Optical illusions, continued ...

Michael Press said:

Since you can pin _all_ the joints in a tetrahedron
without changing the essential aspects of the structure:
stresses applied at the joints act on the struts only in
compression & tension.

The axle location is beyond the joint and beyond the axis of the seat
stays; it's outside the tetrahedron in this setup. This would allow
the joint to become a fulcrum. It's still a bad idea.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Chris M said:

Not to mention that frame with a tensioned cable for a downtube :>😉

The "Slingshot", IIRC. Buycycling loved it, but then.....

Werehatrack said:

Quoted message said:

Sandy Broque writes:

http://www.merida.com/s0_global/main_control.php?group0=tech&group1=flexstay

Quoted message said:

Now what exactly could someone offer in commentary ?

Quoted message said:

The above is guaranteed 100% free of sarcasm, denigration, snotty
remarks, indifference, platitudes, fuming demands that "you do the
math", conceited visions of a better world on wheels according to
[insert NAME here].

Rather than post bland disclaimers about oddly constructed sentences,
try asking a straight forward question without gratuitous adjectives.

The web page was not reasonably edited for English "flat-sping" or for
technical accuracy. The "rear triangle" of the bicycle frame shown is
like those of most conventional frames in that it is a tetrahedron,
the most rigid structural space frame imaginable, supporting only
tension and compression. For this reason these tubes can be as
slender as they are in classic steel frames. The forces haven't
changed, only the frame materials have.

The flexing forces indicated in the web page are imaginary as are the
text contentions.

Looking at the photo, it appears that they may have joined the
chainstays to the dropouts with a pivot joint. I suppose they may be
expecting that the dropout will thereby be able to couple some force
into the seat stay by rotation at the joint. To me, if this has any
actual effect at all, it is a bug, not a feature.

On further digging, I found a line drawing of the frame. It appears
that the photo artifact I spotted is actually just a hole in the
dropout. If they're actually flexing the rear triangles to the degree
claimed with that setup, I would have to agree that this is a bad
idea, but I rather suspect that the illustration is a marketer's
markup with "dramatically emphasized motion". I.e., a lie.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Michael Press said:

Since you can pin _all_ the joints in a tetrahedron
without changing the essential aspects of the structure:
stresses applied at the joints act on the struts only in
compression & tension.

And after finding a better illustration of the frame, I see that their
claim has to be spurious anyway. What I had thought was a joint
(which would not have been at the apex, BTW) was in fact just a hole
in the dropout.

Interestingly, they list two bikes as having "flexstays"; one of them
is a full-suspension unit with what appears to be a fairly ordinary
swingarm, though I suppose it's possible that they have omitted the
pivot on the forward end of the lower set of chainstays. If so, it's
well off into what I consider loony design territory. (No offense
intended to certain indigenous waterfowl of northern North America.)
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Werehatrack said:

Quoted message said:

Sandy Broque writes:

http://www.merida.com/s0_global/main_control.php?group0=tech&group1=flexstay

> Now what exactly could someone offer in commentary ?

> The above is guaranteed 100% free of sarcasm, denigration, snotty
> remarks, indifference, platitudes, fuming demands that "you do the
> math", conceited visions of a better world on wheels according to
> [insert NAME here].

Rather than post bland disclaimers about oddly constructed sentences,
try asking a straight forward question without gratuitous adjectives.

The web page was not reasonably edited for English "flat-sping" or for
technical accuracy. The "rear triangle" of the bicycle frame shown is
like those of most conventional frames in that it is a tetrahedron,
the most rigid structural space frame imaginable, supporting only
tension and compression. For this reason these tubes can be as
slender as they are in classic steel frames. The forces haven't
changed, only the frame materials have.

The flexing forces indicated in the web page are imaginary as are the
text contentions.

Looking at the photo, it appears that they may have joined the
chainstays to the dropouts with a pivot joint. I suppose they may be
expecting that the dropout will thereby be able to couple some force
into the seat stay by rotation at the joint. To me, if this has any
actual effect at all, it is a bug, not a feature.

