Motorcycle tires

Abstract

To provide a two-wheel automobile tire pair which can improve turning performance of a vehicle.SOLUTION: A tire pair comprises a front tire 2 and a rear tire. A center arc index Ac, a middle arc index Am and a shoulder arc index As are obtained based on a contour line TLf of a tread surface 16 of the front tire 2 and a contour line of a tread surface of the rear tire. In the tire pair, the middle arc index Am is larger than the center arc index Ac, and the shoulder arc index As is larger than the middle arc index Am.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a pair of tires for a two-wheeled vehicle.

Background Art

[0002] A two-wheeled vehicle turns by tilting its body. The tread surface of the tire mounted on the two-wheeled vehicle has a rounded shape. In straight running, the portion of the equatorial plane of the tread surface mainly contacts the road surface. In turning running, the outer portion in the axial direction of the tread surface mainly contacts the road surface. In a tire for a two-wheeled vehicle, in order to improve performance such as turning performance and agility, attempts have been made to define the radius of curvature of the tread surface according to the area of the tread surface (for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a two-wheeled vehicle, even if the turning force of the front tire is increased, for example, if the rear tire does not have sufficient turning force, the steering characteristics tend to oversteer. Even if the front tire has high turning performance, if the rear tire has higher turning performance than the front tire, the steering characteristics tend to understeer. For example, even if measures are taken to improve the turning performance of the front tire, depending on the rear tire to be combined, the measures taken for this front tire may not be fully utilized. To improve the performance of the vehicle, it is necessary to tune not only the front tire but also the rear tire.

[0005] This invention has been made in view of these circumstances. The object of this invention is to provide a pair of tires for a motorcycle that can improve the turning performance of the vehicle. [Means for solving the problem]

[0006] A pair of tires for a two-wheeled vehicle according to one aspect of the present invention is a pair of tires comprising a front tire and a rear tire. Each of the front tire and the rear tire comprises a pair of beads, a carcass spanning between a first bead and a second bead of the pair of beads, a band located radially outward of the carcass, and a tread located radially outward of the band. The carcass includes a number of parallel carcass cords, each carcass cord inclined with respect to the equatorial plane. The band includes band cords that extend substantially circumferentially. The tread has a tread surface that contacts the road surface. In the meridional cross-section of each of the front tire and the rear tire, the contour line of the tread surface is divided into five equal parts, thereby dividing the contour line into five parts. The five parts are a center section including the equator, a pair of middle sections connected to the center section, and a pair of shoulder sections connected to the middle sections. The first arc is the arc passing through the equator and both ends of the center section, the second arc is the arc passing through the inner and outer ends and their centers of the middle section, and the third arc is the arc passing through the inner and outer ends and their centers of the shoulder section. The ratio of the radius R1f of the first arc of the front tire to the radius R1r of the first arc of the rear tire (R1f / R1r) is the center arc index, the ratio of the radius R2f of the second arc of the front tire to the radius R2r of the second arc of the rear tire (R2f / R2r) is the middle arc index, and the ratio of the radius R3f of the third arc of the front tire to the radius R3r of the third arc of the rear tire (R3f / R3r) is the shoulder arc index. The middle arc index is greater than the center arc index, and the shoulder arc index is greater than the middle arc index.

[0007] Preferably, in this pair of motorcycle tires, the center arc index is 0.40 or more and 0.60 or less. The shoulder arc index is 0.70 or more and 1.10 or less.

[0008] Preferably, in this pair of motorcycle tires, the radial distance from the equator to the edge of the tread surface is the tread height. In the front tire, the ratio of the tread height to the nominal cross-sectional width is 35% or more and 45% or less. In the rear tire, the ratio of the tread height to the nominal cross-sectional width is 30% or more and 35% or less.

[0009] Preferably, in this pair of motorcycle tires, the ratio of the radius R1f of the first arc to the nominal cross-sectional width of the front tire is 45% or more and 55% or less. In the rear tire, the ratio of the radius R1r of the first arc to the nominal cross-sectional width is 45% or more and 65% or less.

[0010] Preferably, in this pair of motorcycle tires, the tread surface does not have grooves that intersect the equator.

[0011] Preferably, in this pair of motorcycle tires, the angle that the carcass cords make with respect to the equatorial plane is between 20 degrees and 65 degrees.

[0012] More preferably, in this pair of motorcycle tires, the carcass cords are made of organic fibers. [Effects of the Invention]

[0013] According to the present invention, a pair of tires for a motorcycle that can improve the turning performance of the vehicle can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a cross-sectional view showing a portion of a front tire constituting a pair of tires for a motorcycle according to one embodiment of the present invention. [Figure 2]FIG. 2 is a schematic diagram for explaining the structure of the carcass and the band in the front tire. [Figure 3] FIG. 3 is a cross-sectional view for explaining the contour line of the tread surface of the front tire. [Figure 4] FIG. 4 is a developed view showing a modified example of the tread surface. [Figure 5] FIG. 5 is a cross-sectional view showing a part of a rear tire constituting a pair of tires for a two-wheeled vehicle according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram for explaining the structure of the carcass and the band in the rear tire. [Figure 7] FIG. 7 is a cross-sectional view for explaining the contour line of the tread surface of the rear tire.

MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0016] The tire is assembled to the rim. The inside of the tire is filled with air and the internal pressure of the tire is adjusted. In the present disclosure, the tire assembled to the rim is a tire-rim assembly. The tire-rim assembly includes a rim and a tire assembled to this rim.

[0017] In the present disclosure, the state where the tire is assembled to the standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to this tire is referred to as the standard state.

[0018] In the present disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state. The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is assembled to the standard rim are measured in the cross-section of the tire obtained by cutting the tire along a plane including the rotation axis, with the distance between the left and right beads made to coincide with the distance between the beads in the tire assembled to the standard rim.

[0019] The standard rim means the rim defined in the standards on which the tire depends. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are standard rims. Unless otherwise specified, the rim in the present disclosure means the standard rim.

[0020] The standard internal pressure means the internal pressure defined in the standards on which the tire depends. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are standard internal pressures.

[0021] The standard load means the load defined in the standards on which the tire depends. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are standard loads.

[0022] In the present disclosure, the "designated section width" is the "designated section width" included in the "tire designation" defined in JIS D4203 "Motorcycle Tires - Designation and Dimensions".

[0023] In the present disclosure, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The side portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of side portions.

[0024] A pair of motorcycle tires according to an embodiment of the present invention includes a front tire mounted on the front wheel of a motorcycle (not shown) and a rear tire mounted on the rear wheel. The front tire and the rear tire will be described below.

[0025] [Front tire] Figure 1 shows a portion of the cross-section of the front tire 2 (hereinafter also referred to as the meridian cross-section) along the plane containing the rotation axis of the tire 2. In Figure 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of the paper in Figure 1 is the circumferential direction of the tire 2. In Figure 1, the dashed line ELf is the equatorial plane of the tire 2.

[0026] In Figure 1, tire 2 is mounted on rim Rf (regular rim). Air is filled inside tire 2, and the internal pressure of tire 2 is adjusted.

[0027] This tire 2 comprises a tread 4, a pair of sidewalls 6, a pair of beads 8, a carcass 10, a band 12, and an inner liner 14.

[0028] The tread 4 is made of cross-linked rubber. The tread 4 is located radially outward of the band 12. The tread 4 has a tread surface 16 that contacts the road surface. The tire 2 contacts the road surface at the tread surface 16. As shown in Figure 1, in the meridian cross-section, the tread surface 16 is curved such that its equatorial portion protrudes radially outward. The tread of tire 2 (tire 2) has no grooves. This tire 2 is a slick tire.

[0029] In Figure 1, the position indicated by the symbol Ef is the intersection of the tread surface 16 and the equatorial surface. Intersection Ef is the equator of tire 2. If a groove is located on the equatorial surface, the equator Ef is determined based on the virtual outer surface (tread contour line TLf, described later) obtained by assuming the absence of a groove. The equator Ef is also the radial outer edge of tire 2.

[0030] In Figure 1, the position indicated by the symbol Fe is the edge of the tread surface 16. The length indicated by the double arrow TWf is the width of the tread surface 16. The width TWf of the tread surface 16 is expressed as the axial distance from the first edge Fe to the second edge Fe of the tread surface 16. The edge Fe of the tread surface 16 of this tire 2 is the axial outer edge of the tire 2. The width TWf of the tread surface 16 of this tire 2 is also called the total width (see JATMA, etc.).

[0031] Each sidewall 6 is made of cross-linked rubber. The sidewall 6 is connected to the edge of the tread 4. The sidewall 6 is located radially inward of the tread 4.

[0032] Each bead 8 is located radially inward of the sidewall 6. Each bead 8 comprises a core 18 and an apex 20. Although not shown, the core 18 contains steel wires. The apex 20 is located radially outward of the core 18. The apex 20 tapers outward. The apex 20 is made of cross-linked rubber with high rigidity.

[0033] The carcass 10 is located inside the tread 4 and a pair of sidewalls 6. The carcass 10 spans between the first bead 8 and the second bead 8 of a pair of beads 8.

[0034] The carcass 10 includes at least one carcass ply 22. The carcass 10 of this tire 2 is composed of one carcass ply 22. The carcass ply 22 includes a ply body 22a that spans between the first core 18 and the second core 18, and a pair of folded portions 22b that are connected to the ply body 22a and folded back axially from the inside to the outside around each core 18.

[0035] Figure 2 shows the configuration of the carcass 10 together with the band 12, which will be described later. In Figure 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the circumferential direction of the tire 2. The direction perpendicular to the plane of the paper is the radial direction of the tire 2. The front side of the paper is the radially outward direction, and the back side is the radially inward direction.

[0036] As shown in Figure 2, the carcass ply 22 constituting the carcass 10 contains a number of parallel carcass cords 24. In Figure 2, for ease of explanation, the carcass cords 24 are represented by solid lines, but the carcass cords 24 are covered with topping rubber 26.

[0037] Each carcass cord 24 is inclined with respect to the equatorial plane. In Figure 2, the angle indicated by the sign θf is the angle (inclination angle θf) that the carcass cord 24 in the carcass ply 22 makes with respect to the equatorial plane. In this tire 2, the inclination angle θf of the carcass cord 24 is between 20 degrees and 65 degrees.

[0038] In this tire 2, the carcass cord 24 can be made of organic fibers (organic fiber cord). Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. In this tire 2, the carcass cord 24 may also be made of inorganic fibers. In this case, examples of inorganic fibers include glass fibers and carbon fibers. In this tire 2, from the viewpoint of achieving a good balance between strength and handling stability, it is preferable that the carcass cord 24 be an organic fiber cord.

