tire

Abstract

We offer Tire 2, which achieves improved high-speed durability while suppressing the impact on rolling resistance. [Solution] The tire 2 comprises a tread 4 and a band 16. The outer surface 4G of the tread 4 comprises a crown portion 64, a pair of middle portions 66, and a pair of shoulder portions 68. The radius TR1 of the arc representing the contour of the crown portion 64 is 5 to 7 times the axial width Wa of the contact surface of the tire 2 in its standard state. The band 16 comprises a band cord 56 made of organic fiber cord. The shrinkage rate SRs of the band cord 56 at a position corresponding to 70% of the maximum width SW of the tire 2 in its standard state is 70% to 130% of the shrinkage rate SRc of the band cord 56 at the equatorial plane of the tire 2.

Description

Technical Field

[0001] The present invention relates to a tire. More specifically, the present invention relates to a tire mounted on a passenger car.

Background Art

[0002] Tires assumed to be used at speeds of 270 km / h or more are required to have excellent high-speed durability. For example, Patent Document 1 discloses a profile of the outer surface of a tread for the purpose of improving high-speed durability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tire capable of achieving improved high-speed durability while suppressing the influence on rolling resistance.

Means for Solving the Problems

[0005] The tire according to the present invention comprises a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt. The standard state of the tire is when the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 92% of the regular internal pressure, and no load is applied to the tire. The outer surface of the tread comprises a crown portion located in the axial center, a pair of middle portions located axially outward of the crown portion, and a pair of shoulder portions located axially outward of the middle portions. In the meridional cross-section of the tire in the standard state, the contour of the crown portion is represented by an arc centered on the equatorial plane, the contour of each middle portion is represented by an arc tangent to the arc representing the contour of the crown portion, and the contour of each shoulder portion is represented by an arc tangent to the arc representing the contour of the middle portion. The tire, in its standard state, is subjected to a longitudinal load of 75% of the normal load, and the tire is brought into contact with a plane. The position on the outer surface of the tire corresponding to the axial outer end of the tire's contact surface is the contact reference end, and the axial distance from one of the contact reference ends to the other of the tire is the axial width Wa of the contact surface. The radius TR1 of the arc representing the contour of the crown portion is 5 to 7 times the axial width Wa. The belt comprises a belt cord inclined with respect to the circumferential direction. The belt cord is a steel cord. The band comprises a band cord that extends substantially in the circumferential direction. The band cord is an organic fiber cord. The shrinkage rate of the band cord at a position corresponding to 70% of the maximum width of the tire in its standard state is 70% to 130% of the shrinkage rate of the band cord at the equatorial plane of the tire. [Effects of the Invention]

[0006] According to the present invention, a tire can be obtained that can achieve improved high-speed durability while suppressing the impact on rolling resistance. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view showing a part of a tire relating to one embodiment of the present invention. [Figure 2] This is an explanatory diagram illustrating the configuration of the belt and band. [Figure 3] This is a cross-sectional view showing the outline of the outer surface of the tread. [Figure 4] This is a schematic diagram showing an example of the tire's contact patch. [Figure 5] This is a perspective view showing a portion of the band strip used to form the band. [Figure 6] This is a cross-sectional view showing a portion of the outline of the outer surface shown in Figure 3. [Figure 7] This is an explanatory diagram illustrating how to measure the shrinkage rate of a band cord. [Figure 8] This is an explanatory diagram illustrating how to measure the shrinkage rate of a band cord. [Modes for carrying out the invention]

[0008] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0009] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0010] In this invention, the state in which a tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire is called the regular state. The state in which a tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 92% of the regular internal pressure, and no load is applied to the tire is called the standard state.

[0011] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under standard conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire's cross-section, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim. The tire's structure, which cannot be confirmed when the tire is mounted on a standard rim, is confirmed at the aforementioned cross-section.

[0012] A genuine rim refers to a rim defined in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are all considered genuine rims.

[0013] Regular tire pressure refers to the internal pressure specified in the tire's standard. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are all considered regular tire pressures.

[0014] The standard load refers to the load specified in the tire's specifications. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are all considered standard loads.

