In a ground-contact surface shape of a tire, when a tangent angle formed between an axial direction of the tire and a tangent X at each point P on a profile line of the tire is defined as .theta., a tangent angle .theta.1 in a ground-contact end point Pd is 25.degree. or smaller. When a minimum value of the tangent angle .theta. in a region Y which is separated away from a tire equator C by a distance in a range of not less than 0.4 times but not more than 0.7 times a half of the ground-contact width of the tread is defined as .theta.2, and a tangent angle at a 0.9 times point Pq which is separated away from the tire equator C by a distance of 0.9 times the half of the ground-contact width of the tread is defined as .theta.3, a difference (.theta.3-.theta.2) is set in a range of not less than -10.degree. but not more than +10.degree..