Demultiflex fp reduction cranks?

Peter Storey said:

Someone proposes to ride from Brittany to Vladivostok
between now and July 5th. He is going to use "Demultiflex
fp" cranks, which are described here:
zefj.compedalier%20doc.jpgOpen ↗

It's good to see that Rube Goldberg is well and alive
in France.

Quoted message said:

How does this work? Does this work? Apart from additional
friction, what does this system do that's different than
using smaller-than-normal chainrings? And why only a two-
tooth difference in the rings?

If you have to ask, it's to arcane for you to understand,
just shell out the money and shutup, as the manufacturers of
such devices seem to believe. People with complex mechanisms
claim to make energy from nothing, and efficiency from more
mechanism. I see these things come along regularly. It's one
of the entertaining features of the anual InterBike trade
show. Listening to the explanations is an amazing
experience. These guys are excellent "spin doctors". They
should be in politics.

Jobst Brandt [email hidden]

Peter Storey said:

Someone proposes to ride from Brittany to Vladivostok
between now and July 5th. He is going to use "Demultiflex
fp" cranks, which are described here:
zefj.compedalier%20doc.jpgOpen ↗ How does
this work? Does this work? Apart from additional friction,
what does this system do that's different than using smaller-than-
normal chainrings? And why only a two-tooth difference in
the rings?

Imagine if you combined it with a PMP crank! You'd hardly
expend any effort at all !

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

Quoted post said:

Originally posted by Peter Storey
Someone proposes to ride from Brittany to Vladivostok between now and
July 5th. He is going to use "Demultiflex fp" cranks, which are
described here:
zefj.compedalier%20doc.jpgOpen ↗

How does this work? Does this work? Apart from additional
friction, what does this system do that's different than
using smaller-than-normal chainrings? And why only a two-
tooth difference in the rings?

Peter Storey

Dear Peter,

It looks as if a smallish ~32-tooth front ring is engaging not the chain but the toothed inside of a pair of chain rings mounted on a second bottom bracket, which in turn engage the chain.

So the rider gets to shift between the two large front rings with a normal derailleur, while the epicyclic (?) reduction gear connected to the crank lowers the overall gear ratio.

Mechanically, as you suggest, it adds the friction of teeth of the small crank sprocket engaging the interior teeth of the larger sprockets.

In terms of design, it adds a second bottom bracket and a much more complex set of gears (the interior teeth have to be added to the normal sprocket manufacturing process).

Practically, it adds weight and transmits less power without achieving any overall gear ratio that an ordinary set of front and rear sprockets couldn't achieve.

As for the two-tooth difference, it serves only to illustrate how poorly the designer understands simple gearing. Changing from 52 to 54 teeth can only provide a roughly 2% change in overall gearing.

There may be details hard to see in the picture, but as Andrew Muzi and Jobst Brandt have commented, the design just doesn't make any sense. Using this small interior sprocket to change the gear ratio on this large exterior sprocket just wastes power through friction without enlarging the range of gears available.

There are situations where extra gears are required to achieve bizarre results, but this isn't one of them. The only one that I can think of is the extreme high-speed kind of bicycle used to set peculiar speed records while drafting sports cars.

To pedal at 150 mph, you obviously need much higher gearing than the roughly 5-to-1 ratio of 53 x 11. But 11 teeth is about as small as normal rear cogs go, while front sprockets even on odd recumbents rarely exceed a hundred teeth.

One solution is to lengthen the frame and install a second bottom bracket. A 55-tooth ring on the crank connects by chain to an 11-tooth on one side of the second bottom bracket, whose spindle mounts another 55-tooth on the opposite side, chained to another 11-tooth on the rear, giving a 5-to-1-to-5-to-1 tandem-style transmission for an overall 25-to-1 ratio. (The actual numbers of teeth depend on what can be mounted on the second spindle and how ridiculous a ratio is desired. )

11---------------55
| rear BB front bb
wheel 11------------------55

Jobst has suggested that such bicycles are not really being pedalled, but merely being dragged along in the tremendous draft behind the curved windshield mounted on the draft car, but the odd gearing does provide a much higher ratio than would normally be possible.

