A pneumatic tyre comprising: a pair of bead portions having respective bead cores therein, each bead core defining a core innermost end in a tyre radial direction; a carcass ply comprising a main portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions turned up around the respective bead cores from axially inside to outside of the tyre; and an inner liner having an air-impermeable property and extending between the pair of bead portions, wherein in each of the pair of bead portions, the inner liner comprises an innermost end in the tyre radial direction located inwardly of the core innermost ends in the tyre radial direction, characterized in that in a non-rim-assembled state, the pair of bead portions has a bead base diameter being less than 99.7% of a rim diameter (Da) of a standard wheel rim on which the pneumatic tyre is to be mounted, wherein the non-rim-assembled state is defined as a state in which the bead portions are held in such a manner that a distance in the tyre axial direction between bead outer surfaces is equal to a rim width (Wt) of the standard wheel rim, and the bead base diameter is defined as a diameter at an intersection of a tyre radial line (y) and a surface of the bead portion, wherein the tyre radial line (y) passes through a position located in a distance of 1.5 mm inwardly in the tyre axial direction away from an intersection point of a bead outer surface and a tyre axial line that passes a middle-height position of the bead core in the tyre radial direction, and wherein in each of the pair of bead portions, a ratio W/Wa is equal to or more than 1.20 and a ratio W/Wb is greater than 4.50, where "W" represents a maximum thickness in the tyre axial direction of the bead portion, "Wa" represents a carcass thickness from an inner surface in the tyre axial direction of the main portion to an outer surface in the tyre axial direction of the turn-up portion at a middle-height position of the bead core in the tyre radial direction, and "Wb" represents an axial thickness in the tyre axial direction from the outer surface of the turn-up portion to an outer surface of the bead portion at the middle-height position. a pair of bead portions having respective bead cores therein, each bead core defining a core innermost end in a tyre radial direction; a carcass ply comprising a main portion extending between the bead cores of the pair of bead portions, and a pair of turn-up portions turned up around the respective bead cores from axially inside to outside of the tyre; and an inner liner having an air-impermeable property and extending between the pair of bead portions, wherein in each of the pair of bead portions, the inner liner comprises an innermost end in the tyre radial direction located inwardly of the core innermost ends in the tyre radial direction, characterized in that in a non-rim-assembled state, the pair of bead portions has a bead base diameter being less than 99.7% of a rim diameter (Da) of a standard wheel rim on which the pneumatic tyre is to be mounted, wherein the non-rim-assembled state is defined as a state in which the bead portions are held in such a manner that a distance in the tyre axial direction between bead outer surfaces is equal to a rim width (Wt) of the standard wheel rim, and the bead base diameter is defined as a diameter at an intersection of a tyre radial line (y) and a surface of the bead portion, wherein the tyre radial line (y) passes through a position located in a distance of 1.5 mm inwardly in the tyre axial direction away from an intersection point of a bead outer surface and a tyre axial line that passes a middle-height position of the bead core in the tyre radial direction, and wherein in each of the pair of bead portions, a ratio W/Wa is equal to or more than 1.20 and a ratio W/Wb is greater than 4.50, where "W" represents a maximum thickness in the tyre axial direction of the bead portion, "Wa" represents a carcass thickness from an inner surface in the tyre axial direction of the main portion to an outer surface in the tyre axial direction of the turn-up portion at a middle-height position of the bead core in the tyre radial direction, and "Wb" represents an axial thickness in the tyre axial direction from the outer surface of the turn-up portion to an outer surface of the bead portion at the middle-height position.