Coaster brake with a chain tensioiner?



J

James Thomson

Guest
crossposted: rec.bicycles.tech; uk.rec.cycling


The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:

http://www.kinetics.org.uk/html/city2.shtml

My initial reaction is that this shouldn't work: braking will pull the lower
run of chain taut and extend the rear suspension, putting considerable slack
in the upper run of chain.

What have I missed?

James Thomson
 
W

Werehatrack

Guest
On Thu, 29 Jun 2006 16:19:16 +0200, "James Thomson"
<[email protected]> wrote:

>crossposted: rec.bicycles.tech; uk.rec.cycling
>
>
>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>
>http://www.kinetics.org.uk/html/city2.shtml
>
>My initial reaction is that this shouldn't work: braking will pull the lower
>run of chain taut and extend the rear suspension, putting considerable slack
>in the upper run of chain.
>
>What have I missed?


It appears that they may have put a two-sided chain guide on the front
sprocket in an effort to keep the slack from causing the chain to
pitch off, but I agree with your assessment; this isn't a good move.
Without actually having one to examine, it's hard to say just how
ill-conceived the design really is, but the principal problems are
apparent.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
D

dvt

Guest
James Thomson wrote:
> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>
> http://www.kinetics.org.uk/html/city2.shtml
>
> My initial reaction is that this shouldn't work: braking will pull the lower
> run of chain taut and extend the rear suspension, putting considerable slack
> in the upper run of chain.
>
> What have I missed?


I agree, it looks like a bad idea at first glance; it would be nice to
see more detailed photos though. Perhaps they use chain guides on both
sides of the chainring. Even though the chain goes slack under braking,
the guides bring the chain back in place when pedaling resumes. The
tensioner on the back should guide the chain back on the cog after
braking, too.

If my guesses are correct, I think it's a bad solution. Say, for
example, the user wears out the chain. They replace the chain with one
that is a few links too long. Now the chain may derail beyond the guides
during braking.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)
 
P

Phil Cook

Guest
dvt wrote:

>James Thomson wrote:
>> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>
>> http://www.kinetics.org.uk/html/city2.shtml
>>
>> My initial reaction is that this shouldn't work: braking will pull the lower
>> run of chain taut and extend the rear suspension, putting considerable slack
>> in the upper run of chain.
>>
>> What have I missed?

>
>I agree, it looks like a bad idea at first glance; it would be nice to
>see more detailed photos though. Perhaps they use chain guides on both
>sides of the chainring.


Birdys have double chain guards on the front to keep the chain from
falling off when they are folded. The chain on mine (which is a
standard red one) goes very slack when folded. You can't really see
how slack in this picture http://www.kinetics.org.uk/red_fs_gr.jpg but
it would easily fall off without them.
--
Phil Cook looking north over the park to the "Westminster Gasworks"
 
On Thu, 29 Jun 2006 16:19:16 +0200, "James Thomson"
<[email protected]> wrote:

>crossposted: rec.bicycles.tech; uk.rec.cycling
>
>
>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>
>http://www.kinetics.org.uk/html/city2.shtml
>
>My initial reaction is that this shouldn't work: braking will pull the lower
>run of chain taut and extend the rear suspension, putting considerable slack
>in the upper run of chain.
>
>What have I missed?
>
>James Thomson


Dear James,

Motorcycles.

Cheers,

Carl Fogel
 
C

Call me Bob

Guest
On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:

>>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>
>>http://www.kinetics.org.uk/html/city2.shtml
>>
>>My initial reaction is that this shouldn't work:
>>What have I missed?


>Dear James
>Motorcycles.


Perhaps I'm being thick (I frequently am), but I don't see the
correlation. Motorbikes don't routinely have chain tensioners and
coaster brakes, so how do they give a clue to the way the Birdy copes
with that set up?

"Bob"
--

Email address is spam trapped, to reply directly remove the beverage.
 