Carl Fogel

carlfogel said:

Peter Storey said:

Someone proposes to ride from Brittany to Vladivostok
between now and July 5th. He is going to use
"Demultiflex fp" cranks, which are described here:ttp://www.zefj.com/images/pedalier%20doc.jpghttp://www-
.zefj.com/images/pedalier%20doc.jpg How does this work?
Does this work? Apart from additional friction, what
does this system do that's different than using smaller-than-
normal chainrings? And why only a two- tooth difference
in the rings? Peter Storey

Dear Peter,

It looks as if a smallish ~32-tooth front ring is engaging
not the chain but the toothed inside of a pair of chain
rings mounted on a second bottom bracket, which in turn
engage the chain.

So the rider gets to shift between the two large front
rings with a normal derailleur, while the epicyclic (?)
reduction gear connected to the crank lowers the overall
gear ratio.

Mechanically, as you suggest, it adds the friction of teeth
of the small crank sprocket engaging the interior teeth of
the larger sprockets.

In terms of design, it adds a second bottom bracket and a
much more complex set of gears (the interior teeth have to
be added to the normal sprocket manufacturing process).

Practically, it adds weight and transmits less power
without achieving any overall gear ratio that an ordinary
set of front and rear sprockets couldn't achieve.

As for the two-tooth difference, it serves only to
illustrate how poorly the designer understands simple
gearing. Changing from 52 to 54 teeth can only provide a
roughly 2% change in overall gearing.

There may be details hard to see in the picture, but as
Andrew Muzi and Jobst Brandt have commented, the design
just doesn't make any sense. Using this small interior
sprocket to change the gear ratio on this large exterior
sprocket just wastes power through friction without
enlarging the range of gears available.

There are situations where extra gears are required to
achieve bizarre results, but this isn't one of them. The
only one that I can think of is the extreme high-speed kind
of bicycle used to set peculiar speed records while
drafting sports cars.

To pedal at 150 mph, you obviously need much higher
gearing than the roughly 5-to-1 ratio of 53 x 11. But 11
teeth is about as small as normal rear cogs go, while
front sprockets even on odd recumbents rarely exceed a
hundred teeth.

One solution is to lengthen the frame and install a second
bottom bracket. A 55-tooth ring on the crank connects by
chain to an 11-tooth on one side of the second bottom
bracket, whose spindle mounts another 55-tooth on the
opposite side, chained to another 11-tooth on the rear,
giving a 5-to-1-to-5-to-1 tandem-style transmission for an
overall 25-to- 1 ratio. (The actual numbers of teeth depend
on what can be mounted on the second spindle and how
ridiculous a ratio is desired. )

11---------------55
| rear BB front bb
wheel 11------------------55

Jobst has suggested that such bicycles are not really being
pedalled, but merely being dragged along in the tremendous
draft behind the curved windshield mounted on the draft
car, but the odd gearing does provide a much higher ratio
than would normally be possible.

Carl Fogel

Actually, the 52 to 54 tooth difference also serves to show
my feeble mathematical proofreading. Let's try about 4%
instead of 2%. And let's see how this newsreader handles
ASCII art:

11---------------55
| rear BB front bb
wheel 11------------------55

"Peter Storey" <[email hidden]> schreef in bericht
"]news:[email hidden]...

Quoted message said:

Someone proposes to ride from Brittany to Vladivostok
between now and July 5th. He is going to use "Demultiflex
fp" cranks, which are described here:
zefj.compedalier%20doc.jpgOpen ↗

How does this work? Does this work? Apart from additional
friction, what does this system do that's different than
using smaller-than-normal chainrings? And why only a two-
tooth difference in the rings?

Peter Storey

You want to be in W-stok by July 5 or do you want to
commency before that date? Do you know what the roads are
like in Siberia? Sometimes there aren't any, sometimes there
are, but you can only ride them with a humvee.

Bert

--
Posted by news://news.nb.nu

[email hidden], A. Muzi and Carl Fogel all
wrote in various message
news:<[email hidden]>... something
to the effect of

Quoted message said:

"Bulls***t"

Well, no, I don't believe in magic. But I was curious if it
had any effect of any kind (however that effect might be
offset by something else) beyond just adding friction.

Carl mentioned that this rig is suggestive of (but isn't) a
way to create super high gears for motor-paced speed trials.
Likewise, I'd point out a certain facial resemblance to the
DaVinci Tandems drive train which uses back-to-back drive
trains to provide four driving chainrings and the ability to
create very large (effective) chainrings using standard
sizes. But, as in Carl's example, this is not that either.

Please indulge my scientific illiteracy. As a matter of
curiosity, what is the effective size of the chainrings?
Assuming a 52 exterior ring and a 36 "reduction" ring, are
(1) the force required to turn it and (2) the chainlinks-per-
minute passing over the exterior ring any different than a
conventional 52? Or does this combo behave like something
between 36 and 52? Does that help explain the curious choice
of a 52/54 exterior chainring set? For simplicity, let's
ignore the incremental friction.

