JP4921004B2 - Radial tires for motorcycles - Google Patents

Description

  The present invention relates to a radial tire for a motorcycle.

  As a pneumatic tire mounted on a motorcycle, there is a tire including a belt in which a belt cord is spirally wound and substantially extends in a circumferential direction. This belt structure is referred to as a “jointless structure”. Such tires are excellent in straight running stability and durability during high speed running.

  When the motorcycle turns, centrifugal force acts on the motorcycle. For cornering, a cornering force that balances this centrifugal force is required. When turning, the rider tilts the motorcycle inward. Turning is achieved by the camber thrust generated by this inclination. For the purpose of easy turning, motorcycle tires have a tread with a small radius of curvature. When going straight, the center area of the tread is grounded. On the other hand, when turning, the area outside the center area is grounded.

Japanese Patent Application Laid-Open No. 11-291711 discloses a motorcycle tire having improved traction performance during turning while maintaining straight running stability at high speeds. This tire is provided with a pair of shoulder reinforcement layers arranged in the vicinity of the shoulder and spaced apart in the axial direction. The shoulder reinforcing layer includes a reinforcing cord. The angle formed with respect to the circumferential direction of the reinforcing cord is 15 ° or more and 45 ° or less. This reinforcing cord is made of an organic fiber such as nylon fiber, rayon fiber, polyester fiber or the like.
JP-A-11-291711

  In a tire including a belt whose structure is a jointless structure, since the belt cord extends in the circumferential direction, the rigidity of the tread in the axial direction is low. This tire is inferior in turning stability because traction is not sufficiently exhibited during turning.

  In order to improve the turning stability, there is a tire in which a plurality of plies are arranged on the radially outer side or the radially inner side of the belt to increase the rigidity of the tread. If a ply using a cord is used, the tire mass will increase. The tread becomes excessively rigid and the straight running stability is reduced.

  In this tire, the end portions of the belt and the ply extending outward in the axial direction from the equator plane are located in the vicinity of the shoulder. These end portions are concentrated with distortion caused by bending. In this tire, damage due to repeated strain may occur. Such a tire is inferior in durability.

  An object of the present invention is to provide a radial tire for a motorcycle that is excellent in turning stability while maintaining durability and straight running stability.

  A radial tire for a motorcycle according to the present invention includes a pair of beads, a carcass spanned between beads on both sides, a belt positioned radially outward of the carcass, and spaced apart in the axial direction. And a pair of reinforcing layers arranged so as to sandwich the outer side in the direction. The reinforcing layer is folded at the outer end of the belt. The thickness of this reinforcing layer is 0.5 mm or more and 3 mm or less. The ratio of the axial width of the reinforcing layer to the axial width of the tread is 0.1 or more and 0.4 or less. The reinforcing layer includes a lower layer located between the carcass and the belt and an upper layer located on the outer side in the radial direction of the belt. The inner end located on the inner side in the axial direction of the upper layer is the same position as the inner end located on the inner side in the axial direction of the lower layer in the axial direction or inside the inner end of the lower layer. The ratio of the difference between the axial width of the upper layer and the axial width of the lower layer to the axial width of the tread is 0.1 or less. This reinforcing layer includes short fibers. The short fibers are inclined with respect to the circumferential direction. The absolute value of the orientation angle formed with respect to the circumferential direction of the short fibers is 30 ° or more and 60 ° or less. This belt consists of a belt ply. The belt ply includes a belt cord wound spirally and extending substantially in the circumferential direction.

  Preferably, the absolute value of the orientation angle of the short fibers in one reinforcing layer is substantially the same as the absolute value of the orientation angle of the short fibers in the other reinforcing layer. The orientation direction of the short fibers in one reinforcing layer is opposite to the orientation direction of the short fibers in the other reinforcing layer. Preferably, in this tire, the short fibers are paper fibers.

