Carbon Fiber Seat Stays = Better Ride?

Werehatrack wrote:
On 13 Apr 2005 09:07:28 -0700, "Peter Cole"
wrote:


The real analogy would be whether a composite handle buys you anything
on a rubber mallet, that's a more accurate comparison.


Yup.

One lbs owner whose opinions I trust says if he puts the same wheels
and seat on six different bikes and rides each of them over the same
route, he has trouble telling which frame is which. OTOH, he has had
people grouse about how harsh the ride was on a carbon-frame racer,
only to wax ecstatic about the plush feel of a cheaper, aluminum-frame
tourer. The big difference, in his opinion, was the 32 vs 22 tires,
and 20 lbs less inflation pressure on the tourer.

Do you noticed that a large number of pros that usually use carbon
frames switched to alu for the Paris-Roubaix? This is strange, wasn't cf
the best material to absorbe vibrations (and PR has a lot of them...)?
In general I'm a fan of carbon frames, but maybe the "less vibrations"
factor counts less than most think...

Francesco

Francesco Devittori wrote:



Do you noticed that a large number of pros that usually use carbon
frames switched to alu for the Paris-Roubaix? This is strange, wasn't cf
the best material to absorbe vibrations (and PR has a lot of them...)?
In general I'm a fan of carbon frames, but maybe the "less vibrations"
factor counts less than most think...

Francesco

Carbon fiber absorbs all that shock in P-R right up to the point when
the frame breaks.

Mark Hickey wrote:
jim beam wrote:


Mark Hickey wrote:


Tell ya' what then... due to the total lack of any measurements (gee,
why do you suppose the manufacturers didn't try to quantify the
tremendous amount of improvement???), we'll have to settle for you
explaining to us all how much that carbon fiber seat stay
"compresses", and how, under what conditions. And then you can
compare that amount of compression to that in the tire during an event
that would compress the seat stay, and explain to us all how the
difference would be noticeable to the rider.

That'll do...

mark, just like different bulk materials have different properties such
as modulus, density, etc., they also have different shock transmission
characteristics. and that's it. composites have different [usually
attenuated] shock transmission spectra to materials like steel & ti &
aluminum.


I don't entirely disagree with you, and do understand that different
material will transmit different impulses differently... but I can't
help but think that any "pulse" that gets by and through the tire,

why keep repeating this "it doesn't get past the tire" myth? you drive
cars don't you? with massive low pressure tires, suspension, rubber
bushings and cushy seats, are you still able to differentiate between
different road surfaces? of course!

across the rim, up (and down) the spokes, through the hub to the
dropout isn't going to have a tremendous amount of "square wave" left.

no square waves here.

And it's doubly hard for me to imagine something as stiff as an
axially loaded CF tube affecting an already-muted "pulse" enough to
make a real difference.

imagination is not the point. measurement is the point - something this
group seems careful to avoid because it ends debate, willful
misinterpretation & posturing.

To do so would require mm+ "compression" to
make any difference

that's the magnitude myth again. when some dude with the thumping sound
system drives past your house & the crockery rattles on the sideboard,
exactly how much displacement is taking place? hint: it's not mm magnitude.

even to the most finely tuned butt (no flatulence
jokes please), especially when you realize that the "difference" has
to be interpreted by that butt through a saddle designed to absorb
shock.

To me, it's a princess and the pea scenario, and I've yet to see
anything that makes me think the CF stays are anything other than
marketing. I'll gladly change my mind in the presence of data
though... but I suspect there's a very good reason the manufacturers
don't supply it.

why don't you supply it? you're a manufacturer. you can rent an
accelerometer & spectrum analyzer, then publish results of your product
vs. competitor products. enlist the help of some local undergrad
[electrical] engineering students if necessary.


Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

Mark Hickey wrote:
" wrote:


Please explain why compression is an issue?
Grey/Black cast iron does not compress, yet its vibration damping
characteristics are why all the best machine tools use it for frames
and beds.

Don't confuse two different phenomina.