A Muzi <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Imagine if you combined it with a PMP crank! You'd hardly
expend any effort at all !

And now go install it on the mysteriously elusive Egarim
bicycle that stores energy on the flats and releases it back
on the climbs! See
classicrendezvous.comcheckered flag.htmOpen ↗.
Just the thing for randonneurs attempting PBPBPBPBPBP!

On 4 May 2004 07:46:56 -0700, [email hidden] (Peter

Storey) said:

[email hidden], A. Muzi and Carl Fogel all
wrote in various message
news:<[email hidden]>... something
to the effect of

Quoted message said:

"Bulls***t"

Well, no, I don't believe in magic. But I was curious if it
had any effect of any kind (however that effect might be
offset by something else) beyond just adding friction.

Carl mentioned that this rig is suggestive of (but isn't) a
way to create super high gears for motor-paced speed
trials. Likewise, I'd point out a certain facial
resemblance to the DaVinci Tandems drive train which uses
back-to-back drive trains to provide four driving
chainrings and the ability to create very large (effective)
chainrings using standard sizes. But, as in Carl's example,
this is not that either.

Please indulge my scientific illiteracy. As a matter of
curiosity, what is the effective size of the chainrings?
Assuming a 52 exterior ring and a 36 "reduction" ring, are
(1) the force required to turn it and (2) the chainlinks-per-
minute passing over the exterior ring any different than a
conventional 52? Or does this combo behave like something
between 36 and 52? Does that help explain the curious
choice of a 52/54 exterior chainring set? For simplicity,
let's ignore the incremental friction.

Dear Peter,

To go into more detail than my bad description, it looks as
if the front contraptions starts with an ordinary bottom
bracket and a 32 tooth sprocket gear.

But it doesn't run the chain.

Enclosing it somewhat like a chain is a much larger sprocket
with normal gear teeth on the outside and also an inner ring--
with no normal spider arms to support it. This sprocket with
inner and outer teeth is probably sitting on a giant "bottom
bracket" that's just a monster lazy-susan-style bearing ring-
track welded onto three posts way up the front down tube,
the seat tube, and the chain-stay.

A second, slightly smaller sprocket may be attached inboard
of the outer sprocket, just like a normal double. (Or the
"derailleur" may be just a chain-guide and you have the
choice between a single outer sprocket, either 52 or 54.)

Unfortunately, the picture just doesn't show things
worth a damn.

So a crank turns a 32-tooth front gear, which engages the
??-tooth track inside a larger ring gear, which has a 52 or
54 tooth outer rim, which pulls normally on a chain that
runs back to a normal set of rear cogs.

The French text just doesn't make any of this clear. It
may be that there are three sizes of inner sporcket available--
29, 32, or 36--and two pairs of outer sprockets whose
outer teeth are 52 and 54, or 55 and 56. (Or Christ knows
what . . .)

Anyway, if it's just a small normal gear on a normal crank
that drives the inner track of a larger reduction gear that
then drives the chain normally, it's a huge waste of time.

A single rotation of the pedals turns 32 teeth, which in
turn rotates the outer sprocket's inner track of ?? teeth a
distance of only 32 teeth. Assuming that the inner track has
42 teeth, the reduction is
32/42. The outer sprocket then turns 32/42nds of its 54
teeth, which means an effective front sprocket of
(32/42) x 54 = 41.1 teeth.

Basically, an inner reduction gear driving a single outer
gear like this will alway provide an overall ratio somewhere
between the smaller and the larger, which is a waste of time
unless you're using gears to span small distances instead of
a chain, as in a spring watch or a computer printer.
Usually, reduction gears are mounted on the outside on
separate shafts, not inside like this, but that would make
the pointlessness of this contraption rather obvious.

Given a bad picture and my cluelessness, the thing may work
quite differently. But there are only three ways to change
how power is transmitted with gears, chains, and cranks.

33) Change the whole transmission ratio in a fixed manner--
more or fewer teeth, additional step-up or step-down
cogs, longer or shorter cranks, larger or smaller
wheels. (That's what this French thing seems to be, an
extra reduction gear.)

