JP2018070070A - Two-wheeled vehicle tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-wheeled vehicle tire which has rim slippage prevention performance, and improved compatibility of rim assembling and controllability.SOLUTION: A two-wheeled vehicle tire 2 comprises a pair of beads 8. An external surface of a bead 8 portion of this tire 2 comprises a bottom face 32 which contacts a sheet surface of a rim when the tire 2 is mounted to the rim, a side face 34 which contacts a flange of the rim, and a heel surface 36 which is positioned between the bottom face 32 and the side face 34. The heel surface 36 is connected to the bottom face 32 at a junction P1, and is connected to the side face 34 at a junction P2. In a cross section of this tire 2 which is cut in a plane perpendicular to a circumferential direction, a contour of the heel surface 36 is a circular arc C which is convexed outward and has a curvature radius R of 3.5 mm or more, or a straight line L.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a motorcycle tire.

  The tire is fixed to the rim by a bead tightening the rim. If the contact pressure between the bead and the rim is not sufficient, the rim may be displaced with respect to the bead. By reducing the diameter of the bead core relative to the rim diameter, the contact pressure between the bead and the rim is increased. Thereby, rim shift can be suppressed. However, if the core diameter of the bead is reduced, a large fitting pressure is required when fitting the bead to the rim. With this tire, it takes time to mount the tire on the rim. This tire is inferior in rim assembly. Further, if the bead core diameter is reduced, the fitting state may be non-uniform on the circumference of the tire. This can cause an increase in tire runout during running and a decrease in maneuverability.

  The shape of the bead portion affects the rim displacement prevention performance and rim assembly. So far, various studies have been made on the shape of the bead portion. For example, in order to prevent rim displacement without deteriorating rim assemblability, the contact area between the bead portion and the rim has been increased. In this tire, the shape of the bead portion is matched to the shape of the rim. For example, in this tire, the radius of curvature of the heel contour of the bead portion is set to 2.5 mm in accordance with the rim. Further, in the tire for a two-wheeled vehicle disclosed in JP-A-11-192821, the air seal performance is improved without affecting the ease of assembling the rim by providing a convex shape at the heel portion. .

Japanese Patent Laid-Open No. 11-192821

  There is a need for a tire with improved rim slip prevention performance and improved rim assembly. Further, the shape of the bead portion affects maneuverability. In particular, improvement of maneuverability is an important issue for tires for motorcycles. As far as the inventors know, no report has been made on the shape of the bead portion of a motorcycle tire from the viewpoint of improving the maneuverability.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a tire for a two-wheeled vehicle in which maneuverability is improved in addition to rim displacement prevention performance and rim assembly.

  The tire for a motorcycle according to the present invention includes a pair of beads. The outer surface of the bead portion of the tire includes a bottom surface that contacts the seat surface of the rim when the tire is mounted on a rim, a side surface that contacts the flange of the rim, and a bottom surface and the side surface. And a heel surface positioned therebetween. The heel surface is connected to the bottom surface at a connection point P1, and is connected to the side surface at a connection point P2. In the cross section obtained by cutting the tire along a plane perpendicular to the circumferential direction, the contour of the heel surface is an outwardly convex arc C having a curvature radius R of 3.5 mm or more, or a straight line L.

  Preferably, when the contour of the bead portion formed by extending the bottom surface and the side surface assuming that the heel surface does not exist is a virtual contour, the contour of the heel surface protrudes from the virtual contour. Not.

  The bead has a core. Preferably, the connection point P1 is located axially outside the center of the core, and the connection point P2 is located radially inside the center of the core.

  Preferably, a ratio (D1 / Wc) of the axial distance D1 between the center of the core and the connection point P1 to the width Wc of the core is 0.1 or more and 0.6 or less.

  Preferably, a ratio (D2 / Hc) of the radial distance D2 between the center of the core and the connection point P2 to the height Hc of the core is 0.1 or more and 0.6 or less.

  Preferably, the core has a spiral structure composed of a single non-stretchable wire extending substantially in the circumferential direction.