[0039] Band 12 is located radially outward of the carcass 10. Band 12 is laminated on the carcass 10 radially inward of the tread 4. Band 12 is located between the tread 4 and the carcass 10.

[0040] The band 12 includes a helically wound band cord 28. In Figure 2, for illustrative purposes, the band cord 28 is represented by a solid line, but the band cord 28 is covered with topping rubber 30. In this tire 2, the band cord 28 extends substantially circumferentially. More specifically, the angle that the band cord 28 makes with respect to the circumferential direction is 5° or less. The band 12 is also called a jointless band.

[0041] In this tire 2, a cord made of organic fibers (organic fiber cord) can be used as the band cord 28. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. In this tire 2, the band cord 28 may also be a cord made of inorganic fibers. In this case, glass fibers and carbon fibers are suggested as inorganic fibers. The band cord 28 may also be a steel cord.

[0042] In Figure 1, the position indicated by the symbol Bf is the end of band 12. The length indicated by the double arrow BWf is the width of band 12. The width BWf of band 12 is represented by the axial distance from the first end Bf to the second end Bf of band 12. In this tire 2, the ratio of the width BWf of band 12 to the width TWf of the tread surface 16 (BWf / TWf) is between 0.80 and 0.95.

[0043] The inner liner 14 is located inside the carcass 10. The inner liner 14 forms the inner surface of the tire 2. The inner liner 14 is made of cross-linked rubber with a low gas permeability coefficient. The inner liner 14 maintains the internal pressure of the tire 2.

[0044] In Figure 1, the length indicated by the symbol Hf is the tread height. The tread height Hf is the radial distance from the equator Ef to the edge Fe of the tread surface 16.

[0045] In this tire 2, the ratio of the tread height Hf to the nominal section width is preferably 35% or more and 45% or less. By setting this ratio to 35% or higher, sufficient turning force can be obtained with tire 2. From this viewpoint, it is more preferable that this ratio be 37% or higher, and even more preferable that it be 39% or higher. By setting this ratio to 45% or less, sufficient rigidity can be obtained in the side portion of tire 2. From this viewpoint, it is more preferable that this ratio be 43% or less, and even more preferable that it be 42% or less.

[0046] Figure 3 shows the contour of tire 2 in a meridian cross-section. This contour of tire 2 can be obtained, for example, by measuring the outer surface shape of tire 2 in a normal state using a displacement sensor. Of the contour lines, the portion from the first edge Fe of the tread surface 16 to its second edge Fe is the contour line TLf of the tread surface 16 (hereinafter referred to as the tread contour line TLf). For example, if grooves are cut into the tread 4, the contour line of the part with grooves is represented by a virtual contour line obtained as if there were no grooves. The contour line of the tread surface of the rear tire, which will be described later, is obtained in the same manner as this contour line TLf.

[0047] In Figure 3, the tread contour line TLf has a shape symmetrical with respect to the equatorial plane. In this tire 2, the tread contour line TLf is divided into five parts by dividing it into five equal parts.

[0048] Of the five parts, the part located in the center in the axial direction is the center section CLf. The center section CLf includes the equator Ef. The part located axially outside the center section CLf is the middle section MLf. The middle section MLf is connected to the center section CLf. The part located axially outside the middle section MLf is the shoulder section SLf. The shoulder section SLf is connected to the middle section MLf. The five parts are the central section CLf, which includes the equatorial region Ef; a pair of middle sections MLf connected to the central section CLf; and a pair of shoulder sections SLf connected to the middle sections MLF.

[0049] In Figure 3, the position indicated by the symbol CMf is the boundary between the center section CLf and the middle section MLf. Boundary CMf is the edge of the center section CLf and the inner edge of the middle section MLf. The position indicated by the symbol MSf is the boundary between the middle section MLf and the shoulder section SLf. Boundary MSf is the outer edge of the middle section MLf and the inner edge of the shoulder section SLf. The outer edge of the shoulder section SLf is the edge Fe of the tread surface 16. The shoulder section SLf includes the edge Fe of the tread surface 16.

[0050] In this tire 2, the first circular arc is the arc that passes through the equator Ef and both ends CMf of the center section CLf. In Figure 3, arrow R1f is the radius of the first circular arc. Although not shown, the center of the first circular arc lies on the equatorial plane. The second arc is the arc that passes through the inner end CMf and outer end MSf of the middle section MLf, and their centers. In Figure 3, arrow R2f is the radius of the second arc. The center of the middle section MLf is the intersection of the perpendicular bisector of the line segment connecting the inner end CMf and the outer end MSf with the middle section MLf. The third arc is the arc that passes through the inner end MSf and outer end Fe of the shoulder portion SLf, and their centers. In Figure 3, arrow R3f is the radius of the third arc. The center of the shoulder portion SLf is the intersection of the perpendicular bisector of the line segment connecting the inner end MSf and the outer end Fe with the shoulder portion SLf.

[0051] In this tire 2, the ratio of the radius R1f of the first arc to the nominal cross-sectional width is preferably 45% or more and 55% or less. Setting this ratio to 45% or higher suppresses the tendency of tire 2 to cut in during the initial stages of turning. From this perspective, a ratio of 48% or higher is more preferable. Setting this ratio to 55% or less improves initial responsiveness. From this perspective, a ratio of 52% or less is more preferable.

