A pneumatic tire for dirt track racing comprising lateral and circumferential grooves forming blocks on the tread surface. The blocks have leading and trailing edge walls. The trailing edge walls of the blocks are buttressed by inclining the walls at an angle of 20.degree.-60.degree. relative to a line perpendicular to a tangent to the tread, and the edge wall extends into the groove by a distance of approximately one-half the tread width. The leading edge walls of the blocks have a radially outer portion inclined at about zero degrees and a radially inner portion have a radius of curvature of infinity or less, wherein the intersection point between the two portions is at about one-half the groove depth.