On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
<[email protected]> wrote:

>On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>
>>>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>
>>>http://www.kinetics.org.uk/html/city2.shtml
>>>
>>>My initial reaction is that this shouldn't work:
>>>What have I missed?

>
>>Dear James
>>Motorcycles.

>
>Perhaps I'm being thick (I frequently am), but I don't see the
>correlation. Motorbikes don't routinely have chain tensioners and
>coaster brakes, so how do they give a clue to the way the Birdy copes
>with that set up?
>
>"Bob"


Dear Bob,

No, you're not being thick.

Trials motorcycles have used trailing-arm chain tensioners since 1972.

Rod and naked-wire actuated rear hub brakes even longer.

Floating rear brake arms ditto.

Increasing rear suspension travel.

And so on.

Bicycles do have lighter, thinner, flimsier chains that are more prone
to de-railing, but the pitch and tooth height are the same as 428h
motorcycle chain.

Many bicyclists remain unaware of the history and design of the other
two-wheeled vehicles. For example, experienced bike mechanics have
asked on RBT whether motorcycles freewheel, as opposed to behaving
like fixed-gear bikes.

To be fair, I've met motorcycle mechanics who were initially skeptical
of my description of a bicycle derailleur and insisted that it would
ruin the sprocket teeth after a few shifts. (We at RBT have trouble
believing that there are people as unfamiliar with bicycles as some of
our posters are with motorcycles, but they really do exist. I have a
fairly athletic brother-in-law from Maryland who somehow never learned
to ride a bicycle.)

It's a little like doctors and veterinarians, who are often unaware of
each other's worlds.

My father, a surgeon, was puzzled when I described the crude
veterinary treatment for canine sebaceous gland cysts (marble-sized
hair-root pimples from hell), which often consists of sticking a
large-bore needle into the swelling and "manually expressing the
matter," as my vet delicately put it just before he squeezed the lump
and the stuff literally hit the ceiling. Then a bit of digging around
with a sharp needle and removal of some shreds of the oil gland in
hopes that the destruction of the gland would prevent re-infection.

For human sebaceous gland cysts, my father explained, treatment
involves a small incision under local anaesthetic and the neat removal
of the entire distended oil gland, which prevents it from ever
becoming re-infected.

My father's technique for humans was unquestionably better than the
common veterinary approach, but my father's patients were willing to
pay much more than Fido's owners.

They also submitted gracefully to local anaesthetic without being
muzzled. (It's odd, but many dogs will stoically let a vet gouge them
with a needle, but climb the walls hysterically if they see a
hypodermic barrel attached to it. Similarly, lots of dogs shriek and
cry pitifully when the cruel rubber tourniquet is lightly tightened on
their foreleg, but then ignore the actual drawing of blood.)

My father's patients also did not require shaving their thick fur off,
rarely tried to nibble their stitches out after surgery, and scarcely
ever rolled naked on their wounds on a lawn that they used as a toilet
(although insane patients from the state hospital sometimes posed
unusual challenges). They also didn't grow new sebaceous gland cysts
every month from head to toe.

Cheers,

Carl Fogel
 
W

Werehatrack

Guest
On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
<[email protected]> wrote:

>On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>
>>>The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>
>>>http://www.kinetics.org.uk/html/city2.shtml
>>>
>>>My initial reaction is that this shouldn't work:
>>>What have I missed?

>
>>Dear James
>>Motorcycles.

>
>Perhaps I'm being thick (I frequently am), but I don't see the
>correlation. Motorbikes don't routinely have chain tensioners and
>coaster brakes, so how do they give a clue to the way the Birdy copes
>with that set up?


For that amtter, a lot of motorcycles don't even use a chain anymore;
the toothed belt setups seem to be proliferating.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
D

dvt

Guest
[email protected] wrote:
> On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
> <[email protected]> wrote:
>
>> On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>>
>>>> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>>
>>>> http://www.kinetics.org.uk/html/city2.shtml
>>>>
>>>> My initial reaction is that this shouldn't work:
>>>> What have I missed?
>>> Dear James
>>> Motorcycles.