[0052] In this tire 2, the ratio of the radius R2f of the second arc to the radius R1f of the first arc (R2f / R1f) is preferably 0.88 or more and 1.49 or less. By setting the ratio (R2f / R1f) to 0.88 or higher, the tendency of tire 2 to cut in during the initial stages of turning is effectively suppressed. From this perspective, a ratio (R2f / R1f) of 0.98 or higher is more preferable. By setting the ratio (R2f / R1f) to 1.49 or less, sufficient turning force can be obtained with this tire 2. From this viewpoint, a ratio (R2f / R1f) of 1.30 or less is more preferable.

[0053] In this tire 2, the ratio of the radius R3f of the third arc to the radius R2f of the second arc (R3f / R2f) is preferably 0.96 or more and 2.07 or less. By setting the ratio (R3f / R2f) to 0.96 or higher, the tendency of tire 2 to cut in during the initial stages of turning is effectively suppressed. From this perspective, a ratio (R3f / R2f) of 0.98 or higher is more preferable. By setting the ratio (R3f / R2f) to 2.07 or less, sufficient turning force can be obtained with this tire 2. From this viewpoint, a ratio (R3f / R2f) of 1.33 or less is more preferable, and 1.23 or less is even more preferable.

[0054] As mentioned above, the tread surface 16 of this tire 2 does not have grooves. The tread surface 16 does not have grooves that intersect the equator Ef. This tire 2 has higher rigidity in the equatorial surface, which is the part that mainly contacts the road surface during straight-line driving, compared to a tire with grooves that intersect the equator. This tire 2 can quickly transition from straight-line driving to cornering, and its excellent cornering ability is fully utilized.

[0055] Figure 4 shows a modified example of the tread surface 16. As shown in Figure 4, grooves can be etched into the tread surface 16 of this tire 2. By etching grooves into the tread surface 16, a tread pattern like the one shown in Figure 4 can be formed. In Figure 4, the left-right direction is the axial direction of tire 2, and the up-down direction is the circumferential direction of tire 2. The direction perpendicular to the plane of paper in Figure 4 is the radial direction of tire 2. In Figure 4, arrow A indicates the direction of rotation of tire 2. The tread surface 16 makes contact with the road surface from the top to the bottom of the paper in Figure 4. The top of the paper is the first side to make contact, and the bottom of the paper is the last side to make contact. The tread pattern in Figure 4 is an example of a tread pattern that can be engraved on the tread surface 16 of this tire 2. The tread patterns that can be engraved on the tread surface 16 of this tire 2 will be explained using Figure 4.

[0056] As shown in Figure 4, the tread surface 16 has inclined grooves 34 as grooves 32. The inclined grooves 34 are inclined with respect to the circumferential direction. The leading end 36a of the inclined groove 34 is located on the edge Fe side of the tread surface 16. The trailing end 36b of the inclined groove 34 is located on the equator Ef side. The inclined groove 34 comprises a first inclined groove 34a carved between the equator Ef and the first end Fea of ​​the tread surface 16, and a second inclined groove 34b carved between the equator Ef and the second end Feb of the tread surface 16. On this tread surface 16, a plurality of first inclined grooves 34a are arranged circumferentially at a constant pitch. A plurality of second inclined grooves 34b are arranged circumferentially at a constant pitch. The first inclined grooves 34a and the second inclined grooves 34b are arranged alternately in the circumferential direction.

[0057] As shown in Figure 4, the entire first inclined groove 34a is located between the equator Ef and the edge Fe of the tread surface 16. The entire second inclined groove 34b is also located between the equator Ef and the edge Feb of the tread surface 16. Even on this tread surface 16, there are no grooves that intersect the equator Ef. Therefore, even in this case, the tire 2 has higher rigidity in the equatorial surface portion that mainly contacts the road surface during straight-line driving compared to a tire with grooves that intersect the equator. The tire 2 can quickly transition from straight-line driving to cornering driving, and the excellent cornering ability of the tire 2 is fully demonstrated. From the perspective of contributing to improved vehicle turning ability, it is preferable that the tread surface 16 of this tire 2 does not have grooves that intersect the equator Ef.

[0058] [Rear tire] Figure 5 shows a portion of the cross-section of the rear tire 42 (hereinafter referred to as the meridian cross-section) along the plane containing the rotation axis of the tire 42. In Figure 5, the left-right direction is the axial direction of the tire 42, and the up-down direction is the radial direction of the tire 42. The direction perpendicular to the plane of the paper in Figure 5 is the circumferential direction of the tire 42. In Figure 5, the dashed line ELr is the equatorial plane of the tire 42.

[0059] In Figure 5, the tire 42 is mounted on the rim Rr (regular rim). Air is filled inside the tire 42, and the internal pressure of the tire 42 is adjusted.

[0060] The tire 42 comprises a tread 44, a pair of sidewalls 46, a pair of beads 48, a carcass 50, a band 52, and an inner liner 54.

[0061] The tread 44 is made of cross-linked rubber. The tread 44 is located radially outward of the band 52. The tread 44 has a tread surface 56 that contacts the road surface. The tire 42 contacts the road surface at the tread surface 56. As shown in Figure 5, in the meridian cross-section, the tread surface 56 is curved such that its equatorial portion protrudes radially outward. The tread of this tire 42 has no grooves. This tire 42 is a slick tire.

