Originally Posted by
FBinNY
If you're referring to nipple breakage when spokes do not reach and engage the heads, it's anything but an urban myth. It's a well documented fact, and happens to brass as well as aluminum nipples.
There is some debate about the mechanism of failure, whether it's classic notch failure or whether corrosion might play a role, but with the exception of steel nipples, nipples can and do fail if the spokes don't engage the heads properly -- ie. 2mm or so. Nipple failure seems to be more likely with 14g plain gauge spokes vs. butted or15 spokes, so those building with 15g butted spokes are least likely to need worry about it.
To be clear, I don't say that nipples will fail, just that they may, and the risk increases with time and wheel stress. OTOH, since failure an be just about 100% prevented with proper length spokes, it's hard to justify short spoking a wheel you spend serious time and dollars building in the first place.
I don't say that nipples won't break (though it is something rare with brass nipples), but IMHO the reason why brass nipples do is because of manufacturing defects, perhaps combined with bad nipple well and nipple interfacing (and extreme stress). The main reason why I don't think too short spokes are a major cause of nipple breakage, is because the photos I have seen of broken nipples, shows broken nipples even on spokes with the correct length. So nipple breakages seem to occur anywhere on the nipple, even with correct spoke length. Of course, the usual breaking point seem to be around the flared section.
And as said before, DT Swiss 14 mm and 16 mm nipples have full thread engagement when the spoke terminates 1 or 2 mm below the top of the spoke. While the 16 mm nipple may be rare, the 14 mm is quite common, so surely they would be lots of reports with broken 14 mm nipples
Not sure if anyone have made some FE analysis to show whether alu nipples actually are strong enough for hard bicycle use (MTB, loaded touring) without breaking. I have a hard time believing, that the many broken alu nipples reported on mtbr.com are caused by too short spokes. It seems to me that alu nipples may break on even correctly build wheels, simply because alu nipples are only marginally strong enough for MTB use. So if alu nipples are inherently weak, they must surely be more susceptible to stress cracks caused by too short spokes, but that doesn't seem to be the case.
It all suggest to me, that the major cause of nipple breakage is because the nipples were inherently weak to start with because of eg. manufacturing defects. If too short spokes works as a stress riser that causes nipple breakage, one would expect to see systematic and massive failures across factory wheel batches with too short spokes, or with 14 or 16 mm DT Swiss nipples. But that doesn't seem to be the case; brass nipple breakage seems rare and alu nipples seems to break whether the spoke was too short or the correct length.
All in all I will say, that too short spokes, like 3 threads protruding underneath the brass nipple shank, is a cosmetic issue, not a systematic problem, since too short spokes are very common, but brass nipple breakage is indeed rare.