Re: Hey, Jobst, on p39 of The Bicycle Wheel the graph appears to show the ?impossibility of...


"Peter Cole" <peter_cole@xxxxxxxxxxx> wrote in message
news:Cyyyk.21$pp3.20@xxxxxxxxxxx
Andre Jute wrote:
On Sep 12, 1:28 pm, Peter Cole <peter_c...@xxxxxxxxxxx> wrote:

Part of the problem is in the ambiguity of the phrasing of your
charge.

Rubbish. I've said many times in this thread that it is impossible to
compress a steel bicycle spoke. Anyone of the slightest intelligence
who read the thread will know that your second interpretation below
is
the right one.

You say that your statement can't be ambiguous because one possible
meaning is absurd. I would say the same thing about the graph.


*I'd argue against clipping the curve to the X axis in that
information
would be lost. That information describes the compression on a spoke
that could support loading in that mode, not an entirely academic
question given Mavic's new "technology":

"Tracomp

By creating a tubular carbon spoke using unidirectional fiber that
can't
be stretched neither compressed and by fixing it securely on both
sides
to the hub and the rim, we have brought a new concept of spoke work:
it
resists not only in traction but in compression too."

Interesting but irrelevant through three editions of Jobst's book.

Not really, at least not for me. Bicycle innovations are rarely ever
new. The graph you are quibbling over is (arguably) the most complex
in the book. I find it also to be the most elegant.

Showing the hypothetical compression curve yields intuition on how a
combined tension/compression member might change lateral stiffness.
The portion of the curve under the X axis could have been dashed it
would have made no difference to me. As you say, the meaning should be
obvious [to anyone with the slightest intelligence]. I think I'm
qualified.

You have opined that the figure is too complex and that it should be
in an appendix. It is right where it should be, illustrating the
compromises made in lateral stiffness and offset, any simplification
would detract completely from the intuitive model it depicts. It may
be difficult for non-technical readers to grasp, but then its purpose
is to back up the claims made for the effect of offset on spoke
tension and rim lateral stiffness. If you wish to accept those without
fully getting the physics, that's fine. They can't be rebutted without
getting your hands dirty, though.

You state that all of us defending Jobst's book are fan-boy apologists
(to use a little less rude language). The truth is, many of us have
participated in this little group for years and have seen these dust
ups arise with predictable (and depressing) regularity. They follow
the same pattern. You're just new here. Jobst tweaked you over a
mono-paragraphic post and you're picking a fight. Nobody is fooled.
Jobst won't play, the rest of us are just (drearily) writing for the
archive. You're just the latest member of the tweaked-by-Jobst club.
It's a small group, but a troll thread like this brings them all out.

Yes this thread does appear to be following the usual mode. However, if
the model used to predict lateral stiffness put the left spoke elements
in compression then the resulting wheel stiffness is shown to be higher
than it actually is. Those compressed spokes add to the lateral
stiffness.
I don't know if that's the case but the plot certainly says it was and
even though the spokes go slack as quoted by Jobst, does the model
reflect that?

Phil H


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