Crack growth plays an important role in the durability of tires, and it is necessary to evaluate the characteristics of crack growth and tearing energy accurately. Since a crack around the belt edge is subjected mainly to interlaminar shear deformation, a Mode III fatigue test method was developed. In addition, a peel test method was developed to assess the tearing energy. Based on the fatigue and peel test results, the effects of heat aging, temperature and belt stiffness were analyzed. Based on the FE simulation and test results obtained in this study, the following conclusions could be reached. (A new fatigue test device was developed considering the loading mode around the belt edge of tires, and the fatigue test was conducted to analyze the effects of the heat aging, temperature and belt stiffness. As a result, it was shown that the crack growth amount of the specimens heat aged and fatigue tested at high temperature was bigger than that of the specimens fatigue tested at ambient temperature, and the belt stiffness rarely affected the crack growth amount. A new peel test device was developed to measure the tearing energy of tire specimens by minimizing the variance of the strain and kinetic energies, and the converged peel forces were obtained. An equation for the tearing energy of a specimen peel tested using the peel test device developed in this study was proposed. In the equation, the strain occurring in the upper half can be taken into account. Peel tests were conducted for virgin specimens, specimens fatigue tested at ambient temperature, and specimens heat aged and fatigue tested at high temperature. It was shown that the tearing energy of the virgin specimens was similar to that of the specimens fatigue tested at ambent temperature. This means that fatigue did not affect the tearing energy significantly. The tearing energy of the specimens peel tested at high temperature was smaller than that of the specimens peel tested at ambient temperature. This means that temperature affected the tearing energy significantly, but the belt stiffness did not. Specimen A had a higher tearing energy at ambient temperature and at high temperature than specimens Bj and B2. In addition, its tearing energy did not decrease significantly as temperature increased. This result was in agreement with less crack growth in the fatigue tests. In summary, it is needed to develop rubber of which the critical tearing energy is less affected by temperature to improve the fatigue life of tires.