I never had this problem before. Two spokes on the drive side of my road bike's rear wheel broke at the J bend, and I'm trying to identify the cause. The wheel has 32 spokes total, made of steel, laced in a 3 cross pattern, and each spoke has a width of 2mm across all its length.
The first one broke when I accelerated hard at a green light, and the second one when I got home and squeezed the spokes with my hands to check their tension. I assume they were fatigued/damaged beforehand, and the rest of them are too, which will keep breaking if I continue to ride the wheel.
I didn't do any jumps, and I weigh 68kg (150 pounds). But I did lots of climbing (which shifts more weight to the rear wheel), descending (which puts lateral stress on the spokes when leaning into corners), accelerations, and some occasional gravel riding. The 35mm wide tires were always inflated to 65-85 psi.
1000km ago, the wheel got slightly out of true (2mm at most) after being ridden for about 1500km. So I trued the wheel, adding a bit more tension to the spokes at the same time. I don't have a tension meter, but it seemed pretty tensioned, similar to the other wheels I have now or had in the past (not all of them built by me) which never had any issues. The wheel remained true until the spokes broke.
I'm not sure whether the spokes are bad quality, the hub is, or both. The spokes seem to have bitten into / enlarged the holes in the aluminium hub, and I don't know if that's normal.
Is it fine to replace all the spokes, or is the hub faulty and is better to buy an entire new wheel?
Here with an update 2 years after rebuilding the wheel, and many thousand kilometers
When rebuilding the wheel I was more careful to:
- enough tension into the spokes (following the method in Jobst Brandt's book);
- as even as possible spoke tension on each side; I used a tone analyzer app on my smartphone and tried to have each spoke produce the same frequency sound:
|Rear||1||2||3||4||5||6||7||8||9||10||11||12||13||14||15||16||Avg||Max delta (hz)||Max delta (%)|
|Non drive (hz)||454||460||450||468||454||455||456||452||453||455||450||456||458||459||469||450||456.19||19||4.22%|
- stress relieving the spokes;
- setting each spoke's line.
No spoke has broken since then. The wheel didn't even need to be retrued. It's still true today. The advice given in the answers and the information in the book proved to be very accurate and helpful.