  Since the tire includes a belt in which a belt cord is spirally wound and extends substantially in the circumferential direction, the tire has excellent straight running stability. In this tire, the reinforcing layer containing short fibers increases the rigidity in the vicinity of the shoulder. Since the thickness of the reinforcing layer and the orientation angle of the short fibers are adjusted, the rigidity in the vicinity of the shoulder is effectively enhanced. Such a tire is excellent in turning stability. In this tire, since the reinforcing layers are separated in the axial direction, good straight running stability can be maintained. This tire achieves both straight running stability and turning stability while suppressing an increase in tire mass. The outer end of the belt located in the vicinity of the end of the tread is restrained by a reinforcing layer that is folded back at the outer end. In this tire, the concentration of distortion due to bending is suppressed. This tire is excellent in durability because damage due to repeated strain is suppressed.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view showing a part of a pneumatic tire 2 according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 2. The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a belt 12, a reinforcing layer 14, an inner liner 16 and a chafer 18. The tire 2 is a tubeless type pneumatic tire.

  The tread 4 is made of a crosslinked rubber and has a shape protruding outward in the radial direction. The outer surface of the tread 4 forms a tread surface 20 that contacts the road surface. In addition, a tread pattern may be formed by carving a groove in the tread surface 20.

  The sidewall 6 extends substantially inward in the radial direction from the end 22 of the tread 4. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 absorbs an impact from the road surface by bending. Furthermore, the sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 extends from the sidewall 6 substantially inward in the radial direction. The bead 8 includes a core 24 and an apex 26 that extends radially outward from the core 24. The core 24 has a ring shape and includes a plurality of non-stretchable wires (typically steel wires). The apex 26 is tapered outward in the radial direction and is made of a highly hard crosslinked rubber.

  The carcass 10 is spanned between the beads 8 on both sides, and is along the inside of the tread 4 and the sidewall 6. The carcass 10 includes a carcass ply 28. The carcass ply 28 is wound around the core 24 from the inner side toward the outer side in the axial direction. Although not shown, the carcass ply 28 includes a carcass cord and a topping rubber. The absolute value of the angle formed with respect to the circumferential direction of the carcass cord is usually 75 ° to 90 °. In other words, the tire 2 is a radial tire 2. The carcass cord is usually made of an organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. Two or more carcass plies 28 may be used for the carcass 10.

  The belt 12 is located on the radially outer side of the carcass 10. The belt 12 reinforces the carcass 10. A part of the belt 12 is laminated on the carcass 10 in the vicinity of the equator plane. The outer end 30 of the belt 12 is located in the vicinity of the end 22 of the tread 4. The belt 12 includes a belt ply 32. The belt ply 32 is obtained by winding a long belt body in a spiral shape. Although not shown in the drawings, this belt is composed of one or a plurality of belt cords extending in the longitudinal direction and a topping rubber. In other words, the belt ply 32 includes a belt cord that is wound spirally and extends substantially in the circumferential direction. The angle formed with respect to the circumferential direction of the belt cord is 5 ° or less, particularly 2 ° or less. This belt cord has a so-called jointless structure. This belt cord contributes to driving performance during straight traveling. The belt cord further contributes to stability performance and braking performance during straight traveling. Preferable materials for the belt cord include nylon fiber, aramid fiber, polyethylene naphthalate fiber, polyester fiber, rayon fiber, glass fiber, carbon fiber and steel. Two or more belt plies 32 may be used for the belt 12.

  The inner liner 16 is joined to the inner peripheral surface of the carcass 10. The inner liner 16 is made of a crosslinked rubber. The inner liner 16 is made of rubber having a low air permeability. The inner liner 16 serves to maintain the internal pressure of the tire 2.

  The chafer 18 is located in the vicinity of the bead 8. When the tire 2 is incorporated into the rim, the chafer 18 comes into contact with the rim. By this contact, the vicinity of the bead 8 is protected. The chafer 18 is usually made of cloth and rubber impregnated in the cloth. A chafer 18 made of a single rubber may be used.

