
designs). If you want to switch to that problem, what forces
are going to cause the chain to fly off when a tensioned pad
is pressing up against the bottom run of a normally
tensioned chain? The motorcycle chain is moving faster than
the bicycle chain and whipping around the much smaller,
tighter curve of a much smaller, tighter front sprocket.

You guys do understand that a trailing arm chain tensioner
is simply adding spring pressure to a normally tensioned
chain, don't you? That it's literally as sophisticated as a
mouse-trap? That it requires a mount no sturdier than a
flimsy luggage rack or a derailleur?

I'm not arguing that it's a good idea, that it will improve
a fixie, or that it offers perfect tension. I'm certainly
not arguing that the strange bicycle designs work--I expect
that they tear off, just as Peter says. (There were idiot
motorcycle designs like that in the early 1970's, and they
promptly destroyed themselves.)

I'm just pointing out that there's no question that trailing
arm chain tensioners have been used on trials machines by
Honda, Yamaha, Kawasaki, Suzuki, Montesa, Ossa, Bultaco,
Italjet, GasGas, Sherco, and every other trials manufacturer
for the last thirty years without the slightest problem.
They do not tear off the machines for the obvious reasons.
Draw a simple picture, for heaven's sake, see which way the
chain goes on a fixie and a motorcycle, and figure out
whether the moving chain will tear a trailing tensioner off
or brutally force it right back into aligment.

What would you all say if a motorcylist insisted that
there's no way that bicycle tires could be glued to rims and
not tear off?

Carl Fogel

 

[Sheldon Brown]

Quoth Carl Fogel:

> They don't rip off trailing arm chain tensioners as Peter
> insists will happen.
> I have no idea what forces Peter thinks will rip trailing
> arm chain tensioners off--presumably speed, weight, tension,
> or the good fairies of legend, since the tension itself
> merely moves the arm a little further outward against the
> coil spring.

I don't know what led Peter to make that assertion. I would guess that
he was referring to a rigid adjustable tensioner, not to a spring loaded
one, but I could be wrong.

> Peter has not mentioned any fear of the chain flying off the
> chain ring

That is the danger of relying on a chain tensioner for a fixed gear.

> (he talks about the bicycle ripping the tensioner
> off, a perfectly natural consequence of the strange bicycle
> designs). If you want to switch to that problem, what forces
> are going to cause the chain to fly off when a tensioned pad
> is pressing up against the bottom run of a normally
> tensioned chain?

When reverse tension is applied, the lower run will straighten out (a
spring loaded tensioner will permit this) and then the upper chain run
will become slack.

> The motorcycle chain is moving faster than
> the bicycle chain and whipping around the much smaller,
> tighter curve of a much smaller, tighter front sprocket.

A motorcycle chain is much wider and thus laterally stiffer than a
bicycle chain. In my previous posting I alsop supposed:

>>It is my impression (though I make no claim to motorcycle expertise)
>>that the front sprocket of a motorcycle chain is in an area of tight
>>clearance, where there's no room for it to derail.

Am I wrong about that?

> You guys do understand that a trailing arm chain tensioner
> is simply adding spring pressure to a normally tensioned
> chain, don't you?

Only to the bottom run. When back-loaded, the top run will become slack.

> That it's literally as sophisticated as a
> mouse-trap? That it requires a mount no sturdier than a
> flimsy luggage rack or a derailleur?

That's true for a spring loaded one, but not for a rigid one that is
designed to maintain tension in both directions.

> I'm not arguing that it's a good idea, that it will improve
> a fixie, or that it offers perfect tension. I'm certainly
> not arguing that the strange bicycle designs work--I expect
> that they tear off, just as Peter says.

No they don't. As I said, that's a non-issue, at least for the spring
loaded variety.

> I'm just pointing out that there's no question that trailing
> arm chain tensioners have been used on trials machines by
> Honda, Yamaha, Kawasaki, Suzuki, Montesa, Ossa, Bultaco,
> Italjet, GasGas, Sherco, and every other trials manufacturer
> for the last thirty years without the slightest problem.

So what? This newsgroup is about bicycles. Chain tensioners don't work
for fixed gear bikes, and whether they're leading or trailing arm design
doesn't matter diddly.

> What would you all say if a motorcylist insisted that
> there's no way that bicycle tires could be glued to rims and
> not tear off?

It would depend on how big and ornery-looking he was.

Sheldon "Push-bike" Brown
+------------------------------------------------------+
| It were not best that we should all think alike; |
| it is difference of opinion that makes horse-races. |
| -- Mark Twain |
+------------------------------------------------------+
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

 

[[email protected]]

On Sun, 09 Jan 2005 22:42:03 -0500, Sheldon Brown
<[email protected]> wrote:

[snip]

> >>It is my impression (though I make no claim to motorcycle expertise)
> >>that the front sprocket of a motorcycle chain is in an area of tight
> >>clearance, where there's no room for it to derail.
>
>Am I wrong about that?

