Cycling UK Forum

I've never come across spokes breaking in the middle before.
1 was at the cross, 2 might have been but I didn't check, and 3 definitely wasn't.
All over 2 days touring on a wheel that was about 16 months old, not heavily laden (apart from me)

Any idea what I did wrong when building the wheel?

I've only ever had spokes go at the elbow or very occasionally at the nipple (and not when I've built them!). To break in mid span implies very high tension, of the order of a ton or so. Some foreign object in the wheel at speed??

Nothing in the spokes.
All 3 were heads out, gearside
1 was going up a moderate hill, 2 up a steep one, and 3 was on the flat, just riding along. It smacks of fatigue, but in the middle?

That's what I thought too. To quote the bible:-
"Failures at the spoke elbow or threads are nearly always fatigue failures, in contrast a forced break will usually occur about 20mm away from one of the spoke ends......
Tension tests using new spokes of various brands show that all high quality spokes tested break at more than three times the max. tension they would encounter in use. The point of failure was, in all cases, neither in the threads nor at the elbow..."
I've never known Mr Brandt to be wrong yet, so I'm left scratching my head.
Spokes loose enough to cause this would have been felt as a wobbly wheel long before it went pop. I seriously doubt if you could physically overtighten the wheel enough to force a break either. If you solve this one I'd like to know the answer.
PS, they were new spokes I presume?

andrew_s wrote:Nothing in the spokes.
All 3 were heads out, gearside
1 was going up a moderate hill, 2 up a steep one, and 3 was on the flat, just riding along. It smacks of fatigue, but in the middle?

Usually if they go they go at one of the two ends but I have had them go in the middle and all on one wheel. I put it down to a batch of faulty spokes and once the broken ones were replaced it didn't happen again. Ones that go at the ends are usually down to build quality - usually not enough tension and no stress relieving.

My money would be on a dodgy batch, some impurites in the steel. What brand/type were they?

PW wrote:That's what I thought too. To quote the bible:-
"Failures at the spoke elbow or threads are nearly always fatigue failures, in contrast a forced break will usually occur about 20mm away from one of the spoke ends......
Tension tests using new spokes of various brands show that all high quality spokes tested break at more than three times the max. tension they would encounter in use. The point of failure was, in all cases, neither in the threads nor at the elbow..."
I've never known Mr Brandt to be wrong yet, so I'm left scratching my head.
Spokes loose enough to cause this would have been felt as a wobbly wheel long before it went pop. I seriously doubt if you could physically overtighten the wheel enough to force a break either. If you solve this one I'd like to know the answer.
PS, they were new spokes I presume?

OK, I'll diverge from Brandt a bit on this.
Having come across spokes which failed as I stress-relieved, I built a lever to pull spokes at multiples of my body weight.(get eye protection if you do this, its rather exciting)
The only common factor was that the failures were ductile ....you can see the metal has stretched and thinned before failure, because it "necks down" to a smaller diameter right by the failure. But I got failures at the elbow or the shaft.
Also, I found no 14/16/14 gauge spokes that would support 300Kg, not even close to Brandt's "more than 3 times" if you take my 130kgf as a figure for driveside rear static tension.

Various forum members in various threads attribute spoke failure to slack spokes, eg PW's "Spokes loose enough to cause this........." above. edit..or Tony R, "usually not enough tension" (sorry, chaps, to pick you as an example) .I don't understand why?

Colin, I was thinking along the lines of a butted spoke so loose it flexes at the butt, that would possibly fatigue it PDQ. If the sensible solutions don't apply try something silly!

CREPELLO wrote:My money would be on a dodgy batch, some impurites in the steel. What brand/type were they?

I'm with Crep on this.

Only spokes I've had broken - of the modern SS type - have been at the elbow ....... and that's only one, and not what I've built.

Disc brakes a factor?

wearwell wrote:Disc brakes a factor?

I won't diverge from Brandt on this.... he says any torsinal load (ie trying to turn the hub within the rim, eg pedalling, hub brakes) is supported by so many spokes it won't contribute significantly to fluctuating tension on the spokes, and therefore fatigue.

Absolutely no idea,

Some thoughts though.

Did you re-use spokes from another wheel?
What sort of spokes were they, they look like stainless steel but it would be of interest, which spokes exactly.
When you were threading the spokes onto the rim, did you thread these particular spokes on last of all?
If so were they difficult to get past the rim after the third cross and instead of deflecting them gently from the tip of the spoke, did you accidentally bend them inorder to pass the rim, by holding them in the middle and slightly kinking the spoke?

wearwell wrote:Disc brakes a factor?

That's the conclusion I've come to.

Sapim say not to use Laser (2.0/1.5/2.0) spokes on disc brake wheels.
These spokes were new Sapim race (2.0/1.8/2.0), built to something like 120-130Kgf gearside tension. Sapim quote 1350N/mm2 for the centre section, which equates to about 340Kgf. My experience (courtesy of a pedal in my front wheel) is that the nipples aren't as strong as that, and there wasn't any visible sign of ductile failure on the one spoke I did peer at closely.

When lacing a wheel, I put in the heads out spokes on both sides before twisting the hub relative to the rim and adding the heads in crossing spokes. The failed spokes will have had no bend put in at build time.

I think I'll replace all the gearside spokes with Sapim Strong

Spoke 2 took 22 min to replace, between stopping and setting off. Spoke 3 was quicker, but that was at the campsite where the bike didn't fall over when upside down.

andrew_s wrote:....................I think I'll replace all the gearside spokes with Sapim Strong............

That'll probably fix it, whatever causes it!

Sorry to hijack this thread but I am thinking about the spokes on my handbuilt touring bike wheels. They are DT 14 guard stainless steel spokes throughout. The wheels are great and have stayed true and solid despite a fair bit of abuse (some dreadful rocky surfaces and potholes) and a few thousand miles. However given the discussions about double butted and single butted rear wheel spokes I was wondering whether I should upgrade the spokes or should I leave well alone?

As a bit of background I an around 80kg and I tend to tour light - saddle bag/two rear panniers only. My feeling is that the front wheel is just fine to be left alone. I feel that there may be some advantage in re-spoking the driveside only to sapim super strongs. Would this be a sensible approach?