  The reinforcing layer 14 is located on the radially outer side of the carcass 10. The reinforcing layer 14 is disposed so as to sandwich the outer side in the axial direction of the belt 12. The reinforcing layer 14 is along the belt 12. The reinforcing layer 14 is folded at the outer end 30 of the belt 12. The reinforcing layer 14 includes a lower layer 34 positioned between the carcass 10 and the belt 12 and an upper layer 36 positioned on the outer side in the radial direction of the belt 12. The lower layer 34 and the upper layer 36 extend from the vicinity of the outer end 30 of the belt 12 toward the inner side in the axial direction.

  In the tire 2, the outer end 30 of the belt 12 is restrained by the reinforcing layer 14. The inner end 38 positioned on the inner side in the axial direction of the lower layer 34 and the inner end 40 positioned on the inner side in the axial direction of the upper layer 36 are separated from the vicinity of the end 22 of the tread 4 in the axial direction. In the tire 2, the concentration of distortion due to bending on the outer end 30 of the belt 12, the inner end 38 of the lower layer 34, and the inner end 40 of the upper layer 36 is suppressed. Since the occurrence of damage due to repeated strain is suppressed, the tire 2 is excellent in durability.

  In the tire 2, the inner end 40 of the upper layer 36 is inside the inner end 38 of the lower layer 34 in the axial direction. The upper layer 36 covers the inner end 38 of the lower layer 34 via the belt 12. In the tire 2, the inner end 38 of the lower layer 34 is effectively restrained. In the tire 2, durability is further enhanced. The inner end 38 of the lower layer 34 may be disposed at the same position as the inner end 40 of the upper layer 36 in the axial direction.

  The reinforcing layer 14 is obtained by crosslinking the rubber composition. This rubber composition contains short fibers. In other words, the reinforcing layer 14 includes short fibers. The short fibers effectively increase the rigidity of the reinforcing layer 14 while suppressing an increase in the mass of the reinforcing layer 14. As described above, the reinforcing layer 14 is disposed so as to sandwich the outer side in the axial direction of the belt 12. The reinforcing layer 14 increases the rigidity in the vicinity of the shoulder 42. The tire 2 is excellent in turning stability.

  In the tire 2, the short fibers of the reinforcing layer 14 are inclined with respect to the circumferential direction. In the reinforcing layer 14, the rigidity in the axial direction and the rigidity in the circumferential direction are enhanced in a well-balanced manner. Such a reinforcing layer 14 effectively increases the rigidity in the vicinity of the shoulder 42. In the tire 2, the turning stability is further improved.

  In the tire 2, the reinforcing layers 14 on both sides are separated in the axial direction. The reinforcing layer 14 is not disposed at the center 44. In the tire 2, good straight running stability can be maintained. The tire 2 has both straight running stability and turning stability. In the tire 2 provided with such a reinforcing layer 14, an increase in tire mass is also suppressed.

  In FIG. 1, the point PA represents the outer end of the reinforcing layer 14. A double arrow line WT represents an axial distance from the equator plane to the end 22 of the tread 4. In this specification, this axial distance WT is the axial width of the tread 4. A double arrow line WR represents the axial width of the reinforcing layer 14. In the tire 2, the axial width WR is indicated by an axial distance from the outer end PA to the inner end 40 of the upper layer 36. A double arrow line WU represents the axial width of the upper layer 36. This axial width WU is indicated by the axial distance from the outer end PA to the inner end 40 of the upper layer 36. In the tire 2, the inner end 40 of the upper layer 36 is axially inner than the inner end 38 of the lower layer 34. Therefore, the axial width WU matches the axial width WR. A double arrow line WL represents the axial width of the lower layer 34. This axial width WL is indicated by the axial distance from the outer end PA to the inner end 38 of the lower layer 34. A double arrow line WD represents a difference between the axial width WU and the axial width WL. In the tire 2, the difference WD is obtained by subtracting the axial width WL from the axial width WU. Therefore, when the inner end 40 of the upper layer 36 is axially outside the inner end 38 of the lower layer 34, this difference WD is shown as negative. In this case, the axial width WL coincides with the axial width WR.

