Off-road ultra-large tires experience different modes of heat-related fatigue failure in operation due to inherent material defects that grow into visible cracks under service loads. This study implements the cracking energy density theory to predict nucleation life of selected components of a 56/80R63 tire. The method uses an assumed intrinsic flaw, a fatigue crack growth law, and a rubber constitutive law to compute local crack driving forces from strain history loads obtained via FEA. The results show that the lower sidewall, belt endings, and inner tread lug corners are the critical regions for crack initiation with lives 5.03 x 10(5), 1.207 x 10(5), and 2.01 x 10(4) cycles, respectively.