  In the tire for a motorcycle according to the present invention, the contour of the heel surface located between the bottom surface and the side surface is an outwardly convex arc C having a curvature radius R of 3.5 mm or more, or a straight line L. is there. With this structure, the pressure conventionally applied to the heel surface is distributed to the bottom surface and the side surface. Contact pressure on the bottom and side surfaces is improved. The tire force is efficiently transmitted to the rim, so that the tire response is improved. This contributes to improvement in maneuverability. Further, the improvement of the contact pressure on the bottom surface and the side surface improves the rim slip prevention performance. Furthermore, by setting the contour of the heel surface to an outwardly projecting arc C or straight line L with a radius of curvature R of 3.5 mm or more, the bead portion has a bump on the rim when the tire is mounted on the rim. It will be easier to get over. In this tire, the fitting pressure is reduced. In this tire, the rim assembly property is improved. In this tire, rim displacement prevention performance, rim assembly property and maneuverability are improved.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of FIG. FIG. 3 is an enlarged cross-sectional view showing a part of a tire according to another embodiment. FIG. 4 is a graph showing the relationship between the position on the outer surface and the contact pressure in the bead portion of the tire of FIG. 1. FIG. 5 is a graph showing the relationship between the position on the outer surface and the contact pressure in the bead portion of the conventional tire.

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

  FIG. 1 shows a pneumatic tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal 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. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of beads 8, a carcass 10, a belt 12, a band 14, and an inner liner 16. The tire 2 is a tubeless type. The tire 2 is attached to a two-wheeled vehicle. The tire 2 is particularly mounted on the front wheel of a two-wheeled vehicle.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 includes a tread surface 18 that contacts the road surface. Although not shown, the tread surface 18 has a groove. A tread pattern is formed by this groove. The tread surface 18 may not have a groove. The tread 4 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties.

  Each sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 6 prevents the carcass 10 from being damaged. The sidewall 6 absorbs an impact from the road surface by bending.

  Each bead 8 is positioned substantially inward in the axial direction from the sidewall 6. The bead 8 includes a core 20 and an apex 22 that extends radially outward from the core 20. The core 20 includes a non-stretchable wire wound in the circumferential direction. A typical material for the wire is steel. The apex 22 is tapered outward in the radial direction. The apex 22 is made of a highly hard crosslinked rubber.

  In this embodiment, the core 20 is configured by winding a single wire. The core 20 has a spiral structure composed of a single wire extending substantially in the circumferential direction. The core 20 may be configured by winding two or more wires. The core 20 may be configured by winding a tape in which a plurality of wires are arranged in parallel in the circumferential direction. The core 20 may have a cable bead structure. In the cable bead structure, the core 20 includes a core having a circular cross section and a wire spirally wound around the core.

  The carcass 10 includes a carcass ply 24. The carcass ply 24 is bridged between the beads 8 on both sides. The carcass ply 24 is folded around the core 20. The carcass ply 24 includes a main portion 26 that extends from one bead 8 to the other bead 8, and a folded portion 28 that is located on the outer side in the axial direction of the bead 8. The main portion 26 extends along the inside of the tread 4 and the sidewall 6. The folded portion 28 extends along the outside of the bead 8.

  Although not shown, the carcass ply 24 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 65 ° to 90 °. In other words, the carcass 10 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 12 is located on the radially outer side of the carcass 10. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10. The belt 12 includes a belt ply 30. Although not shown, the belt ply 30 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is not less than 10 ° and not more than 35 °. A preferred material for the cord is steel. An organic fiber may be used for the cord. The belt 12 may be composed of two belt plies 30.

  The band 14 is located outside the belt 12 in the radial direction. In the axial direction, the width of the band 14 is larger than the width of the belt 12. Although not shown, the band 14 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 14 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 12 is restrained by this cord, lifting of the belt 12 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The inner liner 16 is located inside the carcass 10. The inner liner 16 is joined to the inner surface of the carcass 10. The inner liner 16 is made of a crosslinked rubber. For the inner liner 16, rubber having excellent air shielding properties is used. A typical base rubber of the inner liner 16 is butyl rubber or halogenated butyl rubber. The inner liner 16 holds the internal pressure of the tire 2.

  FIG. 2 is a cross-sectional view in which a part of the bead 8 portion of the tire 2 of FIG. 1 is enlarged. In the figure, the up and down direction is the radial direction of the tire 2, the left and 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.

