spoke tension maxed
 

I have a wheel that I laced up and was getting it up to tension (about 23-25 on the Park tensionometer), then checked the dish and saw that the rim could go even further toward the drive side to be centered. At that point, I decided the drive-side spokes could manage to go a bit tighter, and upon doing the rounds, tightening the first few a bit tighter, I happened upon a nipple that would twist but would not increase the spoke tension any further no matter how much I twisted the nipple. It seems clear the threads on the spoke and the inside of the nipple are stripped or rounded and giving as soon as a certain tension is reached. I am wondering if anyone has had this very disturbing issue since most of what I hear of as a stripped nipple refers to the outer flats which usually give before the threads. Please correct me if I'm wrong and any similar accounts/theory. I was using DT double-butted 14/15 gauge spokes with matching nipples.

I suspect that, rather than having stripped the threads, you may have simply reached the yield point of the spoke - it's now just elongating permanently under any additional force.

I've had this happen with 1.5mm centre section spokes, but have never gone high enough on the tension to observe it happening on a 1.8. Not saying it can't happen though if the tension is high enough. I don't own a Park meter though, so I don't know what the OPs meter readings translate to in KGF.

Need to know diameter for round spokes or thickness and width for bladed spokes to translate TM-1 readings to tension. What are the relevant dimensions for your spokes?

http://www.parktool.com/documents/e6...d8d5e32c5e.pdf

Is the Park tool chart

For 14 gauge = 1.8 mm, 23 is on the high side [correction]

1.8 = 15g

From the Park chart, 1.8 mm (14/15 gauge spokes, that's 2.0 mm butted to 1.8 mm)
23 = 131 kgf
24 = 148
25 = 167

That's very high.

That range (131-167Kgf) is a bit high. Are you sure you aren't deforming the rim at the spoke holes?

The one thing we can be fairly sure of is that it's not stripped threads, which would manifest very differently. It could be rim distortion, byt more than a nipple turn's worth would be apparent. It's also possible that he's extruding the nipple through the eyelet, or pulling the eyelet out.

But based on how it's acting, and the numbers supplied later, I'll put my money of his having reached tensile yield. I've talked about this before when discussing how crazy folks have gotten operating on the theory that if tension is good, more tension is better and most tension is best.

I avoid tensions in excess of 100kgf, and only go above that if needing to add some tension to the left. I don't build with spoke counts below 24 and know that low count wheels use higher tensions which makes sense, but for most wheels folks build using 24 or more spokes there is no benefit to higher tension than what's needed to keep the wheel in the working tension range.

To the OP, your wheel is too tight for the spokes, back tension on the left off to achieve dish, then consider backing the whole wheel down to where the left flange spokes are at about 65kgf, and the right wherever they end up (probably 105-115kgf), then do the final steps of checking for even tension and truing and relieving. (Stress relief isn't really needed anymore, but you want to correct for spoke twist.

You need to keep in mind that each spoke tightened adds to the tension of every spoke, so that the spokes will always be progressively harder to tighten as you go round the wheel. One only tightens every spoke on one side without loosening the other if there is quite a bit of overall tension to add. Generally it's best if tension is fairly high to loosen one side a small amount on each and then tighten the other.

Hi,

Perhaps loosening the non drive side was the way to go, or
using thicker spokes on the drive side for its higher tension.

rgds, sreten.

Loosening just the left will help. Loosening all spokes, but more on the left will help more.

But switching spokes is essentially a complete rebuild. That's always an option, but before he crosses that bridge, the OP must first decide why he want's that kind of tension.

Hi,

Yes, I'm only carrying on because I want to understand well. The wheel was doing
fine but could do with being a little more dished. Slacken the left or tighten the
right would do it, but the OP went for the latter, and is having presumably yield
problems on the right. So go back slackening the right back to what it was, and
then move the dishing by slackening the left, in hindsight the better option.

In general what is too high spoke tension ? I presume its too near the
yield point and basically will not stay consistently true and need continual
adjustment. A nice tension is lower but still enough to ensure the spoke
always remains under significant tension under normal circumstances.

rgds, sreten.

Loosening the left only will loosen the right also, not as much.

OP's target is way high as already noted...

...but also wonder is the OP has already ran out of threads on some spokes?

