How should spokes sit in nipples to be right?

[Trikeyohreilly]

Hi. I just brought my wheel back from the LBS who didn't seem to like my wheel at all. Hopefully I have successfully added a photo of the spoke in the nipple. What do you think of it please?

[Brucey]

assuming the nipple is a standard type, that spoke is too short. I'd use it like that in an emergency, but I certainly wouldn't build a wheel like that.

cheers

[Samuel D]

I like to have the spoke reach at least as far as the bottom of the slot in the nipple. So I’m with your LBS.

With spokes your length, fewer threads are engaged and the nipple gets loaded in tension. That’s a sure way to have aluminium nipples fail from the fatigue of millions of cyclical loads, but it’s probably not great for brass nipples either.

[wheel71]

If they are 12mm nipples not good. If they are 16mm nipples this would be fine. A view from the other end would be good. Are there threads showing? Ideally when tensioned you should reach the end of the threads. If it's only the one it's easy to replace.

[Samuel D]

If they are 12mm nipples not good. If they are 16mm nipples this would be fine.

What difference would nipple length make?

The longer nipples that I’ve used have not had a longer threaded section. And a longer nipple does nothing to stop the head end being loaded in tension rather than compression if the spoke is too short.

It’s hard to say from the photo exactly how short the spoke is, but it looks poor to me.

[wheel71]

I've used longer nipples which have longer threads to get around this problem before. It was when I used to build a lot of BMX wheels but I don't see why the nipples would be different but maybe they are? I can't imagine why anyone would make a nipple longer without the threads being longer? Seems a bit pointless.

[Samuel D]

Longer nipples give the spoke key something to grasp when the nipple seats are deeply embedded in the rim.

I have not built enough wheels to know all the nipple designs out there. If some have a longer threaded section as you describe, I’d still worry about using them to solve Trikeyohreilly’s problem. Whatever the design, I’d make sure it’s brass to better resist the tension and shear stresses caused by short spokes.

[Brucey]

longer nipples are available with either longer threads or the same length threads as normal. The ones you get from DT and Sapim are often (usually?) the latter type, and are meant for rims that are thicker from the nipple seat to the rim ID. This means they are really for locally reinforced (thickened) rims, rims that have thicker double eyelets than normal, rims that are built with washers beneath the nipples etc. The extra length is there so you can get the spoke key onto the nipple. When using such nipples you should make the spoke ends finish in the normal place (i.e. mid-slot or slightly higher, preferably).

Long nipples with long threads look like they should allow a wheel to be built with shorter spokes, but there are problems. I have seen quite a few such nipples break via stress corrosion cracking. I have also seen such nipples where the hole wasn't drilled centrally, making the nipples prone to simple breakage.

cheers

[Trikeyohreilly]

Thanks for your oppinions. There are no threads showing on the other side. Yes they are 12mm nipples. It was at my LBS as although it has done less than 100 easy miles, a nipple was pulled through the rim. The suggestion was that this may well happen again.

[Samuel D]

Would you describe in more detail what the failure was?

[Trikeyohreilly]

Sure. I've been experimenting with extra dynamo rear lights. This is my dynamo hub wheel. With some extra rear lights roughly wired up I lifted the front wheel of the floor, put two fingers around a spoke at the nipple, and spun the wheel. It wasn't a hard spin but the spoke pulled out of the rim. I think im right in believing that spokes are not supposed to be strong in that direction but I didn't expect it to come right out. Cost me £11 to have it put right so ill not be doing it again!

[alexnharvey]

Did the rim fail or the nipple?

[Brucey]

...the spoke pulled out of the rim.....

no clearer. Specifically the question is, did

a) the spoke pull out of the nipple or
b) the nipple pull through the rim?

cheers

[Trikeyohreilly]

Sorry. The nipple came out. The nipple lost its shoulder, hope that's the right term. Basically it failed at the wider part that's under the rim tape and broke in two allowing the rest of the nipple to come through the eyelet.

[Brucey]

ah, OK, the nipple broke then; this is exactly the kind of failure that I mentioned as a possibility upthread, whenever the spokes are shorter than is ideal. Unless the failed nipple is obviously faulty in some strange way I think it is very likely that you will suffer further failures of this sort.

FWIW a while back I rebuilt a wheel which had rubbish spokes (of the wrong length, which didn't fit the hub) and nipples that were failing. From 36 nipples, two had broken already and of the remaining 34, about five had the same fault as the broken ones; the drilling wasn't central, being quite a long way off centre at the head end of the nipple, but Ok at the other end. The wall thickness of the nipple is usually about 0.75mm and this diminished to about 0.25mm on one side because of the bad drilling, and because the spoke was to short, the head were popping off the nipples. It happens quite often.

cheers