  As shown in the figure, the outer surface of the bead 8 includes a bottom surface 32 that contacts the seat surface of the rim when the tire 2 is mounted on the rim, a side surface 34 that contacts the flange of the rim, A heel surface 36 is provided between the bottom surface 32 and the side surface 34. A point P1 is a connection point between the bottom surface 32 and the heel surface 36. The bottom surface 32 and the heel surface 36 are connected at a connection point P1. A point P2 is a connection point between the side surface 34 and the heel surface 36. The side surface 34 and the heel surface 36 are connected at a connection point P2.

  In the cross section perpendicular to the circumferential direction, the bottom surface 32 extends substantially in the axial direction. The angle formed by the bottom surface 32 and the axial direction is usually 0 ° or more and 20 ° or less. The side surface 34 extends substantially in the radial direction. In this embodiment, on the outer side in the radial direction of the connection point P2, the contour of the side surface 34 includes an arc that protrudes inward. In the tire 2, the contour of the heel surface 36 is a straight line L. The straight line L connects the connection point P1 and the connection point P2.

  FIG. 3 shows an embodiment in which the shape of the heel surface 36 of the bead 8 portion of the tire 2 is changed. The bead 8 has the same structure as the bead 8 shown in FIG. 2 except for the shape of the heel surface 36. In the figure, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

  In this embodiment, the contour of the heel surface 36 is an outwardly convex arc C. The center of the arc C is located inside the bead 8 portion. The arc C connects the connection point P1 and the connection point P2. In this embodiment, the radius of curvature R of the arc C is 3.5 mm or more.

  In the above description, the portion of the bead 8 in FIG. 2 and the portion of the bead 8 in FIG. 3 have been described as different embodiments. However, if the radius of curvature of the arc C is increased in the portion of the bead 8 in FIG. 3, the shape of the arc C approaches the straight line L. That is, it can be considered that the bead 8 in FIG. 2 has an infinite radius of curvature R of the arc C in the bead 8 in FIG. These are tires of the same structure, differing only in the radius of curvature R.

  Hereinafter, the function and effect of the present invention will be described.

  The inventors studied the shape of the bead portion from the viewpoints of prevention of rim displacement, ease of rim assembly, and maneuverability. As a result, it has been found that making the contour of the heel surface an outwardly convex arc C having a curvature radius R of 3.5 mm or more or a straight line L effectively contributes to these.

  FIG. 4 is a graph showing the contact pressure with the rim for the portion of the bead 8 in which the contour of the heel surface 36 is a straight line L. In the measurement of contact pressure, a sheet-like pressure sensor was attached to the bead 8 portion. The tire 2 was mounted on the rim, and a load was applied to the tire 2. At this time, the contact pressure between the bead 8 and the rim was measured. In this graph, the horizontal axis represents the position on the outer surface of the bead 8 portion. On the outer surface of the bead 8 portion, the position at the same radial height as the flange end of the rim is set to 0 mm. This position is referred to as a reference position. In the tire 2, the reference position is a position on the side surface 34. The position on the outer surface of the bead 8 is expressed as the distance to this position measured along the surface of the bead 8 portion from the reference position toward the bottom surface 32 of the rim. The horizontal axis represents this distance. For example, “10 mm” on the horizontal axis represents a position having a distance of 10 mm from the reference position measured along the surface of the bead 8 portion toward the bottom surface 32 from the reference position. Since the side surface 34 is not in contact with the flange at the reference position, the contact pressure is 0 kPa. When the side surface 34 and the flange come into contact, the contact pressure becomes greater than 0 kPa. As shown in the figure, the contact pressure increases rapidly when the position is in the vicinity of 5 mm to 10 mm. This is the contact pressure between the side surface 34 and the flange. Thereafter, the contact pressure once decreases. This indicates that the contact pressure is reduced at the heel surface 36. The contact pressure increases again. This indicates that the contact pressure is increased at the bottom surface 32.

  The contact pressure was measured in each case where the inclination angle CA of the tire 2 was 0 °, 10 °, and 40 °. The solid line in the graph of FIG. 4 represents the contact pressure when the tilt angle CA is 0 °, the dotted line represents the contact pressure when the tilt angle CA is 10 °, and the alternate long and short dash line represents the contact pressure when the tilt angle CA is 40 °. Represents contact pressure.