On further digging, I found a line drawing of the frame. It appears
that the photo artifact I spotted is actually just a hole in the
dropout. If they're actually flexing the rear triangles to the degree
claimed with that setup, I would have to agree that this is a bad
idea, but I rather suspect that the illustration is a marketer's
markup with "dramatically emphasized motion". I.e., a lie.
--

Maybe they saw the Specialized Zertz "see it in action" animation and
got a bit jealous.

Ozark Bicycle said:

Werehatrack said:

On further digging, I found a line drawing of the frame. It appears
that the photo artifact I spotted is actually just a hole in the
dropout. If they're actually flexing the rear triangles to the degree
claimed with that setup, I would have to agree that this is a bad
idea, but I rather suspect that the illustration is a marketer's
markup with "dramatically emphasized motion". I.e., a lie.
--

Maybe they saw the Specialized Zertz "see it in action" animation and
got a bit jealous.

"Any tale you can tell, we can tell taller..."
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Michael Press said:

Since you can pin _all_ the joints in a tetrahedron
without changing the essential aspects of the structure:
stresses applied at the joints act on the struts only in
compression & tension.

And after finding a better illustration of the frame, I see that their
claim has to be spurious anyway. What I had thought was a joint
(which would not have been at the apex, BTW) was in fact just a hole
in the dropout.

Interestingly, they list two bikes as having "flexstays"; one of them
is a full-suspension unit with what appears to be a fairly ordinary
swingarm, though I suppose it's possible that they have omitted the
pivot on the forward end of the lower set of chainstays. If so, it's
well off into what I consider loony design territory. (No offense
intended to certain indigenous waterfowl of northern North America.)

Further excavation produced a drawing of the frame; the swing arm has
a pivot, a very assymmetric chainstay design, and a linkage above the
spring strut whose full functionality is not immediately obvious.
This frame bears many stigmata of what I regard as marketing-driven
engineering.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Ozark Bicycle said:

Werehatrack said:

On further digging, I found a line drawing of the frame. It appears
that the photo artifact I spotted is actually just a hole in the
dropout. If they're actually flexing the rear triangles to the degree
claimed with that setup, I would have to agree that this is a bad
idea, but I rather suspect that the illustration is a marketer's
markup with "dramatically emphasized motion". I.e., a lie.
--

Maybe they saw the Specialized Zertz "see it in action" animation and
got a bit jealous.

"Any tale you can tell, we can tell taller..."

and then:

"Any [censored] you can sling, we can sling farther"

"Sandy Get Your Hype" will open in New Haven this Summer. :-)

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

Quoted message said:

In article <[email hidden]>,

Mike Reed said:

What's the big deal? Ibis, Merlin, and many others have all used
flexing chainstays for suspension in the past.

I thought it was going to be *good* optical illusion, like this one:
http://forum.bikemag.com/photopost/data/504/2990Optical_illusion.JPG

I still don't see the boat.

What boat?

Greg

In article <[email hidden]>,

Werehatrack said:

Michael Press said:

Since you can pin _all_ the joints in a tetrahedron
without changing the essential aspects of the structure:
stresses applied at the joints act on the struts only in
compression & tension.

The axle location is beyond the joint and beyond the axis of the seat
stays; it's outside the tetrahedron in this setup. This would allow
the joint to become a fulcrum. It's still a bad idea.

The axle is part of the tetrahedron; it is one strut in
the tetrahedron. A tetrahedron: 4 vertices, 6 edges, 4
faces. The edges are seat tube, two chainstays, two seat
stays, one axle.

--
Michael Press

Michael Press said:

In article <[email hidden]>,

Werehatrack said:

Michael Press said:

Since you can pin _all_ the joints in a tetrahedron
without changing the essential aspects of the structure:
stresses applied at the joints act on the struts only in
compression & tension.

The axle location is beyond the joint and beyond the axis of the seat
stays; it's outside the tetrahedron in this setup. This would allow
the joint to become a fulcrum. It's still a bad idea.

The axle is part of the tetrahedron; it is one strut in
the tetrahedron. A tetrahedron: 4 vertices, 6 edges, 4
faces. The edges are seat tube, two chainstays, two seat
stays, one axle.