I think you're the one mixing different issues. The sheer mass of a
cast iron bed is what helps keep vibrations to a minimum.

no, cast iron /does/ attenuate shock & vibration relative to other steel
types. that's fact.

If I hit
that table with a hammer, the hammer is going to do the compressing,
not the table, right? The table has mass on its side, and
"compressing" the surface of the table would require compressing a
MUCH larger chunk of iron than the hammer has (since just under the
contact point is more iron, and more behind that, and so on and so
on...).

To grossly over-simplify the issue - for a seat stay to "damp" a
vibration, the vibration has to enter one end at one amplitude, and
exit the other end at a smaller amplitude. Forgive me if I've missed
something obvious, but the only physical phenomenon I can imagine that
would cause that effect would require the stay to compress. There's
simply no other way that a thin-walled piece of carbon fiber is going
to reduce the amplitude of impulses fed into one end.

And I think it's clear that it simply cannot compress to any degree
that would be meaningful in terms of a noticeable change in the ride
qualities of a given bike.

I'll be happy to alter my position if someone - anyone - can explain
to me how the stay could physically damp an impulse significantly. No
one's been able to do that. Ever.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

jim beam wrote:

Mark Hickey wrote:

I don't entirely disagree with you, and do understand that different
material will transmit different impulses differently... but I can't
help but think that any "pulse" that gets by and through the tire,

why keep repeating this "it doesn't get past the tire" myth? you drive
cars don't you? with massive low pressure tires, suspension, rubber
bushings and cushy seats, are you still able to differentiate between
different road surfaces? of course!

You inadvertently make my point. In a car, you hit obstacles that
would cause a crash on a road bike constantly, and barely notice the
feedback through "the system". I doubt I'd be able to notice the
difference if I installed a carbon fiber steering column in my Jeep.

across the rim, up (and down) the spokes, through the hub to the
dropout isn't going to have a tremendous amount of "square wave" left.

no square waves here.

My point exactly.

And it's doubly hard for me to imagine something as stiff as an
axially loaded CF tube affecting an already-muted "pulse" enough to
make a real difference.

imagination is not the point. measurement is the point - something this
group seems careful to avoid because it ends debate, willful
misinterpretation & posturing.

To do so would require mm+ "compression" to
make any difference

that's the magnitude myth again. when some dude with the thumping sound
system drives past your house & the crockery rattles on the sideboard,
exactly how much displacement is taking place? hint: it's not mm magnitude.

And that has nothing to do with the problem at hand. We KNOW we have
a system with a very compliant 5-10mm minimum of easy compression,
with some damping thrown in for good measure. It seems you're
acknowledging that there can't be even 1mm of "compression" in the
stay.

even to the most finely tuned butt (no flatulence
jokes please), especially when you realize that the "difference" has
to be interpreted by that butt through a saddle designed to absorb
shock.

To me, it's a princess and the pea scenario, and I've yet to see
anything that makes me think the CF stays are anything other than
marketing. I'll gladly change my mind in the presence of data
though... but I suspect there's a very good reason the manufacturers
don't supply it.

why don't you supply it? you're a manufacturer. you can rent an
accelerometer & spectrum analyzer, then publish results of your product
vs. competitor products. enlist the help of some local undergrad
[electrical] engineering students if necessary.

Because I know what the numbers would say - that there's no difference
in the "compliance" of my titanium stays and the aluminum, steel or
carbon fiber stays of my competitors. So I would have spent a lot of
time and money doing a study to prove that I don't have any
competitive advantage in my "stay technology" over my competition
(which is what I've always said, BTW). Why in the world would I want
to do that?

The corollary to your suggestion is that those who manufacture a
product that DOES have a measureable advantage over the competition
would be foolish NOT to quantify that advantage in their sales
literature. Yet not one has done so. You do the math.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

On 13 Apr 2005 10:02:01 -0700, "
wrote:

Peter wrote:

Funny thing is that prices all seem to be about the same. I'm sure
debates rage about materials on some carpentry NG.


As a frequenter of both rec.woodworking and rec.bicycles.tech, I can
say, actually, no.