  In the tire 2, the ratio (WR / WT) of the axial width WR of the reinforcing layer 14 to the axial width WT of the tread 4 is 0.1 or more and 0.4 or less. By setting this ratio (WR / WT) to 0.1 or more, the rigidity in the vicinity of the shoulder 42 is enhanced. The tire 2 is excellent in turning stability. In this respect, the ratio (WR / WT) is more preferably equal to or greater than 0.15, and particularly preferably equal to or greater than 0.20. By setting this ratio (WR / WT) to 0.4 or less, the separation distance between the reinforcing layers 14 on both sides in the axial direction can be appropriately maintained. In the tire 2, the straight running stability can be maintained. In this respect, the ratio (WR / WT) is more preferably equal to or less than 0.35, and particularly preferably equal to or less than 0.30.

  In the tire 2, the ratio (WD / WT) of the difference WD to the axial width WT of the tread 4 is 0.1 or less. By setting this ratio (WD / WT) to be 0.1 or less, the overlap between the upper layer 36 and the lower layer 34 in the radial direction can be maintained. Since the reinforcing layer 14 effectively increases the rigidity in the vicinity of the shoulder 42, the tire 2 is excellent in turning stability.

  In FIG. 1, a double arrow line TA represents the thickness of the reinforcing layer 14. This thickness TA is not less than 0.5 mm and not more than 3 mm. By setting the thickness TA to 0.5 mm or more, the rigidity of the reinforcing layer 14 is increased. The reinforcing layer 14 effectively increases the rigidity in the vicinity of the shoulder 42. The tire 2 is excellent in turning stability. In this respect, the thickness TA is more preferably equal to or greater than 0.7 mm, and particularly preferably equal to or greater than 0.9 mm. By setting the thickness TA to 3 mm or less, excessive rigidity due to the reinforcing layer 14 in the vicinity of the shoulder 42 is suppressed. Since the grip force is maintained, the tire 2 can maintain good turning stability. In this respect, the thickness TA is more preferably equal to or less than 2.5 mm, and particularly preferably equal to or less than 2.0 mm.

  In the tire 2, the absolute value of the orientation angle formed with respect to the circumferential direction of the short fibers included in the reinforcing layer 14 is 30 ° or more and 60 ° or less. By setting the absolute value of the orientation angle to 30 ° or more, the rigidity in the axial direction of the reinforcing layer 14 is increased. The reinforcing layer 14 effectively increases the rigidity in the vicinity of the shoulder 42. The tire 2 is excellent in turning stability. From this viewpoint, the absolute value of the orientation angle is more preferably 35 ° or more, and particularly preferably 40 ° or more. By setting the absolute value of the orientation angle to 60 ° or less, excessive rigidity due to the reinforcing layer 14 in the vicinity of the shoulder 42 can be suppressed. Since the grip force is maintained, the tire 2 can maintain good turning stability. From this viewpoint, the absolute value of the orientation angle is more preferably 55 ° or less, and particularly preferably 50 ° or less.

  In the present invention, the orientation angle of the short fibers is measured by the following method. First, an observation sample including the reinforcing layer 14 is sampled from the tire 2 by being cut out along the circumferential direction of the tire 2. This observation sample includes a cross section of the reinforcing layer 14. Next, a cross section of the reinforcing layer 14 is observed with a stereomicroscope. In this cross-sectional observation, the angle formed with respect to the circumferential direction of the longitudinal direction of the short fiber is measured. This angle is measured in the range of −90 ° to + 90 ° with the circumferential direction as the reference (0 °). In this specification, a straight line obtained by connecting both ends of a short fiber is used as the length of the short fiber. This angle is measured for 100 randomly extracted short fibers. Next, the relationship between the angle and the frequency (frequency distribution) is obtained from the angle measurement data. In this relationship, the angle indicating the maximum frequency is shown as the orientation angle formed with respect to the circumferential direction of the short fibers. Specifically, in the graph in which the horizontal axis is the angle and the vertical axis is the frequency, the angle that is the maximum peak of the frequency distribution function showing the relationship between the angle and the frequency is the orientation angle. (A peak is not observed in the reinforcing layer in which short fibers are randomly arranged.) In this specification, in FIG. 1, when the direction from the back to the front of the paper is the reference circumferential direction, this reference The orientation angle of the short fibers extending obliquely from the left side to the right side in the circumferential direction in the circumferential direction is indicated as positive. In this reference circumferential direction, the orientation angle of the short fibers extending obliquely from the right side to the left side of the paper surface is shown as negative.