>> Perhaps I'm being thick (I frequently am), but I don't see the
>> correlation. Motorbikes don't routinely have chain tensioners and
>> coaster brakes, so how do they give a clue to the way the Birdy copes
>> with that set up?
>>
>> "Bob"

>
> Dear Bob,
>
> No, you're not being thick.
>
> Trials motorcycles have used trailing-arm chain tensioners since 1972.
>
> Rod and naked-wire actuated rear hub brakes even longer.
>
> Floating rear brake arms ditto.
>
> Increasing rear suspension travel.
>
> And so on.


[mega OT snip]

Carl, how do motorcycle chains stay in place?

My experience with fixed gear bikes (no rear suspension) shows that a
slack top run will derail the chain, typically when you're riding over
bumps. Very little chain slack is required.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)
 
On Thu, 29 Jun 2006 16:33:35 -0400, dvt <[email protected]> wrote:

>[email protected] wrote:
>> On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
>> <[email protected]> wrote:
>>
>>> On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>>>
>>>>> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>>>
>>>>> http://www.kinetics.org.uk/html/city2.shtml
>>>>>
>>>>> My initial reaction is that this shouldn't work:
>>>>> What have I missed?
>>>> Dear James
>>>> Motorcycles.
>>> Perhaps I'm being thick (I frequently am), but I don't see the
>>> correlation. Motorbikes don't routinely have chain tensioners and
>>> coaster brakes, so how do they give a clue to the way the Birdy copes
>>> with that set up?
>>>
>>> "Bob"

>>
>> Dear Bob,
>>
>> No, you're not being thick.
>>
>> Trials motorcycles have used trailing-arm chain tensioners since 1972.
>>
>> Rod and naked-wire actuated rear hub brakes even longer.
>>
>> Floating rear brake arms ditto.
>>
>> Increasing rear suspension travel.
>>
>> And so on.

>
>[mega OT snip]
>
>Carl, how do motorcycle chains stay in place?
>
>My experience with fixed gear bikes (no rear suspension) shows that a
>slack top run will derail the chain, typically when you're riding over
>bumps. Very little chain slack is required.


Dear Dave,

Dunno--ya got me. It's an interesting question.

Greater side-to-side width of sprocket teeth and chain plates giving
more bearing surface and leverage for stability?

Here are some pictures comparing motorcycle chains and 13-tooth
sprockets:

http://home.comcast.net/~carlfogel/download/chain_a.jpg
http://home.comcast.net/~carlfogel/download/chain_b.jpg
http://home.comcast.net/~carlfogel/download/chain_c.jpg
http://home.comcast.net/~carlfogel/download/chain_d.jpg

Or maybe greater weight and chain speed?

Motorcycle gears reverse the relatively big-front/small-rear situation
on bicycles--I spend most of my bicycle time at about 20 mph in an
overgeared 53x11, but my motorcycle runs a fixed 14x52. If you work
things on a spreadsheet, the chain speed on the bicycle is about 1.3
mph at 20mph, while the motorcycle chain speed is about 6.7 mph, five
times faster.

Or maybe the difference in which gear is smaller?

It might make a difference that the front gear is tiny on a motorcycle
and large on a bicycle. The chain is being pulled onto the tiny
14-tooth gear on the motorcycle, but onto the large 53-tooth gear on
the bicycle.

Or even the greater suspension effect from the motorcycle tire?

Motorycles ride on wide, thick, cushy, heavy, low-pressure tires
compared to bicycles. My 18-inch rear rim mounts a roughly 25-inch
tire 4.50 inches wide. Hell, the three main knobs set in a tight
trials pattern are 3/4" wide and 7/16" high.

