Pneumatic tire with directional tread

A pneumatic tire for high speed passenger cars comprising;

• a directional tread located at a crown portion of a toroidal casing and formed with a plurality of blocks partitioned by a plurality of circumferential grooves, a plurality of U-shaped cross-section transversal grooves arranged into a herringbone pattern at substantially regular intervals along a tire circumferential direction in such a way as to extend from near a tread central area to both tread side areas at an inclination angle with respect to the tread circumferential direction, the tire rotational direction being determined in such a way that a tread central portion of each of the transversal grooves is first brought into contact with the ground, wherein the U-shaped cross-section of each of said transversal grooves is formed in such a way that a radius (R.sub.1) of curvature of a step-out side corner between a side wall and a bottom of each transversal groove which is first brought into contact with the ground along a tire rotating direction is determined smaller than that (R.sub.2) of a kick-out side corner therebetween which is afterward brought into contact with the ground, a ratio R.sub.2 /R.sub.1 of radius of curvature is in the range of 2:1 to 5:1, and the U-shaped cross-section of some of said transversal grooves is formed in such a way that an inclination angle (.theta..sub.1) with respect to a tire radial direction of the step-out side wall which is first brought into contact with the ground is determined preferably smaller than that (.theta..sub.2) of the kick-out side wall which is afterward brought into contact with the ground.