  In the frequency distribution function described above, the full width at half maximum (°) of the maximum peak represents the orientation of short fibers. As the orientation of the short fibers increases, the half width becomes narrower. By increasing the orientation of the short fibers, the axial rigidity of the reinforcing layer 14 can be effectively adjusted. The tire 2 including such a reinforcing layer 14 can appropriately set the rigidity of the reinforcing layer 14 according to the specifications of the tire 2. From this viewpoint, it is preferable that the half width is small. In the tire 2, the half width is preferably 30 ° or less. The full width at half maximum is more preferably 20 ° or less, and particularly preferably 10 ° or less.

  In the tire 2, the reinforcing layer 14 is formed as follows. First, a rubber composition containing short fibers is formed into a preliminary sheet. In this preliminary sheet, the short fibers are arranged substantially in the molding direction. Next, a belt-like sheet is formed by punching out the preliminary sheet. In this punching, the length of the belt-like sheet is inclined obliquely with respect to the molding direction. Accordingly, the short fibers are inclined with respect to the length of the belt sheet. Next, this belt sheet is combined with the green tire that is the tire 2 before vulcanization molding so that the longitudinal direction coincides with the circumferential direction of the tire 2. In the vulcanization process, the tire 2 shown in FIG. 1 is obtained by pressurizing and heating the green tire. In the tire 2 thus obtained, the short fibers of the reinforcing layer 14 are inclined with respect to the circumferential direction. Since the reinforcing layer 14 is folded at the outer end 30 of the belt 12, the inclination of the short fiber in the upper layer 36 with respect to the circumferential direction is opposite to the inclination of the short fiber in the lower layer 34 with respect to the circumferential direction.

  In the tire 2, the absolute value of the orientation angle in one reinforcing layer 14 is substantially the same as the absolute value of the orientation angle in the other reinforcing layer 14. Specifically, the difference between the two is 5 ° or less, particularly 3 ° or less. In the tire 2, a balance of rigidity in the axial direction is maintained. Such a tire 2 is excellent in steering stability.

  In the tire 2, the orientation direction of the short fibers in one lower layer 34 is opposite to the orientation direction of the short fibers in the other lower layer 34. As described above, since the reinforcing layer 14 is folded at the outer end 30 of the belt 12, the orientation direction of the short fibers in one upper layer 36 is also opposite to the orientation direction of the short fibers in the other upper layer 36. In other words, in the tire 2, the orientation direction of the short fibers in one reinforcing layer 14 is opposite to the orientation direction of the short fibers in the other reinforcing layer 14. In the tire 2, the balance of rigidity in the axial direction is maintained with high accuracy. In such a tire 2, the steering stability is further improved.

  In the tire 2, the blending amount of the short fibers in the rubber composition constituting the reinforcing layer 14 is preferably 0.5 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the base rubber. . By setting the blending amount of the short fibers to 0.5 parts by mass or more, the short fibers effectively reinforce the reinforcing layer 14. In the tire 2 including the reinforcing layer 14, the rigidity in the vicinity of the shoulder 42 is effectively increased. The tire 2 is excellent in turning stability. In this respect, the amount of the paper fiber is more preferably 1.0 part by mass or more, and particularly preferably 2.0 parts by mass or more. By setting the blending amount of the short fibers to 10.0 parts by mass or less, the rigidity of the reinforcing layer 14 can be appropriately maintained. Since excessive rigidity in the vicinity of the shoulder 42 is suppressed, the grip force can be maintained. The tire 2 can maintain good turning stability. In this respect, the amount of the paper fiber is more preferably equal to or less than 8.0 parts by weight, and particularly preferably equal to or less than 5.0 parts by weight.