  FIG. 5 is a graph showing the contact pressure with the rim for a bead portion of a conventional tire. The measurement method is the same as that of the tire 2 in FIG. As is apparent from the figure, the contact pressure gradually increases from the side surface through the heel surface to the bottom surface, although there is some increase or decrease. In this measurement, the contact pressure was measured in each case where the tire inclination angle CA was 0 ° and 10 °.

  As is clear from the comparison between FIG. 4 and FIG. 5, in the present tire 2, the pressure applied to the conventional heel surface is distributed to the bottom surface 32 and the side surface 34 compared to the conventional tire. Thereby, the contact pressure on the bottom surface 32 and the side surface 34 is improved. Due to the improvement of the contact pressure, the force generated by the tire 2 is efficiently transmitted to the rim. This improves the reaction speed of the tire 2 with respect to the rider's operation. This shortens the relaxation length of the tire 2. The tire 2 is excellent in responsiveness. In the tire 2, good maneuverability is realized.

  As is clear from the comparison between FIG. 4 and FIG. 5, in the conventional tire, the contact pressure hardly changes even if the inclination angle CA changes. In contrast, in the present tire 2, the contact pressure increases as the inclination angle CA of the tire 2 increases. When the inclination angle is 10 °, the contact pressure increases between the side surface 34 and the bottom surface 32. At an inclination angle of 10 °, the force generated by the tire 2 is transmitted to the rim more efficiently. This improves the responsiveness of the vehicle in the roll direction. At an inclination angle of 40 °, the contact pressure on the side surface 34 is further increased. This improves the steering response when turning. In the tire 2, the maneuverability when the inclination angle CA is large is further improved. In the tire 2, good maneuverability is realized.

  The improvement of the contact pressure on the bottom surface 32 and the side surface 34 improves the rim slip prevention performance. This can shorten the braking distance of the vehicle. Further, the contour of the heel surface 36 is an outwardly convex arc C having a curvature radius R of 3.5 mm or more, or a straight line L, so that when the tire 2 is mounted on the rim, the bead 8 portion becomes the rim. It will be easier to get over bumps. In the tire 2, the fitting pressure is reduced. In the tire 2, the rim assembly performance is improved. In the tire 2, the rim assembling performance is improved while the rim slip prevention performance is improved.

  In the tire 2, the curvature radius R is more preferably 5.0 mm or more. By setting the curvature radius R to 5.0 mm or more, the contact pressure between the side surface 34 and the bottom surface 32 is effectively improved. Due to the improvement of the contact pressure, the force generated by the tire 2 is efficiently transmitted to the rim. This improves the reaction speed of the tire 2 with respect to the rider's operation. This contributes to improvement in maneuverability. Furthermore, this increase in contact pressure effectively improves rim slip. By setting the contour of the heel surface 36 to an outwardly convex arc C having a curvature radius R of 5.0 mm or more, the tire 2 can easily get over the bumps of the rim when the tire 2 is mounted on the rim. In the tire 2, the fitting pressure is reduced. The tire 2 has improved rim assembly performance. From these viewpoints, the curvature radius R is more preferably 10 mm or more, further preferably 15 mm or more, and further preferably 30 mm or more. Most preferably, the radius of curvature R is infinite, that is, the contour of the heel surface 36 is a straight line L.

  The contour formed by extending the bottom surface 32 and the side surface 34 on the assumption that the heel surface 36 does not exist in the portion of the bead 8 is referred to as a virtual contour 38. Specifically, the virtual contour 38 is configured by a tangent line of the contour of the bottom surface 32 at the connection point P1 and a tangent line of the contour of the side surface 34 at the connection point P2. A virtual contour 38 is shown in FIGS. As is apparent from FIGS. 2 and 3, the contour of the heel surface 36 preferably does not protrude from the virtual contour 38. By preventing the contour of the heel surface 36 from protruding from the virtual contour 38, the contact pressure generated on the heel surface 36 is reduced. Thereby, the contact pressure on the bottom surface 32 and the side surface 34 is improved. Due to the improvement of the contact pressure, the force generated by the tire 2 is efficiently transmitted to the rim. This improves the reaction speed of the tire 2 with respect to the rider's operation. This can shorten the relaxation length of the tire 2. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance.