[0062] In Figure 5, the position indicated by the symbol Er is the intersection of the tread surface 56 and the equatorial plane. Intersection Er is the equator of the tire 42. When a groove is located on the equatorial plane, the equatorial Er is determined based on the tread contour line TLr, which will be described later. The equatorial Er is also the radial outer edge of the tire 42.

[0063] In Figure 5, the position indicated by the symbol Re is the edge of the tread surface 56. The length indicated by the double arrow TWr is the width of the tread surface 56. The width TWr of the tread surface 56 is expressed as the axial distance from the first edge Re to the second edge Re of the tread surface 56. The edge Re of the tread surface 56 of this tire 42 is the axial outer edge of the tire 42. The width TWr of the tread surface 56 of this tire 42 is also called the total width (see JATMA, etc.).

[0064] Each sidewall 46 is made of cross-linked rubber. The sidewall 46 is connected to the edge of the tread 44. The sidewall 46 is located radially inward of the tread 44.

[0065] Each bead 48 is located radially inward of the sidewall 46. The bead 48 comprises a core 58 and an apex 60. Although not shown, the core 58 contains steel wires. The apex 60 is located radially outward of the core 58. The apex 60 tapers outward. The apex 60 is made of cross-linked rubber with high rigidity.

[0066] The carcass 50 is located inside the tread 44 and a pair of sidewalls 46. The carcass 50 spans between the first bead 48 and the second bead 48 of a pair of beads 48.

[0067] The carcass 50 includes at least one carcass ply 62. The carcass 50 of this tire 42 consists of one carcass ply 62. The carcass ply 22 includes a ply body 62a that spans between a first core 58 and a second core 58, and a pair of folded portions 62b that are connected to the ply body 62a and folded back axially from the inside to the outside around each core 58.

[0068] Figure 6 shows the configuration of the carcass 50 together with the band 52, which will be described later. In Figure 6, the left-right direction is the axial direction of the tire 42, and the up-down direction is the circumferential direction of the tire 42. The direction perpendicular to the plane of the paper is the radial direction of the tire 42. The front side of the paper is the radially outward direction, and the back side is the radially inward direction.

[0069] As shown in Figure 6, the carcass ply 62 constituting the carcass 50 contains a number of parallel carcass cords 64. In Figure 6, for the sake of clarity, the carcass cords 64 are represented by solid lines, but the carcass cords 64 are covered with topping rubber 66.

[0070] Each carcass cord 64 is inclined with respect to the equatorial plane. In Figure 6, the angle indicated by the sign θr is the angle (inclination angle θr) that the carcass cord 64 in the carcass ply 62 makes with respect to the equatorial plane. In this tire 42, the inclination angle θr of the carcass cord 64 is between 20 degrees and 65 degrees.

[0071] In this tire 42, the carcass cords 64 may be made of organic fibers (organic fiber cords). Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. In this tire 42, the carcass cords 64 may also be made of inorganic fibers. In this case, glass fibers and carbon fibers are presented as inorganic fibers. In this tire 42, it is preferable that the carcass cord 64 be an organic fiber cord, from the viewpoint of achieving a good balance between strength and handling stability.

[0072] Band 52 is located radially outward of the carcass 50. Band 52 is laminated on the carcass 50 radially inward of the tread 44. Band 52 is located between the tread 44 and the carcass 50.

[0073] The band 52 includes a helically wound band cord 68. In Figure 6, for ease of explanation, the band cord 68 is represented by a solid line, but the band cord 68 is covered with topping rubber 70. In this tire 42, the band cord 68 extends substantially circumferentially. More specifically, the angle that the band cord 68 makes with respect to the circumferential direction is 5° or less. The band 52 is also called a jointless band.

[0074] The tire 42 may use a cord made of organic fibers (organic fiber cord) as the band cord 68. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. In this tire 42, the band cord 68 may also be a cord made of inorganic fibers. In this case, glass fibers and carbon fibers are presented as inorganic fibers. The band cord 68 may also be a steel cord.

[0075] In Figure 5, the position indicated by the symbol Br is the end of band 52. The length indicated by the double arrow BWr is the width of band 52. The width BWf of band 52 is expressed as the axial distance from the first end Br to the second end Br of band 52. In this tire 42, the ratio of the width BWr of band 52 to the width TWr of the tread surface 56 (BWr / TWr) is between 0.80 and 0.95.

[0076] The inner liner 54 is located inside the carcass 50. The inner liner 54 forms the inner surface of the tire 42. The inner liner 54 is made of cross-linked rubber with a low gas permeability coefficient. The inner liner 54 maintains the internal pressure of the tire 2.

[0077] In Figure 5, the length indicated by the symbol Hr is the tread height. The tread height Hr is the radial distance from the equator Er to the edge Re of the tread surface 56.

[0078] In this tire 42, the ratio of the tread height Hr to the nominal section width is preferably 30% or more and 35% or less. By setting this ratio to 30% or higher, sufficient turning force can be obtained with this tire 42. From this perspective, a ratio of 32% or higher is more preferable. By setting this ratio to 35% or less, sufficient rigidity can be obtained in the sidewall of the tire 42. From this viewpoint, a ratio of 34% or less is more preferable.