  In the tire 2, the average length (L) of the short fibers is preferably 10 μm or more and 3000 μm or less. By setting the average length (L) to 10 μm or more, the short fibers effectively reinforce the reinforcing layer 14. In the tire 2 including the reinforcing layer 14, the rigidity in the vicinity of the shoulder 42 is effectively increased. The tire 2 is excellent in turning stability. In this respect, the average length (L) is more preferably 50 μm or more, and particularly preferably 100 μm or more. By setting the average length (L) to 3000 μm or less, the short fibers are uniformly dispersed in the reinforcing layer 14. The reinforcing layer 14 has uniform physical properties. The performance of the tire 2 including the reinforcing layer 14 is stable. In this respect, the average length (L) is more preferably 1000 μm or less, and particularly preferably 800 μm or less. In addition, this average length (L) is obtained by measuring the longitudinal length of the short fiber with a stereomicroscope. The average length obtained from 100 short fibers extracted at random is expressed as the average length (L).

  In the tire 2, the average diameter (D) of the short fibers is preferably 1 μm or more and 100 μm or less. By setting the average diameter (D) to 10 μm or more, the short fibers effectively reinforce the reinforcing layer 14. In the tire 2 including the reinforcing layer 14, the rigidity in the vicinity of the shoulder 42 is effectively increased. The tire 2 is excellent in turning stability. From this viewpoint, the average diameter is more preferably 2 μm or more, and particularly preferably 5 μm or more. By setting the average diameter (D) to 100 μm or less, the short fibers are uniformly dispersed in the reinforcing layer 14. The reinforcing layer 14 has uniform physical properties. The performance of the tire 2 including the reinforcing layer 14 is stable. In this respect, the average diameter (D) is more preferably 80 μm or less, and particularly preferably 50 μm or less. In addition, this average diameter (D) is obtained by measuring the diameter of a short fiber with a stereomicroscope. The average diameter obtained from 100 randomly extracted short fibers is expressed as the average diameter (D).

  In the tire 2, the ratio (L / D) of the average length (L) to the average diameter (D) of the short fibers is preferably 10 or more and 2000 or less. When the ratio (L / D) is set to 10 or more, the contact area between the base rubber and the short fibers is increased, so that the short fibers effectively reinforce the reinforcing layer 14. In the tire 2 including the reinforcing layer 14, the rigidity in the vicinity of the shoulder 42 is effectively increased. The tire 2 is excellent in turning stability. In this respect, the ratio (L / D) is more preferably 20 or greater and particularly preferably 40 or greater. By setting the ratio (L / D) to 2000 or less, the short fibers are uniformly dispersed in the reinforcing layer 14. The reinforcing layer 14 has uniform physical properties. The performance of the tire 2 including the reinforcing layer 14 is stable. In this respect, the ratio (L / D) is more preferably equal to or less than 1500, and particularly preferably equal to or less than 1000.

  In the tire 2, an organic fiber is preferable as a material of the short fiber. Examples of organic fibers include synthetic fibers such as nylon fibers, rayon fibers, aramid fibers, polyethylene naphthalate fibers and polyester fibers, and paper fibers. From the viewpoint of reducing the weight of the tire 2 and reducing the cost of the tire 2, the material of the short fiber is preferably paper fiber.

  In the production of paper fiber, first, the raw paper is cut or crushed. This raw paper is further defibrated by beating. The paper fiber thus obtained is a short fiber. Since it is beaten, the surface area of this paper fiber is large.

