Nipple/spoke angle question

[pushstart]

I saw @NovemberDave mention this (maybe on RBR), but I notice that on my asymmetric carbon rims the nipple angle for the spokes that travel across more of the rim is a little sharper than I would like. These are just 33mm rims, so maybe it is a non issue.

Importantly, though, I did *not* use brass nipples. Does this look like a problem here?

Nipples are Sapim 14mm (alloy). Spokes are Sapim Laser.

[NovemberDave]

I have raised that issue several times, on various forums and on our blog. You see it quite often with offset rims, especially carbon ones.

I can't say specifically that it's terminal, or with what degree it is, but we have seen a higher rate of spoke hole failures where this occurs. You can nearly feel in that picture how much stress is going into the spoke, nipple, and rim.

A washer will help some small increment, but in our experience it is not a lot.

I would use brass nipples there.

Correcting the spoke line by bending the spoke at the nipple may help a bit too.

This condition is just another of the many examples of how nothing is free. We are bulding with some offset rims now and I was VERY particular about this issue when we did our evaluation builds with them. A more or less perfectly molded spoke bed is required to avoid what your picture shows.

[pushstart]

Thanks, Dave!

Yeah, I forgot to mention that I did use Polyax washers; I always do that now.

Ok, noted that you think this needs brass. I will probably but that on the task list for next time I swap wheels and can live without these on my bike for awhile. Rebuilding a wheel is always a sad task.

I can probably get away with 12mm nipples here too which might help the angle a bit (?)

Yeah, having built a few offset alloy rims, I was surprised about this on the carbon rim. I thought it was a mfr defect until I read your post saying that this was common for carbon. The rims (Yishun) have been brilliant otherwise, but this certainly makes me wish they weren't offset. That feels like a solution in search of a problem -- at least for most hub/rim combos.

[bm0p700f]

I would be concerned about those bends. What is stopping the nipple from aligning properly.

I have started using asymmetric MTB carbon rims and this is issue is not present. I wonder what's different.

[pushstart]

The spoke holes appear to not be angled at all, and given that the rim bed is ~3mm thick, that holds the nipples pretty straight.

This might be a symptom of this (cheaper) open mold. Maybe the MTB rims you have been building are simply better made or shallow enough that this doesn't present itself so dramatically?

I've got around 1k miles on these now. Since these were cheaper rims (well, for carbon) and failure due to this doesn't sound catastrophic, I'll probably keep riding them until there is a natural wheel-swap point and then re-lace with 12mm wheelsmith brass nipples for a more future-proof wheel. These are my daily commuters so I'd like them to last a couple years / ~20k miles, by which time I might be curious enough to build a new wheelset to replace them.

[alcatraz]

This might sound crazy (i'm not a wheelbuilder) but what prevents us from angling these nds spoke holes by just inserting a drill bit the same size as the nipple at a slight angle?

Seems the nipple holes are very small (or oversized nipples). On all my carbon wheels (alloy pillar nipples) I get much more nipple movement than pictured here.

The washers could even aggravate the issue by forcing the nipple deeper in the narrow hole which means less self-angling.

/a

[NovemberDave]

Alcatraz, I think your idea sounds worth trying, which is why I tried it a few years ago, which didn't work and led me to cut the rim open to see what was up. It's nearly impossible to describe without pictures but imagine the spoke bed of a perfectly built rim being 100% flat around the entire rim. This is tough to achieve. You can pre-mold a perfect spoke bed rim and then insert that into the mold, and then "co-mold" it in with the rest of the layup, but that has challenges. Or you can just mold the entire rim at once and rely on more or less perfect layup with no shifting, and no shifting caused when you inflate the internal bladder (from what I know, this is prevalent because of the issues of pre-molding the ring and then co-molding it). I've even heard of some making a spoke bed ring out of titanium and co-molding that.

One of the benefits of the lower temp resins you can use in disc-only rims is that co-molding is tons easier. But from a shop floor standpoint, the production head would be screaming to use only one resin. You can even see a lot of open mold sites advertising "High Tg Resins" on their disc rims as though it were a benefit! It's actually a pretty significant detriment.

FWIW this issue is not exclusive to offset rims. The rim I cut open in the story above was symmetrical. It's just that offset rims are more prone to it. We recently built some prominent name brand rims (customer supplied) that showed this issue. Again, it's a significant reason we were reticent to use offset rims like the ones we chose for our new 650b gravel wheels (which is not our design - doing your own designs these days is pretty hard to justify). It was only after becoming quite certain that the manufacturer's molding was capable of preventing this issue, and still we're super sensitive to watching for it.

Again, this issue is a bit like prostate cancer - the rim might die from it, or it might die with it. It won't necessarily shorten the rim's life. But it sure doesn't make the rim better. For Pushstart, I'd just say watch it and be aware of it and see what happens. It's very unlikely that the rim will explode. It will most likely occur, if it does, something like "hey the wheel is pretty out of true" (**closely looks at wheel**) "oh crap that spoke hole cracked."

[alcatraz]

What kind of shape was that rim NovemberDave? Is it possible OP can have more luck seeing as this rim appears to be a bit wider than lets say a V-shaped rim?

/a

[NovemberDave]

I've seen it on hard V shaped, toroidal, and U shaped rims.

[pushstart]

I'm not quite brave enough to take a drill to my rims, but if one does crack, I will do that and then cut it open to look at it.

Just to clarify the question of brass vs. alloy nipples here, do the alloy nipples accelerate or exacerbate the risk of rim cracking. I would have thought the risk was that the nipple would crack or something -- which seems like it wouldn't result in a rim failure. Anyway, just want to make sure I understand what I am risking.

Thanks, all!

[NovemberDave]

My thought is that the nipple is being stressed, and brass is better equipped to handle that. But on second thought, in this case it might be desirable to have a weaker nipple as a fuse. The nipple breaking could conceivably prevent the rim from cracking. In any case, just keep an eye on it

[pushstart]

My thought is that the nipple is being stressed, and brass is better equipped to handle that. But on second thought, in this case it might be desirable to have a weaker nipple as a fuse. The nipple breaking could conceivably prevent the rim from cracking. In any case, just keep an eye on it

That sounds like a good plan. And the idea of the nipple being the weak point sounds good too.

Thanks again for the advice!

[alcatraz]

If your spokes are long enough I think what you will end up doing is just bend the spoke at the threads. Even if the nipple breaks it might just be at the exposed part (which isn't completely structural with threads). Just in case I'd still carry some string in the tool kit in case you break a nipple. The spoke will need to be tied to a neighboring spoke to get you home.

It will still look a bit weird and you might have trouble truing the wheel if the nipples develop cracks at and around the tool contact point.

To summarize I think it's a low risk situation. You won't have catastrophic failure and if you need to replace nipples you have the opportunity to make adjustments then and there.

I use an app on my phone for music instrument tuning as a tension meter. It allows me to quickly disassemble and reassemble one spoke at a time without having to do much truing work afterwards. It makes for convenient quick wheel maintenance.

Is this a front wheel? Is the bike completely disc brake? Are both rims asymmetric?

I see some exposed threads on the spokes. Next time the tire is off you better look down one of the spoke holes and check that you can see the spoke in the middle of the nipples. If it's just looks like a hole there it can't be good.

[alcatraz]

.

[pushstart]

Thanks for the advice.

I think that is just dirt/the photo making it look like spoke threads. The spokes are well in, all the way through the rim bed. Carrying string / zip tie is probably a good plan regardless, so I will do that.

Yes, pictured is a front wheel. The rear wheel (same asym rim) has the same issue, though not as pronounced, I think (probably given the closer flanges?).