  In FIG. 2, the symbol CO is the center of the core 20. Here, the center of the core 20 indicates the center of gravity of the contour of the cross section. As shown in the figure, the connection point P1 is preferably located outside the center CO in the axial direction. On the radially inner side of the center CO of the core 20, the pressure from the bead 8 portion to the seat surface of the rim becomes the largest. By positioning the connection point P1 on the outer side in the axial direction from the center CO, the straight line L does not exist on the inner side in the radial direction of the center CO. The pressure from the portion of the bead 8 is effectively applied to the seat surface. In the tire 2, the contact pressure at the bottom surface 32 is effectively improved. Due to the improvement of the contact pressure, the force generated by the tire 2 is efficiently transmitted to the rim. This improves the reaction speed of the tire 2 with respect to the rider's operation. This shortens the relaxation length of the tire 2. In the tire 2, good maneuverability is realized. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance.

  By locating the connection point P1 on the outer side in the axial direction from the center CO, the movement of the bead 8 when the tire 2 rolls is effectively suppressed. In the tire 2, a decrease in durability due to the movement of the bead 8 is prevented. In the tire 2, excellent durability is realized.

  As shown in the figure, the connection point P2 is preferably located radially inward from the center CO. On the outer side in the axial direction of the center CO of the core 20, the pressure from the bead 8 portion to the side surface 34 of the rim becomes the largest. By positioning the connection point P2 radially inward from the center CO, the straight line L does not exist outside the center CO in the axial direction. The pressure from the portion of the bead 8 is effectively applied to the side surface 34. In the tire 2, the contact pressure on the side surface 34 is effectively improved. Due to the improvement of the contact pressure, the force generated by the tire 2 is efficiently transmitted to the rim. This improves the reaction speed of the tire 2 with respect to the rider's operation. This shortens the relaxation length of the tire 2. In the tire 2, good maneuverability is realized. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance.

  By positioning the connection point P2 radially inward from the center CO, the movement of the bead 8 when the tire 2 rolls can be effectively suppressed. In the tire 2, a decrease in durability due to the movement of the bead 8 is prevented. In the tire 2, excellent durability is realized.

  In FIG. 2, the double arrow Wc is the axial width of the core 20. A double-headed arrow D1 is an axial distance between the center CO and the connection point P1. The ratio (D1 / Wc) of the distance D1 to the width Wc is preferably 0.1 or more. By setting the ratio (D1 / Wc) to 0.1 or more, the pressure from the portion of the bead 8 is effectively applied to the sheet surface. In the tire 2, the contact pressure at the bottom surface 32 is effectively improved. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the ratio (D1 / Wc) is more preferably equal to or greater than 0.2. The ratio (D1 / Wc) is preferably 0.6 or less. By setting the ratio (D1 / Wc) to 0.6 or less, the pressure applied to the heel surface in the related art is effectively applied to the bottom surface 32. Thereby, the contact pressure in the bottom face 32 improves. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the ratio (D1 / Wc) is more preferably equal to or less than 0.5.

  The distance D1 is preferably 1 mm or more. By setting the distance D1 to be 1 mm or more, the pressure from the bead 8 portion is effectively applied to the sheet surface. In the tire 2, the contact pressure at the bottom surface 32 is effectively improved. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the distance D1 is more preferably 2 mm or more. The distance D1 is preferably 6 mm or less. By setting the distance D1 to 6 mm or less, the pressure applied to the heel surface in the related art is effectively applied to the bottom surface 32. Thereby, the contact pressure in the bottom face 32 improves. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the distance D1 is more preferably 5 mm or less.

  In FIG. 2, the double-headed arrow Hc is the height in the radial direction of the core 20. A double-headed arrow D2 is a radial distance between the center CO and the connection point P2. The ratio (D2 / Hc) of the distance D2 to the height Hc is preferably 0.1 or more. By setting the ratio (D2 / Hc) to 0.1 or more, the pressure from the portion of the bead 8 is effectively applied to the flange. In the tire 2, the contact pressure on the side surface 34 is effectively improved. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the ratio (D2 / Hc) is more preferably equal to or greater than 0.2. The ratio (D2 / Hc) is preferably 0.6 or less. By setting the ratio (D2 / Hc) to 0.6 or less, the pressure that has been applied to the heel surface 36 in the related art is effectively applied to the side surface 34. Thereby, the contact pressure in the side surface 34 improves. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the ratio (D2 / Hc) is more preferably equal to or less than 0.5.

