F
jim beam wrote:
>
> >
> mark & phil, the charts are not totally legible, but let's see what
we
> can deduce.
>
> 1. the units of frequency is Hertz, [Hz], and that appears to be what
> the horizontal axes are labeled as. i can't read the numbers, but
> they're all 3 digits, apart from origin which is clearly zero.
likely
> units are hundreds of Hz, and the fuzz appears to accord with 100,
200,
> 300, etc up to 600Hz.
>
> 2. the vertical axes are not clear regarding units - could be english
or
> metric. they may also be sensor output or they may be g's. but the
> length of the numerical labels clearly indicate a log scale.
>
> 3. we also have red & blue lines, from which "front axle" & "rear
axle"
> can be read, both for blue lines. therefore, even though illegible,
the
> reds must be handlebar & saddle.
>
> with that much understanding, we can now look at the data.
Can we pause and note how ridiculous this is?
First, we're examing in detail graphs which are clearly part of an
advertising effort by Specialized. These are not part of a scientific
paper of any sort.
Second, we're _guessing_ at what the scales of the graphs are saying.
We're not sure if the units are English or Metric. We're _guessing_ at
what frequencies they've measured.
Third, we're _guessing_ at what the critical curves represent. We
figure they probably have something to do with saddle and handlebars.
But we're not quite positive.
Fourth, we have no information about how the vibrations were excited.
That is, did they apply excitation to a naked hub mounted in the frame?
Or to a 20 mm tire? Or to a 2" diameter balloon tire?
Fifth, we have no information about the mass resting on the saddle, if
any. Was the bike unloaded? Quite possible! That would tend to give
the biggest difference on the advertising graphs. But of course, the
ad copy doesn't say.
Finally, has nobody else noticed that they're claiming special benefit
from the "Zertz" viscoelastic polymer inserts in the seat stays???
Good grief, gentlemen! They're talking about something entirely
different from plain CF seatstays! Your credulity has blinded you!
it's clear
> that for good chunks of both graphs that there /is/ about an order of
> magnitude difference between red & blue. because of sensor
locations,
> this differential /has/ to be resulting from some property of the
frame
> system. [and to be clear, this is /after/ any effect of the
> tire/wheel.] it's also clear that the differential is greater for
> higher frequencies than lower.
Of course. Now let's return to my fourth point: How were the frame
vibrations excited? If those abscissa values are 600 Hz, it's very
unlikely they were shaking the bottom of an inflated tire on a loaded
bike. 600 Hz is about the middle of the musical staff; if try to pump
that frequency into the tire of a spoked wheel, little of it makes it
as far as the hub!
I'd say the odds are great that they excited the axle directly. They
can "scientifically" justify that by saying they're not interested in
the effect of the tire, rim and spokes. But the trouble is a) there's
no way to get a meaningful amount of audible frequency vibration _into_
the axle from the road. And if you did, it would have to be such a
small amplitude that it would be imperceptible to the rider except
through his ears. Again, we don't hear with our butt!
Look, try this: Take a standard musical tuning fork, say an A-440 Hz
fork. Touch it to the end of an aluminum rod, and touch the other end
to your ear, as a mechanic does when diagnosing mechanical sounds.
Note the loudness when you vibrate the tuning fork.
Now repeat, but have the rod touch a bike's hub, while the tuning fork
vibrates against the inflated tire. I just tried this, guys. You can
barely hear the vibration. 440 Hz is almost entirely absorbed by the
tire.
Yet that seems to be the frequency that Specialized says their Roubaix
frame is best at absorbing. WITH ELASTOMERIC INSERTS!
> interpretation? we clearly have a frame system that /is/ shown to
> attenuate vibration by up to 10x, generally better at higher
frequencies
> than lower. if we assume frame design is conventional [the pic /is/
> fairly clear]...
Have you considered reading the rest of the site?? Are you forgetting
that you're looking at an advertisement for a frame with elastomeric
inserts??
and that the frame joints are comparatively rigid, this
> measurement differential /is/ a function of material.
Yup. Specifically, the elastomeric insert material. Look at the
seatpost that uses the same. Or the handlebars.
I'm quite willing to believe that a frame with flexible elastomeric
inserts can be designed to absorb the musical note A-440! And, as an
amateur musician, if I ever find my steel or aluminum frames'
vibrations are interfering with my on-bike music making, I'll promise
to look into a Roubaix frame.
But back to the subject! Does anyone have any tests showing a
NON-elastomeric carbon fiber seat stay reducing vibrations that are of
actual interest to a bike rider?
I thought not.
