A tire comprising a tread portion, a pair of sidewall portions continuous on both sides of the tread portion, bead portions continuous on each sidewall portion, side reinforcing rubbers, and a carcass formed of plies of radially arranged cords extending toroidally between the pair of bead portions, wherein: when the tire is mounted to a rim, and an internal pressure of 250 kPa or more is applied to the tire, in a case where a sectional width SW of the tire is less than 165 mm, a ratio of the sectional width SW to an outer diameter OD of the tire, SW/OD, is 0.26 or less; and in a case where the sectional width SW of the tire is 165 mm or more, the sectional width SW and the outer diameter OD of the tire satisfy a relation expression OD ≥ 2.135 × SW + 282.3 mm; a tire radial outer side of the carcass further includes a belt formed of one or more belt layers; and the tread portion has one or more circumferential grooves (10, 11, 12, 17, 18, 19) continuously extending in a tire circumferential direction; characterised in that the tire is a run-flat tire; in that the side reinforcing rubbers comprise crescent-like cross section disposed on the sidewall portions; in that a relation expression 0.5 ≤ WG / WB ≤ 0.8, is satisfied, where WB represents a half width in the tire width direction of a belt layer maximum in width in the tire width direction of the one or more belt layers in a tire widthwise cross section in a reference state where the tire is mounted to a rim and filled with a predetermined internal pressure with no load applied thereon, and WG represents a tire widthwise distance from a tire widthwise end of the belt layer maximum in width in the tire width direction to a tire widthwise center position of a circumferential groove in the tire widthwise outermost side of the one or more circumferential grooves; and in that the 50% stretch modulus of the side reinforcing rubbers is 1.5 to 6.0 MPa. when the tire is mounted to a rim, and an internal pressure of 250 kPa or more is applied to the tire, in a case where a sectional width SW of the tire is less than 165 mm, a ratio of the sectional width SW to an outer diameter OD of the tire, SW/OD, is 0.26 or less; and in a case where the sectional width SW of the tire is 165 mm or more, the sectional width SW and the outer diameter OD of the tire satisfy a relation expression OD ≥ 2.135 × SW + 282.3 mm; a tire radial outer side of the carcass further includes a belt formed of one or more belt layers; and the tread portion has one or more circumferential grooves (10, 11, 12, 17, 18, 19) continuously extending in a tire circumferential direction; characterised in that the tire is a run-flat tire; in that the side reinforcing rubbers comprise crescent-like cross section disposed on the sidewall portions; in that a relation expression 0.5 ≤ WG / WB ≤ 0.8, is satisfied, where WB represents a half width in the tire width direction of a belt layer maximum in width in the tire width direction of the one or more belt layers in a tire widthwise cross section in a reference state where the tire is mounted to a rim and filled with a predetermined internal pressure with no load applied thereon, and WG represents a tire widthwise distance from a tire widthwise end of the belt layer maximum in width in the tire width direction to a tire widthwise center position of a circumferential groove in the tire widthwise outermost side of the one or more circumferential grooves; and in that the 50% stretch modulus of the side reinforcing rubbers is 1.5 to 6.0 MPa.