Had there been a joint where I had originally thought one was placed,
and had the seatstay axis been as i thought I saw, it would have
broken the tetrahedron. As that's not what is actually the case
(which I noted in another post after finding a line drawing that
clarified the nature of the design) my opinion must be changed
accordingly; I have to say that as far as I can see, and as you
correctly maintained all along, their claims must be spurious.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Dans le message de news:[email hidden],
Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy said:

Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Quoted message said:

> http://www.merida.com/s0_global/main_control.php?group0=tech&group1=flexstay

Quoted message said:

Quoted message said:

It probably requires plenty of snake oil to prevent squeaks! ;-)

If those round stays are flexing as much as they claim, that would
be one SCARY bike to ride, IMHO. I can't imagine mounting V-brakes
on a seat stay that could flex enough to move the dropout (axle)
"several mm's". It'd be like riding a bucking broco.

Given your experience with manufacturers, I am surprised you have
never observed flex testing of frames and forks.

I have seen them. I've just never seen anyone flex a "solid" rear
triangle up and down a few mm's (well, more than ONCE, that is). ;-)

It's not me with the answer, just the Q. But there is a little
discontinuity I perceive in this critique, and those from others. I do not
see here, or in other rear "triangles", the pure tetrahedron. Unless, of
course, one ignores the shape and composition of the materials which connect
the four theoretical dots. That's where I find it hard to accept that a
manufacturer cannot seek a solution there. Also, I think your idea that
ONCE is more than enough only addresses the idea that there is a pivoting
effect of all deflections in the rear triangle. If you don't compel that
preconception, but allow the deflection to arise from planned deformation
throughout the structure, then I think there is room to explore the
potential design. I don't know the answers, but I think I can see the
illogic in the questioning.

Quoted message said:

My point is that the claims that are made for that frame seem to be
dubious, unless they're really NOT round stays, but flat metal strips
surrounded by flexible tubes.

Here's another preconception that I find unconvincing. Were it flat, it
could be ? I don't see why there need be a difference. For example, bamboo
fly fishing rods aren't round, but are typically made of six triangular
tapered parts. They bend. Carbon and glass fibre rods also bend. There
are certainly arguments for decades already about the finer
points of using one of the materials, but I don't think that "flat" is in
the marketing materials except, perhaps, to make the concept accessible to a
broader audience.

Quoted message said:

Quoted message said:

If you can get a chance,
unlikely as it may be, LOOK has a fork testing apparatus. It holds
the pivot at the crown, and the legs are bent backwards up to a
centimeter, for hundreds of thousands of cycles. Décathlon tours
its stores with the frame flex machine, which twists, akternately,
the head tube and the rear triangle, for as much as a centimeter (so
I recall), for hundreds of thousands of cycles.

Twisting is one thing. I can twist my frame in a hard uphill sprint.
That's been discussed here to death, and there are plenty of sprint
photos to back up the fact that this happens on real bikes ridden by
real riders.

But there's virtually nothing short of tossing it under a truck that's
going to find 3mm of "vertical travel" in the rear end. Try it on
your own frame. Take a static meaurement and then load 400 (or heck,
800) pounds on the saddle and measure again (seat tube top to
dropout). If you measure a 3mm+ delta, you've either got a suspension
frame or a broken frame.

First, I think we both agree that such movement arises from shock. But I
think that they are saying (however inelegantly or without explanations to
this particular forum) is that they are solving the enigma presented. I am
sure that not all changes in bike design come from rigid application of
rigid formulae. It may be worth flexing the thinking muscles also.

Quoted message said:

You're missing the point - I'm not sure if it's on purpose, or if you
just don't understand why a test that requires a hydraulic press to
deform a frame just MIGHTnot have a whole lot of connection with the
"real world ride performance".

I don't understand why the test equipment is more important than the test
objective. If rolling steel drums don't mimic pavement, yet provide clues
on real tire performance, I am certainly not the one to object. Same with
the test beds for all components. But when one approaches real-world
testing, then it is with riders, and there is a very strong bias amongst
writers here to discredit human perception and evaluation. So, how to test
?

I can't criticize the ideas presented by Merida, not can I support them.
But why would you, or others who doubt, not ask some questions of them
directly ? I am just not convinced by those who discard ideas based on
jarred, calcified grey cells.

Quoted message said:

Or not - when you consider some of the silly things that DO sell,
there's gotta be a lot of people who buy into that kind of thing.

