Author Topic: Cracked nipples  (Read 4102 times)

trailplanner

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Cracked nipples
« on: April 30, 2021, 05:12:20 PM »
No, not what you are thinking, but spoke nipples failing regularly.  Front and rear. 

I have an Mk4 Audax, DT R411 36-spoke asymmetric rims on Hope Pro4 hubs and have had 6-7 nipple failures.  All the same shearing point as the nipple widens.  Not just when riding either.  My bike is quietly resting behind my work desk and I have heard two fail while the bike is stationary! I can hear the nipple head roll to the bottom of the wheel.

Bad batch?  Originally built by Thorn. I note it uses washers.  Could this be the problem?  Should I replace them all?

Danneaux

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Re: Cracked nipples
« Reply #1 on: April 30, 2021, 05:33:11 PM »
My original 2011 Sherpa Mk2's wheel nipples also cracked spontaneously while the bike was at rest, same as yours. I could hear them ping and fail as the bike rested against my fireplace. Mine split at the same location on the nipple not long after purchase. No washers used. I replaced them all with DT plated brass nipples and retensioned/retrued with no problems After. I presumed they were a bad batch.

Best,

Dan.

steve216c

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Re: Cracked nipples
« Reply #2 on: April 30, 2021, 07:45:48 PM »
I never heard of this phenomenon. Fascinating although potentially dangerous if nipple broke when riding.
Iíve had nipple jamming stuck or threading or rims splitting around nipple but never had a nipple doing a Lemming on me.
I recently built a new front wheel using Sapim spokes. Hopefully the supplied Sapim nipples are up to the job. Do we know what spoke models Thorn wheel builds typically use?
If only my bike shed were bigger on the inside...

Danneaux

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Re: Cracked nipples
« Reply #3 on: April 30, 2021, 08:07:23 PM »
FWIW, I've never had a problem with DT, Wheelsmith/Asahi or Sapin nipples I've purchased for my own builds so long as they were plated brass. Aluminum alloy nipples don't age well and tend to crack or seize over time no matter how prettily anodized or how much anti-seize one uses when building.

A few years back, member Slammin' Sammy had a whole batch of Sapim Race spokes break on him while his bike was stored in his shed. They were black rather than silver as I recall. I once read of a similar case where the bike was stored near a pool or pool chemicals; it seems chlorine can weaken stainless to a point where it become brittle. His were apparently a bad batch, reported elsewhere and by others at the time.

Back in the day (late 1970s), I got batch after batch of plated Robergel Trois Etoilles spokes that were hydrogen-embrittled from poor chroming processes. Made for weekly wheel rebuilds and that got old really quick.

Best,

Dan.

trailplanner

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Re: Cracked nipples
« Reply #4 on: May 01, 2021, 07:46:41 AM »
Dan might have a point.  Some nipples are covered with tubeless sealant (Stans) from my earlier experiments in going tubeless.  I have not quite given up on that experiment, but I am running with tubes now.  Perhaps the sealant chemicals are weakening the nipples?  That would be concerning.  The nipples are as fitted by Thorn for the initial wheel build and are brass plated.

Shall I order a new set, plus a spoke tension meter and have a go at rebuilding?  Or shall I just take it to someone who knows what they are doing?   Should I stop riding?

Photo attached - another one to add to my collection.



Danneaux

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Re: Cracked nipples
« Reply #5 on: May 01, 2021, 11:04:56 AM »
Tubeless sealants I've encountered contain ammonia and that can cause problems with aluminum nipples, _but_ if the rim has been taped correctly, no sealant "should" be getting on the nipples. Still, I have seen it happen if the tape doesn't fully seat. If there is contact, then you would see corrosion of the aluminum nipple. Plated brass should be resistant to this but I have seen them discolor and your appear to be a little corroded in the photo you posted. If you ride on salted roads, that can be a factor.

I still have my photos someplace, but my nipples cracked on the corners so the flats peeled/chipped/fractured away and then into the heads as if the brass were embrittled. The spokes were aligned with the nipples and the rim had spherical seats. The rebuild gave no trouble.

