Pneumatic tire including discharge terminal parts

A pneumatic tire comprising

• a tread portion with a tread face for contacting the ground,
• a pair of sidewall portions,
• a pair of bead portions with a bead core therein,
• a carcass extending between the bead portions,
• a belt disposed radially outside the carcass and radially inside the tread portion,
• said tread portion comprising
• a tread cap rubber and
• a tread base rubber disposed radially inside the tread cap rubber,
• said tread base rubber comprising
• a collector part disposed radially inside the tread cap rubber and
• discharge terminal parts extending radially outwardly from the collector part to the tread face, penetrating the tread cap rubber,
• the tread cap rubber being made of an insulation rubber material the volume resistivity of which is not less than 1×108 ohm cm,
• the insulation rubber material compounded from 100 parts by weight of a rubber base comprising one or more materials selected from diene rubber and copolymers of a conjugated diene monomer and an aromatic vinyl compound,
• 30 to 100 parts by weight of silica, and 3 to 20 parts by weight of carbon black,
• the tread base rubber being made of a first electrically conductive rubber material the volume resistivity of which is not more than 1×107 ohm cm,
• the first electrically conductive rubber material compounded from 100 parts by weight of a rubber base comprising one or more materials selected from diene rubber and copolymers of a conjugated diene monomer and an aromatic vinyl compound,
• 0 to 50 parts by weight of silica, and
• not less than 25 parts by weight of carbon black,
• an electrical conductor extending from said collector part to the bead portions,
• the hardness Hs1 of the insulation rubber material being less than the hardness Hs2 of the first electrically conductive rubber material at a temperature of 25 degrees C., and
• the loss tangent δ2 of the first electrically conductive rubber material being less than the loss tangent δ1 of the insulation rubber material,
• the wear resistance of the first electrically conductive rubber material being higher than the wear resistance of the insulation rubber material,
• said discharge terminal parts defining a first portion of the tread face and said tread cap rubber defining a second portion which is the remaining part of the tread face, whereby in the tread face the first portion and second portion are different from each other with respect to hardness, loss tangent and wear resistance such that in comparison with the second portion the first portion is higher in hardness, lower in loss tangent and higher in wear resistance, and wherein said discharge terminal parts include a mushroom shaped discharge terminal part which comprises a wide part at the tread face and a radially inner narrow main part extending from the wide part to the collector part.