What if it actually works ? What then ? I imagine there are reasons people
don't buy into new stuff. Like me, I recall, when someone said that
wired-on tires were not going to be wired-on any more, but have fabric -
strings - in the hoop to hold things together. I didn't buy that idea for a
minute. Well, not right away. I didn't like the image, but I'm just a
consumer. Things change. People learn. But I thank you for your views
that allow me to ask yet more questions.
--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

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

Quoted message said:

Dans le message de news:[email hidden],
Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy said:

Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

>> http://www.merida.com/s0_global/main_control.php?group0=tech&group1=flexstay

Quoted message said:

> It probably requires plenty of snake oil to prevent squeaks! ;-)
>
> If those round stays are flexing as much as they claim, that would
> be one SCARY bike to ride, IMHO. I can't imagine mounting V-brakes
> on a seat stay that could flex enough to move the dropout (axle)
> "several mm's". It'd be like riding a bucking broco.

Given your experience with manufacturers, I am surprised you have
never observed flex testing of frames and forks.

I have seen them. I've just never seen anyone flex a "solid" rear
triangle up and down a few mm's (well, more than ONCE, that is). ;-)

It's not me with the answer, just the Q. But there is a little
discontinuity I perceive in this critique, and those from others. I
do not see here, or in other rear "triangles", the pure tetrahedron.
Unless, of course, one ignores the shape and composition of the
materials which connect the four theoretical dots. That's where I
find it hard to accept that a manufacturer cannot seek a solution
there. Also, I think your idea that ONCE is more than enough only
addresses the idea that there is a pivoting effect of all deflections
in the rear triangle. If you don't compel that preconception, but
allow the deflection to arise from planned deformation throughout the
structure, then I think there is room to explore the potential design.
I don't know the answers, but I think I can see the illogic in the
questioning.

Quoted message said:

My point is that the claims that are made for that frame seem to be
dubious, unless they're really NOT round stays, but flat metal strips
surrounded by flexible tubes.

Here's another preconception that I find unconvincing. Were it flat,
it could be ? I don't see why there need be a difference. For
example, bamboo fly fishing rods aren't round, but are typically made
of six triangular tapered parts. They bend. Carbon and glass fibre
rods also bend. There are certainly arguments for decades already
about the finer
points of using one of the materials, but I don't think that "flat" is
in the marketing materials except, perhaps, to make the concept
accessible to a broader audience.

They bend because the force on the end of the rod is normal to the rod.
The seat and chain stays are axially loaded in compression and tension
only. If they bent any appreciable amount (to allow 3mm of vertical
compliance) the whole rear triangle would fail in buckling. Even curved
seat stays are a gimmick.
If they were soft enough to allow for that kind of deflection they would
also deflect laterally and would be
almost unrideable. Look up Johnson and Euler for elastic instability.

Phil H

In article <[email hidden]>,
"Sandy" <[email hidden]> wrote:

[flexing bicycle triangle discussion excised]

Quoted message said:

What if it actually works ? What then ?

By `actually works' you speak about the chain stays and
seat stays flexing perceptibly; as much, say, as forks
flex. Then the flexing of the stays might play havoc with
the drive train; smacking the chain around, perhaps
inducing auto-shifts.

--
Michael Press

In article
<[email hidden]>,

Phil Holman' piholmanc@yourservice said:

They bend because the force on the end of the rod is normal to the rod.
The seat and chain stays are axially loaded in compression and tension
only. If they bent any appreciable amount (to allow 3mm of vertical
compliance) the whole rear triangle would fail in buckling. Even curved
seat stays are a gimmick.
If they were soft enough to allow for that kind of deflection they would
also deflect laterally and would be
almost unrideable. Look up Johnson and Euler for elastic instability.

Gabby Johnson and who? Leonhard or Houston?

--
Michael Press

G.T. said:

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

Quoted message said:

In article <[email hidden]>,

Mike Reed said:

What's the big deal? Ibis, Merlin, and many others have all used
flexing chainstays for suspension in the past.

I thought it was going to be *good* optical illusion, like this one:
http://forum.bikemag.com/photopost/data/504/2990Optical_illusion.JPG

I still don't see the boat.

What boat?

I'm pretty sure there's a little man in the boat, but it's covered.

