Poor quality spokes on Trek Xcaliber 8 (Bontrager Mustang Elite) rims

[juzzle]

Over the last 8 weeks, I've traveled 4000 km across mainly smooth asphalt pavements in Europe. in that time, 22 of my 28 rear rims spokes have failed - 3/5 times at the hub (shearing at the bent return). I've had the rim professionally respoked and straightened three times, mainly with silver spokes (as opposed to black) due difficulties finding the right size black spokes. After each straightening, the rim is true, balanced and the spokes tight (and on note). However, it never lasts long.

Only one of the new silver spokes has failed. My suspicion, albeit based on limited evidence is that a) black spokes are somehow deficient, b) the spokes provided by Bontrager are rubbish, and c) that the 29" rim isn't the most durable rim for long journeys with panniers (I am carrying a modest 22 kg balanced across two paniers).

I've also noticed that another form of failure is the spoke pulling out from the nipple at the rim. It's as if the thread and nipple are not intimately connected sufficient to resist the stress.

I have been extremely gentle when riding to avoid repeat failures - staying the saddle with smooth controlled movements, and avoiding bumps and cobbles wherever possible - however it seems not matter what I do, failure of the spokes and the chain reaction that follows is unavoidable.

I consider this a design flaw. Either rim is too soft (encouraging concentric or lateral movement and fatigue) or the 29" rim needs both thicker spokes and perhaps more of them.

Does anyone have any thoughts on the matter of spoke durability?

[Trevtassie]

Not enough spokes

[tcdev]

You don't mention how much you weigh! I'm ~106kg (~230lbs) and I had two spokes snap within a few weeks of one another on my rear 29" Giant PXC-2 rim (32 spokes). The LBS referred it back to Giant and they rebuilt both wheels (under warranty) with heavier-duty spokes and I haven't had an issue since.

[2rismo]

I bash the crap out of my X-Cal 8 but I don't carry luggage and I'm 86kg.