[0015] In this invention, the speed symbol is, for example, a symbol defined in the JATMA standard that represents the maximum speed at which a tire can travel when loaded with the mass indicated by its load index under specified conditions. A tire with a speed symbol of W or higher means a tire with a speed symbol of W or Y.

[0016] As will be described later, in the formation of the band of the present invention, while applying a load to the band code, the band code is wound in a spiral shape. The tension generated by applying a load to the band code acts on the tire as a restraining force. In the band of the tire, the band code is in a stretched state. By releasing the band code from the tire, the band code contracts. The contraction rate of the band code reflects the restraining force of the band in the tire.

[0017] In the present invention, the contraction rate of the band code is measured as follows. The method for measuring the contraction rate will be described using FIGS. 7 and 8. The band of the tire includes a band code wound in a spiral shape. FIG. 7 schematically shows the state of the band code B in the band of the tire. For the measurement of the contraction rate, first, the tread of the tire is peeled off so that the band code B is exposed. The length of the exposed band code B is measured, and a reference line D representing the reference length Lf (for example, 100 cm) is attached to the band code B. Then, the band code B is peeled off from the tire and left to stand for 24 hours in an environment where the temperature is adjusted within the range of 20°C to 30°C. After standing, as shown in FIG. 8, the distance between the reference lines attached to the band code B is measured, and the length La of the band code B after contraction is obtained. The contraction rate SR (unit: %) is calculated by the following formula. SR (%) = (Lf - La) / Lf × 100 The greater the contraction rate SR, the higher the restraining force of the band, and the smaller the contraction rate SR, the lower the restraining force of the band.

[0018] In the present invention, 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 sidewall 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 sidewall portions. The central portion of the tread portion is also called the crown portion. The end portion of the tread portion is also called the shoulder portion.

[0019] [Practices that formed the basis of this invention] A tread with a flat outer surface (hereinafter referred to as a flat tread) is advantageous in terms of rolling resistance, but disadvantageous in terms of high-speed durability when a camber angle is applied (hereinafter referred to as high-speed durability). A tread with a rounded outer surface (hereinafter referred to as a round tread) is advantageous in terms of high-speed durability, but disadvantageous in terms of rolling resistance. Rolling resistance and high-speed durability are inversely related, and it is difficult to achieve both at the same time by controlling the profile of the tread's outer surface.

[0020] In a tire in motion, deformation and recovery are repeated. The radial position of the tread fluctuates. This tread movement affects rolling resistance and high-speed durability.

[0021] The tire tread comprises a belt and a band. The belt and band are located radially inward of the tread. The belt consists of a belt cord made of steel cord and inclined with respect to the circumferential direction. The band consists of a band cord made of organic fiber cord and extends substantially in the circumferential direction. The belt and band restrain the tread. This suppresses the movement of the tread. The belt and band can contribute to suppressing the increase in rolling resistance and the decrease in high-speed durability caused by tread movement.

[0022] Despite adopting a round tread, which is advantageous for high-speed durability, there were cases where the tire's high-speed durability did not reach the expected level. To clarify the cause, the inventors investigated the restraining force of the belt and band. As a result, the inventors found that the restraining force at the edge of the tread (hereinafter referred to as the shoulder portion) tends to be lower than the restraining force at the central portion of the tread (hereinafter referred to as the crown portion), and that this affects the potential for improvement in high-speed durability.

[0023] Therefore, based on the aforementioned findings, the inventors diligently studied technologies that can improve high-speed durability while suppressing the impact on rolling resistance, and have completed the invention described below.

