A pneumatic radial tire for passenger vehicles comprising a carcass composed of plies of radially arranged cords toroidally extending between a pair of bead portions, wherein, when the tire is fitted on a rim and prepared to have an internal pressure of 250 kPa or higher, if the tire has a section width SW of less than 165 (mm), an SW/OD ratio of the section width SW to an outer diameter OD of the tire is 0.26 or less, if the tire has a section width SW of 165 (mm) or greater, the section width SW and the outer diameter OD of the tire satisfy the relational expression: OD ≥ 2.135 × SW + 282.3, characterised in that the tire has two circumferential main grooves (2, 2a, 2b) extending in a tread circumference direction on a tread, the two circumferential main grooves (2, 2a, 2b) and ground contact ends in a tire width direction defining a plurality of land rows (3, 3a, 3b), the land rows (3, 3a, 3b) include a center land row (3, 3a) defined between the two circumferential main grooves (2, 2a, 2b), and two outer land rows (3, 3b) defined by the ground contact ends in the tire width direction and the circumferential main grooves (2, 2a, 2b), the center land row (3, 3a) is a rib-shaped land continuously extending in the tread circumference direction, the center land row (3, 3a) having center lug grooves each opening into one of the two circumferential main grooves (2, 2a, 2b) and terminating within the center land row (3, 3a), the outer land rows (3, 3b) are rib-shaped lands continuously extending in the tread circumference direction, each of the outer land rows (3, 3b) having outer lug grooves and outer auxiliary lug grooves, the outer lug grooves each opening into one of the ground contact ends in the tire width direction and terminating within the outer land row (3, 3b), the outer auxiliary lug grooves opening into the circumferential main groove (2, 2a, 2b) defining the outer land row (3, 3b), the outer auxiliary lug grooves having a groove width smaller than the groove width of the outer lug grooves and extending in a tread width direction; wherein the center land row (3, 3a) has first center lug grooves each opening into one of the two circumferential main grooves (2, 2a) and terminating within the center land row (3, 3a), the one of the circumferential main grooves (2, 2a) being on the side that faces outward when the tire is fitted; and the center land row (3, 3a) further has second center lug grooves or center auxiliary lug grooves, the second center lug grooves each opening into the other of the circumferential main grooves (2, 2b) and terminating within the center land row (3, 3a), the center auxiliary lug grooves each opening into the other of the circumferential main grooves (2, 2b) to extend in the tread width direction within the center land row (3, 3a), the center auxiliary lug grooves having a groove width smaller than the groove width of the center lug grooves; the first center lug grooves each opening into the one of the circumferential main grooves (2, 2a) and the second center lug grooves or the center auxiliary lug grooves each opening into the other of the circumferential main grooves (2, 2b) are alternately formed in the tread circumference direction.