34) Change the transmission ratio so that it varies during a
crank cycle--the BioPace oval ring scheme, which has
exactly the same gear ratio as a round sprocket with the
same number of teeth over a single cycle, but which
varies the ratio smoothly during the cycle, raising and
lowering it according to the oval bulge, supposedly to
favor the knees by making things easier when the knee is
most vulnerable or else to allow a higher ratio when the
knee is feeling most powerful. But this doesn't look
like what the French contraption does.

35) Change the whole transmission ratio so that it varies
automatically according to load--a constant velocity or
CVT transmission, which in theory lets Lance stop
worrying about shifting gears and pedal at a steady
rate and load, no matter what the bicycle is doing--
slogging up a mountain, cruising on the flats, or
descending like a bomb, the transmission ratio rises
and falls so that your feet think they're on a
perfectly steady trainer. In practice, such CVT gizmos
are over-complicated, waste power, add weight, and
don't work too well anyway. But the French dingus may
be trying to do something like this. If so, it's
probably just as unsuccessful as the rest.

Ultimately, all transmissions can treated as black boxes
that convert the circular movement of your foot on the pedal
to circular movement of the rear tire on the ground.
Consider a 700c tire connected to an 11-tooth cog connected
by chain to a 53-tooth front sprocket connected to a 175 mm
pedal arm. If you work out the exciting arithmetic, the rear
tire moves 9.3 inches for every inch the pedal moves. Change
to a 26 front sprocket x 34 rear cog and the rear tire moves
about 1.4 inches for every inch the pedal moves.

The fewer gears, chains, levers, belts, and baling wire used
to achieve this, the less energy lost in transmission. A
normal system has a range of transmission ratios as high and
as low as anyone can practically use, so adding more gears
is as self-defeating as Jobst and Andrew suggested.

Carl Fogel

Peter Storey said:

[email hidden], A. Muzi and Carl Fogel
all wrote in

Quoted message said:

"Bulls***t"

Well, no, I don't believe in magic. But I was curious if it
had any effect of any kind (however that effect might be
offset by something else) beyond just adding friction.

It produces an effectively lower gear. Like a small
chainring.

Quoted message said:

Please indulge my scientific illiteracy. As a matter of
curiosity, what is the effective size of the chainrings?

The number of exterior teeth multiplied by the number of
teeth on the interior ring, divided by the number of tooth-
holes on the inside of the exterior ring. We don't know the
latter figure, but by eye it must be about a 48, which with
52 exterior and 36 internal would give an equivalent to an
39t chainring.
--
David Damerell <[email hidden]>
Distortion Field!

[email hidden] wrote :

Quoted message said:

.....

Unfortunately, the picture just doesn't show things
worth a damn.

So a crank turns a 32-tooth front gear, which engages the
??-tooth track inside a larger ring gear, which has a 52
or 54 tooth outer rim, which pulls normally on a chain
that runs back to a normal set of rear cogs. ....

A single rotation of the pedals turns 32 teeth, which in
turn rotates the outer sprocket's inner track of ?? teeth
a distance of only 32 teeth. Assuming that the inner track
has 42 teeth, the reduction is
32/42. The outer sprocket then turns 32/42nds of its 54
teeth, which means an effective front sprocket of
(32/42) x 54 = 41.1 teeth.

You got it right. French is my language, but it doesn't make
understanding their ad any easier.

There are other ways, I think, to achieve roughly the
same effect:

Quoted message said:

2) Change the transmission ratio so that it varies during
a crank cycle--the BioPace oval ring scheme, which has
exactly the same gear ratio as a round sprocket with
the same number of teeth over a single cycle, but which
varies the ratio smoothly during the cycle, raising and
lowering it according to the oval bulge, supposedly to
favor the knees by making things easier when the knee
is most vulnerable or else to allow a higher ratio when
the knee is feeling most powerful. But this doesn't
look like what the French contraption does.

It is roughly the same as Biopace. I can't see from the
picture whether the phases of least effort would be at the
top and bottom or at the sides, but it is roughly the scheme
developped by Shimano Biopace and a few other elliptic
patterns. It's funny that some of them preferred to have the
high parts of the ellipse when the cranks were vertical,
while other schemes were designed exactly the other way. All
of these schemes were short lived.

Michel Gagnon

On 9 May 2004 18:40:56 -0700, [email hidden] (Michel Gagnon)

Quoted message said:

[email hidden] wrote :

Quoted message said:

.....

Unfortunately, the picture just doesn't show things worth
a damn.

So a crank turns a 32-tooth front gear, which engages the
??-tooth track inside a larger ring gear, which has a 52
or 54 tooth outer rim, which pulls normally on a chain
that runs back to a normal set of rear cogs. ....

