公开(公告)号：JPS60116508A

公开(公告)日：1985-06-24

申请号：JP22451283

申请日：1983-11-30

Applicant: BRIDGESTONE CORP

Inventor： TOKUNAGA SEIICHIROU ,  IKEDA NOBUTADA

IPC: B60C11/00 ,  B60C11/04 ,  B60C11/11

Abstract: PURPOSE:To improve resistance to rolling and resistance to abrasion in all seasons by forming a tread part of the captioned tire, to be used for a bus and the like for heavy load, into a compound tread with an upper part rubber of predetermined hardness and a lower part rubber of predetermined hardness and loss tangent. CONSTITUTION:The layer 5 of tread rubber is formed by the layer 6 of an upper part rubber in the radial outward direction and the layer 7 of a lower part rubber in the radial inward direction. Said layer 6 is made of a cap rubber of JIS hardness below 75 deg. at -20 deg.C, while said layer 7 is made of a base rubber of JIS hardness above 54 deg. at 100 deg.C and loss tangent below 0.22 at 50Hz, 25 deg.C and 2% strain. The upper part rubber 6, forming an independent block 12 with four main grooves and a lateral groove 9, is formed in such a manner as a block pattern is formed for a new product, and after abrasion of the tread, it is changed into a rib pattern which leaves a scraped part 9b as a notch. Thus, resistance to rolling and resistance to abrasion can be improved in all seasons.

公开(公告)号：JPS60203506A

公开(公告)日：1985-10-15

申请号：JP5947584

申请日：1984-03-29

Applicant: BRIDGESTONE CORP

Inventor： TOKUNAGA SEIICHIROU ,  IKEDA NOBUTADA

IPC: B60C11/00 ,  B60C11/04 ,  B60C11/11

Abstract: PURPOSE:To enhance the degree of satisfying the performance required for an all-season type pneumatic tire for a bus etc., by building up a cap rubber and a base rubber, both having prescribed characteristics, in a predetermined manner so as to form a tire tread into a compound tread part. CONSTITUTION:A compound tread part 4 is formed with both an upper rubber layer 6, which is situated above a surface connecting bottoms of shallow parts 9a-11a of transverse grooves 9-11, and a lower rubber layer 7, which is divided in transverse direction at just below the upper layer by main grooves 8 and forms a rib pattern in the peripheral direction. At this time, the upper rubber layer 6 is formed with a cap rubber whose JIS-based hardness at -20 deg.C does not exceeds 75 degrees, while the lower rubber layer 7 whose JIS-based hardness at 100 deg.C is at least 54 degrees and whose loss tangent value for 50Hz, 25 deg.C, and strain of 2% is 0.22 or less. With this constitution, the performance required for a tire can be satisfied all the year round.