[0079] Figure 7 shows the contour lines of the rear tire 42 in a meridian cross-section. Of the contour lines shown in Figure 7, the portion from the first edge Re of the tread surface 56 to its second edge Re is the contour line TLr of the tread surface 56 (hereinafter referred to as the tread contour line TLr).

[0080] In Figure 7, the tread contour line TLr has a shape symmetrical with respect to the equatorial plane. In this tire 42, the tread contour line TLr is divided into five parts by dividing it into five equal parts.

[0081] Of the five parts, the part located in the center in the axial direction is the center section CLr. The center section CLr includes the equator Er. The part located axially outside the center section CLr is the middle section MLr. The middle section MLr is connected to the center section CLr. The part located axially outside the middle section MLr is the shoulder section SLr. The shoulder section SLr is connected to the middle section MLr. The five parts are the central section CLr, which includes the equatorial section Er; a pair of middle sections MLr connected to the central section CLr; and a pair of shoulder sections SLr connected to the middle sections MLr.

[0082] In Figure 7, the position indicated by the symbol CMr is the boundary between the center section CLr and the middle section MLr. Boundary CMr is the edge of the center section CLr and the inner edge of the middle section MLr. The position indicated by the symbol MSr is the boundary between the middle section MLr and the shoulder section SLr. Boundary MSr is the outer edge of the middle section MLr and the inner edge of the shoulder section SLr. The outer edge of the shoulder section SLr is the edge Re of the tread surface 56. The shoulder section SLr includes the edge Re of the tread surface 56.

[0083] In this tire 42, the first circular arc is the arc that passes through the equator Er and both ends CMr of the center section CLr. In Figure 7, arrow R1r is the radius of the first circular arc. Although not shown, the center of the first circular arc lies on the equatorial plane. The second arc is the arc that passes through the inner end CMr and outer end MSr of the middle section MLr, and their centers. In Figure 7, arrow R2r is the radius of the second arc. The center of the middle section MLr is the intersection of the perpendicular bisector of the line segment connecting the inner end CMr and the outer end MSr with the middle section MLr. The third arc is the arc that passes through the inner end MSr and outer end Re of the shoulder portion SLr, and their centers. In Figure 7, arrow R3r is the radius of the third arc. The center of the shoulder portion SLr is the intersection of the perpendicular bisector of the line segment connecting the inner end MSr and the outer end Re with the shoulder portion SLr.

[0084] In this tire 42, it is preferable that the ratio of the radius R1r of the first arc to the nominal section width is between 45% and 65%. Setting this ratio to 45% or higher suppresses the rear tires 42 from cutting in during the initial stages of turning. From this perspective, a ratio of 54% or higher is more preferable. Setting this ratio to 65% or less improves initial responsiveness. From this perspective, a ratio of 62% or less is more preferable.

[0085] In this tire 42, the ratio of the radius R2r of the second arc to the radius R1r of the first arc (R2r / R1r) is preferably between 0.81 and 1.36. By setting the ratio (R2r / R1r) to 0.81 or higher, the tendency of the tire 42 to cut in during the initial stages of turning is effectively suppressed. From this perspective, a ratio (R2r / R1r) of 0.83 or higher is more preferable. By setting the ratio (R2r / R1r) to 1.36 or less, sufficient turning force can be obtained with this tire 42. From this viewpoint, it is more preferable that the ratio (R2r / R1r) is 1.09 or less, and even more preferable that it is 0.92 or less.

[0086] In this tire 42, the ratio of the radius R3r of the third arc to the radius R2r of the second arc (R3r / R2r) is preferably 0.62 or more and 1.26 or less. By setting the ratio (R3r / R2r) to 0.62 or higher, the tendency of the tire 42 to cut in during the initial stages of cornering is effectively suppressed. From this perspective, a ratio (R3r / R2r) of 0.81 or higher is more preferable. By setting the ratio (R3r / R2r) to 1.26 or less, sufficient turning force can be obtained with this tire 42. From this viewpoint, a ratio (R3r / R2r) of 1.08 or less is more preferable, and 0.96 or less is even more preferable.

[0087] As mentioned above, the tread surface 56 of this tire 42 does not have grooves. The tread surface 56 does not have grooves that intersect the equator Er. This tire 42 has higher rigidity in the equatorial surface portion, which is the part that mainly contacts the road surface when driving straight, compared to a tire with grooves that intersect the equator. This tire 42 can quickly transition from driving straight to driving in a turn, and its excellent cornering ability is fully utilized.

[0088] This tire 42, like the tread surface 16 of the front tire 2 described above, can also have grooves cut into its tread surface 56. In this case, similar to the tread surface 16, the tread pattern (not shown) is constructed so as not to include grooves that intersect the equator Er. This tire 42 has higher rigidity in the equatorial surface portion that mainly contacts the road surface during straight-line driving compared to a tire with grooves that intersect the equator. This tire 42 can quickly transition from straight-line driving to cornering driving, and the excellent cornering ability of this tire 42 is fully demonstrated. In this tire 42, it is preferable that the tread surface 56 does not have grooves that intersect the equator Er, from the viewpoint of contributing to improved vehicle turning ability.

[0089] [Tire vs] A tire pair according to one embodiment of the present invention consists of the front tire 2 described above and the rear tire 42. In this tire pair, in order to effectively contribute to improving the turning performance of the vehicle, the tread contour line TLf of the front tire 2 and the tread contour line TLr of the rear tire 42 are set in an exquisite balance.