Bill "tsk" S.

"Sandy" <[email hidden]> wrote:

A lot of words.

Sandy, I don't know if you just enjoy being obtuse, or reply just to
hear your keyboard click... but the subject at hand is very simple,
and not the psychodrama you're making it out to be.

The question is: "has someone finally found a way to flex a solid
tetrahedron on the back of a bicycle several mm's?".

In your world, we're being rigid (pun intended) and unemotional about
the issue. Yep, guilty as charged. Physics is like that - creativity
only works if it follows the rules, no matter how contrarian you wanna
be.

If Merida had actually (as you hint is possible) included some
whiz-bang new technology that allows their round carbon fiber stays to
flex in a manner that no previous stays have ever flexed - I have to
believe they might have mentioned it in passing, don'tcha think?

It's clear that lots of people believe that carbon stays DO flex
enough to do what Merida claims. All that's required to get us to
this discussion is that their ad writer is guilty of this
misconception.

You also seemed to miss the point of my "flat stays surrounded by
flexible tubes" it seems. I guess you're just too rigid and set in
your ways to accept new technology. ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Quoted message said:

Dans le message de news:[email hidden],
Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy said:

Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

>> http://www.merida.com/s0_global/main_control.php?group0=tech&group1=flexstay

Quoted message said:

> It probably requires plenty of snake oil to prevent squeaks! ;-)
>
> If those round stays are flexing as much as they claim, that would
> be one SCARY bike to ride, IMHO. I can't imagine mounting V-brakes
> on a seat stay that could flex enough to move the dropout (axle)
> "several mm's". It'd be like riding a bucking broco.

Given your experience with manufacturers, I am surprised you have
never observed flex testing of frames and forks.

I have seen them. I've just never seen anyone flex a "solid" rear
triangle up and down a few mm's (well, more than ONCE, that is). ;-)

It's not me with the answer, just the Q. But there is a little
discontinuity I perceive in this critique, and those from others. I do not
see here, or in other rear "triangles", the pure tetrahedron. Unless, of
course, one ignores the shape and composition of the materials which connect
the four theoretical dots. That's where I find it hard to accept that a
manufacturer cannot seek a solution there. Also, I think your idea that
ONCE is more than enough only addresses the idea that there is a pivoting
effect of all deflections in the rear triangle. If you don't compel that
preconception, but allow the deflection to arise from planned deformation
throughout the structure, then I think there is room to explore the
potential design. I don't know the answers, but I think I can see the
illogic in the questioning.

Quoted message said:

My point is that the claims that are made for that frame seem to be
dubious, unless they're really NOT round stays, but flat metal strips
surrounded by flexible tubes.

Here's another preconception that I find unconvincing. Were it flat, it
could be ? I don't see why there need be a difference. For example, bamboo
fly fishing rods aren't round, but are typically made of six triangular
tapered parts. They bend. Carbon and glass fibre rods also bend. There
are certainly arguments for decades already about the finer
points of using one of the materials, but I don't think that "flat" is in
the marketing materials except, perhaps, to make the concept accessible to a
broader audience.

Quoted message said:

Quoted message said:

If you can get a chance,
unlikely as it may be, LOOK has a fork testing apparatus. It holds
the pivot at the crown, and the legs are bent backwards up to a
centimeter, for hundreds of thousands of cycles. Décathlon tours
its stores with the frame flex machine, which twists, akternately,
the head tube and the rear triangle, for as much as a centimeter (so
I recall), for hundreds of thousands of cycles.

Twisting is one thing. I can twist my frame in a hard uphill sprint.
That's been discussed here to death, and there are plenty of sprint
photos to back up the fact that this happens on real bikes ridden by
real riders.

But there's virtually nothing short of tossing it under a truck that's
going to find 3mm of "vertical travel" in the rear end. Try it on
your own frame. Take a static meaurement and then load 400 (or heck,
800) pounds on the saddle and measure again (seat tube top to
dropout). If you measure a 3mm+ delta, you've either got a suspension
frame or a broken frame.

First, I think we both agree that such movement arises from shock. But I
think that they are saying (however inelegantly or without explanations to
this particular forum) is that they are solving the enigma presented. I am
sure that not all changes in bike design come from rigid application of
rigid formulae. It may be worth flexing the thinking muscles also.

