A tire has an intended tire rotational direction and comprises a tread portion having a tread surface defined between tread edges and a pair of buttress surfaces defined as extending radially inwardly from the respective tread edges. One or each of the buttress surfaces is provided with a plurality of protrusions protruding axially outwardly and arranged in the tire circumferential direction. The protrusions include a curved protrusion which extends radially inwardly from the tread surface while curving toward the intended tire rotational direction.