From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Spoke tensiometers
Date: 29 Sep 1997 03:27:20 GMT

Charli Beristain writes:

> There is a good article by John S Allen on "check spoke tension by
> ear" ... don't know his web site.. but I think if you go to Sheldon
> Brown's web site and look up wheelbuilding.. he references it.

It may be a well written article but it does not represent reality, or
for that matter theory, because the spoke thickness and its swaged
length if any as well as its total unsupported length affect the
primary resonant frequency.  To make up for that, most high
performance wheels have their spokes interleaved so they have no
distinct free length and their tone is a damped mixture of the two
spokes and the friction at the crossing point.  That is why I say,
pluck the spoke near the nipple, because you cannot excite the
principal frequency of interleaved spokes.

I often wonder whether people who write these articles really use
these methods or just theorize about them.  This was one of the first
methods I tried because my engineering colleagues brought it up.  We
found that only non interleaved spoking worked and that even this was
not easy to assess.  We got a microphone to look at the spectrum and
found that it was every bit a noisy as it sounded and that a spectrum
analyzer could show you what a good musician might decipher... but
then he mould have to compute and plot response curves based on spoke
measurements of the specific wheel.  A good tensiometer gets there
more conveniently, repeatably, and accurately.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tensiometer questions
Date: 3 Sep 1999 00:08:23 GMT

Jon Isaacs writes:

> Regarding tensioning by tone.  Is this to say that with a spectrum
> analyzer or maybe just a guitar tuner or a decent A/D card in a
> computer and a proper algorithm that one could measure the tension
> in the spokes?

I don't think so because this assumes the whole spoke is oscillating
freely and that it is uniform in thickness.  The thickness part is
less important because the ends have only a slight effect, not making
the major excursions.  Nevertheless, the ends are essentially clamped
and this affects frequency as well.

My first attempt at tension measurement, before I built a tensiometer,
was exactly as you propose, except that the spokes were not
interleaved.  Even with the relatively clear tone such a spoke makes
(similar to radial), it's primary frequency came out in the midst of
many side bands, something no easily detected by ear.  If I had had a
standard against which to compare it, that might have worked better.
The tensiometer was calibrates on a tensile tester.

Interleaved spokes are therefore, best plucked next to the nipple to
excite a higher harmonic that is less affected by the other end where
it touches an adjacent spoke.  The higher tone is distinctly apparent
in comparison to plucking the spoke at mid span.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tensiometer questions
Date: 2 Sep 1999 18:04:42 GMT

Peter (who?) writes:

>> Is this number supplied with the tensiometer?

> Yes, each tensionometer comes with a calbrtated for that tool/ chart.

Are you sure you know anything about this instrument whose name you
cannot spell?

> The chart lists spoke diameters, like 1.8mm that you use when
> building with that gauge or thickness of spokes-measure the center
> section, off the 'butt'-

The only tensiometer that can be zeroed on the spoke is the Avocet/DT
tensiometer, that also measures from one side of the spoke sop the
thickness does not enter into the measurement.

> For most wheels, regardless of spoke gauge, lacing, number(like 28
> or 36), and rim, the TENSION is the same, in kilograms of force, the
> NUMBER will change for spoke gauges, for 14g(2.0mm) the number read
> on the tool will be higher but the tension will be the same as on a
> 1.8mm spoke.

That is a basic flaw in the tension specification.  Tension is
dependent on the number of spokes and rim cross section, and not on
spoke cross section.  As you say, the measurement may differ with
instruments that measure across the spoke cross section, however,
tension is dependent on the number of spokes for any specific rim.

> I use one all the time-great tool-lets' you know instantly how close
> you are to being finished and getting those four wheel variables
> correct at the same time(tension, true, round and dish).

I agree that a tensiometer is useful for assessing tension but it is
not necessary to measure each spoke, a sample of two or three on one
side is enough.  Tone is an accurate way to check uniformity.

> All the rot about pitch, high 'C' above middle 'E', is crappola
> unless you are a musician and maybe not even then-

Not even then, because tone is dependent on length, thickness and
tension, the last of which varies with number of spokes and rim.
Beyond that, interleaved spokes produce an unpredictable harmonic with
the adjacent spoke.  Tone is good for achieving uniform tension but
not for assessing absolute tension.

> get one , great tool-IMO

That would be great if we could only get the Avocet instrument into
production.  The trouble with that is that wheel builders are a
strange lot, who prefer to not read books on wheels and not use
tensiometers for something they believe they do best by guess.
Therefore, tensiometers are hard to sell to bike shops and harder to
get bike shops to use.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tensiometer questions
Date: 3 Sep 1999 00:16:09 GMT

Harry anonymous writes:

>> I agree that a tensiometer is useful for assessing tension but it
>> is not necessary to measure each spoke, a sample of two or three on
>> one side is enough.  Tone is an accurate way to check uniformity.

> I disagree.  This "2 or 3 spoke" method must be how Mavic build their
> Heliums as I have found new wheels with some spokes at zero tension and
> their neighbors with 150% the average.  This must have a wonderful effect on
> the strain on the rim and also implies that if the tensions are even then a
> rim of only 2/3 the weight/strength could have been used.

That three adjacent spokes or even two are not representative of the
tension in all spokes requires a stretch of the imagination.  If they
were, as you imply, different from the rest, the wheel would be out of
true.  A tensiometer is used to determine whether a wheel is tight
enough and not too tight, not to measure each spoke to detect equal
tension because this is a fruitless pursuit with the type of
adjustment that need to be made.  Tone IS an accurate and valid method
for comparing tension, whether you can hear it or not.

As for Mavic Heliums, they are radial and are even easier to test by
tone.  I don't believe that wheels that you found lacking would pass
any tone test so why do you hold this forth as proof that tone does
not work?

By the way, who are you?  What's the secrecy?

Jobst Brandt      <jbrandt@hpl.hp.com>