Quoted message said:

You're missing the point - I'm not sure if it's on purpose, or if you
just don't understand why a test that requires a hydraulic press to
deform a frame just MIGHTnot have a whole lot of connection with the
"real world ride performance".

I don't understand why the test equipment is more important than the test
objective. If rolling steel drums don't mimic pavement, yet provide clues
on real tire performance, I am certainly not the one to object. Same with
the test beds for all components. But when one approaches real-world
testing, then it is with riders, and there is a very strong bias amongst
writers here to discredit human perception and evaluation. So, how to test
?

I can't criticize the ideas presented by Merida, not can I support them.
But why would you, or others who doubt, not ask some questions of them
directly ? I am just not convinced by those who discard ideas based on
jarred, calcified grey cells.

Quoted message said:

Or not - when you consider some of the silly things that DO sell,
there's gotta be a lot of people who buy into that kind of thing.

What if it actually works ? What then ? I imagine there are reasons people
don't buy into new stuff. Like me, I recall, when someone said that
wired-on tires were not going to be wired-on any more, but have fabric -
strings - in the hoop to hold things together. I didn't buy that idea for a
minute. Well, not right away. I didn't like the image, but I'm just a
consumer. Things change. People learn. But I thank you for your views
that allow me to ask yet more questions.

Dans le message de news:[email hidden],
Mark Hickey <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

"Sandy" <[email hidden]> wrote:

A lot of words.

Sandy, I don't know if you just enjoy being obtuse, or reply just to
hear your keyboard click... but the subject at hand is very simple,
and not the psychodrama you're making it out to be.

The question is: "has someone finally found a way to flex a solid
tetrahedron on the back of a bicycle several mm's?".

Let's start with that, for a dumb, non-math, non-engineer.
I look at your words, and I look at the actual bicycle, and I don't see a
tetrahedron.
Tetra - four
Hedron - sides
I am not sure either of them actually pertain.
/Four/ - first, look at the attachment point to the main triangle. It's
distant from the point where the seatstays or the chainstays converge. So,
not being contrarian, but just an observer, I don't see a simple FOUR.
/Side/ - if you mean a regular plane, again, I don't see that except by
connecting the dots of the most outlying points. The surfaces described by
the curved chainstays and seatstays don't develop a "hedron". So, unless
the math actually covers the folds and waves of the projectible surfaces
(yes, of course, there are numerous potential results, unless you can
describe all the dimensions of all the edge components), you don't have the
second element.

My reaction in the present case is not to buy into the simplified marketing
web-page. My proposal is that someone who has the ability to generate a
technical question actually posit that question, in the friendliest of terms
(to elicit the friendliest of replies) directly to the company that makes
the claims.

As a consequence (hoped for, not guaranteed) of productive questions and
answers, it may develop that there are real areas of new knowledge that go
beyond the oversimplified and underestimating ones that have been posted
here.

You don't have a tetrahedron, so what do you have, and how can it behave
differently, and how can materials contribute to changing the kind of
behavior obtained ? That's not as astute a question as an engineer could
pose, but is it really better to avoid asking, to repeat the mythical,
inaccurate and deceptive reflexive answers that arise here ?

It's not a contrarian position, I repeat. While I have not a deep knowledge
of engineering, I have a good enough practial perception of both things I
can put my hands and eyes on, and on empty (not yours) jingoistic refusals
to allow new information to be gathered and assimilated.

Again, thanks for the chance to refine my questioning.
--
Bonne route !

Sandy
Verneuil-sur-Seine FR

Sandy Broque said:

Let's start with that, for a dumb, non-math, non-engineer. I look
at your words, and I look at the actual bicycle, and I don't see a
tetrahedron.

Quoted message said:

Tetra - four
Hedron - sides

Quoted message said:

I am not sure either of them actually pertain.

Would you please lay off the "dumb, non-math, non-engineer" stuff for
this thread? That only sets you up for a let down because in spite of
the disclaimers you discuss mathematical and engineering matters
regularly here. Just pose the questions and let them ride.