[0090] In this tire pair, the following center arc index Ac, middle arc index Am, and shoulder arc index As are used to appropriately set the tread contour lines TLf and TLr. The center arc index Ac is the ratio (R1f / R1r) of the radius R1f of the first arc of the front tire 2 to the radius R1r of the first arc of the rear tire 42. The middle arc index Am is the ratio (R2f / R2r) of the radius R2f of the second arc of the front tire 2 to the radius R2r of the second arc of the rear tire 42. The shoulder arc index As is the ratio (R3f / R3r) of the radius R3f of the third arc of the front tire 2 to the radius R3r of the third arc of the rear tire 42.

[0091] In this tire pair, the middle arc index Am is greater than the center arc index Ac, and the shoulder arc index As is greater than the middle arc index Am. With this tire combination, the camber thrust of the rear tire (42) decreases during the initial stages of turning. This tire combination makes it easier to change the direction of the vehicle. In the initial stages of turning, the turning ability of the front tires 2 improves compared to that of the rear tires 42, causing the front tires 2 to turn first. The vehicle can maintain its turning ability without its steering characteristics exhibiting an oversteer tendency. During secondary turns, the difference between the turning ability of the front tire 2 and the rear tire 42 is kept to a minimum. This tire pair maintains good stability. Because the vehicle's orientation can be sufficiently changed during the initial phase of a turn, it can ensure sufficient turning ability, compensating for any lack of turning force during the secondary turn. As a result, the vehicle can achieve high turning ability and stability. This tire combination improves turning force in the initial stages of a turn, and enhances turning ability and stability during the secondary turns. This tire combination can improve the vehicle's turning ability.

[0092] In this tire pair, the center arc index Ac is preferably 0.40 or more and 0.60 or less. This improves the turning force in the initial stage of turning and improves turning ability and stability in the secondary stage of turning. This tire pair can improve the turning ability of the vehicle. From this viewpoint, the center arc index Ac is more preferably 0.50 or more, and even more preferably 0.51 or more. The center arc index Ac is more preferably 0.58 or less.

[0093] In this tire pair, the shoulder arc index As is preferably between 0.70 and 1.10. This improves the turning force in the initial stage of turning and improves turning ability and stability in the secondary stage of turning. This tire pair can improve the turning ability of the vehicle. From this viewpoint, the shoulder arc index As is more preferably 0.80 or higher, and even more preferably 0.83 or higher. The shoulder arc index As is more preferably 0.88 or lower.

[0094] In this tire pair, from the viewpoint of improving the vehicle's turning ability, it is more preferable that the center arc index Ac is 0.40 or more and 0.60 or less, and the shoulder arc index As is 0.70 or more and 1.10 or less.

[0095] As mentioned above, in the front tire 2, the ratio of tread height Hf to nominal section width is preferably 35% or more and 45% or less. In the rear tire 42, the ratio of tread height Hr to nominal section width is preferably 30% or more and 35% or less. In this tire pair, from the viewpoint of improving the turning performance of the vehicle, it is more preferable that the ratio of the tread height Hf to the nominal section width is 35% or more and 45% or less for the front tire 2, and that the ratio of the tread height Hf to the nominal section width is 30% or more and 35% or less for the rear tire 42.

[0096] As mentioned above, in the front tire 2, it is preferable that the ratio of the radius R1f of the first arc to the nominal section width is 45% or more and 55% or less. In the rear tire 42, it is preferable that the ratio of the radius R1r of the first arc to the nominal section width is 45% or more and 65% or less. In this tire pair, from the viewpoint of improving the turning ability of the vehicle, it is more preferable that the ratio of the radius R1f of the first arc to the nominal cross-sectional width of the front tire 2 is 45% or more and 55% or less, and that the ratio of the radius R1r of the first arc to the nominal cross-sectional width of the rear tire 42 is 45% or more and 65% or less.

[0097] As described above, the present invention provides a pair of tires for a motorcycle that can improve the turning performance of the vehicle. [Examples]

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0099] [Example 1] A pair of motorcycle tires was obtained, consisting of a front tire (120 / 70ZR17) with the basic configuration shown in Figure 1 and the specifications shown in Table 1 below, and a rear tire (190 / 55ZR17) with the basic configuration shown in Figure 4 and the specifications shown in Table 1 below. The nominal cross-sectional width Wf of the front tire was 120, and the nominal cross-sectional width Wr of the rear tire was 190. The front and rear tires of this Embodiment 1 are slick tires. The tread surfaces of the front and rear tires do not have grooves that intersect the equator. This is indicated by "Y" in the "Groove" column of Table 1.

[0100] [Examples 2-9 and Comparative Examples 1-4] The radius of the first arc R1f, the radius of the second arc R2f, the radius of the third arc R3f, and the tread height Hf of the front tire, and the radius of the first arc R1r, the radius of the second arc R2r, the radius of the third arc R3r, the nominal section width Wr, and the tread height Hr of the rear tire were adjusted to obtain the ratios (R2f / R1f), (R3f / R2f), (R1f / Wf), (Hf / Wf), (R2r / R1r), (R3r / R2r), (R1r / Wr), (Hr / Wr), the center arc index Ac, the middle arc index Am, and the shoulder arc index As shown in Tables 1 and 2 below, thereby obtaining the tire pairs of Example 2-9 and Comparative Example 1-4. The tread surfaces of Examples 1, 8, and 9, and Comparative Examples 1 and 4, were provided with grooves that intersect the equator. This is indicated by "N" in the "Grooves" column of Tables 1 and 2. The rear tire size for Examples 3 and 4 and Comparative Example 1 was 200 / 55ZR17. The rear tire size for Comparative Example 4 was 180 / 55ZR17. Except for the configurations shown in Tables 1 and 2, the configuration was set to be the same as that of Example 1.