[snip]

Dear Sheldon,

Well, yes, you were pretty much wrong about that.

Sorry.

There's generally room to derail the chain off the small
front (countershaft) sprocket on a motorcycle. Loosen the
rear axle, move the wheel forward, and pull the loosened
chain off.

Generally, however, this would be pointless. The rear
sprocket comes out of the chain about as easily as a bicycle
rear wheel comes out of the rear cluster. If we want to work
on the chain itself or replace it, we usually undo the
masterlink if we want to work on a chain.

In the case of my machine, I used to swap the standard
14-tooth trials cog with a 17-tooth highway cog, a somewhat
unusual practice. Obviously, there's room up front if a 17
can replace a 14 without any concern.

Motorcycles emphatically do not rely on putting the front
sprocket near the cases to stop the chain from coming off.
If the chain ever touched the engine case, even at walking
speed, it would leave deep gouges.

(Honest, motorcycle engineering is not that crude. Sochiro
Honda never told 'em to try moving the countershaft sprocket
closer to the nearest engine wall to keep the chain in
place.)

However, the heavy chains are moving so fast around such a
sharp corner that the end of a broken chain can fly off and
smash through the engine case in front of the cog (or just
wad up somehow and do the same thing), so sometimes there's
a thicker case wall if the case is steel and sometimes
there's a curved protector in front of more delicate cases.
But these are firewalls, so to speak, not guides.

Think of bicycles--they don't rely on metal restraints in
front of the chain ring or behind the rear cog to keep the
chain in place.

Again, I agree that spring chain tensioners may well add
nothing to fixies and that they seem to get alone fine
without such gadgets.

But any claim or even implication that a trailing-arm
chain-tensioner would be torn off simply contradicts
widespread experience with numerous brands of two-wheeled
fixed-gear chain-driven two-sprocket devices with far more
power, speed, and acceleration than bicycle dealers sell.

(The comparison doesn't seem like apples and locomotives to
me--sounds more like bananas and plantains.)

Carl Fogel

 

[Jim Adney]

On Sun, 09 Jan 2005 22:42:03 -0500 Sheldon Brown
<[email protected]> wrote:

>Quoth Carl Fogel:

>> You guys do understand that a trailing arm chain tensioner
>> is simply adding spring pressure to a normally tensioned
>> chain, don't you?
>
>Only to the bottom run. When back-loaded, the top run will become slack.

I see no problem with a spring loaded bottom run tensioner. If you're
worried about what then happens to the top run, just add another
spring loaded tensioner there.

I suspect the only noticable effect will be an excessive amount of
backlash. That alone, however, would make the effort pretty pointless.

-
-----------------------------------------------
Jim Adney [email protected]
Madison, WI 53711 USA
-----------------------------------------------

 

[A Muzi]

> On Sun, 09 Jan 2005 22:42:03 -0500, Sheldon Brown
> <[email protected]> wrote:
> [snip]
summarize - a chain tensioner is inadequate to bear
fixed bike chain tension loads as the chain is pulled
tight on the bottom forcefully

[email protected] wrote:
> But any claim or even implication that a trailing-arm
> chain-tensioner would be torn off simply contradicts
> widespread experience with numerous brands of two-wheeled
> fixed-gear chain-driven two-sprocket devices with far more
> power, speed, and acceleration than bicycle dealers sell.

At risk of going well beyond anything I actually know about-

I generally agree with Sheldon here but maybe if the
tensioner were extremely robust it could be done. (I've
never seen a MC tensioner). After all, some engines have a
timing chain tension adjuster and that has to be more force
when taut than a bicycle.

Let me end that if it _is_ possible, none of the spindly
**** sold in our industry is going to cut it. Most
"tensioners" are not as well made as a Tourney, perform
worse and cost a lot more.

But if it were 14mm seamless tube brazed into a rigid
triangle with a chainstay at the base. . .

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[m-gineering]

A Muzi wrote:

>
> I generally agree with Sheldon here but maybe if the
> tensioner were extremely robust it could be done. (I've
> never seen a MC tensioner). After all, some engines have a
> timing chain tension adjuster and that has to be more force
> when taut than a bicycle.
>
> Let me end that if it _is_ possible, none of the spindly
> **** sold in our industry is going to cut it. Most
> "tensioners" are not as well made as a Tourney, perform
> worse and cost a lot more.
>

Ok, here is one: http://www.depo.nl/witfiets.gif Only on this design the
extra cog ( at 10:00 behind the chainset) is used only to hide the chain
in the frame, the chain is still tensioned in the conventional manner.
Bikes are fitted with a coasterbrake.




