Gary Young said:jim beam said:Gary Young said:On Thu, 21 Dec 2006 05:56:35 -0800, jim beam wrote:
> [email hidden] wrote:
>> Ben C? writes:
>>
>>> [snip]
>>>> After spokes are laced into a wheel, tensile stresses, at elbows
>>>> and threads, are augmented by spoke tension that is in itself not
>>>> threateningly high (about 1/3 yield) but because elbows were at
>>>> yield, they remains at yield, not being able to sustain any higher
>>>> stress. Subsequently, in use, where spoke tension is cyclically
>>>> changing from the carried load, and because cyclic stresses near
>>>> yield are the cause of fatigue failures in metals, spokes break.
>>> Thank you for the explanation.
>>> I have one question: does it follow that this kind of fatigue
>>> failure at the elbow is more likely in wheels built with too-high
>>> spoke tension? Provided the residual stress hasn't been relieved
>>> successfully of course.
>> There are rims today that have such heavy cross sections that they can
>> be tensioned higher than needed. Therefore, with some deep
>> (aerodynamic) cross sections, a tensiometer may be required to arrive
>> at the appropriate tension. In most wheels, rims are the limiting
>> factor today because few if any use sockets and rely on eyelets that
>> carry spoke loads on only the outer wall of the rim. This generally
>> causes rim cracking before spokes that have been stress relieved fail.
>>
>>> It seems to, because you say "augmented". If we built the wheel
>>> with looser spokes (but not so loose they went completely slack and
>>> flexed during the cycle), the mean stress in the cycle at the elbows
>>> would be reduced a bit.
>> That is not a problem for reasonable rims with 32-36 spokes. The
>> reason for using that many spokes is that a single spoke failure with
>> fewer, generally means end of ride because the wheel goes too far out
>> of alignment in tight fitting (modern) frames to continue. We are not
>> making progress.
> indeed we are not making progress. or more correctly, /you/ are not
> making progress.
>
> lower stress means lower fatigue. that's real basic. otoh,
> insufficient spoke tension can mean excessive bending and therefore
> fatigue. but you don't grasp the causal relationships because the fact
> that it's bending that causes fatigue seems to be one that you just
> don't understand. you're stuck on this fanciful notion of residual
> stress which you [conveniently] say is unobservable, unmeasurable, but
> which can be eliminated by the waving of hands - and as long as you
> think and keep saying that, you'll never be taken seriously by any
> manufacturer because you'll keep evidencing your ignorance.
I've never really understood why you keep bringing up this theme of
manufacturers not taking Jobst seriously, especially since it seems to do
more damage to your case than to Jobst's.
Unless I'm mistaken, Jobst has worked for some major manufacturers,
including Porsche and HP. Are you suggesting that the bicycle industry
hires a better class of engineers than Porsche and HP?
ask him for how long he worked at either and under what circumstances he
left. hey, on paper, he looks like a good candidate. reality is, he
doesn't know what he's doing. it's only a matter of time until any
employer finds out.
I just did a quick google search and found a 1970 HP in-house journal that
mentions Jobst. I take this means you're doing here what you do so often
-- making up facts to support your prejudices.
Quoted message said:Quoted message said:Mind you, I'm not arguing that Jobst's affiliations are conclusive proof
that he's right. But it does give him a certain level of credibility not
matched by a lone anonymous gunslinger who refuses to state what training
and experience qualify him to lecture us on materials science.
Oh, and another thing -- there are bicycle manufacturers who do take Jobst
seriously, including some who manufacture products that he's designed.
Can you say the same about yourself?
i can say that he managed to convince fsa to sell a tensiometer he
designed, but without doing the math for the effect spoke gauge has on
it. now, you tell me, was the "buy" decision for fsa made by an
engineer or a sales dude who believed jobst's pitch?
I have no idea who made the decision. Do you have specific information
that it wasn't reviewed by an engineer or are you just making up facts
again?
i'm not making anything up. read "the book" and tell me, on the page
where he gives his formula for his tensiometer, where spoke gauge is
taken into account.
Quoted message said:
And what about my question -- have any bike manufacturers adopted your
ideas?
i'm not selling anything gary, so i have no interest in trying to pitch
stuff i have no interest in supporting.
Quoted message said:Quoted message said:
Quoted message said:> talking of ignorance, have you figured out how to account for spoke
> gauge in calculating tensiometer deflection yet?
I'm not sure what you're driving at here, but it does give me the
opportunity to note that FSA takes Jobst seriously enough to be
manufacturing his tensiometer design.
all it tells /me/ is that they believed him and that fsa's decision
maker didn't understand the math! but then again, jobst has had
hundreds of people on r.b.t. believing he knows about stress relief for
years, even though he doesn't understand the principles of fatigue or
deformation. or even basic mechanics come to that - he doesn't
understand why a traditional j-bend spoke is fundamentally susceptible
to fatigue because of its shape! it's not like his mistakes are not
heaped about all over his book. all it takes is for someone to /read/
and think since most of his mistakes are /really/ fundamental.
You're missing my point. I'm not arguing that the fact that FSA is
manufacturing Jobst's tensiometer proves that it's a good design (for one
thing, I don't know anything about tensiometer design and, for another, FSA
is the company that also manufacturers those stupid three-flanged wheels).
The point is that you're the one who injects the
manufacturer-as-final-authority argument into these discussions time and
again. And that argument cuts against you,
actually, that's true if you take it across the board - but some
"manufacturers" don't manufacture. wtb, fsa, ritchey, etc. what i mean
when i say "manufacturer" is the producer that's done the work and
research, mavic, sapim, campy, shimano, etc.
Quoted message said:since Jobst has more
manufacturing backing behind him than you do. In other words, it's not a
good argument (if it were, you wouldn't have to invent facts to explain
the discrepancies).
jobst is older, but i have experience, thanks. and i haven't published
a book with fundamental errors and then denied them. repeatedly.
Quoted message said:
Ultimately, what I'm hoping is that you'll stop making the argument
because your jibes have little or no evidentiary value and contribute
greatly to the nastiness and high-strung tone of your postings.
i want corrections and an end to the [censored]. if you recognize when
smoke is being blown up you, that's your problem, not mine.
