Pneumatic tire for automobile and its fabrication method

A method of fabricating a pneumatic tire for an automobile, comprising the steps of:

• wrapping belt layers on an outer periphery of a forming drum;
• and
• wrapping a strip member comprising an unvulcanized rubber composition member having a width of 5 through 30 mm and a thickness of 0.5 through 3.0 mm on an outer peripheral side of the belt layers in a tire circumferential direction while overlapping at least a portion thereof at every turn;
• arranging two layers of the belt layers including a first belt layer on a side of a carcass layer and a second layer on an outer peripheral side thereof on an outer side of the carcass layer in the tread portion and constituting the tread portion in a two-layered structure of a cap tread layer and an under tread layer;
• constituting the under tread layer by a center region defined by a range of 30 through 70% of a width of the first belt layer centering on a tire equator and a range of 0.5 through 2.0 mm as a center region thickness T1 from the second belt layer in a tire diameter direction and shoulder regions each of which are defined by a region between the center region and an outer side, a range of 1.0 through 5.0 mm as a shoulder region thickness T2 thereof and a distance between an end portion of the first belt layer and the outer side being 30 mm at a maximum, said center region and said shoulder regions comprising rubber composition members different from each other;
• arranging at the center region a rubber layer having a blending system in which JIS-A hardness falls in a range of 65 through 80 and an amount of blending a softening member relative to rubber 100 weight parts is smaller than a blending amount thereof of the cap tread layer by 10 weight parts or more;
• and
• arranging art the shoulder regions a rubber layer having a blending system in which the JIS-A hardess falls in a range of 50 through 70 and an amount of blending a softening agent relative to the rubber 100 weight parts is smaller than a blending amount thereof of the cap tread layer by 10 weight parts of more;
• wherein a kind of the unvulcanized rubber composition constituting the strip member is made to differ in accordance with a position of a tire meridian section to thereby form a tread portion having a multiple composition structure;
• wherein a ratio (tan δ2/tan δ1) of loss tangent (tan δ2) of the rubber layer of the shoulder regions to loss tangent (tan δ1) of the rubber layer of the center region is ⅔ or smaller;
• wherein the kind of the unvulcanized rubber composition constituting the strip member is made to differ in accordance with positions of the cap tread layer and the under tread layer to thereby form the tread portion having a multiple composition structure;
• and
• wherein the shoulder region thickness T2 is larger than the center region thickness T1.