[email protected] wrote:
> Carl Fogel writes:
>
>>>> Friction, for example, confuses things. When the hammer bends the
>>>> spoke, it tries to drag the spoke inward over both posts. This
>>>> raises the tension slightly, so the lower the hammer force, the
>>>> less frictional distortion. The Park posts are just fixed,
>>>> polished metal, but I think that more expensive gauges may have
>>>> roller-posts to reduce friction.
>
>>> How much do you suppose friction might affect readings? In the
>>> other thread where I posted a photo of my sanded (or similar process
>>> reduced diameter) butted spokes, there is clearly a texture on the
>>> spoke that would perhaps make friction a bigger issue with a solid
>>> post tool like the Park. I wonder if my spokes were much looser
>>> than I thought.
>
>> I don't know what the practical effect of the friction would be.
>> But I suspect that the friction for ordinary-finish spokes is pretty
>> much accounted for on the Park tables.
>
> Stiction is a problem with these instruments and that is why I used
> ball bearings to support the spoke. You can find how much effect that
> has with your instrument by rotating it a few degrees about the spoke,
> returning to the position from which you started. This releases
> stiction and also shows the zeroing effect that is not present by
> giving a different reading depending on where the instrument is
> stopped. A common way of reducing stiction is to vibrate the subject
> (spoke) by tapping on it, lightly yet sharply, without changing its
> position.
so how much difference does it make? if you want to get really
pedantic, you also need to allow for localized [elastic and plastic]
deformation at the contact points, [something exaggerated by the
"stiction relief" method you propose] but clearly, that's not going to
amount to much.
>
>> You could test for accuracy by hanging known weights in the normal
>> spoke tension range on a spoke and comparing readings from a ~$60
>> Park gauge and a ~$400 DT gauge. Possibly some bike magazine has
>> compared the accuracy of different spoke tension gauges, but I don't
>> know of any articles.
>
> That will get you nowhere.
eh? measuring /known/ tension won't get you anywhere?
> That does not affect stiction which in a
> sense is micro-welding. That is why I chose a rounded anvil to press
> on the spoke.
you're missing the point.
>
>> For practical wheel-building purposes, I suspect that the Park
>> tension gauge works fine. That is, it will give reasonably accurate
>> absolute tension (mine showed ~187 pounds for a known weight of ~190
>> pounds) and it will show small tension differences--I've tested a
>> number of spokes with squeeze forces in 21 steps from 0 to 100
>> pounds, and the gauge reflected the 5-lb squeeze force increase.
>
> I see bicycling is once more being so provincial that the term
> tensiometer must remain foreign as do many other concepts in bicycle
> hardware.
>
> http://www.m-w.com/dictionary/tensiometer
jeepers, that's disingenuous. jobst, even if you didn't know the first
thing about tensiometers, [and i wonder about you in this regard since
you don't know about wire stiffness as a function of thickness] hanging
known weights to produce known tension, then making a table of results
/will/ give you a usable tool, stiction and all. insulting claptrap
about definitions of the word can't disguise this fact, much as you want
to trivialize and dismiss it.
>
>> I doubt that it matters for practical wheel building whether your
>> absolute tension is 100, 110, or 120 kgf, any more than it matters
>> whether the tensions are all within 5 kgf or each other, or the rim
>> is true to within 0.1 mm, 0.5 mm, 1.0 mm, or even 2.0 mm.
>
> If you have access to better information, why not get it. Try
> wiggling your tensiometer and see what you get.
what do /you/ get?
>
>> In any case, your spokes are almost certainly looser than you think.
>> After all, on a narrow, well-braced 700c rim, Dianne's tests showed
>> that inflating the tire "to 120 psi dropped this spoke's tension
>> from about 99 kgf to about 83 kgf, a decrease of about 16 kgf or
>> roughly 35 pounds."
>
> That is only a problem for folks who use the instrument to tune the
> wheel, every spoke reading the same value. This reminds me of gears
> on bicycle, that some folks use to start at a traffic light running
> through six to eight gears like a loaded highway truck. Gears are for
> climbing hills, tensiometers are for assessing wheel tension, a couple
> of spokes after final tensioning will do.
so what?
>
> http://tinyurl.com/67gwc
>
>> So anyone who tensions spokes on a bare rim to 100 kgf is probably
>> actually riding around on spokes tensioned to only 83 to 90 kgf, a
>> considerably larger error than is likely with the Park tension
>> gauge.
>
> That number isn't so fixed as it may seem, rims being of different
> materials and cross section and having a different number of spokes.
spoke count doesn't determine tension jobst.
> An example of this effect is in "the Bicycle Wheel" just to avoid
> great discoveries being made about this later. My spokes have the
> tension that I measure. What is done with the wheel subsequently is
> another matter.
istr you having a great deal of difficulty saying what tension you
actually use. so as to avoid being seen to climb down on this whole
fiasco about "tension as high as the rim can bear" presumably.
