How do get such high tension in your spokes?
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?
I have never seen a spoke stretch. How are you measuring them?
Held next to each other with the ends butted perpendicularly up against a flat surface.
Originally Posted by J.B. Weld
These 2 spokes were from a newly opened box of 72 DT spokes, both 286mm, but one was stretched while building a wheel.
Last edited by Godlikedog; 05-18-2013 at 10:14 PM.
Can't argue with that picture. I've built a lot of wheels with that particular spoke, and replaced a lot of broken ones and have never personally seen that happen.
What tensiometer are you using?
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Spokes are not plain 304 - they are a work hardened stainless, with a yield strength of 180+ kpsi. (See the sapim web site for examples) Maybe you have a bad batch or something.
If your wheel is truly built with the spokes at the yield limit, then give the spokes a good stress relieve squeeze, and they should fail.
Well, that's something I haven't seen before with DT competitions, the nipples usually start to round out well before the spokes stretch. I've seen it before with DT revolutions when I had to make large tension adjustments to make a bent wheel ridable and really cranked on it with the spoke wrench, but it's something I've yet to encounter on a regular wheel build.
If I had to take a guess I'd suspect that the tensiometer is either miscalibrated or measuring on a scale other than kilograms.
Also, how much are your spokes getting twisted?
Well, failing is stretching at this point. And they have already failed. A weird thing about most stainless steels is that their yield strength is about a third of their ultimate tensile strength. These spokes are not a typical stainless steel alloy, but their yield strength is nowhere near 180 kpsi.
Originally Posted by beanbag
Thanks for all your replies. I have figured it out, and it is that my tensiometer is not in kgf. Looking for a photo of the wheelsmith tensiometer I noticed that they come with a calibration sheet, which I must've lost a long time ago, and this is why there were no units printed on the scale, I should have thought of that. I thought it was really clever that they had designed a tensiometer that didn't care what diameter the spokes were. But they didn't.
The interesting thing for those reading this is that the yield strength of spokes is not as high as people think. Tensile strength is often quoted, but yield strength is what really matters, and for stainless steels it can be quite low compared to the tensile strength. It seems to be about 150 kgf for 14/15 butted DT spokes. I don't know exactly because I don't have the calibration sheet for my meter, but looking at other calibration sheets on the internet, the yield strength should be somewhere around 150 kgf, which is 85,000 psi, if not a little less. If you ever find yourself turning the nipple and the tension just isn't changing, you have hit the yield limit, and it's not that far away.
Wheelbuilding seems so much easier to me tonight than it did this morning.
I'm amazed that this issue hasn't come up much before, but I realize it's because of a few things coming together that made me get there. It started because I misinterpreted my tensiometer by a factor of about double/half. I got kinda insecure about my wheel building ability because I could never get my spoke tension as high as other people were getting. I would crank on those nipples, and they would round out, and people were seeming to get such high tensions even with aluminum nipple, and some people would just use dry spokes and nipples! This combined with a sort of guru notion of master wheel builders made me think I was just not getting it. And then the spokes were always too long, because they were stretching, but I thought there was some skill for choosing spoke lengths that I was missing. But it turns out I was just trying to get the tension much too high.
This resulted in me using grease on the threads so I could crank them up, and finally buying hex nipples so I could use a socket and a T-handle to torque them, so it was quite easy for me to torque them up. The final thing that let me do it, because apparently usually the rim will not withstand this much tension and it is the limiting factor, is that I am using a 50mm rim, a Surly Rabbit Hole, and I guess it's lateral stiffness let me get to such high tensions without it "Pringling".
I thought it was bizarre that this problem almost basically doesn't exist yet I was encountering it, I could find nothing about it on the internet, just people saying how strong these spokes really are, calculations that they can support 650 lbs each, but no mention of their yield strength and it's relative smallness compared to their ultimate tensile strength. But it makes sense now, with those few reasons coming together in a perfect storm, that this issue would occur very rarely.
Edit: spelling errors
Last edited by Godlikedog; 05-18-2013 at 10:21 PM.
That would only be true for annealed stainless, of which no self-respecting spoke is made. Upon work hardening, the ultimate tensile strength of stainless increase, but the yield strength increases even faster.
Originally Posted by Godlikedog
and go to the chart on pg 6, "effect of cold work". For 302 stainless, which is what the sapim spokes are made of, the ultimate / tensile strength starts off as 90 / 40 kpsi annealed, and keeps increasing past 180 / 150 kpsi upon work hardening. This is consistent with the info on sapim's web page, and I can't comment on the DT swiss spokes because they won't say their secret recipe.
However, I see in Jobst Brandt's book a chart on spoke strength for DT swiss 1.8 swaged spokes that appears to have a yield point of 180 kg. But that is in the old days and spokes are supposed to be better now. If your spokes can't survive 150 kg, then that means that the DT Swiss Revolution spokes can't survive above 110 kg either.
BTW, you can easily calibrate your spoke meter by hanging a wire off a ceiling beam, and putting your weight onto it. Then use the tension meter on this wire.
I can't believe how little information there is on the web about this - the yield strength of spokes. I would expect a Google search to turn up data from people who have tested it and discussed it, comparing the different brands and analyzing it from every direction, but I just don't see it.
