I built a Mavic open sport rim up with a record hub and 36, 14 gauge champion spokes.I miscalculated with the spoke measurement and received shorter but usable spokes.When finished some of the threads on the spokes were visible maybe 2 threads worth.And not on all the spokes.I really thought nothing of it assuming it was alright until 1 of the spokes broke!!This is after about 6 weeks and maybe 600 miles of riding.Anything to worry about?The wheel was properly and evenly tensioned.Could too short spokes compromise the wheel?

I have done it early in my wheel building and didn't have any broken spokes because of it. I have used double butted spokes on all of the wheels I have built and that may have contributed to the early one holding up.

are you certain that they broke? maybe they just stripped out. maybe...

I got a set of XT/Rhyno Lites from Jensen at a great price. After about 18 months I noticed what I initially thought to be a couple broken spokes. Closer inspection revealed the heads broke off the nipples. These wheels were built with "no name" spokes so I measured them and bought the same lengths of DT Competitions. I later learned the problem wasn't sub par spokes - they were simply too short. Long way of saying don't be surprised if the nipples fail if the spokes don't extend all the way the the head.

The nipple head must be in compression, which means the spoke must thread up into it.
If the spoke is too short, the nipple shaft will be under full spoke tension, and will likely separate from the head.

I'm not great at wheels but I think you should be fine. Before you panic and relace or replace the wheels just replace the broken spoke and consider tightening all the spokes a little more most people tend to lace wheels a little to loose for easy trueing.

Even if he was 20 kgf low on his tension, I doubt he'd get nearly enough turn on the nipples to make up for that discrepancy.

To the OP. If I ended up that short I'd have aborted the build as soon as I realized it and exchanged for the proper spokes. I didn't build my own wheelset to end up with wheels less properly spec'ed than what I can buy off the shelf. I built them so that I could control the quality and end up with a set not just built 'as well,' but one hopefully built better. I say re-build them right and learn from the mistake.

-Jeremy

Shimagnolo, I've said this before way back in another thread - the nipple drawings you are using are INCORRECT. A standard profile nipple has approx 1/2mm of vertical downward thickness from the flat BEFORE it starts to curve in toward the rim seat.

Your drawing misleads people into thinking that coming up 1/2 to 1mm short of the flat is already too short - which is not the case.

So long as the spoke end penetrates the lower portion of the head AND the rim seat thickness - things are okay. Typically, this point is roughly 1mm below the flat.

OP, don't look too much at the threads showing on the nipple barrel side - look down instead into the top (head) of the nipple. If you came up more than a millimeter short of the flat - i.e., it appears to be 2-3mm below the flat - then YES, your spokes are too short.

=8-)

OP

Were your spoke lengths roughly 294.00 and 291.00?

Just curious...

=8-)

DT "normal" length nipples are 12mm long. I'd guess you're using these because they're common, included free with DT bagged spokes, and generally included free when you buy the spokes in bulk (I haven't a clue whether DT serves bike shops that way or it's just traditional).

They have 1mm deep slots so the end of the nipple is 11mm below the slot bottom.

Spokes have 56 threads per inch. With two showing your threads start .9mm away from the bottom of the nipple.

Add it together and your spoke threads start 11.9mm below the nipple slot.

DT spokes have 9mm of thread.

Subtract and you find that your spokes end 2.9mm below the slot.

Breakage is likely.

Which spokes have thread showing? Are they all in one half of the hub? That's a length problem in that side.

Is every other spoke on one side (every fourth nipple) short? That's a lacing problem in that wheel half.

Obviously multiple errors are possible.

You're splitting hairs. Shimagnolo's point is that the spoke must engage the head of the nipple, which acts as a nut, vs. the shank which should be thought of as an extension stem for turning the nut from the outside. I do agree with you that there's a bit of fudge room in the gray area between correct and incorrect, but builders should be mindful of the concept.

My personal guideline is that the first full thread must reach 2mm up into the head from the base. As you note that can be well short of the slot depending on the nipple, but assuming there's enough thread, better long than short.

Not splitting hairs FBinNY...

His graphic nullifies the existence of head space that is engaged when short of the flat by 1mm...thereby giving the impression that even 1mm short of the flat is already too short.

See attached pic...



=8-)

Lots of great points here.I'm going to examine distance from the head and maybe change all spokes.By the way the short ones are on the drive side.

Update!Spoke broke right at the nipple end.Upon closer examination the broken spoke was on the driveside where all the spokes were of proper length.(non drive were a little short.)In addition they are 14g.15 g was used on the non drive side as advised on this forum.(good or bad?)Go figure..

trek330....

You haven't answered my question.




=8-)

Did the spoke break or did the nipple break? All the nipple geometry and diagrams above explain how a too-short spoke can cause a nipple to fail.

Just about

Broke right after the nipple.But again the spoke was of proper length.

Spoke breakage at the thread end is not really related to spoke length. After all, all spokes, like all screws have some unused thread in tension below the nut.

Usually when spokes break at the nipple it's because the nipple doesn't line up well with the line of the spoke causing a bend where the spoke emerges. If the last thread is just inside the nipple so much the worse because the bend will be at a thread rather than the full diameter area. Look at the rest of the wheel and see how the nipples and spokes are aligned.

... or perhaps a spoke was damaged somehow.

Is is possible that the wheel was laced to the spokes are in the wrong-offsetted hole in the rim (ie the ND side spokes cross over to the DS of the rim and vise versa)? I accidentally built a wheel like that many years ago, left it like that because I was lazy, and spokes started popping like mad after not too long. I cannot remember if they were breaking at the nipple or at the elbow, but I recall being surprised at the way they were breaking... so it is likely it was at the nipple because most spokes break at the elbow.

edit:
If the wheel is laced wrong then correcting this will give you and extra mm or two of length to use to correctly tension the wheel!

Laced properly all around.

+1

Had to rebuild a 28H, 3X, high-flange hub in a 26" rim b/c of that.

How does this happen and how do I fix it or avoid it?

If you used 3X lacing for 36H on a low flange Record hub in a 700c rim - this problem likely does not apply in your case.

=8-)