Quoted message said:RonSonic said:Quoted message said:Claims for the immortality of squeezed spokes seem to be
confined to anecdotes from a small group on
rec.bicycles.tech, whose metallurgical theories seem to be
well-nigh unknown elsewhere and whose explanations do not
seem to rule out improved spoke material, manufacture, or
design as the source of the alleged improvement in fatigue
resistance, to name a few alternatives.All too often, the stress-relief adherents reply to skeptics
by challenging others to devise tests to disprove the
stress-relief theory, as if the burden of proof were not on
those proposing the theory.The trouble is that spoke fatigue does not lend itself to
easy testing to demonstrate effects, much less causes, which
is exasperating for those who strongly believe either way.Tthe spoke-squeezing stress-relief theory may be perfectly
sound. Or it may be mistaken, while something other than
stress-relief makes spoke-squeezing helpful. Or it may be
just another incarnation of tying-and-soldering, something
plausible, deeply believed in, and ultimately untrue.I can tell a high-school physics class that several posters
on rec.bicycles.tech believe that spoke-squeezing is the
most important step in wheel-building, although they often
seem to disagree with each other on the fine points. But I
can't yet point to anything other than a strong belief and
personal anecdotes to demonstrate the claimed effect, much
less to an unchallenged metallurgical theory.Here's what I can tell you about spoke squeezing....
I've played guitar for over 35 years, and we've got the same problem: a nickel
steel alloy under tension in a system of countervailing tensions that we insist
remain at the intended tension despite repeated stress cycles and the fact that
the entire stressed system is not symmetrical. On a bike the asymmetry is wheel
dishing on a guitar it's the steel strings v a wood and steel bar neck.If you do not stretch the strings while tuning up a new set, tuning will NOT be
stable until time and playing stresses do the job for you. Even then, the tuning
will not be AS stable. The string will wear out before it completely settles in.
With a guitar and it's .010 - .025 string thicknesses (only counting the core
wire) at relatively low tension you get out of tuneness, with the much heaver
gauge and tension of a spoke you get real damage.On a guitar the mechanism is pretty well defined. Yes, metal stretches and is
work hardened. I know how hard I work a guitar string to settle it in and I
doubt the wheel builders are applying that much force relative to the spoke
gauge, but I'm sure it's a factor. Also all of the attachment points are
imperfect, the wrap at the tuning post and the knotting of the string at the
ball end all need to be seated in and a temporary increase in tension does that
nicely. I'll suggest both are a factor in a wheel build. Those nipples are not
perfectly seated on perfect surfaces, the bend in the spoke is obviously not
mated perfectly to the hub. I know that mashed little nub at the end is not
perfect and symmetrical and mated perfectly to the flange. There is unevenness
there that will ether be corrected in the build or it'll introduce problems
later.I'm a guitar and amp mechanic, not a bike tech, but I'll put my money on the
spoke stretchers. I do know how steel wire behaves under tension and it tells me
that prestressing during a build and tensioning makes sense.Quoted message said:Similarly, I can tell a high-school physics class that a
poster on rec.bicycles.tech believes that both his tires
come of the ground at the same time when he sprints, but I
can't yet point to any evidence other than his claim that
this happens, much less to an unchallenged theory explaining
this kangaroo-like behavior.I'll believe someone with enough muscle and lack of finesse could make that
happen. Or at least something that feels like that. That bike's a lively thing
that resonates and bounces in all sorts of ways.Quoted message said:All that I can do is keep asking and try not to be too
unkind. After all, a dozen sprinters may be posting at this
very moment about their bouncing rear tires and wondering
how I can be so ignorant.Have fun with it.
Ron
Dear Ron,
We may not be talking about the same thing.
If I follow you, you're saying that unless stretched beyond
their normal tension, guitar strings not only go out of tune
but also suffer some kind of damage.This doesn't sound like the spoke problem, which is that the
spoke simply breaks. If the inner wire of the guitar strings
broke, then it would be the same thing as the bicycle spoke
problem, but I think that the tuning and damage that you
have in mind involve the outer wire wrapped around the core.As I understand it, the theory is that stretching bicycle
spokes beyond their normal tension by squeezing pairs of
them together relieves stress at a microscopic level, not
that it prevents the spokes from later losing tension. The
spokes are not sagging or slackening--they're fracturing.I suspect that the stretching of the guitar strings is a
matter of external friction involving how the outer wire is
wound around the core wire and how whole wire is wound
around the drum of the tuning peg than the kind of
sub-microscopic stress relief that Jobst Brandt has in mind
with bicycle spokes.Seating and preventing slackening is a possible benefit of
stretching spokes, but I think that the usual claim is that
this is not at all what's going on--the spoke squeezing is
supposed to relieve internal stresses in the solid metal of
the spoke that would otherwise lead to the spoke breaking in
two.With guitar strings, I expect that the outer wire wrapped
around the inner core complicates failure. At least on metal
violin strings, it's usually the outer spiral-wound wire
that fails, not the inner core wire.Still, the parallel of music strings is so interesting that
I refuse to stoop to any puns about putting my finger on the
problem or fretting about it.
It is a fine fiddle we're in.
I very definitely left the winding issues out of it - a whole nother can of
worms.
But what happened right before the spoke broke. Did adjacent spokes go slack, or
that spoke suddenly relieve its own tension. I'm thinking that what would simply
cause a string to go out of tune, would in the context of the much greater
forces in a wheel cause breakage.
Anyway, something to riff on.
Ron