Originally Posted by beanbag
I hope someone else can do a little testing and see what they come up with.
Are people able to get over 110 kgf in their revolution spokes?
If you type in google "spoke strength testing", the first result that comes up is this one:
spoke strength--double butting - Road Bike, Cycling Forums ...
Apr 30, 2009 – I have tested the tensile strength of DT 14g and 14/15g spokes using a tensile testing machine. The results I got after pulling multiple spokes of ...
The guy says 715 lbs for 14/15 spokes. You can assume that is ultimate, so go to my chart, guess any alloy you want, and walk back the figure for yield strength.
But first you should calibrate your tension meter to see if anybody should care about spokes at the tensions you used.
This thread should serve as a reminder that you should do a cursory spoke pluck test to see if your tensions are in the ballpark.
Ive built somewhere around 100 wheel sets, almost all to 130 kgf, some to 120 kgf. The stress relieving process adds a crapload of tension on top of that, very easily another 20kgf. Ive never stretched a single spoke. Some dynamic loads from riding should exceed 150 kgf as well.
Something crazy is going on with your spokes.
Is your spoke tension ever lower after stress relieving?
Originally Posted by One Pivot
Why do people stop at around 140 kgf? My recent experience is that you just can't seem to get it any higher, and you don't quite realize that it's 'cuz you're at the yield limit.
It would seem the reason that 130 kgf -140 kgf is the max that people tension their spokes to is because it is the max they can tension their spokes to, because another quarter turn of the nipple just doesn't seem to do anything, except push the spoke another 0.1 mm through the nipple. You don't really realize you're at the yield limit unless you just keep going twisting the nipples, and then you are just stretching them .45 mm per complete turn; a complete turn at that point is a lot of turning, but .45mm doesn't look like much. The spokes don't snap or anything.
This makes the most sense. Nobody reports that they get more tension in their spokes than around 140. Although I saw someone say 169 somewhere, but there are straight gauge spokes, too.
Seriously, think about that. You'd occasionally have builders say they were building at 200kgf - if they could, and what with carbon rims and fat bike rims, you probably could if the spokes could do it. But do you have people reporting that? We've got various strengths of nipples, spoke wrenches that grab all 4 sides, hex nipples that can be turned with a socket. Every top builder says they go to 120 to 140 kgf, not "but if I have a carbon rim I go to 200 and use the strongest nipple available". "Good enough" arguments are fine and all to explain most people's reasons, but you'd still expect some outliers, some people who take it to the extreme. I mean it's the frickin' internet. Something like: "I have a carbon rim with eyelets, titanium nipples, a spoke wrench that grabs all 4 sides, and I take it up to 250 kgf".
A quarter turn of the nipple is only about 0.1 mm of spoke stretch, and if you're at a point where you just can't get the tension any higher, you might not even notice that you hit the yield point. And maybe stress-relieving is just stretching (plastically) the spokes just a teeny bit so that they get below the yield limit (i.e. trade some plastic stretch for some elastic stretch), which might result in them have a higher fatigue strength.
And what does the ultimate tensile strength matter? As long as it's higher than the yield strength. We can correlate the ultimate tensile strength with an amount of cold working and then calculate a yield limit? Maybe someone with a sapim spoke could see if they can get it over 150kgf. If it matters ... It does seem like this is an interesting piece of information that has been missing. The yield strength is certainly much more important than the ultimate tensile strength, which is talked about on occasion.
I don't know why I'm arguing these points. I guess it just seems like this is an important thing to know, somehow. And people are saying it can't be true that the yield strength of the spokes is so low.
I challenge someone to take a 14/15 spoke above 160 kgf.
I could have counterfeit spokes or something, but everything is pointing toward: the yield strength of these spokes is somewhere around 150kgf.
Last edited by Godlikedog; 05-19-2013 at 02:27 AM.
Any old wire?
Originally Posted by beanbag
Actually I'd have to use the spoke, this Wheelsmith meter isn't agnostic to spoke diameter.
Was there any observable deformation to the diameter or shape of the elongated spoke?
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Yes it is. Do you have the instructions for it?
Originally Posted by Godlikedog
You are supposed to hold the meter against the spoke (or any old wire), and have the measuring plunger thing touch the spoke, but NOT the spoke-bending-in-the-middle-thing. Then you rotate the outer diameter of the indicator so that it reads zero. Then you let the spoke-bending-in-the-middle-thing touch and deflect the spoke, and THEN you read the number off the dial.
I think you should get your meter working right before you start quoting numbers for spoke tension.
Oh sorry, I was thinking of the Jobst Brandt FSA tensiometer, which I thought was wheelsmith but now I see it is a different kind.
In that case, find a wire with a diameter close to your spoke diameter.
The center of the spoke does seem to be about .01 mm smaller than a fresh spoke. It's hard to get an exact measurement, but after averaging ten measurements for each, here is about a .01 mm difference, 1.754 vs 1.763. When holding both the spokes in the calipers at the same time, it is clear that the longer one is skinnier because it slips down - the calipers don't grip it.
Originally Posted by urmb
Wow. What sort of rim are you using that can handle such tensions without tearing the nipples out? What do your spoke holes look like? Any deformation?
Because the rim would collapse.
Originally Posted by Godlikedog
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