  The raw paper is obtained from kraft pulp, semi-chemical pulp, mechanical pulp, non-wood pulp, waste paper pulp and the like. Kraft pulp includes softwood kraft pulp and hardwood kraft pulp. Non-wood pulp materials include kenaf, bagasse, bamboo, cotton, seaweed and the like. Waste paper pulp is obtained by deinking used copy paper, used newspaper, corrugated paper, and the like. From the viewpoint of strength, paper obtained from kraft pulp is preferable, and paper obtained from conifer kraft pulp is particularly preferable. Paper obtained from kraft pulp includes unbleached kraft paper and bleached kraft paper. From the viewpoint of the global environment and low cost, raw paper obtained from used newspaper is preferable.

  In the tire 2, natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene copolymer, polychloroprene are used as the base rubber compounded in the rubber composition constituting the reinforcing layer 14. And acrylonitrile-butadiene copolymer and isobutylene-isoprene copolymer. Two or more kinds of rubbers may be used in combination.

  In the tire 2, the rubber composition constituting the reinforcing layer 14 includes a filler, a crosslinking agent, a vulcanization accelerator, a softening agent, a plasticizer, an organic reinforcing agent, an anti-aging agent, etc. in addition to the base rubber and the short fibers. Of chemicals. In consideration of the workability and performance of the tire 2, an optimal chemical is blended in the rubber composition in an optimal amount.

  The size and angle of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A radial tire for a motorcycle of Example 1 having the basic configuration shown in FIG. 1 and having the specifications shown in Table 2 below was obtained. The tire size is 185 / 55ZR17 M / C 73V. One carcass ply was used for the carcass. The material of the carcass cord used for this carcass ply is rayon fiber. The fineness of this carcass cord is 1650/2 dtex. The angle formed with respect to the circumferential direction of the carcass cord is 90 °. One belt ply was used for the belt. The material of the belt cord used for this belt ply is aramid fiber. The fineness of this belt cord is 1650/2 dtex. The angle formed with respect to the circumferential direction of the belt cord is 0 °. The ratio (WR / WT) of the axial width WR of the reinforcing layer to the axial width WT of the tread is 0.3. This reinforcing layer is folded at the outer end of the belt. The thickness TA of this reinforcing layer is 1.0 mm. The inner end of the upper layer and the inner end of the lower layer are at the same position in the axial direction. Therefore, the ratio (LA / WT) of the difference LA between the axial width WU of the upper layer and the axial width WL of the lower layer to the axial width WT is zero. This reinforcing layer is made of a rubber composition containing 5 parts by mass of short fibers with respect to 100 parts by mass of the base rubber. The material of this short fiber is an aramid fiber. The absolute value of the orientation angle of the short fibers is 45 °.

[Comparative Examples 4 and 5 and Examples 4, 5 and 6]
Tires were obtained in the same manner as in Example 1 except that the ratio (WR / WT) was as shown in Tables 1 and 2 below.

[Comparative Examples 2 and 8 and Examples 3, 10 and 11]
Tires were obtained in the same manner as in Example 1 except that the thickness TA was as shown in Tables 1 and 3 below.

[Comparative Examples 1 and 9 and Examples 2 and 12]
A tire was obtained in the same manner as in Example 1 except that the absolute value of the orientation angle of the short fibers was changed.

[Comparative Examples 3, 6 and 7 and Examples 7, 8 and 9]
Tires were obtained in the same manner as in Example 1 except that the ratio (WR / WT) and ratio (WD / WT) were as shown in Tables 1 and 2 below.

[Comparative Example 10]
A tire was obtained in the same manner as in Example 1 except that the reinforcing layer was not folded. In this tire, the reinforcing layer includes two reinforcing layers, and includes a first reinforcing layer that constitutes an upper layer and a second reinforcing layer that constitutes a lower layer. In the vicinity of the outer end of the belt, the outer end of the upper layer and the outer end of the lower layer are located.

[Examples 13, 14 and 15]
A tire was obtained in the same manner as in Example 1 except that the material of the short fiber was as shown in Table 4 below.

[Comparative Example 11]
A tire was obtained in the same manner as in Example 1 except that the ratio (WR / WT) and the ratio (WD / WT) were as shown in Table 4 below. In this tire, the reinforcing layer is not folded back, and the reinforcing layer includes a first reinforcing layer constituting an upper layer and a second reinforcing layer constituting a lower layer. This tire is a conventional tire.

