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:
http://www.zefj.com/images/pedalier%20doc.jpg

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:
http://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?

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

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: http://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

--

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: http://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:
http://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

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
http://www.classicrendezvous.com/USA/checkered_flag.htm. 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.

1) 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.)

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.

3) 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:

http://www.zefj.com/images/pedalier%20doc.jpg

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:
http://www.zefj.com/images/pedalier%20doc.jpg

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