As I explained, the "rear triangle" of a bicycle frame is a
tetrahedron with four triangular faces. The frame seen from the side
has two obvious triangles, left and right. Seen from below, the
chainstays and axle make a triangle, and from the rear, the axle and
seat stays make fourth triangular face of the tetrahedron. A regular
tetrahedron, in contrast, has four regular triangles. With the
education you profess to have you had to pass that test in geometry,
so I see no excuse for your argumentation, regardless of not being an
engineer or mathematician.

Quoted message said:

/Four/ - first, look at the attachment point to the main triangle.
It's distant from the point where the seatstays or the chainstays
converge. So, not being contrarian, but just an observer, I don't
see a simple FOUR. /Side/ - if you mean a regular plane, again, I
don't see that except by connecting the dots of the most outlying
points. The surfaces described by the curved chainstays and
seatstays don't develop a "hedron". So, unless the math actually
covers the folds and waves of the projectible surfaces (yes, of
course, there are numerous potential results, unless you can
describe all the dimensions of all the edge components), you don't
have the second element.

I take it you have seen a Hetchins frame. These do not flex and their
rear triangles are far more distorted than the ones in question. They
are part of a tetrahedron and the curves tubes are large enough in
diameter to not buckle. If that is not convincing, you should
consider the rear brake that puts seat stays into bending. The loads
are insufficient to cause any significant deflection and the saddle
does not articulate up and down from braking.

http://www.worldclasscycles.com/old-het-4.jpg

Quoted message said:

My reaction in the present case is not to buy into the simplified
marketing web-page. My proposal is that someone who has the ability
to generate a technical question actually posit that question, in
the friendliest of terms (to elicit the friendliest of replies)
directly to the company that makes the claims.

That would be a highly naive gesture. The company knows full well
what the BS in their advertisement is. These things are not conjured
in a vacuum. A team has a meeting where the thrust of the promotion
is discussed and tested for obvious weak points. In this case the
person who composed the web page failed to spell check, which is an
indication of less than good management oversight.

Quoted message said:

As a consequence (hoped for, not guaranteed) of productive questions
and answers, it may develop that there are real areas of new
knowledge that go beyond the oversimplified and underestimating ones
that have been posted here.

If you really believe you can influence such a project then you have
never tried it, especially with thinly staffed companies that abound
in the bicycle industry.

Quoted message said:

You don't have a tetrahedron, so what do you have, and how can it
behave differently, and how can materials contribute to changing the
kind of behavior obtained ? That's not as astute a question as an
engineer could pose, but is it really better to avoid asking, to
repeat the mythical, inaccurate and deceptive reflexive answers that
arise here ?

That's your perception. I don't believe others in this discussion are
as convinced that this is not a tetrahedron as you are.

Quoted message said:

It's not a contrarian position, I repeat. While I have not a deep
knowledge of engineering, I have a good enough practial perception
of both things I can put my hands and eyes on, and on empty (not
yours) jingoistic refusals to allow new information to be gathered
and assimilated.

Stop these disclaimers, they only serve to dig your superior attitude
deeper into the hole that it is in.

Quoted message said:

Again, thanks for the chance to refine my questioning.

I am not cajoled by your mock courtesy.

Jobst Brandt

Dans le message de news:[email hidden],
[email hidden] <[email hidden]> a
réfléchi, et puis a déclaré :

Quoted message said:

Sandy Broque said:

Let's start with that, for a dumb, non-math, non-engineer. I look
at your words, and I look at the actual bicycle, and I don't see a
tetrahedron.

Quoted message said:

Tetra - four
Hedron - sides

Quoted message said:

I am not sure either of them actually pertain.

Would you please lay off the "dumb, non-math, non-engineer" stuff for
this thread? That only sets you up for a let down because in spite of
the disclaimers you discuss mathematical and engineering matters
regularly here. Just pose the questions and let them ride.

No chiding !! I can address the linguistically inexplicable engineering
terms, like your non-triangles below.

Quoted message said:

As I explained, the "rear triangle" of a bicycle frame is a
tetrahedron with four triangular faces. The frame seen from the side
has two obvious triangles, left and right. Seen from below, the
chainstays and axle make a triangle, and from the rear, the axle and
seat stays make fourth triangular face of the tetrahedron. A regular
tetrahedron, in contrast, has four regular triangles. With the
education you profess to have you had to pass that test in geometry,
so I see no excuse for your argumentation, regardless of not being an
engineer or mathematician.