[0024] [Summary of Embodiments of the Invention] The present invention relates to a tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt, wherein the standard state of the tire is when the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 92% of the normal internal pressure, and no load is applied to the tire, the outer surface of the tread comprises a crown portion located axially in the center, a pair of middle portions located axially outward of the crown portion, and a pair of shoulder portions located axially outward of the middle portions, and in the meridional cross-section of the tire in the standard state, the contour of the crown portion is represented by an arc centered on the equatorial plane, the contour of each middle portion is represented by an arc tangent to the arc representing the contour of the crown portion, and the contour of each shoulder portion is The tire is represented by an arc tangent to an arc representing the contour of the middle section, and the position on the outer surface of the tire corresponding to the axial outer end of the contact surface of the tire, obtained by applying a longitudinal load of 75% of the normal load to the tire in the standard state and bringing the tire into contact with a plane, is the contact reference end, the axial distance from one of the contact reference ends to the other of the tire is the axial width Wa of the contact surface, the radius TR1 of the arc representing the contour of the crown section is 5 to 7 times the axial width Wa, the belt comprises a belt cord inclined with respect to the circumferential direction, the belt cord is a steel cord, the band comprises a band cord substantially extending in the circumferential direction, the band cord is an organic fiber cord, and the shrinkage rate of the band cord at a position corresponding to 70% of the maximum width of the tire in the standard state is 70% to 130% of the shrinkage rate of the band cord at the equatorial plane of the tire.

[0025] The tire of the present invention can achieve improved high-speed durability while suppressing the impact on rolling resistance. Although the mechanism by which this effect is achieved is not yet clear, it is presumed to be as follows.

[0026] In the tire of the present invention, the radius TR1 of the arc representing the contour of the crown portion is set to be between 5 and 7 times the contact width Wa of the contact surface of the tire. This results in a tread with a flat outer surface. As mentioned above, a flat tread has an advantageous effect on rolling resistance. The tread of this tire can contribute to suppressing the influence on rolling resistance. On the other hand, as mentioned above, flat treads are disadvantageous in terms of high-speed durability. However, in this tire, the shrinkage rate of the band cords in the shoulder portion of the tread is taken into consideration. Specifically, the shrinkage rate of the band cords at a position corresponding to 70% of the maximum width of the tire in its standard state is set to be between 70% and 130% of the shrinkage rate of the band cords at the equatorial plane of the tire. In this tire, the shrinkage rate of the band cords in the shoulder portion is set to be about the same as the shrinkage rate of the band cords in the crown portion. The movement of the shoulder portion is sufficiently restrained. The bands, along with the belt made of steel cord, can contribute sufficiently to restraining the movement of the tread portion. The belt and band of the present invention are particularly effective for tires intended for use at speeds of 270 km / h or higher, in other words, for tires with a speed rating of W or higher. These tires can achieve improved high-speed durability. Restricting the movement of the tread area can also contribute to reducing rolling resistance. This tire can achieve improved high-speed durability while minimizing the impact on rolling resistance.

[0027] Preferably, at the contact surface of the tire, the ratio of the central contact length at the center of the contact width of the contact surface to the reference contact length at a position corresponding to 80% of the contact width of the contact surface is the shape index F80, and the shape index F80 is 1.10 or more and 1.40 or less. This creates a tire contact shape that can suppress the impact on high-speed durability and the impact on rolling resistance. This tire can maintain good high-speed durability and low rolling resistance. Since wear at the crown is suppressed, this tire can also maintain good wear resistance.

[0028] Preferably, the ratio TR2 / TR1 of the radius TR2 of the arc representing the contour of the middle section to the radius TR1 of the arc representing the contour of the crown section is 0.35 or more and 0.40 or less, and the ratio TR3 / TR1 of the radius TR3 of the arc representing the contour of the shoulder section to the radius TR1 of the arc representing the contour of the crown section is 0.09 or more and 0.13 or less. As a result, the radius of the arc representing the contour of the shoulder section is set to be smaller than that of conventional tires. In other words, the shoulder section is rounded compared to conventional shoulder sections. When a flat tread is used for the tread, this tire can suppress the localized increase in contact pressure at the contact edge, which is a concern under conditions where high loads are applied to the shoulder section, such as during limit driving or high-speed driving. This tire can suppress the occurrence of wear at the contact edge and the decrease in high-speed durability. This tire can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance.

