The invention relates to a tyre having a radial carcass reinforcement made up of a single layer of reinforcing elements anchored in each of the beads by being turned up around a bead wire, reinforced by a stiffener. According to the invention, the two working crown layers are only present so as to form the crown reinforcement over at least 75% of the width of the tread, the absolute value of the difference between the absolute values of the angles α2 and α1 being greater than 8°, α2 being larger than α1 in terms of absolute value, the mean angle α satisfying the relationship 13+131 *exp(-L/100) < α < 20+164*exp(-L/ 100), the reinforcing elements of the carcass reinforcement being cords having, in the test known as the permeability test, a flow rate of less than 20 cm³/min, a rubber compound being present within the cords and, in the sidewall of the tyre, the profile of the outer surface of the tyre is at a constant distance from the carcass reinforcement layer between the points F and A, and meets the outer surface of the bead at the point C, forming two successive circular arcs.