A tyre comprising a tread portion , wherein the tread portion is provided with a tread ground contacting surface and at least one main groove having an opening at the tread ground contacting surface and extending continuously in a tyre circumferential direction, in a reference state in which the tyre is mounted on a standard rim, inflated to a standard inner pressure, and placed on a flat surface with zero camber angle, when the tread portion of the tyre is loaded with a standard tyre load, the tread ground contacting surface is in contact with the flat surface, the at least one main groove has a bottom surface and two groove wall surfaces extending outwardly in a tyre radial direction from the bottom surface , in a lateral cross section taken perpendicular to a length direction of the at least one main groove , at least one of the two groove wall surfaces is provided with an inner groove wall portion connected with the bottom surface and a protruding portion connected with the inner groove wall portion and having a protruding end protruding inwardly in a groove width direction from a groove reference line obtained by extending the inner groove wall portion , characterized in that the protruding portion has an inclined surface portion which is inclined and extends between the protruding end and the tread ground contacting surface , wherein an angle between the inclined surface portion and the tread ground contacting surface is an obtuse angle of 160 degrees or more, and in the reference state, when a tyre load of 1.20 times the standard tyre load is applied to the tread portion , the whole inclined surface portion is in contact with the flat surface. the tread portion is provided with a tread ground contacting surface and at least one main groove having an opening at the tread ground contacting surface and extending continuously in a tyre circumferential direction, in a reference state in which the tyre is mounted on a standard rim, inflated to a standard inner pressure, and placed on a flat surface with zero camber angle, when the tread portion of the tyre is loaded with a standard tyre load, the tread ground contacting surface is in contact with the flat surface, the at least one main groove has a bottom surface and two groove wall surfaces extending outwardly in a tyre radial direction from the bottom surface , in a lateral cross section taken perpendicular to a length direction of the at least one main groove , at least one of the two groove wall surfaces is provided with an inner groove wall portion connected with the bottom surface and a protruding portion connected with the inner groove wall portion and having a protruding end protruding inwardly in a groove width direction from a groove reference line obtained by extending the inner groove wall portion , characterized in that the protruding portion has an inclined surface portion which is inclined and extends between the protruding end and the tread ground contacting surface , wherein an angle between the inclined surface portion and the tread ground contacting surface is an obtuse angle of 160 degrees or more, and in the reference state, when a tyre load of 1.20 times the standard tyre load is applied to the tread portion , the whole inclined surface portion is in contact with the flat surface. <EOS>