[0029] Preferably, the ratio RW1 / Wa of the axial distance RW1 from the equatorial plane to the boundary between the crown and middle sections to the axial width Wa of the contact surface is 0.15 or more and 0.25 or less, and the ratio RW3 / Wa of the axial distance RW3 from the boundary between the middle and shoulder sections to the contact reference end to the axial width Wa is 0.10 or more and 0.15 or less. As a result, the flat contour of the crown section of the tread's outer surface profile effectively contributes to reducing rolling resistance, and the rounded contour of the shoulder section effectively contributes to suppressing localized increases in contact pressure at the contact end. This tire can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance.

[0030] Preferably, in the meridional cross-section of the tire in the standard state, the ratio TR1 / TRb of the radius TR1 of the arc representing the crown contour to the radius TRb of the arc having its center on the equatorial plane of the tire and passing through the equator of the tire and the contact reference edge is 1.66 or more and 1.96 or less. As a result, the flat contour of the crown portion of the tread's outer surface profile can effectively contribute to reducing rolling resistance, and the rounded contour of the shoulder portion can effectively contribute to suppressing localized increases in contact pressure at the contact edge. This tire can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance.

[0031] Thus, the tire of the present invention can achieve improved high-speed durability while suppressing the impact on rolling resistance. Furthermore, this tire has the potential to achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance. These points will be explained in detail below using tire 2 shown in Figure 1 as an example.

[0032] [Details of the Embodiments of the Invention]

[0033] Figure 1 shows a part of a tire 2 according to one embodiment of the present invention. This tire 2 is a pneumatic tire for a passenger car. The tire 2 shown in Figure 1 is mounted on a rim R (regular rim).

[0034] Figure 1 shows a portion of the cross-section of tire 2 along a plane containing the axis of rotation of tire 2 (not shown). The cross-section shown in Figure 1 is also called a meridian cross-section. The direction indicated by the double arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. The direction indicated by the double arrow RD is the radial direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the circumferential direction of tire 2. The dashed line EL extending radially represents the equatorial plane of tire 2.

[0035] In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2. The direction indicated by arrow RD1 is the radial outward direction of tire 2, and the direction indicated by arrow RD2 is the radial inward direction of tire 2.

[0036] In Figure 1, the position indicated by the symbol Eq is the intersection of the outer surface 2G of tire 2 (specifically, the tread surface, which will be described later) and the equatorial plane. Intersection point Eq is the equator of tire 2. If the groove is located on the equatorial plane, the equatorial Eq is determined based on the virtual outer surface obtained by assuming the absence of the groove. The equatorial Eq is the radial outer end of tire 2.

[0037] In Figure 1, the position indicated by the symbol PW is the axial outer end of tire 2 (hereinafter referred to as outer end PW). If there are decorations such as patterns or letters on the outer surface 2G, outer end PW is identified based on a virtual outer surface (the dashed line LV in Figure 1) obtained by assuming there are no decorations. In Figure 1, the length indicated by the double-headed arrow SW represents the maximum width of tire 2. The maximum width SW of tire 2 is the axial distance from one outer end PW to the other outer end PW (not shown). The outer ends PW are also called the maximum width position. The maximum width SW obtained under normal conditions is the cross-sectional width of tire 2 (see JATMA, etc.). In Figure 1, the position indicated by the symbol P70 is a position on the outer surface 2G of tire 2 that corresponds to 70% of the maximum width SW of tire 2. Position P70 is identified in tire 2 under standard conditions. In tire 2 under standard conditions, the ratio of the axial distance from the equatorial plane to position P70 to the axial distance from the equatorial plane to the maximum width position PW is 70%.

[0038] The tire 2 comprises a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, a pair of chafers 18, an inner liner 20, and a pair of insulation 22.

[0039] The tread 4 is located radially outward of the carcass 12. The tread 4 is made of cross-linked rubber. The tread 4 is in contact with the road surface. Tread 4 has grooves 24 cut into it. This forms the tread pattern. In Figure 1, the position indicated by the symbol TS is the boundary between the tread 4 and the sidewall 6 (described later) on the outer surface 2G of the tire 2. Boundary TS is also the edge of the outer surface 4G of the tread 4.

