What caused a spoke to fail in the middle?

[knonist]

A spoke failed on the non cassette side of my rear wheel today, and the wheel is only out of true by a little.


When another spoke failed on the cassette side a few weeks ago, the wheel was badly out of true. (The spoke failed near the hub, only in the bit where the spoke joined the holes near the hub)

When the LBS replaced the spoke last week, they claimed they re-tensioned the spokes, so in theory, the other spoke shouldn’t be affected.
As the wheel is only out of true by a little, does it mean it is not bearing much load / tension?
If so, why would it failed in the middle? And would the other spokes over tensioned due to that?

I’m trying to find out what caused the spoke to fail and

 

[Crackle]

How old is the wheel?

 

[knonist]

How old is the wheel?

maxium 2 years old

it is similar to this, but it is called "Bontrager SSR w/Clix", they came with the trek 7.6fx I got.
http://bontrager.com/model/08253

 

[spandex]

stress fracture (they do not brake there) unless there was something there to make it happen.

 

[knonist]

stress fracture (they do not brake there) unless there was something there to make it happen.

no impact at fail, and the rim didnt distorted that much, so I dont think it is stress..

I might take it to the lab and have it check out next week

 

[dan_bo]

I can imagine there was a fault on the spoke at the point of failure.

 

[accountantpete]

I can only think that it was a duff spoke unless there is a fundamental design error.

Spokes transmit a force on the wheel/tyre but also transmit back an equal force back to the hub/frame which moves the bike- it sounds like these conflicting forces met in the middle of your spoke and it didn't like it!

 

[knonist]

I can only think that it was a duff spoke unless there is a fundamental design error.

Spokes transmit a force on the wheel/tyre but also transmit back an equal force back to the hub/frame which moves the bike- it sounds like these conflicting forces met in the middle of your spoke and it didn't like it!

I think the very same spoke "survived" in the pass for 2 years.
Plus, the wheel has just been re-true and re-tensioned last week, and I even pay extra for a service/ inspection to ensure everything is OK.

Therefore any serious damage on the spokes should have been picked up at the time.

unless the LBS is “creating business” for themselves..

 

[MartinC]

The spokes on the cassette side are more highly tensioned 'cos of the dish on the wheel and if you lose one on this side the wheel tends to go out of true more that if you lose one on the other side.

Spokes tend to break on the drive side at the elbow where the spoke goes through the hole in the hub flange because this is where the fatigue from the constant changes in tension as you ride is worst. This is why straight pull spokes are better.

If a spoke is overtensioned it's more likely to damage the rim than break the spoke - cracks around the nipple hole or even pulling the nipple out.

It's most likely that the spoke broke in the middle because it was damaged or faulty. Blaming the LBS is a bit paranoid.

 

[knonist]

The spokes on the cassette side are more highly tensioned 'cos of the dish on the wheel and if you lose one on this side the wheel tends to go out of true more that if you lose one on the other side.

Spokes tend to break on the drive side at the elbow where the spoke goes through the hole in the hub flange because this is where the fatigue from the constant changes in tension as you ride is worst. This is why straight pull spokes are better.

If a spoke is overtensioned it's more likely to damage the rim than break the spoke - cracks around the nipple hole or even pulling the nipple out.

It's most likely that the spoke broke in the middle because it was damaged or faulty. Blaming the LBS is a bit paranoid.

The reason I think the bike shop is responsible is because:

a) it just came back from repair 2 weeks ago, and this will be my third visit since to resolve some improperly done job.

I remembered reading something on the web saying it is not worth replacing once spoke as the rest will soon follow, thus all the spokes should be replace at once. I asked the staff if I need to do so, and they said no, and said re-tensioning will do.

 

[MartinC]

Often, but by no means always, on an old wheel the first spoke to go will lead to many 'cos they're all fatigued and the extra stress of the missing spoke can mean they all start to go.

The second spoke to go here just sounds like the random c**p that life throws up - it may have been a duff one or something nicked at some point and weakened it. This isn't something I'd expect the LBS to spot (even if they were good) and doesn't seem related to the other spoke repair.

 

[fossyant]

Expect a few spokes to go. Did the spoke snap in the middle of the spoke, or down next to the hub where the elbow is ?

The wheel sounds well tensioned if it's not gone out of true, but, it's a relatively cheap factory wheel....you can expect this to happen. You don't know the quality of the spokes used.

Had 6 spokes go on a rear wheel I was using for commuting on my MTB - factory wheels..... I've replaced the spokes and re-tensioned, and the wheel's been fine since the bike went back to off-road duties.

If it was a handbuilt wheel, by the LBS, and after replacing a spoke/re-tensioning, another had gone, then the LBS would most likely just fix it FOC !

 

[fossyant]

Ah, just noticed your other post in Commuting....not quite so cheap wheels.....

Same goes really, as they are not LBS built, so he can only repair. My colleague has a Madone 5.2 Pro, and he's always having spoke problems with his Bonty's....