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.
The only force may be tension but what breaks spokes is not force but stress. The stress at both the bend and the head includes shear. Tension and shear add up but not simply. (Sophomore engineering, Morh's Circle where they weed out those who aren't up to it.) The two stresses love to hang out at stress risers. The straight portion of the spoke is in pretty close to pure tension and the after Mohr's Circle total stress is virtually the very easy to calculate average tension across the spoke section.