Pneumatic tire for front wheel of motorcycle

Abstract

A pneumatic tire for a front wheel of a motorcycle comprises a pair of bead cores, a radial carcass toroidally extending between the pair of bead portions, a belt disposed on a radially outer surface of the carcass, and a tread portion disposed thereon, wherein the carcass is comprised of at least one carcass ply containing organic fiber cords, and the belt is a spiral belt layer formed by spirally winding a continuous rubberized cord or a continuous ribbon-shaped body containing plural cords therein in a widthwise direction of the tire, and the tread portion has a two-layer structure comprised of a cap rubber layer and a base rubber layer in at least a central region in the widthwise direction of the tire, or a reinforcing layer is disposed inside an innermost carcass ply or on an inner surface of an innerliner, or the bead core is a helically wound laminate of a single steel wire having a polygonal shape at a section of the bead core in the radial direction.

What is claimed is:  
     
         1 . A pneumatic tire for a front wheel of a motorcycle comprising a pair of bead cores embedded in a pair of bead portions, a carcass toroidally extending between the pair of bead portions and wound around the bead core from an inside of the tire toward an outside thereof, a belt disposed on an outer surface of a crown portion of the carcass in a radial direction of the tire, and a tread portion disposed on an outer surface of the belt in the radial direction, wherein the carcass is comprised of at least one carcass ply containing organic fiber cords arranged at a cord angle of 60-90° with respect to an equatorial plane of the tire, and the belt is a spiral belt layer formed by spirally winding a continuous rubberized cord or a continuous ribbon-shaped body containing plural cords therein in a widthwise direction of the tire so as to extend the cord substantially in a circumferential direction of the tire, and the tread portion has a two-layer structure comprised of a cap rubber layer and a base rubber layer in at least a central region in the widthwise direction of the tire.  
     
     
         2 . A pneumatic tire according to  claim 1 , wherein a Shore A hardness of the cap rubber layer is harder than that of the base rubber layer.  
     
     
         3 . A pneumatic tire according to  claim 2 , wherein the Shore A hardness of the cap rubber layer is within a range of 55-75°.  
     
     
         4 . A pneumatic tire according to  claim 2 , wherein a difference of Shore A hardness between the cap rubber layer and the base rubber layer is not less than 2°.  
     
     
         5 . A pneumatic tire according to  claim 1 , wherein a thickness A of the cap rubber layer and a thickness B of the base rubber layer satisfy a relation of B/(A+B)=0.2-0.5.  
     
     
         6 . A pneumatic tire for a front wheel of a motorcycle comprising a pair of bead cores embedded in a pair of bead portions, a carcass toroidally extending between the pair of bead portions and wound around the bead core from an inside of the tire toward an outside thereof, a belt disposed on an outer surface of a crown portion of the carcass in a radial direction of the tire, and a tread portion disposed on an outer surface of the belt in the radial direction, wherein the carcass is comprised of at least one carcass ply containing organic fiber cords arranged at a cord angle of 60-90° with respect to an equatorial plane of the tire, and the belt is a spiral belt layer formed by spirally winding a continuous rubberized cord or a continuous ribbon-shaped body containing plural cords therein in a widthwise direction of the tire so as to extend the cord substantially in a circumferential direction of the tire, and at least one reinforcing layer is disposed inside an innermost carcass ply or on an inner surface of an innerliner at a width corresponding to 20-120% of a width of the spiral belt layer and is a rubber layer or a rubberized cord layer.  
     
     
         7 . A pneumatic tire according to  claim 6 , wherein the width of the reinforcing layer is 20-60% of the width of the spiral belt layer.  
     
     
         8 . A pneumatic tire for a front wheel of a motorcycle comprising a pair of bead cores embedded in a pair of bead portions, a carcass toroidally extending between the pair of bead portions and wound around the bead core from an inside of the tire toward an outside thereof, a belt disposed on an outer surface of a crown portion of the carcass in a radial direction of the tire, and a tread portion disposed on an outer surface of the belt in the radial direction, wherein the carcass is comprised of at least one carcass ply containing organic fiber cords arranged at a cord angle of 60-90° with respect to an equatorial plane of the tire, and the belt is a spiral belt layer formed by spirally winding a continuous rubberized cord or a continuous ribbon-shaped body containing plural cords therein in a widthwise direction of the tire so as to extend the cord substantially in a circumferential direction of the tire, and the bead core is a helically wound laminate of a single steel wire having a polygonal shape at a section of the bead core in the radial direction.  
     
     
         9 . A pneumatic tire according to  claim 8 , wherein the radial section of the bead core is any one of quadrilateral shape to hexagonal shape.  
     
     
         10 . A pneumatic tire for a front wheel of a motorcycle comprising a pair of bead cores embedded in a pair of bead portions, a carcass toroidally extending between the pair of bead portions, a belt disposed on an outer surface of a crown portion of the carcass in a radial direction of the tire, and a tread portion disposed on an outer surface of the belt in the radial direction, wherein the carcass is comprised of at least one carcass ply containing organic fiber cords arranged at a cord angle of 60-90° with respect to an equatorial plane of the tire and wound around the bead core from an inside of the tire toward an outside thereof to form a turnup portion, and the belt is a spiral belt layer formed by spirally winding a continuous rubberized cord or a continuous ribbon-shaped body containing plural cords therein in a widthwise direction of the tire so as to extend the cord substantially in a circumferential direction of the tire, and a bead filler having a Shore A hardness of 60-99° is arranged at an outside of the turnup portion of the carcass ply in an axial direction of the tire.  
     
     
         11 . A pneumatic tire according to  claim 10 , wherein the carcass further comprises at least one down ply located at an outside of the turnup portion of the carcass ply and the bead filler is arranged at an outside of the down ply in an axial direction of the tire.  
     
     
         12 . A pneumatic tire according to  claim 10 , wherein the carcass further comprises at least one down ply located at an outside of the turnup portion of the carcass ply and the bead filler is arranged between the turnup portion and the down ply.