Re: Carbon Fiber Seat Stays = Better Ride?



J

jim beam

Guest
Steve Sr. wrote:
> I have seen carbon fiber seat stays being advertized as improving the
> "comfort" and the ride "quality" of a bike. Serotta even goes so far
> as putting a bearing at the dropout end on their high end bikes to
> allow the seat stays to flex and act as springs to soften the ride. Or
> at least this is what is claimed. Other manufacturers make similar
> claims.
>
> So given a regular full titanium frame like a Litespeed Tuscany how
> much if any difference would be made by having the seat stays made of
> carbon fiber? Would the difference be noticeable or not? Has anybody
> done any _quantatative_ measurements or studies on this or is it all
> subjective?
>
> Thanks for your thoughts.
>
> Steve


it should have a noticably softer ride. materials people are very
familiar with the superior shock transmission characteristics of
composites. that's why tools like hammers that otherwise cause
repetitive strain injuries are so often made with composite shafts. [in
this case, wood can also be called a composite.]

the trouble with this group however is that the people making the
loudest "it makes no difference" noises would never do anything
definitive like rent instumentation that would quantify the situation -
it would prove them luddites. as for actually /riding/ a bike with such
new fangled technology? well, that's just not going to happen. no
siree bob.
 
jim beam wrote:

<snip>

<Has anybody done any _quantatative_ measurements or studies on this
or is it all subjective>

Has anyone, including manufacturers, tried to quantify this with strain
gauges and instrumentation? Just curious.
 
jim beam <[email protected]> wrote:

>it should have a noticably softer ride. materials people are very
>familiar with the superior shock transmission characteristics of
>composites. that's why tools like hammers that otherwise cause
>repetitive strain injuries are so often made with composite shafts. [in
>this case, wood can also be called a composite.]
>
>the trouble with this group however is that the people making the
>loudest "it makes no difference" noises would never do anything
>definitive like rent instumentation that would quantify the situation -
>it would prove them luddites. as for actually /riding/ a bike with such
>new fangled technology? well, that's just not going to happen. no
>siree bob.


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 Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
 
I haven't seen one for bicycles.. but there is a lot of data available
in engineering.
Vibration damping is a known property, it is measured and is often a
design driver. CF has "better" damping than Steel/Alu/Ti .. All else
being equal there WILL be a difference in ride characteristics, how
much a difference might be noticeable to you or may well be minutia for
a lab to determine.

How this fact is applied in each case is a different matter, the
bicycle industry has a long history of marketing driven design and
engineering decisions. This tends to leave people jaded about claims
like these.
 
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.
 
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.

App
 
Mark Hickey wrote:
> jim beam <[email protected]> wrote:
>
>
>>it should have a noticably softer ride. materials people are very
>>familiar with the superior shock transmission characteristics of
>>composites. that's why tools like hammers that otherwise cause
>>repetitive strain injuries are so often made with composite shafts. [in
>>this case, wood can also be called a composite.]
>>
>>the trouble with this group however is that the people making the
>>loudest "it makes no difference" noises would never do anything
>>definitive like rent instumentation that would quantify the situation -
>>it would prove them luddites. as for actually /riding/ a bike with such
>>new fangled technology? well, that's just not going to happen. no
>>siree bob.

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


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.

the jobstian tire red herring makes no account of dynamic loading
because it never suits his arguments on this kind of subject, but the
fact remains that a tire can & does transmit shock impulse via its
sidewall /and/ it's air filling. the sidewall transmits "tension loss"
pulses. the air transmits compression just like it does sound.
 
jim beam <[email protected]> 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,
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.
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. To do so would require mm+ "compression" to
make any difference 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.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
 
"[email protected]" <[email protected]> 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. 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
 
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:
> "[email protected]" <[email protected]> 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
 
On 13 Apr 2005 10:02:01 -0700, "[email protected]"
<[email protected]> 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.
 
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
 
[email protected] wrote:
> 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
>

google "carbon fiber vibration absorption" = 95,300 hits.

#1 = http://www.macqc.com/industrial.php

if this is smoke, it's pretty damned pervasive smoke given some of the
absorption spectra i saw as an undergrad.

bottom line, sure, i /could/ go out & rent the gear & do this stuff for
you, but frankly, i don't see why i should be the one with the burden of
proof when all /you/ need to do is make google your friend. just
because the marketing departments of some manufactures get their hands
on the advertising copy doesn't automatically mean 100% of their words
are lies.
 
jim beam wrote:
> [email protected] wrote:
> >
> > Faith is sometimes a wonderful thing. But I'm not sure that

applies to
> > faith in the latest techno-fashion. Give us numbers, Jim.
> >
> >

> google "carbon fiber vibration absorption" = 95,300 hits.
>
> #1 = http://www.macqc.com/industrial.php
>
> if this is smoke, it's pretty damned pervasive smoke given some of

the
> absorption spectra i saw as an undergrad.
>
> bottom line, sure, i /could/ go out & rent the gear & do this stuff

for
> you, but frankly, i don't see why i should be the one with the burden

of
> proof when all /you/ need to do is make google your friend.


