531colin wrote:interestedcp wrote:.......... when the spoke untwist the spoke tension may go out of spec ...............
No. You turn the nipple. If the nipple binds on the spoke, then the spoke twists. When you stress the wheel, (or ride the wheel) and that spoke is (partially) un-loaded, the nipple twists in the rim.
The only way the spoke tension can be altered is if the nipple binds on the spoke when you tighten it, but then mysteriously binds on the rim when the spoke un-winds.
as I said at the outset, a badly-built wheel may ping, and it may also go out of true, but they are not cause and effect.
It doesn't make sense at all to me.
If a spoke is twisting while the nipple is turned, the spoke tension is increased; not because the spoke have elongated because it has been stretched when advancing up the thread, but because it has been physically twisted, and therefore has become "shorter" as measured between the flange hole and the nipple seat.
Since the effective length of the spoke has become shorter by twisting, it logically follows that the effective spoke length will be longer when the spoke untwist again; this is also true if the nipple is rotating synchronously with the untwisting spoke, since thread engagement is unchanged but effective spoke length is increased by the untwisting.
I think it is rather obvious that spoke unwinding will reduce spoke tension. So does Jobst Brandt in his his book (page 50), and Roger Musson in his; "Professional Guide to Wheel Building": v. 6.02, p. 95:
The first few pedal strokes.
If you hear a tinkling sound then the spokes had some twist in them that should have been released in the building process. If you hear that sound on other people’s wheels it tells you the builder didn’t understand spoke twist. The spokes should not make a sound. The sound comes from movement of the nipple at the rim interface or within the spoke threads. That movement will likely change the nipple thread engagement and cause the wheel to lose a bit of trueness.
That spokes twist when tightening them and that backing off when tightening the nipple helps with releasing spoke wind up, is easily observed by attaching a tape flag to a spoke before tightening it. (see Jobst Brandt: The Bicycle Wheel, p. 50).
Also, this video at around 1 minute: https://www.youtube.com/watch?v=72UfDNLM2FQ&hd=1