Yours appear decapitated. I have sometimes seen that occur if the spokes are too short. This causes the brass alone to carry the load just beneath the head without the spoke shaft to share support. Rim burrs can also be a cause. I can't see the rim/spokes/nipples from here, but it would be helpful to look at them in some detail.

Here are others' takes on decapitated/broken nipples (more frequent with aluminum):
https://www.velonews.com/gear/tech-faq-why-spoke-nipples-break-and-replacing-spokes-and-not-nipples/
https://www.roadbikereview.com/threads/spoke-nipple-breaking-off-at-the-head.365677/
https://www.wheelfanatyk.com/blog/wheel-building-tip-no-9-succeed-with-alu-nipples/
https://www.wheelfanatyk.com/blog/wheel-corrosion/

Wheelbuilding is a good learning experience and useful skill to have especially on tour.

Best,

Dan.
« Last Edit: May 01, 2021, 11:06:36 AM by Danneaux »

trailplanner

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Re: Cracked nipples
« Reply #6 on: May 04, 2021, 09:10:18 AM »
Dan. You're right. Time to learn wheel building.  I was going to learn to play the piano, but I need a greater challenge ;-)

I'll check spoke length, but as I understand it, asymmetric rims compensate for the flange offset and the spoke lengths should be equal on both sides.  Set the tension you want on the DS and adjust the non-DS to bring the wheel rim into the centre line. Zip ties for the moment, but if I enjoy the experience then a proper wheel stand.  Tensioner ordered, decent spoke key, nipples and washers too.

btw, my Andra 30s on the Sherpa have not moved one iota in their lifetime - just bearing and rim wear required a new wheel after 10,000km.  These wheels suffered all forms of abuse for long off-road/road tours, which is why the Sherpa is the first choice for the rough/heavy terrain.

I am off down the rabbit hole (to watch Youtube mostly).  Will surface for air at some time in the future and report back.

Thanks for the links.  Very useful.

PH

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Re: Cracked nipples
« Reply #7 on: May 04, 2021, 10:07:55 AM »
Tensioner ordered, decent spoke key, nipples and washers too.
I have access to a good wheel building kit, it belongs to the local CTC group but usually lives with me!  It includes a Park Tools tension meter, yet I find this iPhone app to be more consistent
https://www.youtube.com/watch?v=ChFIIe0aPb4

I've not come across cracked nipples, I'd have thought the rim would crack first, something I have had a couple of times.  Do the spokes go all the way to the top of the slot? 

EDIT - Thanks Dan for the links, just glanced through them now, but will have a proper read later.
« Last Edit: May 04, 2021, 10:14:13 AM by PH »

trailplanner

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Re: Cracked nipples
« Reply #8 on: May 10, 2021, 03:29:30 PM »
ping - there goes another one !! I think it best to take the bike off the road until the spares arrive and I can replace all the nipples.

mickeg

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Re: Cracked nipples
« Reply #9 on: May 10, 2021, 06:22:47 PM »
A good tension gauge is expensive, it may be cheaper to do the nipple replacement labor yourself and then see if a bike shop can check the tension.  Some shops would refuse I expect, they want to charge for the whole job.

A friend of mine volunteers for a bike charity as an unpaid mechanic.  He checked mine on my Nomad, and then rechecked them after I tightened them up a few minutes later, no cost.  But I had donated to that charity so that may have been a special case.

If the nipples you buy are different brand than the ones you remove, you might need a second spoke wrench.

I generally just tighten mine up until they feel as tight as spokes on other bikes that I own.  My Nomad is the only bike I had tension gauged.

trailplanner

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Re: Cracked nipples
« Reply #10 on: May 10, 2021, 08:36:28 PM »
I think I have found the root cause  :)

Using a spoke length calculator - https://www.prowheelbuilder.com/spokelengthcalculator I can see the spoke lengths are different for these asymmetric rims and the wheel has been laced with the same length spokes (290mm). 

The non-drive side (rear) should be 291.4mm.  The non-disc side (front) also should be longer (291.4mm).  Note the asymmetric rims are laced to compensate for the centre line offset, which is different rear and front, so they are laced differently (cassette takes up the dish on the rear, and the disc takes the dish on the front).  The idea of asymmetric rims is to even up the spoke tension to build stronger wheels. 

