Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-11-24
2001-09-11
Ball, Michael W. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S532000, C152S533000, C152S549000
Reexamination Certificate
active
06286575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to pneumatic tires for motorcycles, and more particularly to a pneumatic tire for a front wheel of a motorcycle capable of preventing the occurrence of shimmy in the high-speed running to improve a steering stability, particularly straight running stability.
2. Description of Related Art
In the pneumatic tire particularly mounted onto a front wheel of a motorcycle, the steering performances such as handling and the like are considered to be important, so that it is usual to adopt a belt comprised of at least two belt layers, cords of which belt layers being crossed with each other, or so-called cross structure belt up to the present time.
With the recent advancement of weight reduction and higher performances in a vehicle, a micro-oscillation of a handle or so-called shimmy phenomenon is actualized in the motorcycle. Particularly, it is strongly demanded to prevent the occurrence of shimmy at a high frequency zone. However, the tire having the above cross structure belt is difficult to flexibly absorb the pushing up of micro-irregularities on the road to the tread surface of the tire and the micro-oscillation of the handle resulted therefrom.
And also, the motorcycle is more important to ensure the stability of the vehicle body in the high speed or extra-high speed running. In the above pneumatic tire for the motorcycle, however, the pushing quantity of a central portion of the tread becomes large with the increase of the speed to decrease the ground contacting area of the tread, which causes the lowering of the stability in the high speed running.
On the other hand, a tire having a belt formed by spirally winding a cord having a high modulus of elasticity such as high-modulus polyester or rayon fiber cord, aromatic polyamide fiber cord or the like on the outer periphery of the carcass ply in a widthwise direction of the tire or so-called spiral structure belt is used for a rear wheel of the motorcycle. This tire has many characteristics that the outward pushing of the tread is prevented by hoop effect of the spiral structure belt even in the high speed running, and heat generation and rolling resistance are small owing to small movement of tread rubber, and the wear resistance is excellent, and the decrease of the ground contacting area with the rise of the speed is small. However, when the tire having the above spiral structure belt is used in the front wheel of the motorcycle taking count of steering performances such as steering stability and the like, since the cord in the belt extends substantially in the circumferential direction of the tire, the bending rigidity of the tread portion in the widthwise direction thereof is too low as compared with the cross structure belt, and hence the handle response, gripping force on road surface and the like are largely lacking and the steering performances are degraded. Therefore, the tire having the spiral structure belt is not used in the front wheel of the motorcycle.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a pneumatic tire for a front wheel of a motorcycle capable of preventing the occurrence of shimmy at a high frequency zone and improving the steering stability in the high speed running.
The inventor has noticed that the tire having the spiral structure belt has characteristics that the tread portion is flexible, the change of ground contact shape in the high speed running is less, the high speed stability is excellent and the like as compared with the conventional cross structure belt and made various studies in order to solve the problem of degrading the steering performances due to the low bending rigidity in the ground contacting region when such a tire is applied to the front wheel of the motorcycle and as a result, the invention has been accomplished.
According to a first aspect of the invention, there is the provision of 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.
In a preferable embodiment of the invention, a Shore A hardness of the cap rubber layer is harder than that of the base rubber layer, and the Shore A hardness of the cap rubber layer is within a range of 55-75°, and a difference of Shore A hardness between the cap rubber layer and the base rubber layer is not less than 2°, and thickness A of the cap rubber layer and thickness B of the base rubber layer satisfy a relation of B/(A+B)=0.2−0.5.
According to a second aspect of the invention, there is the provision of 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 each being symmetric with respect to the equatorial plane and disposed on the inside and directly adjacent 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.
In a preferable embodiment of the invention, the width of the reinforcing layer is 20-60% of the width of the spiral belt layer.
According to a third aspect of the invention, there is the provision of 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.
In a preferable embodimen
Ball Michael W.
Bridgestone Corporation
Fischer Justin
Sughrue Mion Zinn Macpeak & Seas, PLLC
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