I am baffled by this. I keep buying too long spokes, I've been so frustrated that all the calculators seem to be off, or so I thought. As I'm building the wheel they are poking through the nipples up to 3 or 4 mm. But then I take one off to compare it to a fresh one from the box of 72 DT Competition (14/15) spokes and find that it is 4 mm longer than the fresh one. I thought maybe I had grabbed a different spoke from somewhere else by mistake.
But no, after some testing, I realize I have hit the yield limit for the spoke. I just tried tightening a spoke more to see if it would stretch or if the tension would increse. I turned the nipple >5 complete turns: no increase in tension. I removed the spoke and it was 4mm longer than a fresh one. Thus, I hit the yield limit of the spoke. Simple, period, end of story. But my tensiometer says I'm in the low 70's (although the idiot thing doesn't have any units printed on it; I'm assuming its kgf). I do some math and find that that is just about right: a 1.8mm radius section is 1/250th of a square inch, 304 stainless steel has a yield strength around 35,000 to 40,000 psi, which is 40,000/250 = 160 lb. per spoke. Which is 73 kgf. So that makes sense with my readings.
But I read all the time on here people going over 120 kgf, over 140 even. Someone mentioned 169.
WTF? I'm baffled. And it seems, from what I read on the internet, that spokes aren't the limiting factor in a high tension wheel, that the rim is.
If I do a google search, people are saying that spokes can take much more stress than we put on them, and nobody ever mentions the issue of their spokes stretching (plastically) and thus hitting a limit of spoke tension. But I clearly have hit the yield limit. I have always felt that I had been building kinda weak wheels 'cuz my spoke tension is only n the 70's, but others go well over 100. I never understood how they could get such high tension.
Even Jobst Brandt, who seems to be one of the top bicycle wheel gurus, said that spoke tension rarely gets to 50% of their yield strength in some post on his website. But I have hit it. Fairly easily, in fact.
I don't get it.
Do your spokes stretch plastically as you build your wheels?
But no, after some testing, I realize I have hit the yield limit for the spoke. I just tried tightening a spoke more to see if it would stretch or if the tension would increse. I turned the nipple >5 complete turns: no increase in tension. I removed the spoke and it was 4mm longer than a fresh one. Thus, I hit the yield limit of the spoke. Simple, period, end of story. But my tensiometer says I'm in the low 70's (although the idiot thing doesn't have any units printed on it; I'm assuming its kgf). I do some math and find that that is just about right: a 1.8mm radius section is 1/250th of a square inch, 304 stainless steel has a yield strength around 35,000 to 40,000 psi, which is 40,000/250 = 160 lb. per spoke. Which is 73 kgf. So that makes sense with my readings.
But I read all the time on here people going over 120 kgf, over 140 even. Someone mentioned 169.
WTF? I'm baffled. And it seems, from what I read on the internet, that spokes aren't the limiting factor in a high tension wheel, that the rim is.
If I do a google search, people are saying that spokes can take much more stress than we put on them, and nobody ever mentions the issue of their spokes stretching (plastically) and thus hitting a limit of spoke tension. But I clearly have hit the yield limit. I have always felt that I had been building kinda weak wheels 'cuz my spoke tension is only n the 70's, but others go well over 100. I never understood how they could get such high tension.
Even Jobst Brandt, who seems to be one of the top bicycle wheel gurus, said that spoke tension rarely gets to 50% of their yield strength in some post on his website. But I have hit it. Fairly easily, in fact.
I don't get it.
Do your spokes stretch plastically as you build your wheels?