All the nipple failures are non-drive side rear and front non-disc side.  So I conclude the spoke lengths are too short (1.4mm) which is not enough to fully thread into the nipple and hence the fractures.  If I look at each nipple they are clearly not long enough in each alternate hole, front and rear.

So I need 32 new spokes length 292mm (plus replace the fatigued nipples).

The spoke tensioner is great.  My daughter's new wheels had a spot on even tension, but greater difference drive side vs non-drive side.  I tensioned my wheels using the Park Tools WTA online app.  Then I fine-tuned afterwards to correct any lateral movement, and that worked well.  The spoke tension difference was less using the asymmetric rims.

I'll ring SJS, as they built the original wheels, and see if they agree.  It is, as Dan suggests, a useful skill to have in the field. It would be nice to know I can take a good shot at rebuilding a wheel.

I tried the spoke frequency, but a spoke tensioner is much faster.


JohnR

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Re: Cracked nipples
« Reply #11 on: August 04, 2021, 09:12:01 AM »
As I had noted here http://thorncyclesforum.co.uk/index.php?topic=14150.msg106789#msg106789 , I've recently had a nipple failure on the front wheel of my Mercury which is just over one year since purchase and has now clocked up 6,000 miles. As the local distortion of the rim was dowards the disc side then the broken nipple would have been on a non-disc side spoke which has me wondering if it suffers the problem of all the spokes on that side being slightly shorter than optimum. This leaves me with a dilemma: Should I pull off the nice tubeless rim tape (two layers - the broken nipple was conveniently near the end of the tape so I peeled back the first layer and poked a hole in the 2nd layer to get to that nipple, no trace of the head to be found) in order to check if the spokes come to the top of the nipples or just be aware of the risk of nipple failure? Changing to slightly longer spokes where needed is effectively a complete wheel rebuild (what is the warranty on Thorn bikes although this problem might be classified as a latent defect)?. I'm not completely sure but I reckon that the failure occurred when I encountered a particularly nasty pothole while checking the route on my Garmin.

Danneaux

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Re: Cracked nipples
« Reply #12 on: August 04, 2021, 03:05:07 PM »
John,

I suggest you contact Thorn/SJS Cycles so they are aware of the problem and see what develops from there. They may have some ideas or suggestions to offer.

Best,

Dan.

JohnR

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Re: Cracked nipples
« Reply #13 on: August 05, 2021, 06:10:19 PM »
I've been in contact with Robin Thorn who noted (i) brass nipple failure is not common (unlike alloy nipples) but anything CAN fail; (ii)
sometimes the steel eyelet will cut into the plating and this causes a stress riser; and (iii) They normally build with boiled linseed which acts as a lubricant and stops the nipples loosening.

He asked for some photos of the heads of other nipples so I removed the rim tape and took the attached photos, labelled according to whether they are disc side or non-disc side spokes. Effectively the ends of the disc side spokes are level with the top of the head while the ends of the non-disc side spokes are level with the groove in the head. I would have thought that this is enough penetration as the threaded part of the spoke above the bottom of the groove won't provide any significant increase in overall strength.

I also found the head of the broken nipple which has a fairly rough and dirty surface. The latter may be the result of sitting in the rim for a few weeks.

I therefore see this as an isolated failure, perhaps caused by the pothole impact. Any thoughts?

trailplanner

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Re: Cracked nipples
« Reply #14 on: August 14, 2021, 09:07:05 PM »
I suspect an isolated incident.  My wheel builds definitely had spokes too short on one side and the spoke head was 1-1.5mm below the nipple crown and these consistently failed.  I rebuilt the wheel myself investing in the tension gauge (park Tool) and borrowing a friends truing stand.  Robin was very helpful and got me back on the road.  I have since bought some HUNT wheels and I am very pleased with them and reuse my 700C wheels across a few bikes I own to change them from fast road bikes to touring capable, with stronger wheels.  Discs allow you to do that easily, after adjusting the calliper alignment, which only takes a moment.