Pneumatic tire having specified grounding tread

A pneumatic tire comprising:

• a carcass layer;
• a belt layer being disposed on a periphery of the carcass layer;
• a tread rubber including a cap tread and an undertread;
• a pair of side wall rubbers;
• a pair of rim cushion rubbers;
• and a rubber grounding tread that is exposed to a road contact surface of the tread rubber and penetrates the cap tread and the undertread to contact the belt layer in an electrically conductive manner;
• the grounding tread including a widened portion having a cross-sectional area that widens toward a contact surface with the belt layer at a contact portion with the belt layer;
• the widened portion of the grounding tread having a profile shape that bulges outward in a tire width direction;
• the undertread including a thickened portion that has a gauge that increases toward each contact surface with the grounding tread at the portion of the grounding tread penetrating the undertread;
• and
• a gauge G1 of a flat portion of the undertread and a gauge G2 of the thickened portion of the undertread have a relationship of 1.5≤G2/G1≤2.5.