  The distance D2 is preferably 1 mm or more. By setting the distance D2 to be 1 mm or more, the pressure from the portion of the bead 8 is effectively applied to the flange. In the tire 2, the contact pressure on the side surface 34 is effectively improved. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the distance D2 is more preferably 2 mm or more. The distance D2 is preferably 6 mm or less. By setting the distance D2 to 6 mm or less, the pressure that is conventionally applied to the heel surface 36 is effectively applied to the side surface 34. Thereby, the contact pressure in the side surface 34 improves. This contributes to improvement in maneuverability. Furthermore, the improvement of the contact pressure improves the rim slip prevention performance. In this respect, the distance D2 is more preferably 5 mm or less.

  In the above, the relationship between the connection points P1 and P2 and the core 20 has been described in the portion of the bead 8 in FIG. These relationships are the same in the portion of the bead 8 in FIG. That is, in FIG. 3, the connection point P1 is preferably located on the outer side in the axial direction from the center CO. The connection point P2 is preferably located radially inward from the center CO. The ratio of the distance D1 to the width Wc (D1 / Wc) is preferably 0.1 or more, and more preferably 0.2 or more. The ratio (D1 / Wc) is preferably 0.6 or less, and more preferably 0.5 or less. The distance D1 is preferably 1 mm or more, and more preferably 2 mm or more. The distance D1 is preferably 6 mm or less, and more preferably 5 mm or less. The ratio (D2 / Hc) of the distance D2 to the height Hc is preferably 0.1 or more, and more preferably 0.2 or more. The ratio (D2 / Hc) is preferably 0.6 or less, and more preferably 0.5 or less. The distance D2 is preferably 1 mm or more, and more preferably 2 mm or more. The distance D2 is preferably 6 mm or less, and more preferably 5 mm or less.

  As described above, it is preferable that the core 20 has a spiral structure including a single wire extending in the substantially circumferential direction. By configuring the core 20 in this way, the core 20 can effectively apply pressure to the rim. This core 20 improves the contact pressure between the bead 8 and the rim. This contributes to an improvement in responsiveness of the tire 2. The improvement of the contact pressure improves the rim slip prevention performance. Furthermore, the core 20 having a spiral structure composed of one wire extending in the circumferential direction can be appropriately expanded and contracted in the circumferential direction. This contributes to shock absorption when the tire 2 gets over the gap. In the tire 2, excellent responsiveness and absorbability are realized.

  In the present invention, the dimensions and angles of the tire 2 and each member 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. In the present specification, the normal load means a load defined in a standard on which the tire 2 depends. “Maximum value” published in “Maximum load capacity” in the JATMA standard, “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “LOAD CAPACITY” in the ETRTO standard are normal loads.

  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 two-wheeled vehicle tire of Example 1 having the structure shown in FIG. 1 was obtained. The tire size was 120 / 70R17. Table 1 below shows the specifications of this tire. The contour of the heel surface of the tire is a straight line. This is shown as “straight line” in the heel shape column of the table. In this tire, the core has a spiral structure composed of a single wire. This is shown as “single” in the core structure column.

[Comparative Example 1]
In the tire of Comparative Example 1, the contour shape of the heel surface is an arc as shown in Table 1. This tire is the same as the tire of Example 1 except for the contour shape of the heel surface. This is a conventional tire.

[Example 2-6]
In the tire of Example 2-6, the shape of the contour of the heel surface is an arc whose curvature radius is as shown in Table 1. These tires are the same as the tires of Example 1 except for the radius of curvature of the heel surface.

[Example 7-9]
Tires of Examples 7-9 were obtained in the same manner as Example 2 except that the distance D1 was changed and the ratio (D1 / Wc) was changed as shown in Table 2 below. In the ninth embodiment, the connection point P1 is located on the inner side in the axial direction from the center CO. This is indicated by the negative value of the ratio (D1 / Wc).

[Examples 10-12]
Tires of Examples 10-12 were obtained in the same manner as Example 2 except that the distance D2 was changed and the ratio (D2 / Hc) was changed as shown in Table 2 below. In the ninth embodiment, the connection point P2 is located radially outside the center CO. This is indicated by the negative value of the ratio (D2 / Hc).