Believe it or not, I've actually used Google before. That makes at
least two of us, eh?

But the number of hits on Google isn't the number I was looking for.
After all, if you google "space alien abduction" you get about 174,000
hits. Do you therefore figure space alien abductions are nearly twice
as likely as carbon fiber vibration absorption?

As to why you should be the one with the burden of proof: ISTM that
you're the one making claims contrary to most engineering principles.
Those on the other side of this argument are saying a tube whose total
axial compression is perhaps 0.001" can't have a detectable effect on
ride quality, given that the deflection of the tire and saddle are at
least 100 times bigger. Your extraordinary claims should require
extraordinary proof.

We could be wrong. And perhaps the princess really could detect the
pea through 20 mattresses. But I'd prefer some non-advertising
evidence about that.

Do you know of a blind test where riders could distinguish frames that
were identical except for the carbon stays? Alternately, do you know
of instrumented tests that clearly showed a significant difference?

- Frank Krygowski
 
[email protected] wrote:



> 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 p lastic 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.


At a basic level, you are very confused. Energy is a property of matter
and vibration is a process in matter. Vibration is not "just another
form of energy" although vibrating matter has some. Vibration is not
energy because e.g. all vibrations have amongst other things a period
of oscillation and the associated energy does not. Compression may
involve plastic deformation but it may not. Absorption of energy is not
storage of energy, that is why you use damping materials, to absorb
energy, and these work by wasting it as heat, not storing it.


You have this very long-winded discourse about crystal shapes and so on
which nicely obfuscates the crucial point, namely how on earth this
mechanism that you describe acts in an essentially incompressible
member where all those molecular systems you mention essentially aren't
deforming in the first place, and ergo leave essentially no opportunity
for the fancy effects you invoke.

..
 
41 wrote:
> [email protected] wrote:
>
>
>
> > 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 p lastic 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.

>
> At a basic level, you are very confused. Energy is a property of

matter
> and vibration is a process in matter. Vibration is not "just another
> form of energy" although vibrating matter has some.


I was trying to over simplify.. I do agree with most of what you say,
but I don't know if it furthers the discussion or simply takes things
out on another tangent.. I also don't know of a better way to describe
it... it really is the structure of the material that accounts for the
effect.
 
[email protected] wrote:
> jim beam wrote:
>
>>[email protected] wrote:
>>
>>>Faith is sometimes a wonderful thing. But I'm not sure that

>
> applies to
>
>>>faith in the latest techno-fashion. Give us numbers, Jim.
>>>
>>>

>>
>>google "carbon fiber vibration absorption" = 95,300 hits.
>>
>>#1 = http://www.macqc.com/industrial.php
>>
>>if this is smoke, it's pretty damned pervasive smoke given some of

>
> the
>
>>absorption spectra i saw as an undergrad.
>>
>>bottom line, sure, i /could/ go out & rent the gear & do this stuff

>
> for
>
>>you, but frankly, i don't see why i should be the one with the burden

>
> of
>
>>proof when all /you/ need to do is make google your friend.

>
>
> Believe it or not, I've actually used Google before. That makes at
> least two of us, eh?
>
> But the number of hits on Google isn't the number I was looking for.
> After all, if you google "space alien abduction" you get about 174,000
> hits. Do you therefore figure space alien abductions are nearly twice
> as likely as carbon fiber vibration absorption?


i don't think vibration absorption "likely" - i've seen it tested in the
lab!

>
> As to why you should be the one with the burden of proof: ISTM that
> you're the one making claims contrary to most engineering principles.
> Those on the other side of this argument are saying a tube whose total
> axial compression is perhaps 0.001" can't have a detectable effect on
> ride quality, given that the deflection of the tire and saddle are at
> least 100 times bigger. Your extraordinary claims should require
> extraordinary proof.


yes, that tube compression calc stuff was a screw-up. i cut & pasted a
formula from a spreadsheet that was wrong! teach me not to cheat.

returning to the debate, "my" claims are not extroardinary, merely
statements of fact. read andrew's description of the factors that
influence vibration absorption in carbon composites. as for "tire &
saddle" stuff, again, it's wrong to confuse static with dynamic
properties. your hi fi is not the same switched off as it is working is
it? the static properties are identical in each state.

>
> We could be wrong. And perhaps the princess really could detect the
> pea through 20 mattresses. But I'd prefer some non-advertising
> evidence about that.


what is the velocity of the pea?

