A passenger-vehicle pneumatic radial tire comprising: a carcass consisting of one or more carcass plies of radially arranged cords toroidally extending between a pair of bead portions; and a tread rubber disposed on a tire radial outer side of the carcass, wherein when the tire is assembled to a rim and filled with an internal pressure of 250 kPa or more, an SW/OD ratio of a sectional width SW to an outer diameter OD (mm) of the tire is 0.26 or less if the tire has the sectional width SW of less than 165 (mm), whereas the sectional width SW and the outer diameter OD (mm) of the tire satisfy a relation of 2.135 × SW + 282.3 ≤ OD if the tire has the sectional width SW of 165 (mm) or more, CHARACTERISED IN THAT: the tread rubber has a dynamic storage modulus E' at 30 °C of 6.0 MPa to 12.0 MPa and a loss tangent tanδ at 60 °C of 0.05 to 0.15, and when a tread surface is equally divided into four regions (CP, SP) in a tire width direction, and two regions on a tire widthwise inner side are each referred to as a center portion and two regions on a tire widthwise outer side are each referred to as a shoulder portion, a shoulder circumferential sipe extending in a tire circumferential direction is disposed in the shoulder portion; wherein the shoulder portion is equally divided into three regions in the tire width direction, the shoulder circumferential sipe is disposed only in a center region of the three regions of the shoulder portion. a carcass consisting of one or more carcass plies of radially arranged cords toroidally extending between a pair of bead portions; and a tread rubber disposed on a tire radial outer side of the carcass, wherein when the tire is assembled to a rim and filled with an internal pressure of 250 kPa or more, an SW/OD ratio of a sectional width SW to an outer diameter OD (mm) of the tire is 0.26 or less if the tire has the sectional width SW of less than 165 (mm), whereas the sectional width SW and the outer diameter OD (mm) of the tire satisfy a relation of 2.135 × SW + 282.3 ≤ OD if the tire has the sectional width SW of 165 (mm) or more, CHARACTERISED IN THAT: the tread rubber has a dynamic storage modulus E' at 30 °C of 6.0 MPa to 12.0 MPa and a loss tangent tanδ at 60 °C of 0.05 to 0.15, and when a tread surface is equally divided into four regions (CP, SP) in a tire width direction, and two regions on a tire widthwise inner side are each referred to as a center portion and two regions on a tire widthwise outer side are each referred to as a shoulder portion, a shoulder circumferential sipe extending in a tire circumferential direction is disposed in the shoulder portion; wherein the shoulder portion is equally divided into three regions in the tire width direction, the shoulder circumferential sipe is disposed only in a center region of the three regions of the shoulder portion. the tread rubber has a dynamic storage modulus E' at 30 °C of 6.0 MPa to 12.0 MPa and a loss tangent tanδ at 60 °C of 0.05 to 0.15, and when a tread surface is equally divided into four regions (CP, SP) in a tire width direction, and two regions on a tire widthwise inner side are each referred to as a center portion and two regions on a tire widthwise outer side are each referred to as a shoulder portion, a shoulder circumferential sipe extending in a tire circumferential direction is disposed in the shoulder portion; wherein the shoulder portion is equally divided into three regions in the tire width direction, the shoulder circumferential sipe is disposed only in a center region of the three regions of the shoulder portion.