Abstract: A large size pneumatic rubber tire for bad or rough roads comprises a number of main grooves in a tread of the tire arranged on both sides of a center circumferential line of the tread and in parallel with one another substantially equally oblique to the center circumferential line and a number of auxiliary grooves in the tread substantially in parallel with one another oblique in a direction opposite to the direction of the main grooves to connect the two main grooves adjacent in a circumferential direction. The main and auxiliary grooves have comparatively wide groove widths, respectively, and divide the tread into a center zone and two size zones. These zones respectively consist of circumferentially arranged respectively substantially same shaped center blocks and side blocks defined by the main and auxiliary grooves.