[0101] [Performance evaluation] The front and rear tires were mounted onto their respective standard rims, inflated, and the internal tire pressure was adjusted to the standard level. The front and rear tires were mounted on a large motorcycle (engine displacement = 1000cc). The motorcycle was driven on a dry asphalt test course, and a subjective evaluation (on a 10-point scale) was conducted by a test rider. The evaluation criteria include initial turning ability, transient characteristics, and turning ability and stability during secondary turning. The evaluation results are shown as indices in Tables 1 and 2 below. A higher number indicates better performance.

[0102] [Table 1]

[0103] [Table 2]

[0104] As shown in Table 1-2, the tire pair of the embodiment has been confirmed to contribute to improving the turning performance of the vehicle. From this evaluation result, the advantages of the present invention are clear. [Industrial applicability]

[0105] The technologies described above, which can contribute to improving the turning ability of vehicles, can also be applied to tire pairs for various types of motorcycles. [Explanation of Symbols]

[0106] 2. Front tire 4, 44... tread 8, 48...bead 10, 50...carcass 12, 52...band 22, 62... Carcass ply 24, 64...carcass code 28, 68...band code 42... Rear tire

Claims

1. A tire pair consisting of a front tire and a rear tire, Each of the aforementioned front tire and rear tire is The vehicle comprises a pair of beads, a carcass spanning between a first bead and a second bead of the pair, a band located radially outward of the carcass, and a tread located radially outward of the band. The carcass includes a number of parallel carcass codes, each carcass code being inclined with respect to the equatorial plane. The angle that the carcass code makes with respect to the equatorial plane is between 20 degrees and 65 degrees. The band includes a band code that extends substantially in the circumferential direction, The tread has a tread surface that contacts the road surface, In the meridian cross-section, by dividing the contour line of the tread surface into five equal parts, the contour line is divided into five parts. The five aforementioned parts are a central section including the equator, a pair of middle sections connected to the central section, and a pair of shoulder sections connected to the middle sections. The first arc is the arc that passes through the equator and both ends of the center portion. The arc passing through the inner end and outer end of the middle section and its center is the second arc. The arc passing through the inner end and outer end of the shoulder portion and its center is the third arc. The ratio of the radius R1f of the first arc of the front tire to the radius R1r of the first arc of the rear tire (R1f / R1r) is the center arc index. The ratio of the radius R2f of the second arc of the front tire to the radius R2r of the second arc of the rear tire (R2f / R2r) is the middle arc index. The ratio of the radius R3f of the third arc of the front tire to the radius R3r of the third arc of the rear tire (R3f / R3r) is the shoulder arc index. The middle arc index is greater than the center arc index, and the shoulder arc index is greater than the middle arc index, The radial distance from the equator to the edge of the tread surface is the tread height. The ratio of the tread height to the nominal cross-sectional width of the front tire is greater than the ratio of the tread height to the nominal cross-sectional width of the rear tire. In the aforementioned front tire, the ratio of the tread height to the nominal cross-sectional width is 35% or more and 45% or less. Tires for motorcycles.

2. The aforementioned center arc index is 0.40 or more and 0.60 or less. The aforementioned shoulder arc index is 0.70 or more and 1.10 or less. A pair of tires for a two-wheeled vehicle according to claim 1.

3. In the rear tire, the ratio of the tread height to the nominal cross-sectional width is 30% or more and 35% or less. A pair of tires for a two-wheeled vehicle according to claim 1 or 2.

4. In the aforementioned front tire, the ratio of the radius R1f of the first arc to the nominal cross-sectional width is 45% or more and 55% or less. In the aforementioned rear tire, the ratio of the radius R1r of the first arc to the nominal cross-sectional width is 45% or more and 65% or less. A pair of tires for a two-wheeled vehicle according to any one of claims 1 to 3.

5. The tread surface does not have grooves that intersect the equator. A pair of tires for a two-wheeled vehicle according to any one of claims 1 to 4.

6. The carcass cord is a cord made of organic fibers. A pair of tires for a two-wheeled vehicle according to any one of claims 1 to 5.

7. In the front tire, the ratio of the radius R2f of the second arc to the radius R1f of the first arc (R2f / R1f) is 0.88 or more and 1.49 or less. The ratio of the radius R3f of the third arc to the radius R2f of the second arc (R3f / R2f) is 0.96 or more and 2.07 or less. A pair of tires for a two-wheeled vehicle according to any one of claims 1 to 6.

8. In the rear tire, the ratio of the radius R2r of the second arc to the radius R1r of the first arc (R2r / R1r) is 0.81 or more and 1.36 or less. The ratio of the radius R3r of the third arc to the radius R2r of the second arc (R3r / R2r) is 0.62 or more and 1.26 or less. A pair of tires for a two-wheeled vehicle according to any one of claims 1 to 7.

Images