Originally Posted by
cyccommute
I can’t agree. The only force on a spoke is tension. There is no other force acting on the spoke at all. In fact, if you try to compress a wire spoke, it will simple collapse. Fatigue of the spoke head is related to the cycle of tension decreasing and increasing as the spoke moves past the contact patch as the wheel rolls down the road.
Yes, however, the idea is that they do not fail in use because of excessive tensile loading but due to fatigue from repetitive cyclic tensile loading.
If it were a simple tensile strength issue, the spokes would fail as soon as you sat on the seat or hit your first bump.
Rather, it is that initial pre-load overlaid with the successive stress reduction/relaxation and re-application of the load as the wheel rotates that causes eventual fatigue life failure (look up S-N curves).