A single rotation of the pedals turns 32 teeth, which in
turn rotates the outer sprocket's inner track of ?? teeth
a distance of only 32 teeth. Assuming that the inner
track has 42 teeth, the reduction is
32/42. The outer sprocket then turns 32/42nds of its 54
teeth, which means an effective front sprocket of
(32/42) x 54 = 41.1 teeth.

You got it right. French is my language, but it doesn't
make understanding their ad any easier.

There are other ways, I think, to achieve roughly the
same effect:

Quoted message said:

2) Change the transmission ratio so that it varies during
a crank cycle--the BioPace oval ring scheme, which has
exactly the same gear ratio as a round sprocket with
the same number of teeth over a single cycle, but
which varies the ratio smoothly during the cycle,
raising and lowering it according to the oval bulge,
supposedly to favor the knees by making things easier
when the knee is most vulnerable or else to allow a
higher ratio when the knee is feeling most powerful.
But this doesn't look like what the French contraption
does.

It is roughly the same as Biopace. I can't see from the
picture whether the phases of least effort would be at the
top and bottom or at the sides, but it is roughly the
scheme developped by Shimano Biopace and a few other
elliptic patterns. It's funny that some of them preferred
to have the high parts of the ellipse when the cranks were
vertical, while other schemes were designed exactly the
other way. All of these schemes were short lived.

Michel Gagnon

Dear Michel,

Thanks for your confirmation that the ad for that odd
transmission from France is not much clearer to a native
French speaker.

I honestly can't see any ovalization of the inner or outer
rings that resembles the BioPace oval chain rings, but
perhaps you've spotted a detail that I'm missing:

zefj.compedalier%20doc.jpgOpen ↗

It really looks like nothing more than a badly misused
circular interior reduction gear scheme, mistakenly borrowed
from old-fashioned spring watches, where such gear-to-gear
connections replace chains. It appears to use ordinary
circular gears and would produce a steady, non-ovalized
resistance.

But there may be some hidden details in the large outer
ring. The ad includes the mysterious initials "VTC," which
might refer to some French equivalent for Constant Veloctiy
Transmission, or CVT.

I just checked, but Google shows nothing except our thread
for "demultiflex," whatever it is.

Carl Fogel

Quoted message said:

The ad includes the mysterious initials "VTC," which might
refer to some French equivalent for Constant Veloctiy
Transmission, or CVT.

No mystery. The line of text ("Adaptable sur tous cadres:
course, VTT, VTC"😉 translates as "Adaptable to all frames:
race, MTB, hybrid". VTT is "vélo tout terrain", literally
"all-terrain bike". VTC is "vélo tout chemin" - literally
"all trail bike", the French name for a hybrid.

James Thomson

James Thomson said:

Quoted message said:

The ad includes the mysterious initials "VTC," which
might refer to some French equivalent for Constant
Veloctiy Transmission, or CVT.

No mystery. The line of text ("Adaptable sur tous cadres:
course, VTT, VTC"😉 translates as "Adaptable to all frames:
race, MTB, hybrid". VTT is "vélo tout terrain", literally
"all-terrain bike". VTC is "vélo tout chemin" - literally
"all trail bike", the French name for a hybrid.

James Thomson

Dear James,

Aha, that explains things. Thank heavens we have no catchy
set of initals for hybrids to confuse matters--yet.

While the gizmo could be fitted on a mountain bike, I
shudder at the thought of what typical off-road mountain-
bike mud and grit would do to the two gears where the inner
gear's teeth mesh with the cog-track of the outer gear.

Thanks,

Carl Fogel

(Peter Storey) said:

Someone proposes to ride from Brittany to Vladivostok
between now and July 5th. He is going to use "Demultiflex
fp" cranks, which are described here:
zefj.compedalier%20doc.jpgOpen ↗

He might make the voyage, but I highly doubt that the
pictured crank system will.

Quoted message said:

How does this work? Does this work? Apart from additional
friction, what does this system do that's different than
using smaller-than-normal chainrings?

I am guessing that the advantage lies in conspicuously
sporting a couple of manly 50-something tooth sprockets,
while only having to drive through an effective 30-something
tooth ring.

Quoted message said:

And why only a two-tooth difference in the rings?

Why sport one big manly ring when you can have two? Also, if
the inner driven track is not very close in size to the
outer chainring perimeters, then the effective big ring
becomes higher than 30-something teeth, and that makes it
harder to pedal!

Chalo Colina