Reduced rolling resistance pneumatic radial tire

Claim 1

A heavy duty pneumatic radial tire comprising; a carcass consisting of at least one layer of inextensible cords substantially radially arranged, a breaker consisting of at least two layers of metal cords to form a main reinforcement with said carcass, and bead portions including stiffeners, said carcass having a ratio of radii R/R' within a range of 0.65-0.85 and f within a range of 3-8 mm when said tire mounted on a a normal rim is filled with a normal inner pressure, R' is a radius of a standard circle passing through points B, E, C, wherein point B is an intersection of the carcass and a line extending in parallel with a rotating axis of the tire and passing through a point spaced from a rim diameter line l by a distance h that is 15% of radial height SH of the tire, point C is an intersection of the carcass and a line extending through the point B and perpendicular to said rotating axis of the tire, and point E is an intersection of a line extending through a middle point D of a line segment BC and in parallel with said rotating axis and a line extending through a carcass maximum width point F and perpendicular to the rotating axis, R is a radius of profile curvature of a shoulder passing through said point C, and f is the maximum distance between an arc of said standard circle and the remaining carcass line smoothly extending from said profile curvature of said shoulder to said point B having a single carcass curvature reverse position and wherein when said tire mounted on the normal rim is filled with the normal inner pressure, each sidewall of the tire has a radial profile over a radially inner zone of the sidewall of 20-45% of the radial height SH such that a curvature 1/ρ of a surface of the sidewall at a location 32.5% of the radial height corresponding to a center of the profile is less than 6×10 -3 mm -1 , said curvature being a mean value of curvature obtained by differentiating a cubic curve indicating the profile, and when the tire mounted on the rim is filled with the inner pressure from 5% of a nominal pressure to the normal inner pressure, a bulged deformation in the zone radially inward of the carcass maximum width position being much greater than that in the zone radially outward of the carcass maximum width position which is substantially unnoticeable.