Ron Damon

What, if anything, can be learnt about the cause of this spoke breakage from the image?


broken spoke on non-drive side

Bill Kapaun

Bad luck.

Duragrouch

Nothing unusual. Spoke threads are rolled and not cut, so not as bad as cut, but thread minor diameter is still less than spoke body, so constitutes a stress concentration. Spoke also has the most bending stress right above the nipple (for rims that are not "aimed and drilled"). So pretty normal.

Trakhak

I broke several spokes, front and rear, in the wheels of a Specialized Langster that I'd bought new. I was surprised and annoyed that it began breaking spokes after only about six months of riding. (I bought that bike the first year of production. It had several other problems that Specialized corrected in later years.)

It, too, had black spokes. Some broke at the nipple, most at the elbow. I eventually rebuilt both wheels with new spokes.

My guess is that the black finish was meant to conceal the dull finish of low-grade steel.

delbiker1 

I learnt they need to be replaced.

Chuck M 

I don't know if it is my eyes playing tricks, but it looks like there is an angle where the spoke exit the nipples on the adjacent spokes.

pdlamb

On both sides, so it's probably not an optical illusion. I'd guess detensioning the wheel and putting a drop of oil on each nipple head might allow the nipple to rotate in the wheel when you re-tension. The wheel might be under-tensioned, but again that's an "internet expert" guess.

FBinNY 

This may be the issue. Ideally spoke holes in rims are such that the nipple can float and properly align with the spoke.

Some rims are drilled too close to the nipple diameter forcing it to align with the hole rather than the spoke.

If not properly stress relieved, the angle creates a local dead load.
Added to working loads this can bring the total stress beyond the fatigue limit.

If I see this kind of bend, I make doubly sure to stress relieve and retrue the wheel. If I made spec. decisions, the rim's maker would be told to address the problem or lose my business.

When dealing with rims, the phrase "wiggle room" needs to be taken literally.

79pmooney

My first thought also. I want to see a photo from the front or read that shows whether the spokes are also bent to the side,

I lube each nipple hole with a cotton swab and marine grease before lacing up new wheels. Primarily to make turning the nipples the last few turns easier but it doesn't hurt here.

I wonder if this wheel has more spoke crosses than the rim designers envisioned. A radial laced wheel has spookes that hit the rim at 90 degrees. X1 or X2 are close to that. A X4 wheel with a Campy Tipo hub has spokes that come in far off 90 degrees (like 81 degrees using vert quick and dirty math and not going out the garage to measure anything). So that would be 9 degrees. Or a real bend at a nipple that isn't allowed to align itself.

I have broken spokes from bends there. Not a lot. I haven't focused on them when I build and it appears it shows.

FBinNY 

No matter what, it boils down to wiggle room.

Since this is an OEM wheel, it's a manufacturing or spec. defect, and IMO the manufacturer's responsibility to make it right.

To be clear, it's the OEM's job to make sure hub, rim, spokes, and number of crosses all are compatible. As I said earlier, I would not have accepted these rims, but it would probably have been OK if the finished wheel were properly stress relieved.

zandoval 

Your Turn...

HTupolev

Quote:

broken spoke on non-drive side

Possibly insufficient tension.

As you're riding, the section of the rim at the contact patch gets flexed upwards a little relative to the hub. This momentarily shortens the spokes that are "passing through" the contact patch, causing them to drop in tension. If their tension was low in the first place (which is often the case for rear NDS spokes), they might go slack enough to wiggle and flex, which can fatigue the spoke where it contacts either the nipple or the hub.

Immediate fix is to replace the spoke. But when that happens, the wheel should be checked for appropriate spoke tension, and adequate spoke-to-spoke tension consistency. The failure may have been a fluke, but if it wasn't, you'll want to address the problem sooner rather than later.

79pmooney

Totally agree. I'm one who often pushes boundaries to get my bike stuff to do what I want. (Set up my triples to run decently in small-small so I don't have to do two double shifts when I am climbing at my limit and the hill levels out for a bit. I love to climb! I live for it. That practice shortening the life of my cogs and chains? Oh well.) V-brake levers and powerful (road-pull) calipers. Stoppers that don't lock up wheels or want to skid. Yes, braking from the hoods suffers but I'm from the pre-areo brake lever days. Was taught to ride the drops whenever the going gets iffy and still do.

Light to very light spokes and as many crosses as I can do because I love the ride.

