Highly durable, lightweight tires of a pneumatic radial type for passenger cars are constructed with a tread portion having on its outer peripheral surface a plurality of grooves arranged circumferentially of the tire and a belt layer formed from an array of steel cords and disposed in the tread. Each of the steel cords results from twisting a selected number of steel filaments each of specified contents of C, Si and Ni and has a specified level of tensile strength. The distance of rubber from a bottom end of each of the grooves to an outer surface of the steel cord array is defined to be of a specified range as determined cross-sectionally of the tire.