1. A method of designing a tire profile including a tread, a shoulder, a sidewall, and an adjustment portion between the shoulder and the sidewall, and wherein the adjustment portion is flat, the method comprising the steps of: inputting numeric values of a radius of curvature of the shoulder and an inclination angle of the adjustment portion; and using a computer to calculate numeric values of a length of the adjustment portion and a radius of curvature of an upper sidewall based on the input numeric values in order to provide the adjustment portion being in contact with the shoulder at an upper end and being in contact with the sidewall at a lower end.