Plastic deformation causes the mechanical properties of the spoke to change due to 'work hardening.' This is shown by the positive slope of the stress strain curve in the plastic region. This work hardening increases the yield stress of the cold worked wire and decreases its ductility. The effects of work hardening may be reduced by heating the wire to a high temperature (700 C). This is illustrated below.

The ductility of the two states can be estimated by:
Percent Elongation to Fracture = 100 (L_F - L₀ /L₀)

The yield stress can be estimated from the break point between the steep linear elastic region of these curves and the plastic deformation region with a slope about 1% of that in the elastic range. After annealing the yield stress is reduced to about 20% of that of the cold worked sample

From: McMahon & Graham,
"The Bicycle & the Walkman," Merion (1992)