Dans le message de news:
[email protected],
Mark Hickey <
[email protected]> a réfléchi, et puis a déclaré :
> "Sandy" <[email protected]> wrote:
>> BTW, there was another testing apparatus I saw recently. It's
>> Décathlon's frame twister, and I saw it with their new titanium
>> bike, in action. You may be surprised to see how far a rear
>> triangle will move when subjected to what they say is equivalent to
>> an 80 kg rider climbing hard. Not just sideways, but up and down.
>> But I don't have clear recall of any distance, just that it had gone
>> over 600 000 cycles without failure.
> I don't doubt that "twisting" to an easily measurable magnitude is
> possible with a strong rider (and we've all seen the photos of the
> ubersprinters on noodly steel frames with the wheels in visibly
> different planes)... but I'd be interested in seeing any numbers
> relative to a purely up/down flex in a "rigid" frame. I haven't seen
> anyone (including those who market curved stays) provide meaningful
> data on "suspension effect". I'm not familiar with the frame you
> mention - perhaps it's designed for some actual rear wheel vertical
> travel?
>
Here's the link the Décathlon's very brief description of the product (a
normal racing bike) :
http://www.decathlon.fr/Magasin/produit.asp?int_DeptId=25022&int_DeptPereId=33009&int_PfId=549820
I have not seen Le Cycle's review, if they did one yet. But, for another
frame you may well be familiar with, a Cannondale Six 13 Pro, they offer
these deflection results :
Headtube : 8mm
Bottom bracket : 0.53mm
Rear triangle : 2.92 mm
Those are all static loads, using the testing procedure they use for all
evaluations. They are not pedaling efforts over many cycles, and the force
applied, while uniform for all tests, seems lower than typical use. They
also don't do combined force measurements, and I don't know how that would
be informative. But there is measurable deflection in a single application
of force to a constructed frame. When I looked at the testing equipment at
Décathlon and at the Salon, I was struck by how much movement there was for
the entire frame in all directions.
There is a German testing institute which does similar stuff ; perhaps a
German correspondent could offer insight, but I don't have any of that
material.
But I think the suggestions, to measure vibration attenuation (or not) with
a rider in place, is the *only* sensible point of departure for argument.
After all, base zero for the perception of vibration damping is in the
neurons of one's posterior. To say that we won't experience any perception
of change in vibration damping, depending on the system proposed, is almost
to say that we never experience vibrations in the rear end, the hands or the
pedals. While the abstract materials and engineering experts may want to
show that the effects are negligible, their arguments all posit this
"negligible" on the basis of inert measurement devices.
The butt is not heavily populated with sensors, but the human organism seems
to perceive that there is some baseline vibration, right ? If that were not
the case, one would be unable to tell a difference, exclusively as to
vibration, between a tireless and metal-saddled bike and an equipped one.
So diminution occurs, and after adding the saddle and tires, you get some
sort of residual vibration perceived for each bike. And there is a comfort
factor that results.
Then, if saddles are pivotal for comfort, reducing vibration, why is it that
ones which do a lot of vibration attenuation are less comfortable on long
rides. Referring to pillow-type saddles, of course. And the effects are
not appreciated (I didn't write measured) until you are out on a longer
ride. And the less vibration experienced over 3-5 hours means less fatigue,
I believe.
One last note, trying not to write a novel, is about the point Mr Krygowski
was trying to make about the inserts not attenuating if they are only in
line with the structure where they are placed. I took his comment about
ringing, and actually picked up a loose seatpost. I suspended it on a
string, struck it, and listened. Then, I held it only by thumb and
forefinger, and struck it, and the ringing turned dull. Try it, yourself.
If you get the same result, then you have to agree that there is a chance
that a sophisticated thumb and forefinger could do something with
vibrations. To go further, as he will likely say that the mounted post,
with saddle, doesn't act the same way, I did that, too. A similar, but
obviously less impressive result. But it all goes to point to the baseline
of the (minor) residual vibration as perceived where you sit, pedal and hold
the bike. Only from that experienced baseline are measurements worth
discussing regarding the effectiveness of damping systems.
Humbly submitted as the ignoramus I will be called ...
--
Sandy
Verneuil-sur-Seine
*******
La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.
