Why am I snapping spokes so much

[Asymptotic]

So I use this wheel-set for training, just because Shimano hubs are fairly durable:

http://www.shimano.com.au/publish/conte ... ype-..html

In the last three months I have snapped 4 rear spokes, all drive-side. Have had the wheel professionally rebuilt, and made sure I was at the shop when they checked each spokes tension. I weigh 68kg, ride a 29er HT and do XCO and XCM exclusively. Rim has never been damaged in a crash,
on all instances of spokes snapping, none has been caused by rocks hitting/entering the wheel.

Am starting to wonder if there is something wrong with the hub flange perhaps? The straight pull spokes are also a pain to get replacements for as every bike shop I ring up plays the whole "your the first person we've ever heard this happening to, so we never carry these particular spare spokes"

Any ideas on alternate diagnosis's please?

[thisisatest]

you broke 3 spokes total? how many before full rebuild? full rebuild= full new spokes, right?

[Asymptotic]

First time I snapped 3 spokes - they were replaced. Yesterday I snapped one spoke, which was one of those 3 replaced.

Sorry, I should have clarified better as to what getting the wheel rebuilt meant - when the 3 spokes were replaced, the LBS loosened off all the other spokes completely and started from scratch.

[thisisatest]

i do not recall ever having a spoke that has been replaced break again.
i'm still going with my first hunch and think it's simply a bad batch of spokes.
second possibility is your frame is out of alignment. if so, and your bike is "crabbing" slightly, it's putting side load on the wheel constantly. this setup, exaggerated, is how wheel companies would test for spoke fatigue life...

[Asymptotic]

Thanks for your comments thisisatest

I don't think the frame is out of alignment (Scott Scale), as it's less than 6mths old. I don't know how common it is to get a bad batch of spokes?

TBH looking at standard spokes in comparison to straight pull, the latter appear to be so much more fragile given that only ~ 1mm of thread attaches it to the hub flange.

It's frustrating because other riders who I've talked to look at me strangely and ask if I've been riding downhill and then point to their Shimano wheels that they've had for 4+ years without incident.

[Rider10]

Where are the spokes breaking? At the nipple or at the head?

Breaking spokes is normally indicative of a poorly built wheel. Uneven spoke tension causes some spokes to do much more work than they should and that leads to breakages.

[TheRookie]

TBH looking at standard spokes in comparison to straight pull, the latter appear to be so much more fragile given that only ~ 1mm of thread attaches it to the hub flange.

Are you saying they thread into the flange, my straight pulls have a conventional nipple, only having 1mm of thread engaged implies the spoke is too short but that depends on what is actually breaking and where....spokes rarely snap in the middle and on my commuters rear wheel (bought used and done 2k miles) I've had 2 strip threads from spoke and 2 nipples snap their heads off only 2 spokes have actually snapped and that was corrosion where it entered the nipple.

[Asymptotic]

TBH looking at standard spokes in comparison to straight pull, the latter appear to be so much more fragile given that only ~ 1mm of thread attaches it to the hub flange.

Are you saying they thread into the flange, my straight pulls have a conventional nipple, only having 1mm of thread engaged implies the spoke is too short but that depends on what is actually breaking and where....spokes rarely snap in the middle and on my commuters rear wheel (bought used and done 2k miles) I've had 2 strip threads from spoke and 2 nipples snap their heads off only 2 spokes have actually snapped and that was corrosion where it entered the nipple.

Every time the spokes have snapped off at the hub flange, exactly above where they are threaded. My wheels are the opposite to yours, the nipple threads into the rim - not the hub.

Correction, I don't know where I pulled the 1mm measurement from - just measured properly and the spokes are threaded through a 9mm flange.

[thisisatest]

shimano spokes have a nipple at the rim that threads into the rim, Ksyrium-style. at the other end, the spoke itself is threaded, but it just slips through the spoke hole at the hub and is held by a very thin cylindrical "nut".
im assuming there hasnt been any damage to the wheel or right-side spokes due to a chain going over the largest cassette cog?

when it comes to your frame's alignment, its age has nothing to do with it. if it's out of alignment, it's because it was made that way. best way to look for this is to ride/coast in a straight line while another rider follows directly behind you and simply observes if the rear wheel is actually following the front. when riding without hands on the bars, if you have to lean to one side slightly to keep the bike going straight, that's a red flag.
DO NOT use a "frame alignment gauge" such as the park tool one, it measures very indirectly and is especially non-applicable with carbon frames. if someone has a frame jig or alignment table for framebuilding, that references the steerer tube, bottom bracket shell, dropouts (and possibly seatpost, but not necessary), that's ok too.

[c90sx]

i work at a shop and we see this happen time to time. if u have had all the spokes replaced and they are still breaking it might be the way you get on the bike. if you are the type of person that gets one leg on then gets a rolling start then throws there leg over then it is not uncommon to break spokes. we see this time to time. the reason for this is when you throw your leg over it puts a heavy load in one single spot of the wheal which will cause spokes to break. hope this helps.

[Zen Cyclery]

Assuming the spokes haven't been damaged from an external force, it may be worth checking the tension. This seems to be commonplace with these designs and may be a result of inadequate tension.