--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

 

[Ryan Cousineau]

In article <[email protected]>,
m-gineering <[email protected]> wrote:

> A Muzi wrote:
>
> >
> > I generally agree with Sheldon here but maybe if the
> > tensioner were extremely robust it could be done. (I've
> > never seen a MC tensioner). After all, some engines have a
> > timing chain tension adjuster and that has to be more force
> > when taut than a bicycle.
> >
> > Let me end that if it _is_ possible, none of the spindly
> > **** sold in our industry is going to cut it. Most
> > "tensioners" are not as well made as a Tourney, perform
> > worse and cost a lot more.
> >
>
> Ok, here is one: http://www.depo.nl/witfiets.gif Only on this design the
> extra cog ( at 10:00 behind the chainset) is used only to hide the chain
> in the frame, the chain is still tensioned in the conventional manner.
> Bikes are fitted with a coasterbrake.

So Marten, between the disc wheels, air-free tires, and strange chain
line, how are these things to ride?

--
Ryan Cousineau, [email protected] http://www.wiredcola.com
Verus de parvis; verus de magnis.

 

[Tom Sherman]

Ryan Cousineau wrote:

> In article <[email protected]>,
> m-gineering <[email protected]> wrote:
> ...
>>Ok, here is one: http://www.depo.nl/witfiets.gif Only on this design the
>>extra cog ( at 10:00 behind the chainset) is used only to hide the chain
>>in the frame, the chain is still tensioned in the conventional manner.
>>Bikes are fitted with a coasterbrake.
>
>
> So Marten, between the disc wheels, air-free tires, and strange chain
> line, how are these things to ride?

That bike is cooler looking than Fabrizio Mazzoleni is in his best
"EuroPro" kit!

--
Tom Sherman - Near Rock Island

 

[Phil Brown]

<< Try 'walking' the wheel into place by slacking one axle nut
at a time - no lever needed. >>


That's the way.
Phil Brown

 

[Qui si parla Campagnolo]

Carl writes and geezzz, am I worn out-<< Dear Sheldon,

I'm simply pointing out that trials machines have had
trailing-arm chain tensioners for over 30 years.

Motorcycles function pretty much as fixed gear bicycles,
only with considerably greater forces and speeds.

They don't rip off trailing arm chain tensioners as Peter
insists will happen.

I have no idea what forces Peter thinks will rip trailing
arm chain tensioners off--presumably speed, weight, tension,
or the good fairies of legend, since the tension itself
merely moves the arm a little further outward against the
coil spring.

And yes, motorcycles rather easily accelerate more than 3.25
times as fast as bicycles. I keep getting the feeling that a
number of bicycle dealers have never even looked at a
motorycle, much less ridden one.

Consider that practically any 250cc 200+ pound motorcycle
can spin its 4-inch wide rear tire with a 200-pound rider
from a dead stop.

Peter has not mentioned any fear of the chain flying off the
chain ring (he talks about the bicycle ripping the tensioner
off, a perfectly natural consequence of the strange bicycle
designs). If you want to switch to that problem, what forces
are going to cause the chain to fly off when a tensioned pad
is pressing up against the bottom run of a normally
tensioned chain? The motorcycle chain is moving faster than
the bicycle chain and whipping around the much smaller,
tighter curve of a much smaller, tighter front sprocket.

You guys do understand that a trailing arm chain tensioner
is simply adding spring pressure to a normally tensioned
chain, don't you? That it's literally as sophisticated as a
mouse-trap? That it requires a mount no sturdier than a
flimsy luggage rack or a derailleur?

I'm not arguing that it's a good idea, that it will improve
a fixie, or that it offers perfect tension. I'm certainly
not arguing that the strange bicycle designs work--I expect
that they tear off, just as Peter says. (There were idiot
motorcycle designs like that in the early 1970's, and they
promptly destroyed themselves.)

I'm just pointing out that there's no question that trailing
arm chain tensioners have been used on trials machines by
Honda, Yamaha, Kawasaki, Suzuki, Montesa, Ossa, Bultaco,
Italjet, GasGas, Sherco, and every other trials manufacturer
for the last thirty years without the slightest problem.
They do not tear off the machines for the obvious reasons.
Draw a simple picture, for heaven's sake, see which way the
chain goes on a fixie and a motorcycle, and figure out
whether the moving chain will tear a trailing tensioner off
or brutally force it right back into aligment.

What would you all say if a motorcylist insisted that
there's no way that bicycle tires could be glued to rims and
not tear off? >><BR><BR>


Hey carl, do you even have a fixie, ever had one?

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

 

[Qui si parla Campagnolo]

I'll ask again Carl, show ius a picture of your fixed gear bike.

Mine is at

http://www.fixedgeargallery.com/chisholm.htm

I just wonder if you have any personal experience with fixed gear bicycles.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"