HEAVY DUTY PNEUMATIC TIRE
FIG2 is a cross-sectional view showing a side portion of the tire shown in FIG1 
FIG2 shows the flexible zone of the tire 2 shown in FIG1. In FIG2, the right-left direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the surface of the sheet of FIG2 is the circumferential direction of the tire 2. In FIG2, an arrow R represents the radius of the arc representing the shape of the body portion 42. The radius R is specified on the basis of the shape of the inner surface of the body portion 42. In FIG2, a solid line LG is a reference line that passes through the axially outer edge of the shoulder circumferential groove 28s and that extends in the radial direction. A reference character PG is the intersection between the reference line LG and the inner surface of the body portion 42. The intersection PG is a reference point of the portion immediately below the shoulder circumferential groove 28s, in the body portion 42. In the tire 2, a length WR from the end TE of the tread surface 22 to the axially outer edge of the shoulder circumferential groove 28s is normally set in a range of not less than 10% and not greater than 25% of the tread width TW. The length WR is measured along the tread surface 22.
cross-sectional view
14
belt
12
carcass
38
outer end
18
inner liner
42
body portion
16
cushion layer cushion layers
36
apex
['1. A heavy duty pneumatic tire having an aspect ratio of not greater than 75%, comprising: a tread configured to, at a tread surface thereof, come into contact with a road surface; a pair of sidewalls each extending inward in a radial direction from an end of the tread; a pair of beads located radially inward of the sidewalls; a carcass extending from one bead to the other bead, at an inner side of the tread and the pair of sidewalls; a belt located between the tread and the carcass; and a pair of cushion layers each located between an end of the belt and the carcass, wherein each bead includes a core and an apex located radially outward of the core, in the radial direction, a zone from an inner end of each cushion layer to an outer end of the apex corresponding thereto is a flexible zone, and a ratio of a length in the radial direction of the flexible zone to a cross-sectional height of the carcass is not less than 0.25 and not greater than 0.', '2. 2. The heavy duty pneumatic tire according to claim 1, wherein the carcass includes at least one carcass ply, the carcass ply includes: a body portion which extends between one core and the other core; and a pair of turned-up portions which are connected with the body portion and are  turned up around the cores from an inner side toward an outer side in an axial direction, and the body portion in the flexible zone has a shape represented by an arc.']