[Comparative Example 12]
A tire was obtained in the same manner as in Example 1 except that the reinforcing layer was not provided. This tire is a conventional tire.

[Real car evaluation]
A prototype tire was mounted on the rear wheel of a commercially available motorcycle (4 cycles) having a displacement of 600 cm ³ . The rim has an MT of 5.50 × 17, and the tire has an internal air pressure of 290 kPa. A conventional tire is attached to the front wheel. The tire size of this front wheel is 120 / 70ZR17. The rim is MT3.50 × 17, and the air pressure of the tire is 250 kPa. According to the rider, on a circuit course composed of dry asphalt roads, turning from 100 km / h to 150 km / h and turning straight from 250 km / h to the maximum speed of the vehicle (about 280 km / h) Sensory evaluation was performed on turning stability, straight running stability and grip force. Lap time was also measured. The durability of the tire was evaluated by visually confirming the damage status of the tire after the running test. These evaluation results are represented by index values in Table 1, Table 2, Table 3, and Table 4 below. The straight running stability, turning stability, grip force and durability indicate that the larger this value, the better. The lap time indicates that the smaller the index value, the better (the lap time is faster).

  As shown in Table 1, Table 2, Table 3, and Table 4, the tires of the examples are excellent in turning stability while maintaining durability and straight running stability. From this evaluation result, the superiority of the present invention is clear.

  The radial tire according to the present invention can be mounted on various motorcycles.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Tire 4 ... Tread 6 ... Side wall 8 ... Bead 10 ... Carcass 12 ... Belt 14 ... Reinforcement layer 16 ... Inner liner 18 ... Chafer 20 ... Tread surface 22 ... End 24 ... Core 26 ... Apex 28 ... Carcass ply 30 ... Outer end 32 ... Belt ply 34 ... Lower layer 36 ... Upper layer 38 40 ... Inner end 42 ... Shoulder 44 ... Center

Claims (3)

A pair of beads, a carcass spanned between the beads on both sides, a belt positioned radially outward of the carcass, and a pair spaced apart in the axial direction and arranged to sandwich the axially outer side of the belt With a reinforcing layer,
This reinforcing layer is folded at the outer edge of this belt,
The thickness of this reinforcing layer is 0.5 mm or more and 3 mm or less,
The ratio of the axial width of the reinforcing layer to the axial width of the tread is 0.1 or more and 0.4 or less,
This reinforcing layer is composed of a lower layer located between the carcass and the belt, and an upper layer located radially outside the belt,
The inner end located on the axially inner side of the upper layer is the same position as the inner end located on the axially inner side of the lower layer in the axial direction or the inner side of the inner end of the lower layer,
The ratio of the difference between the axial width of the upper layer and the axial width of the lower layer to the axial width of the tread is 0.1 or less,
This reinforcing layer contains short fibers,
This short fiber is inclined with respect to the circumferential direction,
The absolute value of the orientation angle formed with respect to the circumferential direction of the short fibers is 30 ° or more and 60 ° or less,
This belt consists of a belt ply,
The belt ply includes a belt cord wound in a spiral and extending substantially in the circumferential direction ,
A radial tire for a motorcycle in which an angle formed with respect to a circumferential direction of the belt cord is 5 ° or less . The absolute value of the orientation angle of the short fibers in one reinforcing layer is substantially the same as the absolute value of the orientation angle of the short fibers in the other reinforcing layer,
The difference between the absolute value of the orientation angle of the short fibers in one reinforcing layer and the absolute value of the orientation angle of the short fibers in the other reinforcing layer is 5 ° or less,
The tire according to claim 1, wherein the orientation direction of the short fibers in one reinforcing layer is opposite to the orientation direction of the short fibers in the other reinforcing layer.   The tire according to claim 1 or 2, wherein the short fibers are paper fibers.

Images