- Frank Krygowski
>
> >
> mark & phil, the charts are not totally legible, but let's see what
we
> can deduce.
>
> 1. the units of frequency is Hertz, [Hz], and that appears to be what
> the horizontal axes are labeled as. i can't read the numbers, but
> they're all 3 digits, apart from origin which is clearly zero.
likely
> units are hundreds of Hz, and the fuzz appears to accord with 100,
200,
> 300, etc up to 600Hz.
>
> 2. the vertical axes are not clear regarding units - could be english
or
> metric. they may also be sensor output or they may be g's. but the
> length of the numerical labels clearly indicate a log scale.
>
> 3. we also have red & blue lines, from which "front axle" & "rear
axle"
> can be read, both for blue lines. therefore, even though illegible,
the
> reds must be handlebar & saddle.
>
> with that much understanding, we can now look at the data.
Can we pause and note how ridiculous this is?
First, we're examing in detail graphs which are clearly part of an
advertising effort by Specialized. These are not part of a scientific
paper of any sort.
Second, we're _guessing_ at what the scales of the graphs are saying.
We're not sure if the units are English or Metric. We're _guessing_ at
what frequencies they've measured.
Third, we're _guessing_ at what the critical curves represent. We
figure they probably have something to do with saddle and handlebars.
But we're not quite positive.
Fourth, we have no information about how the vibrations were excited.
That is, did they apply excitation to a naked hub mounted in the frame?
Or to a 20 mm tire? Or to a 2" diameter balloon tire?
Fifth, we have no information about the mass resting on the saddle, if
any. Was the bike unloaded? Quite possible! That would tend to give
the biggest difference on the advertising graphs. But of course, the
ad copy doesn't say.
Finally, has nobody else noticed that they're claiming special benefit
from the "Zertz" viscoelastic polymer inserts in the seat stays???
Good grief, gentlemen! They're talking about something entirely
different from plain CF seatstays! Your credulity has blinded you!
it's clear
> that for good chunks of both graphs that there /is/ about an order of
> magnitude difference between red & blue. because of sensor
locations,
> this differential /has/ to be resulting from some property of the
frame
> system. [and to be clear, this is /after/ any effect of the
> tire/wheel.] it's also clear that the differential is greater for
> higher frequencies than lower.
Of course. Now let's return to my fourth point: How were the frame
vibrations excited? If those abscissa values are 600 Hz, it's very
unlikely they were shaking the bottom of an inflated tire on a loaded
bike. 600 Hz is about the middle of the musical staff; if try to pump
that frequency into the tire of a spoked wheel, little of it makes it
as far as the hub!
I'd say the odds are great that they excited the axle directly. They
can "scientifically" justify that by saying they're not interested in
the effect of the tire, rim and spokes. But the trouble is a) there's
no way to get a meaningful amount of audible frequency vibration _into_
the axle from the road. And if you did, it would have to be such a
small amplitude that it would be imperceptible to the rider except
through his ears. Again, we don't hear with our butt!
Look, try this: Take a standard musical tuning fork, say an A-440 Hz
fork. Touch it to the end of an aluminum rod, and touch the other end
to your ear, as a mechanic does when diagnosing mechanical sounds.
Note the loudness when you vibrate the tuning fork.
Now repeat, but have the rod touch a bike's hub, while the tuning fork
vibrates against the inflated tire. I just tried this, guys. You can
barely hear the vibration. 440 Hz is almost entirely absorbed by the
tire.
Yet that seems to be the frequency that Specialized says their Roubaix
frame is best at absorbing. WITH ELASTOMERIC INSERTS!
> interpretation? we clearly have a frame system that /is/ shown to
> attenuate vibration by up to 10x, generally better at higher
frequencies
> than lower. if we assume frame design is conventional [the pic /is/
> fairly clear]...
Have you considered reading the rest of the site?? Are you forgetting
that you're looking at an advertisement for a frame with elastomeric
inserts??
and that the frame joints are comparatively rigid, this
> measurement differential /is/ a function of material.
Yup. Specifically, the elastomeric insert material. Look at the
seatpost that uses the same. Or the handlebars.
I'm quite willing to believe that a frame with flexible elastomeric
inserts can be designed to absorb the musical note A-440! And, as an
amateur musician, if I ever find my steel or aluminum frames'
vibrations are interfering with my on-bike music making, I'll promise
to look into a Roubaix frame.
But back to the subject! Does anyone have any tests showing a
NON-elastomeric carbon fiber seat stay reducing vibrations that are of
actual interest to a bike rider?
I thought not.
- Frank Krygowski