>
> Do you know of a blind test where riders could distinguish frames that
> were identical except for the carbon stays? Alternately, do you know
> of instrumented tests that clearly showed a significant difference?


can't say i've bothered to look because i have some familiarity with the
theory of the materials. you are right, quantification is a good
objective, but frankly, i doubt the value for this group as some of its
most vocal members will disregard any fact you care to present because
"it doesn't fit" their preconceptions, education be damned.

let me ask, have you ridden a bike that's been converted from a steel to
a carbon fork? [conversion of an existing bike eliminates all other
variables.] if you do that with a bike you own & love, you will be able
to differentiate a "before" & "after" of the carbon vibration
transmission quite easily. same for a carbon seat post.

>
> - Frank Krygowski
>
 
Mark Hickey wrote:
> "[email protected]" <[email protected]> wrote:
>
>
> I'll buy that, but don't see how it's going to make any meaningful /
> significant / noticeable difference.


That I wont argue.. quantifying the difference is probably the job of a
lab.

> Bottom line is, in order for the
> above to work, there has to be at LEAST 1mm of "absorption" somewhere
> in the short, stiff seat stay, and I have to believe the actual
> compressability of the stay is at least an order of magnitude smaller
> than that. Even at 1mm, it would get lost in the MUCH larger
> "dendretic systems" (heh) of the saddle.
>


Sure there are a lot of issues that can have a much bigger difference,
but it is additive, kind of like insulation on your house, you can
always add more but at some point it isn't worth it anymore.

>
> Mark Hickey
> Habanero Cycles
> http://www.habcycles.com
> Home of the $695 ti frame
 
jim beam wrote:
> [email protected] wrote:
> >
> >
> > But the number of hits on Google isn't the number I was looking

for.
> > After all, if you google "space alien abduction" you get about

174,000
> > hits. Do you therefore figure space alien abductions are nearly

twice
> > as likely as carbon fiber vibration absorption?

>
> i don't think vibration absorption "likely" - i've seen it tested in

the
> lab!


On a bicycle? If so, give us the results! If not, you'll have to
clearly demonstrate that the situation is close enough to be
equivalent.

Here's a proposal for a simplified lab test: One vertical seatstay
tube of steel, versus one of carbon fiber. Use a shaker table or other
mechanism to vibrate the bottom. Mount an accelerometer at the top,
hook it to data acquisition equipment. Sound good so far?

But we're not done, and this is the critical part: Between the
vibrator and the tube, put a 1" diameter rubber tube inflated to 100
psi, to simulate the tire. And at the top, between the tube and the
accelerometer, put a bicycle seat. And put a 150 pound weight on the
seat. Now measure the difference in vibration amplitude at the seat's
top.

Of course, if you want to do a better job, you can find a way to model
the spokes, the seatpost, etc. Or hell, just mount a bike frame,
vibrate the botttom of the rear tire and measure the effect at the
saddle's top surface. Just don't forget the 150 pound weight on the
saddle.

> returning to the debate, "my" claims are not extroardinary, merely
> statements of fact.


Classic! IOW:
"Here's proof of my views: 'MY VIEWS ARE TRUE!' There! Guess I showed
you!"

read andrew's description of the factors that
> influence vibration absorption in carbon composites. as for "tire &
> saddle" stuff, again, it's wrong to confuse static with dynamic
> properties.


You'll need to explain that in much more detail. If there are specific
inertial effects you're imagining, you'll have to explain them. In
particular, you'll have to explain how they get attenuated by a stiff
carbon tube, but do not get attenuated by an air cushion (the tire) and
a sprung hammock (the saddle).


> > Do you know of a blind test where riders could distinguish frames

that
> > were identical except for the carbon stays? Alternately, do you

know
> > of instrumented tests that clearly showed a significant difference?

>
> can't say i've bothered to look...


Ah.

because i have some familiarity with the
> theory of the materials.


As do I.

you are right, quantification is a good
> objective, but frankly, i doubt the value for this group as some of

its
> most vocal members will disregard any fact you care to present...


Ah.

because
> "it doesn't fit" their preconceptions, education be damned.


Funny!


>
> let me ask, have you ridden a bike that's been converted from a steel

to
> a carbon fork? [conversion of an existing bike eliminates all other
> variables.] if you do that with a bike you own & love, you will be

able
> to differentiate a "before" & "after" of the carbon vibration
> transmission quite easily. same for a carbon seat post.


No, I haven't. A friend has. She says "Well, I _think_ it makes a
difference." And it probably does - but the difference she feels could
come from many factors besides the material difference. IOW, the
replacement fork is unlikely to be an exact match for her steel fork in
static stiffness, in rake (offset), in mass... and it's _certainly_ not
an exact match in appearance!

There's a POWERFUL placebo effect in everything related to cycling.
That's why heartfelt convictions aren't nearly as convincing as real
data, or as convincing as the results of physics-based calculations, or
as convincing as blind comparison tests. So far, all you've provided
are heartfelt convictions.

- Frank Krygowski
 

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