The purpose of this study is to improve the accuracy of durability predictions for motorcycle body components through the implementation of a fatigue analysis that uses the finite element method (FEM) to identify the fatigue failure characteristics of arc welds, die-cast aluminum alloys, and thermo-plastics. In addition to highly accurate load conditions and stress analysis, a fatigue analysis that also takes into consideration the fatigue failure mechanism is essential to making accurate durability predictions. Fatigue tests were carried out under several load conditions using specimens of several different shapes that simplified the actual structures. The fatigue life of the weld toe is assumed to be the difference of the crack propagation rate due to the loading mode. The durability of die-cast aluminum alloys was found to be sensitive to the microscopic structure due to the casting process. The factors that influenced the fatigue behavior of the plastics were the stress gradient and the viscoelastic behavior. These comprehensive fatigue characteristics were applied to the fatigue analysis codes fe-safe and FEMFAT. The master S-N curve approach was used to evaluate the fatigue of the weld zone. Then the correlation between the durability predictions and the actual life were analyzed under rough road running conditions. This procedure was found to be an effective means of accurately predicting the fatigue life of motorcycle body components.