So rims that aren't fussy as to spoke orientation, yeah! But I haven't broken enough spokes at the rim to raise it to awareness when buying. Thanks, FB, now I'll look harder. (And see if maybe spoke holes want to be tweaked on rims I really want for other reasons if these don't allow proper alignment. The Velocity Aeros seemed to be poorish in that respect. My two city bikes are my only clincher bikes now and I am guessing those wheels are going to go to a natural death. Not spoke shedders despite being Aero'd and on their second or so rim. Winter PNW lava grit brake wear.)

FBinNY 

Keep in mind that things rarely fail due to a single cause.

Spokes rarely break at the first thread stress riser.

Spokes bent at the nipple are fairly common, and yet this isn't a common cause of breakage. In any case there's a far worse bend at the other end.

But, a bend at the stress riser, that wasn't stress relieved, possibly compounded by other factors is simply too much.

Andrew R Stewart 

Do I see a tad of corrosion at the spoke's broken end? Are the nipples Al? Andy

FBinNY 

Definitely a consideration, especially if it broke while the OP was trying to turn the nipple.

Hopefully the OP would have mentioned that.

OTOH based on cosmetics alone, I lean to downplaying corrosion worries.

KCT1986

More information about the wheel/build would be helpful.

Position of the broken spoke (DS, NDS, Disk brake side)?
# of spokes, cross pattern?
Unusual hub, flange diameter?
Butted spokes?
How deep within the nipple the first thread was (assuming that the break was there)
Bike type & use.

Ron Damon

• The wheel is not OEM, but rather hand built.
• It is 20" (ETRTO406), 24-spokes laced two-cross.
• It has broken spokes twice since 2018, this time being the second time.
• The spoke broke while riding.

cyccommute 

The spoke may be too short or, more properly, have insufficient threads engaged with the nipple. In some Specialized OEM wheels of a certain age this is a common failure. The spokes don’t go through the nipple to the nipple head slot by several spoke threads in almost all of the ones that fail this way. The wheel can be properly tensioned and a nipple driver will still engage the nipple slot…can’t turn it but can still be put in there.

Ron Damon

Broken spoke today at 12 o'clock. Replaced previous broken spoke, still intact today, at 6 o'clock.

FBinNY 

Everything I said still applies, except blaming an OEM. Transfer that blame to whoever spec'd and built it.

Doubly so if both spokes broke the same way.

BTW some of the nipples nicely align with the spokes and some don't. Is it possible that the rim is drilled forward and back (rare but not unheard of), and not laced to match? Otherwise it's hard to explain some, but not all unaligned nipples.

‐------------

Side note, having nothing to do with the issue.

I note that the wheel isn't mirrored (all trailing spokes either elbow in or out). Most hand builders mirror for a number of reasons. Machine built wheels are often built unmirrored because it's faster for a production worker. So, while this wouldn't cause failure at nipples, it argues against the wheel being hand built by a skilled builder.

Ron Damon

I just noticed that the first broken spoke a couple of years back was the antipode of this second broken spoke today. That is, on this 24-spoke wheel, the first spoke broke at 12 spokes plus/minus this second broken spoke or exactly on the opposite side or 180 degrees apart, both times on the non-drive side. What does this tell us, if anything?

FBinNY 

I hate coincidences, but can't find a logical connection.

In any case, your main concern should be where to go from here.

Two spokes in two years isn't something I'd get worked up over.
Based on the long interval, I'd simply replace the spoke and true the wheel. With any luck the next break will be a year or more away.

If that next break happened sooner, I'd note the shrinking interval, and either rebuild or say last chance.

Duragrouch

Spokes angled at nipples: Very common on smaller wheel bikes, because with hubs being the same hole ring diameter as bigger wheels, you're gonna have more leading or trailing angle at the rim (for crossed spokes), and I don't think most rim makers take this into account, they just drill the holes pure radial, and there isn't enough nipple hole clearance for the nipple to swivel enough to be in alignment with the spoke. Every spoke on my 406 2X wheels are like that. Note: They are cheap Dahon single-wall rims, so the material is thick at the nipple hole, even thicker if that is actually a thin double-wall as some have speculated, I have not yet had apart since then to look closely.

I have not stress-relieved my wheel spokes. Only saw bit decades ago about doing that with feet, didn't seem precise to me. In recent days I read how to properly do this on sheldonbrown, gripping adjacent parallel spokes.

Duragrouch

Only thing I can think of is if the rim was oval unspoked/unloaded, and both of those spokes were at the (major? it's been a long time) axis of the oval, so both more highly tensioned to achieve a good radial true. Or the rim slightly tacoed, and the broke spokes were trying to pull it flat. But there's not that many spokes, so not huge odds of coming up exactly opposite in spoke roulette.