=8-)

That would manifest differently, with squealing if the nipple forced it's way farther (and the tension would increase) or difficulty turning and/or excessive spoke twist which has a specific feel and should become noticeable for what it is.

OP didn't mention sounds? Also noted stripped threads - which is possible - however I would think that at some point a spoke would snap at the shank/thread transition from the excessive torsion if thread runout is occuring.

=8-)

A stripped thread wouldn't maintain constant tension. It would act like other stripped threads, tightening a bit, then slipping back one thread. If stripped badly the spoke would not sustain any meaningful tension at all.

The yield point of the spoke is in excess of what you will be able to get by tightening the nipple. It's at least 450 to 500 pounds.

OP:

If you don't mind, what is the position of the end of the spoke in question in relation to the nipple. Just curious...

Also, are the threads closer to the spoke end stripped...or the ones closer to the shank - or the entire set?

=8-)

Uh, sorry to disappoint, but not quite. Here's the math.

18/8 or ANSI 304 stainless steel (the stuff spokes are made of) has a tensile strength of about 90,000psi, and a yield of 42,000 (citation).

a 1.8mm spoke has a cross-sectional area of .00394"

(formula, D squared/4 x Pi. or 1.8 / 25.4 = .071" x .071 / 4 x 3.14 = .00394")

Area x pressure = tension, or .00394 x 42,100 = 166#s, /2.2 = 75kgf yield tension. Note that the yield isn't where the spoke breaks, only where it's permanently distorted.

BUT the ultimate tensile strength on the same spoke = 355#s or 161.3kgf.

So if you were to hang a weight of 161.3kg from a 1.8mm spoke it would stretch then snap. The reason the OPs spoke isn't snapping, is that by elongating it relieves the load since both ends are at a fixed distance.

One nice thing is that the OP has figured out that his spoke tension gauge is fairly accurate reading 165kgf vs a theoretical 161.3kgf. Not too shabby.


BTW- tensioning beyond yield (but not above tensile) is why so many people don't like light spokes because they stretch. Yes they do when over tensioned.

BTW- tensioning beyond yield (but not above tensile) is why so many people don't like light spokes because they stretch. Yes they do when over tensioned.

But you have to admit...they're hella nice spokes to have when building with super-light rims of the days of old!

=8-)

I agree. I very rarely, just about never use plain gauge 2mm spokes, and most of the wheels I build are on 1.8, 1.7 or even 1.5mm spokes (center width). Light spokes and light rims build great wheels. My commuter is built with 15g DB spokes (that's what I had handy, and they weren't selling) with Mavic 26' rims and are on track to be the first wheels I've ever had last until the brake track wore through.

My point was that contrary to what some think, it's actually easy to over tighten wheels far beyond the yields of spokes, though this is the first time I've seen anyone pass the ultimate strength mark.

I understand the disbelief on the possibility of the threads being stripped because it is almost always the shape of the nipple that gives way first rendering the wrench useless. However, I cannot think of anything else it would be; that is because I could simply turn the nipple ad infinitum and nothing would seem to change except a click about once every revolution. Stretching the spoke through the nipple was not occurring, nor a warp in the rim as far as I could tell (Sun CR-18 single-eyelets are pretty stout); I have since rebuilt the wheel with a new set of spokes and everything went fine. That said, it was not a good technique to try and dish the wheel by tightening the drive side that was already near tolerance rather than to work on loosening the other side.

All the sizes matched but I am guessing the spoke may have been cut slightly warped at the LBS (the second group was bought at another shop that sells all pre-cut GT spokes). Anyway, wheel's built, still have to ride test it, but I wonder what I should do with the old spokes and if I could or should reuse them, despite being rather spooked.

The click on each rotation is a sign of stripped threads. The crest of the spoke-threads is skipping over one crest of the nipple threads once per revolution to maintain static position. If the nipples have been turned numerous times in the past for truing, the softer brass threads can easily have worn out. The old spokes are most likely fine.

Yes, it would have been nice if you'd said in your first post that it would click back when rotated a full turn. Read posts 16 and 17 where the signs of a stripped nipple were described.

In any case you're wheel is still outrageously tight, and needs to be brought back to real world tensions. At the same time, it would appear that this nipple and perhaps the spoke also need to be replaced.