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
