A run-flat tire comprising: an aspect ratio being in a range of from 50% to 60%; a tread portion; a pair of sidewall 11 portions; a pair of bead portions each having a bead core therein, each of said bead portions having a thickness in a range of from 12 to 16 mm at a position that has a 17mm height from a bead base-line; a carcass consisting of a single ply of cords which extends between bead cores through the tread portion and sidewall portions; a pair of sidewall reinforcing layers each having a crescent cross-sectional shape and disposed axially inwardly of the carcass in each said sidewall portion, said sidewall reinforcing layers made of rubber having a complex elastic modulus in a range of from 6 to 12 MPa, said sidewall reinforcing layers having radially outer ends positioned higher than a buttress position that has a height (H 2) of 0.72 times a tire section height (H 0) from the bead base-line, said sidewall reinforcing layers having radially inner ends positioned lower than a first bead position that has a height (H 4) of 0.22 times of the tire section height (H 0) from the bead base-line; a pair of sidewall rubber elements each of which is disposed axially outwardly of the carcass in each said sidewall portion; and a pair of bead apex elements each of which extends and tapers radially outwardly of the tire from said bead core, the bead apex elements having a height (H 2) in a range of from 0.30 to 0.48 times of the tire section height (H 0) from the bead base-line; characterized in that the tire has the following relations to: 0.009 ≤ ti ⁢ 1 / 10.3 - 0.32 ⁢ P ⋅ LI ≤ 0.011 0.0092 ≤ ti ⁢ 2 / 8.5 - 0.32 ⁢ P ⋅ LI ≤ 0.0108 0.009 ≤ ti ⁢ 3 + ti ⁢ 4 / 7.5 - 0.32 ⁢ P ⋅ 2 ⁢ LI ≤ 0.011 and 0.0092 ≤ ts ⁢ 3 + ts ⁢ 4 / 12 ⋅ LI ≤ 0.0108 wherein "ti1" (unit: mm) is a thickness of said sidewall reinforcing layer at a tire overall-width position that has a height of 0.55 times the tire section height from the bead base-line, "ti2" (unit: mm) is a thickness of said sidewall reinforcing layer at the buttress position, "ti3" (unit: mm) is a thickness of said sidewall reinforcing layer at the first bead position, "ti 4" (unit: mm) is a thickness of said sidewall reinforcing layer at a second bead position that has a height of 0.34 times the tire section height from the bead base-line, "ts3" (unit: mm) is a thickness of said sidewall rubber element at the first bead position (H 4), "ts4" (unit: mm) is a thickness of said sidewall rubber element at the second bead position (H 5), "P" (unit: MPa) is a complex elastic modulus of said sidewall reinforcing layer, and "LI" (index) is a load index of the tire. an aspect ratio being in a range of from 50% to 60%; a tread portion; a pair of sidewall 11 portions; a pair of bead portions each having a bead core therein, each of said bead portions having a thickness in a range of from 12 to 16 mm at a position that has a 17mm height from a bead base-line; a carcass consisting of a single ply of cords which extends between bead cores through the tread portion and sidewall portions; a pair of sidewall reinforcing layers each having a crescent cross-sectional shape and disposed axially inwardly of the carcass in each said sidewall portion, said sidewall reinforcing layers made of rubber having a complex elastic modulus in a range of from 6 to 12 MPa, said sidewall reinforcing layers having radially outer ends positioned higher than a buttress position that has a height (H 2) of 0.72 times a tire section height (H 0) from the bead base-line, said sidewall reinforcing layers having radially inner ends positioned lower than a first bead position that has a height (H 4) of 0.22 times of the tire section height (H 0) from the bead base-line; a pair of sidewall rubber elements each of which is disposed axially outwardly of the carcass in each said sidewall portion; and a pair of bead apex elements each of which extends and tapers radially outwardly of the tire from said bead core, the bead apex elements having a height (H 2) in a range of from 0.30 to 0.48 times of the tire section height (H 0) from the bead base-line; characterized in that the tire has the following relations to: 0.009 ≤ ti ⁢ 1 / 10.3 - 0.32 ⁢ P ⋅ LI ≤ 0.011 0.0092 ≤ ti ⁢ 2 / 8.5 - 0.32 ⁢ P ⋅ LI ≤ 0.0108 0.009 ≤ ti ⁢ 3 + ti ⁢ 4 / 7.5 - 0.32 ⁢ P ⋅ 2 ⁢ LI ≤ 0.011 and 0.0092 ≤ ts ⁢ 3 + ts ⁢ 4 / 12 ⋅ LI ≤ 0.0108 wherein "ti1" (unit: mm) is a thickness of said sidewall reinforcing layer at a tire overall-width position that has a height of 0.55 times the tire section height from the bead base-line, "ti2" (unit: mm) is a thickness of said sidewall reinforcing layer at the buttress position, "ti3" (unit: mm) is a thickness of said sidewall reinforcing layer at the first bead position, "ti 4" (unit: mm) is a thickness of said sidewall reinforcing layer at a second bead position that has a height of 0.34 times the tire section height from the bead base-line, "ts3" (unit: mm) is a thickness of said sidewall rubber element at the first bead position (H 4), "ts4" (unit: mm) is a thickness of said sidewall rubber element at the second bead position (H 5), "P" (unit: MPa) is a complex elastic modulus of said sidewall reinforcing layer, and "LI" (index) is a load index of the tire.