The first part of this paper will outline the conception of the testing apparatus (Figure 1), along with its operation and preliminary results. The second part of the paper will discuss a new methodology used to correlate the dependence of crack growth rate for strain crystallizing natural rubbers in terms of tearing energy. The tearing energy which depends on the type of elastomer, geometry and stress strain behavior of a particular specimen demonstrates a direct correlation with the crack growth rate at different R-ratios (= min tearing energy/max tearing energy).