But I doubt this suspension effect, since the trials chains stay in
place just fine as the motorcycle and rider slam into and over huge
ledges and logs with considerably greater force than road bicycles
experience rolling over small pavement irregularities.

Perhaps different power characteristics?

The bicycle chain is under great tension from a motor that drives in
comparatively smooth, low-speed cycles--50-100 rpm from a rubbery
collection of meat and bone. The motorcycle chain takes less tension
(remember its much greater chain speed at the same 20 mph) from 500 to
5,000 rpm in nasty little shocks from an explosion-driven piston. It
might be that the smooth, heavy torque of the bicycle chain makes it
more likely to go twang! and fly off.

(It often comes as a surprise to bicyclists, who can easily exert 150
foot pounds of torque by standing on a pedal that a mildly tuned 125cc
motorcycle engine that can easily blast past them produces only 5
foot-pounds of torque. The secret is that the motorcycle torque is
produced a thousand times per minute and in first gear may have an
30-to-1 internal-to-rear-sprocket ratio, compared to a bicycle at 50
rpm with a 1 to 2~5 front to rear ratio.)

Whatever's going on, popping a chain off a bicycle sprocket is
annoying and frequent enough to lead to chain-watchers and dire
predictions about the perils of fixed-gear bikes, while popping a
chain off a motorcycle sprocket is almost unheard of, even though the
average motorcylist is usually embarrassed if anyone checks his chain
tension (yes, the chain is too loose, so loosen the axle and use the
snail adjusters, that's what they're for).

Cheers,

Carl Fogel
 
D

dvt

Guest
[email protected] wrote:
> On Thu, 29 Jun 2006 16:33:35 -0400, dvt <[email protected]> wrote:
>
>> [email protected] wrote:
>>> On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
>>> <[email protected]> wrote:
>>>
>>>> On Thu, 29 Jun 2006 11:35:11 -0600, [email protected]net wrote:
>>>>
>>>>>> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>>>>
>>>>>> http://www.kinetics.org.uk/html/city2.shtml
>>>>>>
>>>>>> My initial reaction is that this shouldn't work:
>>>>>> What have I missed?
>>>>> Dear James
>>>>> Motorcycles.
>>>> Perhaps I'm being thick (I frequently am), but I don't see the
>>>> correlation. Motorbikes don't routinely have chain tensioners and
>>>> coaster brakes, so how do they give a clue to the way the Birdy copes
>>>> with that set up?
>>>>
>>>> "Bob"
>>> Dear Bob,
>>>
>>> No, you're not being thick.
>>>
>>> Trials motorcycles have used trailing-arm chain tensioners since 1972.
>>>
>>> Rod and naked-wire actuated rear hub brakes even longer.
>>>
>>> Floating rear brake arms ditto.
>>>
>>> Increasing rear suspension travel.
>>>
>>> And so on.

>> [mega OT snip]
>>
>> Carl, how do motorcycle chains stay in place?
>>
>> My experience with fixed gear bikes (no rear suspension) shows that a
>> slack top run will derail the chain, typically when you're riding over
>> bumps. Very little chain slack is required.

>
> Dear Dave,
>
> Dunno--ya got me. It's an interesting question.


[snip -- man, you're prolific]

> Whatever's going on, popping a chain off a bicycle sprocket is
> annoying and frequent enough to lead to chain-watchers and dire
> predictions about the perils of fixed-gear bikes, while popping a
> chain off a motorcycle sprocket is almost unheard of, even though the
> average motorcylist is usually embarrassed if anyone checks his chain
> tension (yes, the chain is too loose, so loosen the axle and use the
> snail adjusters, that's what they're for).


So you're saying that motorcycles rarely drop the chain, even if the
chain is very loose. But bicycles *do* drop chains frequently. For one
reason or another, they're quite different in that regard.

