High performance tire tread

A pneumatic radial tire comprising a tread provided with at least two longitudinal main grooves extending circumferentially in a substantially zigzag or wavy line to divide the tread width into two tread shoulder parts and a tread crown part therebetween, said crown part having a width of about 30 to 65% of the tread width;

• each tread shoulder part having a plurality of generally axially extending narrow grooves to form circumferentially substantially separated blocks;
• the width of the narrow grooves being in a range of 0.5 to 5 mm and said narrow grooves having a volume index in a range of 2.5 to 15;
• each shoulder part having a circumferential stiffness index in a range of 30 to 70;
• wherein the circumferential stiffness index in the shoulder part and the volume index of the narrow grooves are defined as follows:
• the Volume Index=V/(SXd)X100
• wherein:
• V=total volume of the cut grooves in the shoulder part
• S=surface area of the shoulder part
• d=depth of the longitudinal main groove
• the Circumferential Stiffness Index=(Kpt/Kpo)X100
• wherein:
• Kpt=circumferential stiffness in the shoulder part after the narrow grooves are provided
• Kpo=circumferential stiffness in the shoulder part before the narrow grooves are provided
• Circumferential Stiffness=F/y
• wherein:
• F=tangential force in the circumferential direction of the tire at the ground contacting surface of the shoulder part
• y=variation of the ground contacting surface in the circumferential direction of the tire.