Pneumatic tire with tread having sipes with expanded diameter sections

A pneumatic tire including a plurality of land blocks defined by circumferential grooves extending in a tire circumferential direction and lateral grooves extending in a tread width direction, each of the land blocks provided with a plurality of sipes formed to extend to a predetermined depth from a tread surface inward in a tire radial direction, each of the sipes having an end portion communicating with at least any one of the circumferential grooves and the lateral grooves, at least one of the plurality of sipes including an expanded diameter section on an inner end of the sipe in the tire radial direction, the expanded diameter section formed by increasing a width of the sipe, wherein

• in a bottom portion of the sipe, a shallow bottom portion where the depth of the sipe is smallest is formed in a center portion of the sipe in a longitudinal direction thereof,
• the expanded diameter section is smallest in diameter in a center portion thereof and largest in diameter in side portions thereof,
• in the center portion of the expanded diameter section, the expanded diameter section curves and extends from the shallow bottom portion toward each of sidewalls of the land block, and increases gradually in size from the shallow bottom portion toward each of the sidewalls of the land block, and
• each side portion of the expanded diameter section has a substantially constant diameter along a length of 10% to 35% of the entire length of the expanded diameter section from both ends of the expanded diameter section in the longitudinal direction thereof.