Yesterday I broke yet another spoke in my Shimano R550 rear wheel. Again it was the left non-drive side, right at where the spoke enter the rim. The weather was miserable, just barely not raining, the sky dark grey, just over 10°C, humidity 99.999% (I guess). I only had 3–4 km to Høje Taastrup station when I discovered the broken spoke, it was held in place by the wheel magnet, so it didn't rattle around like the first time. I managed to get to the station before the wheel got too bad.
The wheels are radially laced in front and the drive side rear, 2× in the non-drive side rear, which is a very nice way to reduce the dish needed in the rear wheel because of the casette. My theory is that the spokes break where they enter the rim because they enter the rim at an angle and the holes in the rim are drilled perpendicular to the rim, not because they are too weak for the tension. This also explain why the radial spokes don't break, even though the rear drive-side spokes must have a significantly higher tension than all the others.
Anyway, I'm pissed off, especially because the Danish Shimano distributor define spokes as a wearing part, hence they don't repair it on the guarantee, and it's just over 20 € each time (How can a spoke cost that much?).
I certainly won't buy Shimano wheels again.