I was not trying to squirm into a regular tetrahedron or other carbon forms.
You may want corrective lenses at your age. Or admit to being an
impressionist (not cubist) engineer. The only common straight line in this
assembly, lately, seems to be the wheel axle. For us engineering-impaired,
I offer :

"Triangle is a convex polygon with three segments joining three
non-collinear points. Each of the three segments is called a side, and each
of the three non-collinear points is called a vertex"

and, so you don't wonder if French triangles are different :

"En géométrie, un triangle se définit rigoureusement sur une surface comme
une figure fermée à trois côtés, ces trois côtés étant des arcs de
géodésiques de cette surface. "

Quoted message said:

Quoted message said:

/Four/ - first, look at the attachment point to the main triangle.
It's distant from the point where the seatstays or the chainstays
converge. So, not being contrarian, but just an observer, I don't
see a simple FOUR. /Side/ - if you mean a regular plane, again, I
don't see that except by connecting the dots of the most outlying
points. The surfaces described by the curved chainstays and
seatstays don't develop a "hedron". So, unless the math actually
covers the folds and waves of the projectible surfaces (yes, of
course, there are numerous potential results, unless you can
describe all the dimensions of all the edge components), you don't
have the second element.

I take it you have seen a Hetchins frame. These do not flex and their
rear triangles are far more distorted than the ones in question. They
are part of a tetrahedron and the curves tubes are large enough in
diameter to not buckle. If that is not convincing, you should
consider the rear brake that puts seat stays into bending. The loads
are insufficient to cause any significant deflection and the saddle
does not articulate up and down from braking.

http://www.worldclasscycles.com/old-het-4.jpg

Quoted message said:

My reaction in the present case is not to buy into the simplified
marketing web-page. My proposal is that someone who has the ability
to generate a technical question actually posit that question, in
the friendliest of terms (to elicit the friendliest of replies)
directly to the company that makes the claims.

That would be a highly naive gesture. The company knows full well
what the BS in their advertisement is. These things are not conjured
in a vacuum. A team has a meeting where the thrust of the promotion
is discussed and tested for obvious weak points. In this case the
person who composed the web page failed to spell check, which is an
indication of less than good management oversight.

Well, if they refused, or waffled, or prevaricated, you could report that in
support.

Quoted message said:

Quoted message said:

As a consequence (hoped for, not guaranteed) of productive questions
and answers, it may develop that there are real areas of new
knowledge that go beyond the oversimplified and underestimating ones
that have been posted here.

If you really believe you can influence such a project then you have
never tried it, especially with thinly staffed companies that abound
in the bicycle industry.

Not looking to influence - just to inquire and obtain reasonable answers.

Quoted message said:

Quoted message said:

You don't have a tetrahedron, so what do you have, and how can it
behave differently, and how can materials contribute to changing the
kind of behavior obtained ? That's not as astute a question as an
engineer could pose, but is it really better to avoid asking, to
repeat the mythical, inaccurate and deceptive reflexive answers that
arise here ?

That's your perception. I don't believe others in this discussion are
as convinced that this is not a tetrahedron as you are.

Wasn't it you who just recently wrote that seatstays can be delicately thin,
as they do not contribute significantly to rigidity at the back ?

Quoted message said:

Quoted message said:

It's not a contrarian position, I repeat. While I have not a deep
knowledge of engineering, I have a good enough practial perception
of both things I can put my hands and eyes on, and on empty (not
yours) jingoistic refusals to allow new information to be gathered
and assimilated.

Stop these disclaimers, they only serve to dig your superior attitude
deeper into the hole that it is in.

Paranoia may not always be treatable.

Quoted message said:

I am not cajoled by your mock courtesy.

Did you think this was addressed to you ? Did you read the attributions ?
No, you didn't even include them. Oh, well ...
I haven't paid attention to your pronouncements for a while, already.

A sig-line just for you -
--
Sandy

The above is guaranteed 100% free of sarcasm,
denigration, snotty remarks, indifference, platitudes, fuming demands that
"you do the math", conceited visions of a better world on wheels according
to [insert NAME here].
(NOT)