Low aspect ratio truck tire

A pneumatic radial ply truck tire with an aspect ratio below 0.70 having a tread, a casing including two sidewalls, one or more radial plies extending from and wrapped about two annular beads and a belt reinforcement structure located radially between the tread and the plies, the tread having a plurality of circumferentially extending continuous grooves delimiting a plurality of tread ribs, the radially outer surfaces of the plurality of tread ribs defining a radially outer tread surface, the axially outer edges of the tread surface being adjacent to the sidewalls, the distance halfway between the tread edges defining the centerline of the tread:

• in a cross section of the tread, the radially outer tread surface has a maximum diameter D at the tread centerline and, on each side of the centerline, three radii of curvature R.sub.1, R.sub.2, and R.sub.3 wherein the first radius of curvature R.sub.1, having its center C1 substantially on the equatorial plane, extends from a point P0 on the centerline of the tread to a point P1 located in the range of between 30% and 50% of half the treadwidth from P0 defining thereby a first radially outer convex tread surface;
• the second radius of curvature R.sub.2, having its center C2 substantially on a line passing through P1 and C1, extends from the point P1 to a point P2 located in the range of between 70% and 90% of half the treadwidth from P0 defining thereby a second radially outer convex tread surface;
• the third radius of curvature R.sub.3, having its center C3 external to the tire and substantially on a line passing through P2 and C2 and extending from the point P2 to the tread edge defining thereby a third radially outer concave tread surface.