At the local hardwood lumber supplier, the salesman is sometimes
amused by the people who have obviously developed a particularly
strong fondness for one kind of wood.

OTOH, it's hard to beat lignum vitae if you need to make clock
bearings.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Mark Hickey wrote:
" wrote:

Please explain why compression is an issue?
Grey/Black cast iron does not compress, yet its vibration damping
characteristics are why all the best machine tools use it for frames
and beds.

Don't confuse two different phenomena.

DAMN! Why do the really interesting discussions have to happen when I'm
actually busy with work! Sorry if this rambles around a bit..



I think you're the one mixing different issues. The sheer mass of a
cast iron bed is what helps keep vibrations to a minimum. If I hit
that table with a hammer, the hammer is going to do the compressing,
not the table, right

Actually no... it has to do with the granular (molecular) structure of
the material, Cast Iron has long needle like grains or crystals which
are very different than the crystalline structure of just about any
other metal. Most metals have a crystal structure referred to as Face
Centered Cubic or Body Centered Cubic (FCC BCC) the important word
being Cubic, imagine grains of salt all bonded edge to edge or better
yet bricks in a wall. Cast Iron has a structure the looks more like a
ball of needles or a bundle of twigs, all pointed in different
directions. The needles bond to each other where they touch but there
are voids between them and in the case of grey cast iron there is
molecular carbon in the form of graphite.


To grossly over-simplify the issue - for a seat stay to "damp" a
vibration, the vibration has to enter one end at one amplitude, and
exit the other end at a smaller amplitude. Forgive me if I've missed
something obvious, but the only physical phenomenon I can imagine
that
would cause that effect would require the stay to compress.

Vibration at a basic level is just another form of energy and in your
example it goes in at one end and comes out at the other. Compression
involves plastic deformation of the material and would be more properly
concidered absorption, the energy entering causes a molecule to change
shape, in effect storing the energy to be released as it returns to its
original shape. Think of it this way .. at a molecular level the
Vibration energy has to transfer from crystal to crystal throughout the
matrix in order to get from one end to the other. If we go back to the
bundle of twigs/wall of bricks analogy (though for cast iron "ball of
pins" is much more accurate), Tap one brick on the end of a row and the
brick at the other end moves as well, but with the bundle of twigs the
chaotic structure allows a lot more movement of one piece before it
impacts on another, additionally some of that energy is transferred in
different directions further reducing the amount of energy getting to
the other end. Because of this the energy is, to all intents and
purposes, dissipated within the structure.

Sure it's over simplified but that is what happens, the material itself
acts as an insulator. CF has a structure that is far closer to the
bundle of twigs metaphor than the ball of pins but the same thing is
happening, there is a "loss" of energy as the vibration moves through
the material.



I'll be happy to alter my position if someone - anyone - can explain
to me how the stay could physically damp an impulse significantly.
No
one's been able to do that. Ever.

It really does work this way, I know I'm asking a lot for some anonymos
internet poster but there is a lot of data available. There was some
really good info at www.matweb.com at one point but I have not had
cause to go there in years.

Now all that being said I am about to backtrack a bit.. above you
introduce the qualifier "significantly" and to be perfectly honest I
too have my doubts about just how worthwhile this "improvement" would
be. Taking it as a given that the material does damp vibrations I
worked QA at an aerospace place for a number of years and if vibration
damping was a design requirement the engineering specs for the CF part
were horrifically complex, fiber length, fiber orientation, wet-out and
compression were all critical, do the manufacturers take that kind of
care for mass market bike parts?. There WILL be some improvement at
least... how much I really can't say.

Andrew

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

On Wed, 13 Apr 2005 02:27:05 GMT, wrote:

If you consider the concept of off axis loading of a seat stay

Something I do all the time, since I usually run out of other
things to think about halfway through long rides.

--
bpo gallery at http://www4.tpgi.com.au/users/mvw1/bpo

jim beam wrote:


imagination is not the point. measurement is the point - something
this
group seems careful to avoid because it ends debate, willful
misinterpretation & posturing.

FWIW, in the long-running debates over "ride quality", the only numbers
I recall seeing have been from the magic-material skeptics.

