totalnewbie

Recently a spoke (Sapim cx-ray) on my front wheel (road bike) broke off. The nipple at the rim broke in half, causing the spoke to fall off. At closer look I noticed the spoke was twisted at about 90 degrees around its own axis (it's a flat spoke so that's why I noticed) near the nipple and maybe that is what caused the nipple to break. Initially I thought that was the intentional design but when compared to other spare spokes that came with the wheel, I saw that it's not.

I took the wheel and the spare spokes (same brand, Sapim cx-ray) to the LBS. They pointed out to me that the spare spokes are a couple of mms too long (intended for the rear wheel) and if I were to use them on the front wheel (should they fit), over time the spoke will be prone to breakage since the force is "unbalanced" if one spoke is different from the others. I asked him to try anyway and I would pay him regardless. He did but reported back that when he tried to true the wheel afterwards, he has problems with tensioning of other spokes to balance the whole thing. He blamed it on the uneven spoke. So I ended up placing a request to send the wheel to OEM so they could fit it with the exact length of spokes that was broken....

anyway, there are a few things I don't quite understand and I wonder if anyone can shed some light on this matter:

1. Since the nipple is screwed on, shouldn't the thread of the spoke be able to account for any minute difference in length, and thus adjustable and should be able to fit onto the wheel?
2. If I were to fit a spoke that is 2mm longer (same brand same make),why would that spoke be more prone to breakage? I thought the spoke tension is related to the cross section area and not the length.
3. I can imagine that the longer spoke (if fitted onto the wheel) may poke onto the inner tube (by 2mm in my case) and may increase the chance of puncture. This sounded to me the more reasonable explanation why all spokes shall have the same length, not the breakage issue the mechanic mentions. Who is right?

prathmann

Shouldn't be an issue as long as the spoke isn't so long that it extends into the rim channel and can puncture the tube - or that you run out of threads so the nipple can't be tightened properly. I've replaced broken spokes using whatever replacements I happened to have on hand as long as they were within a few mm of the other spokes on the wheel and never encountered any difficulties.

dabac

Whether you can use a longer spoke or not depends on how the original build was planned.
On a normal, 12 mm nipple on a DT spoke, the spoke can overshoot the nipple head with 2-3 mm.
If the original build had spokes ending flush with the head, you've got about that much margin.
You can push it a little by drilling out a few mm of thread from the narrow end of the nipple.
Or by putting a washer under the nipple.
W/o knowing how your wheels were built - on the short, mid or long end of the tolerance range, it's impossible to say what'll be doable in your case, what margins there are left.
On single-wall rims, having the spokes end flush or a little short is important. On double-wall rims I've never seen a spoke go so far through the nipple as to trouble the rim tape or the tube.
And as long there are threads enough left, even a slightly longer spoke should tighten up just fine and cause no further trouble for the wheel.
If it was the nipple that broke, why do you need to replace the spoke?
Wouldn't a new nipple be enough to fix it?
Nipples breaking in half is quite unusual.
Too short spokes can contribute to that.
I've sheared off the flanges occasionally, but never split a nipple on a properly sized spoke.