Cause of broken spokes (pictures included) 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 are some pictures:
The grooves/enlargement shown at the hub are all normal.
The path to a wheel that doesn't break spokes is use premium quality spokes (DT, Sapim, and Wheelsmith are the usual poster children), set their line properly at the rim and hub, and stress relieve them properly during building. Fatigue breakages are almost universally the result of one or more of those things not happening.
Setting the spoke line is when in the early phases of building a wheel, the bends are manipulated to neatly wrap around the hub flanges, so that the bend area itself isn't floating unsupported. Stress relief is when the spokes are intentionally overloaded in tension to eliminate residual stresses at the bends that remain from forming them. If those stresses are left in place, the fatigue limit of the material can be crossed in those areas with the cyclic loading of the wheel from riding, which leads to failure. Spokes otherwise operate under the fatigue limit of the material, hence a well-built wheel being able to rarely or never break spokes in fatigue. (This is a paraphrasing of the explanation offered in &quot;The Bicycle Wheel&quot; by Jobst Brandt. It's proven true for me and many others. There is a lot more written on the subject on this site and elsewhere.)
It's likely that what happened here is your spokes were picking up fatigue at the j-bends all along from not being stress relieved and/or having their line set, and then increasing the tension exacerbated the problem, hence the breakages soon after. Increasing tension on a wheel that needs it is not a bad idea per se, but it does run this risk, especially since undertensioned wheels have a good chance of also having the above problems. Stress relieving once a wheel has been used extensively doesn't necessarily work because accumulated fatigue will have weakened the spokes some amount.
Fixing the wheel with its existing spokes may not work, because you have reason to suspect they've been heavily fatigued. The main paths to making it reliable are either rebuild with new spokes or replace it entirely.