So why did you say that James was missing motorcycles? It doesn't appear
relevant to his question.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)
 
On Thu, 29 Jun 2006 17:38:45 -0400, dvt <[email protected]> wrote:

>[email protected] wrote:
>> On Thu, 29 Jun 2006 16:33:35 -0400, dvt <[email protected]> wrote:
>>
>>> [email protected] wrote:
>>>> On Thu, 29 Jun 2006 19:26:15 GMT, Call me Bob
>>>> <[email protected]> wrote:
>>>>
>>>>> On Thu, 29 Jun 2006 11:35:11 -0600, [email protected] wrote:
>>>>>
>>>>>>> The R&M Birdy City folding bike uses a coaster brake with a chain tensioner:
>>>>>>>
>>>>>>> http://www.kinetics.org.uk/html/city2.shtml
>>>>>>>
>>>>>>> My initial reaction is that this shouldn't work:
>>>>>>> What have I missed?
>>>>>> Dear James
>>>>>> Motorcycles.
>>>>> Perhaps I'm being thick (I frequently am), but I don't see the
>>>>> correlation. Motorbikes don't routinely have chain tensioners and
>>>>> coaster brakes, so how do they give a clue to the way the Birdy copes
>>>>> with that set up?
>>>>>
>>>>> "Bob"
>>>> Dear Bob,
>>>>
>>>> No, you're not being thick.
>>>>
>>>> Trials motorcycles have used trailing-arm chain tensioners since 1972.
>>>>
>>>> Rod and naked-wire actuated rear hub brakes even longer.
>>>>
>>>> Floating rear brake arms ditto.
>>>>
>>>> Increasing rear suspension travel.
>>>>
>>>> And so on.
>>> [mega OT snip]
>>>
>>> Carl, how do motorcycle chains stay in place?
>>>
>>> My experience with fixed gear bikes (no rear suspension) shows that a
>>> slack top run will derail the chain, typically when you're riding over
>>> bumps. Very little chain slack is required.

>>
>> Dear Dave,
>>
>> Dunno--ya got me. It's an interesting question.

>
>[snip -- man, you're prolific]
>
>> Whatever's going on, popping a chain off a bicycle sprocket is
>> annoying and frequent enough to lead to chain-watchers and dire
>> predictions about the perils of fixed-gear bikes, while popping a
>> chain off a motorcycle sprocket is almost unheard of, even though the
>> average motorcylist is usually embarrassed if anyone checks his chain
>> tension (yes, the chain is too loose, so loosen the axle and use the
>> snail adjusters, that's what they're for).

>
>So you're saying that motorcycles rarely drop the chain, even if the
>chain is very loose. But bicycles *do* drop chains frequently. For one
>reason or another, they're quite different in that regard.
>
>So why did you say that James was missing motorcycles? It doesn't appear
>relevant to his question.


Dear Dave,

The fact that the little folding bicycle manages to work, despite his
doubts, might be related to the fact that motorcycles also work in
many ways, despite occasional unintended claims to the contrary around
here.

I'm probably overly sensitive on the subject, having been lectured at
amusing length about how a chain tensioner would be instantly torn off
any fixie.

Most of the lecturers never seemed to grasp the basic point that
motorcycles are a) fixed gear, and b) quite happy running trailing-arm
chain tensioners. (I can see three such machines on a trailer from my
window that have been running them for a total of 66 years.)

The lecturers are stuck on converting a double-jointed derailleur
chain tensioner never intended for fixies instead of using a
brick-simple trailing arm.

Similarly, the little folding bicycle appears to work fine, given its
chain-guide as noted in other posts. But people here leapt to the
conclusion that its chain must pop off the instant that the coaster
brake is applied, not from experience, but from what might be called
prejudice.

Cheers,

Carl Fogel
 
J

James Thomson

Guest
"Phil Cook" <[email protected]> a écrit:

> Birdys have double chain guards on the front to keep the chain from
> falling off when they are folded. The chain on mine (which is a
> standard red one) goes very slack when folded. You can't really see
> how slack in this picture http://www.kinetics.org.uk/red_fs_gr.jpg but
> it would easily fall off without them.