I think Mark's point is good: If there really were some easily
measurable benefit to a magic layer of carbon fiber - or titanium, or
"real" steel, or aluminum or bamboo - then the manufacturers of such
frames would be using the data in their ad copy.

Or at least, the magic-material proponents would be giving data in
Usenet. But instead we seem to be getting arguments like "Why don't
you rent some measurement equipment and prove my point?"

Faith is sometimes a wonderful thing. But I'm not sure that applies to
faith in the latest techno-fashion. Give us numbers, Jim.

- Frank Krygowski

wrote:
Mark Hickey wrote:

" wrote:


Please explain why compression is an issue?
Grey/Black cast iron does not compress, yet its vibration damping
characteristics are why all the best machine tools use it for frames
and beds.

Don't confuse two different phenomena.


DAMN! Why do the really interesting discussions have to happen when I'm
actually busy with work! Sorry if this rambles around a bit..



I think you're the one mixing different issues. The sheer mass of a
cast iron bed is what helps keep vibrations to a minimum. If I hit
that table with a hammer, the hammer is going to do the compressing,
not the table, right


Actually no... it has to do with the granular (molecular) structure of
the material, Cast Iron has long needle like grains or crystals which
are very different than the crystalline structure of just about any
other metal. Most metals have a crystal structure referred to as Face
Centered Cubic or Body Centered Cubic (FCC BCC) the important word
being Cubic, imagine grains of salt all bonded edge to edge or better
yet bricks in a wall. Cast Iron has a structure the looks more like a
ball of needles or a bundle of twigs, all pointed in different
directions. The needles bond to each other where they touch but there
are voids between them and in the case of grey cast iron there is
molecular carbon in the form of graphite.


To grossly over-simplify the issue - for a seat stay to "damp" a
vibration, the vibration has to enter one end at one amplitude, and
exit the other end at a smaller amplitude. Forgive me if I've missed
something obvious, but the only physical phenomenon I can imagine

that

would cause that effect would require the stay to compress.


Vibration at a basic level is just another form of energy and in your
example it goes in at one end and comes out at the other. Compression
involves plastic deformation of the material and would be more properly
concidered absorption, the energy entering causes a molecule to change
shape, in effect storing the energy to be released as it returns to its
original shape. Think of it this way .. at a molecular level the
Vibration energy has to transfer from crystal to crystal throughout the
matrix in order to get from one end to the other. If we go back to the
bundle of twigs/wall of bricks analogy (though for cast iron "ball of
pins" is much more accurate), Tap one brick on the end of a row and the
brick at the other end moves as well, but with the bundle of twigs the
chaotic structure allows a lot more movement of one piece before it
impacts on another, additionally some of that energy is transferred in
different directions further reducing the amount of energy getting to
the other end. Because of this the energy is, to all intents and
purposes, dissipated within the structure.

Sure it's over simplified but that is what happens, the material itself
acts as an insulator. CF has a structure that is far closer to the
bundle of twigs metaphor than the ball of pins but the same thing is
happening, there is a "loss" of energy as the vibration moves through
the material.



I'll be happy to alter my position if someone - anyone - can explain
to me how the stay could physically damp an impulse significantly.

No

one's been able to do that. Ever.


It really does work this way, I know I'm asking a lot for some anonymos
internet poster but there is a lot of data available. There was some
really good info at www.matweb.com at one point but I have not had
cause to go there in years.

Now all that being said I am about to backtrack a bit.. above you
introduce the qualifier "significantly" and to be perfectly honest I
too have my doubts about just how worthwhile this "improvement" would
be. Taking it as a given that the material does damp vibrations I
worked QA at an aerospace place for a number of years and if vibration
damping was a design requirement the engineering specs for the CF part
were horrifically complex, fiber length, fiber orientation, wet-out and
compression were all critical, do the manufacturers take that kind of
care for mass market bike parts?. There WILL be some improvement at
least... how much I really can't say.

Andrew

wow, great one! never heard a dendritic structure referred to as "a
bundle of twigs" before but it's not a bad analogy!


Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame