Originally Posted by elcruxio

Why is the elbow localized but the butting points aren't? Is is because one is straight but the other isn't.

In order for the elbow to actually move during use (assuming it's conforming to the hub flange via elastic deformation) the spoke elastic stretch would have to release almost completely, ie. the spoke would have to go almost slack. That would be a problem sure, but no just for the elbow.

Here's a fun analogy. If it takes 5000N to fully compress a spring and you add 6000N of force after which you cycle the force between 5500N and 6000N, how much does the spring wear out? It doesn't, because it doesn't move. It's the same with the elbow. If it's impossible to say whether it's plastically or elastically deformed before detensioning the wheel, the elbow is "fully compressed" when tensioned.



There was so much irrelevant fluff that I considered ignoring this post altogether but this last paragraph... Yeesh!

Righto, so let's establish that you ear is not more accurate than a tensionmeter for a multitude of reasons. Firstly in order to accurately listen to the minute differences in spoke pitch you need to be fairly practiced in relative pitches, ie. musical training.

Secondly, a tensionmeter measures a different thing than pitch. A tensionmeter isn't really affected by the variables that cause massive changes to pitch. A tensionmeter measures how much the spoke deforms which isn't affected much by crossings or minor changes in spoke length.

Things that affect pitch however:
Spoke length
Effective spoke length (hub flange drilling, rim drilling, threading depth etc.)
Spoke crossings
Spoke thickness
Spoke tension

Pitch isn't accurate in any wheel because spoke lengths and threading lengths vary so much. One could be lead to believe that the differences in modern spokes and components are so small that they don't have an effect. They'd be wrong. As a reference, the frets on modern bass guitars are measured to the tenth of a millimeter along the whole scale length of 860+mm. Basses aren't that bothered about that but since spokes are so short (usually less than 300mm) they are more akin to violin strings. And the violin is extremely particular about correct string length for the correct pitch.

Pitch works best with radial wheels or with untucked wheels where the crossings just go over the other spokes and not under, ie. there's not as much contact between spokes.

With traditionally built 2x or 3x tucked wheels the spoke crossings act as frettings, ie. they change the pitch. How much? No one knows as it depends on the tension and length of the crossing spoke and on and on it goes.

So rough adjustment with pitch and then final adjust with a tensionmeter.

Since we're apparently playing that fun credential game, I've played instruments since I was under 10 years old. I currently play the violin, viola, cello and bass guitar. I setup the bass guitar myself and do minor adjustments to the violin family instruments. Bigger things I let the luthier do, because unlike building wheels, building bowed string instruments is an actual art as well as a science.



Yes. That is called fatigue limit. It happens within elastic deformation. It's typically around 40% of UTS. I couldn't find the strength values of DT swiss spokes but I could deduct from some destructive tests that it's around 1100 MPa. 40% of that is 440 MPa or 44kgf/mm^2. For a 2mm spoke shoulder that's around 141kgf.

So even if the elbow hasn't been set and flexes to shape instead, if there is sufficient tension on the wheel, the spoke should never go over it's fatigue limit. And under the fatigue limit it can go through essentially unlimited cycles.

You know, I have to thank you. This has been very informative. I now have better answers to how the spoke stress cycling works and why those 2,3mm elbows really are a good idea. The fatigue limit of that elbow is over 180kgf.