[Example 13]
A tire of Example 13 was obtained in the same manner as in Example 2 except that the core was configured by winding a tape in which a plurality of wires were arranged in parallel in the circumferential direction. The fact that the core is formed by winding a tape in which a plurality of wires are arranged in the circumferential direction is shown as “tape” in the column of the core structure.

[Maneuverability]
The prototype tire was incorporated into a standard rim (size = MT3.50) and mounted on the front wheel of a two-wheeled vehicle having a displacement of 1000 cc. The internal pressure of this tire was 250 kPa. A commercially available tire (size: 190 / 55ZR17) was mounted on the rear wheel, and air was filled so that the internal pressure was 290 kPa. This motorcycle was run on a circuit course with asphalt on the road surface, and sensory evaluation was performed by the rider. Evaluation items as maneuverability are responsiveness, turning steering performance, and absorbability. The results are shown in Table 1-2 below with a ten-level evaluation. Larger values are preferred.

[Rim assembly]
Using the tire changer, the trial tire was attached to and removed from the regular rim (size = MT3.50). The sensory evaluation by the operator was performed about the ease of attachment and removal. The results are shown in Table 1-2 below with a 10-step evaluation. Larger numbers are preferable.

[Rim slip prevention]
By a beat unseating resistance test according to JIS D4230, a load from the lateral direction was applied to the bead portion, and the resistance force when the bead was detached from the rim was measured. The results are shown in Table 1-2 below with a 10-step evaluation. Larger values are preferred.

[durability]
The prototype tire was assembled in a regular rim (size = MT3.50), and the tire was filled with air to adjust the internal pressure to 250 kPa. This tire was mounted on a drum-type running test machine, and a vertical load of 80% of the normal load was applied to the tire. This tire was run on the drum at a speed of 80 km / h. The time until the bead was damaged was measured. The results are shown in Table 1-2 below in three stages A, B and C. Durability is excellent in the order of A, B, and C. B or higher is acceptable.

  As shown in Table 1-2, the tire of the example has a higher evaluation than the tire of the comparative example. From this result, the superiority of the present invention is clear.

  The tire described above can be applied to various two-wheeled vehicles.

2 ... tyre 4 ... tread 6 ... side wall 8 ... bead 10 ... carcass 12 ... belt 14 ... band 16 ... inner liner 18 ... tread surface 20. .. Core 22 ... Apex 24 ... Carcass ply 26 ... Main part 28 ... Folded part 30 ... Belt ply 32 ... Bottom 34 ... Side surface 36 ... Heel surface 38 ... Virtual contour

Claims (6)

A tire with a pair of beads,
The outer surface of the bead portion of the tire includes a bottom surface that contacts the seat surface of the rim when the tire is mounted on the rim, a side surface that contacts the flange of the rim, and a bottom surface and the side surface. With a heel surface located between,
The heel surface is connected to the bottom surface at a connection point P1, and is connected to the side surface at a connection point P2.
For a two-wheeled vehicle, the contour of the heel surface is an outwardly convex arc C having a curvature radius R of 3.5 mm or more or a straight line L in a cross section obtained by cutting the tire along a plane perpendicular to the circumferential direction. tire.   When the contour of the bead portion formed by extending the bottom surface and the side surface assuming that the heel surface does not exist is a virtual contour, the contour of the heel surface does not protrude from the virtual contour. Item 2. The tire for a motorcycle according to item 1. The bead has a core,
The tire for a two-wheeled vehicle according to claim 1 or 2, wherein the connection point P1 is located axially outside the center of the core, and the connection point P2 is located radially inward from the center of the core.   The ratio (D1 / Wc) of the axial distance D1 between the center of the core and the connection point P1 to the width Wc of the core is 0.1 or more and 0.6 or less. tire.   The ratio (D2 / Hc) of the radial distance D2 between the center of the core and the connection point P2 to the height Hc of the core is 0.1 or more and 0.6 or less. Tires for motorcycles.   The tire for a two-wheeled vehicle according to any one of claims 1 to 5, wherein the core has a spiral structure composed of a single non-stretchable wire extending in a substantially circumferential direction.

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