Thanks Phil.

The chain of the pictured bike follows a very strange path from chainring to
derailleur. Is there a hook that holds the chain like that while the bike is
folded?

James Thomson
 
J

James Thomson

Guest
<[email protected]> a écrit:

> The fact that the little folding bicycle manages to work, despite
> his doubts, might be related to the fact that motorcycles also
> work in many ways, despite occasional unintended claims to the
> contrary around here.


> I'm probably overly sensitive on the subject, having been lectured
> at amusing length about how a chain tensioner would be instantly
> torn off any fixie.


> Most of the lecturers never seemed to grasp the basic point that
> motorcycles are a) fixed gear, and b) quite happy running trailing
> -arm chain tensioners. (I can see three such machines on a trailer
> from my window that have been running them for a total of 66 years.)


> The lecturers are stuck on converting a double-jointed derailleur
> chain tensioner never intended for fixies instead of using a
> brick-simple trailing arm.


> Similarly, the little folding bicycle appears to work fine, given its
> chain-guide as noted in other posts. But people here leapt to the
> conclusion that its chain must pop off the instant that the coaster
> brake is applied, not from experience, but from what might be called
> prejudice.



Dear Carl,

When you wrote:

"The fact that the little folding bicycle manages to work..."

and

"the little folding bicycle appears to work fine..."

were you writing from experience, or from what *might* be called prejudice?

And when you wrote:

"people here leapt to the conclusion that its chain must pop off the instant
that the coaster brake is applied"

to whom were you refering?


James Thomson
 
D

dvt

Guest
[email protected] wrote:
> The fact that the little folding bicycle manages to work, despite his
> doubts, might be related to the fact that motorcycles also work in
> many ways, despite occasional unintended claims to the contrary around
> here.


How do you know this bicycle works? Who here has claimed that it won't work?

> I'm probably overly sensitive on the subject, having been lectured at
> amusing length about how a chain tensioner would be instantly torn off
> any fixie.


How does this relate to derailing a chain on the bike in question?

James made the other points I wished to make, but with more clarity than
I usually achieve.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)
 
P

Phil Cook

Guest
James Thomson wrote:

>"Phil Cook" <[email protected]> a écrit:
>
>> Birdys have double chain guards on the front to keep the chain from
>> falling off when they are folded. The chain on mine (which is a
>> standard red one) goes very slack when folded. You can't really see
>> how slack in this picture http://www.kinetics.org.uk/red_fs_gr.jpg but
>> it would easily fall off without them.


>The chain of the pictured bike follows a very strange path from chainring to
>derailleur. Is there a hook that holds the chain like that while the bike is
>folded?


Yes there is a hook on the deraileur to help take up the slack.
See here http://www.kinetics.org.uk/html/touring3.shtml

--
Phil Cook looking north over the park to the "Westminster Gasworks"
 
On Fri, 30 Jun 2006 08:49:50 -0400, dvt <[email protected]> wrote:

>[email protected] wrote:
> > The fact that the little folding bicycle manages to work, despite his
>> doubts, might be related to the fact that motorcycles also work in
>> many ways, despite occasional unintended claims to the contrary around
>> here.

>
>How do you know this bicycle works? Who here has claimed that it won't work?
>
>> I'm probably overly sensitive on the subject, having been lectured at
>> amusing length about how a chain tensioner would be instantly torn off
>> any fixie.

>
>How does this relate to derailing a chain on the bike in question?
>
>James made the other points I wished to make, but with more clarity than
>I usually achieve.


Dear Dave and James,

You're right.

Re-reading the sentence below leads me to believe that someone was
trying to say that the slack in the chain would prevent braking rather
than the chain coming off:

"My initial reaction is that this shouldn't work: braking will pull
the lower run of chain taut and extend the rear suspension, putting
considerable slack in the upper run of chain."

Cheers,

Carl Fogel