[0040] The tread 4 has a tread body 26 and a pair of wings 28. The tread body 26 is the main contact point with the road surface. Each wing 28 is positioned between the tread body 26 and the sidewall 6. The tread body 26 and the sidewall 6 are joined via the wings 28. The wings 28 are made of cross-linked rubber with adhesive properties in mind.

[0041] The tread body 26 comprises a cap layer 30 located on the outermost radial side and a base layer 32 located on the innermost radial side. The tread body 26 of this tire 2 is composed of two layers: a cap layer 30 and a base layer 32. The cap layer 30 is made of cross-linked rubber, taking into consideration contact with the road surface, wear resistance, and grip performance. The base layer 32 is located radially inside the cap layer 30. The base layer 32 is covered by the cap layer 30. The base layer 32 is made of low-heat-generating cross-linked rubber.

[0042] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located on the axially outer side of the carcass 12. The sidewall 6 is made of cross-linked rubber designed for cut resistance.

[0043] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is in contact with the rim R. The clinch 8 is made of cross-linked rubber with wear resistance in mind.

[0044] Each bead 10 is located radially inward of the sidewall 6. The bead 10 is located axially inward of the clinch 8. The bead 10 comprises a core 34 and an apex 36. The core 34 extends circumferentially. Although not shown, the core 34 contains steel wires. The apex 36 is located radially outward of the core 34. The apex 36 is made of cross-linked rubber with high rigidity. The apex 36 tapers radially outward.

[0045] The carcass 12 is located inside the tread 4, a pair of sidewalls 6, and a pair of clinches 8. The carcass 12 spans between a pair of beads 10.

[0046] The carcass 12 comprises at least one carcass ply 38. The carcass 12 of this tire 2 is composed of two carcass plies 38. Of the two carcass plies 38, the carcass ply 38 located on the inner side of the radially inner side of the tread 4 is the first carcass ply 40, and the carcass ply 38 located on the outer side is the second carcass ply 42.

[0047] The first carcass ply 40 is folded back axially from the inside to the outside at each bead 10. The first carcass ply 40 comprises a first ply body 40a and a pair of first folded portions 40b. The first ply body 40a spans between the pair of beads 10. Each first folded portion 40b is connected to the first ply body 40a and is folded back at each bead 10. The ends of the first folded portions 40b are located radially outward from the axial outer end PW of the tire 2.

[0048] The second carcass ply 42 is folded back axially from the inside to the outside at each bead 10. The second carcass ply 42 comprises a second ply body 42a and a pair of second folded portions 42b. The second ply body 42a spans between the pair of beads 10. Each second folded portion 42b is connected to the second ply body 42a and is folded back at each bead 10. The ends of the second folded portions 42b are located radially inward from the outer end of the apex 36. The ends of the second folded portions 42b are covered by the first folded portion 40b. The second ply body 42a is the outermost of the at least one ply body that the carcass 12 has.

[0049] Although not shown in the diagram, the carcass ply 38 constituting the carcass 12 contains numerous parallel carcass cords. The carcass cords intersect with the equatorial plane. The carcass 12 of this tire 2 has a radial structure. The carcass cords are cords made of organic fibers (hereinafter referred to as organic fiber cords). Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0050] Figure 2 is an explanatory diagram illustrating the configuration of belt 14 and band 16. In Figure 2, the direction indicated by the double arrow CD is the circumferential direction of tire 2. The front side of the paper is the radially outward direction, and the back side is the radially inward direction. The configuration of belt 14 and band 16 will be explained using Figures 1 and 2.

[0051] The belt 14 is located radially inward of the tread 4. The belt 14 is located radially outward of the carcass 12. In this tire 2, the belt 14 is laminated to the carcass 12 on the radially inward side of the tread 4.

[0052] The belt 14 comprises a plurality of belt plies 44 arranged radially. The plurality of belt plies 44 include an inner belt ply 46 located on the innermost side and an outer belt ply 48 located on the outermost side. The belt 14 of this tire 2 consists of two belt plies 44, specifically an inner belt ply 46 and an outer belt ply 48. The inner belt ply 46 is laminated to the carcass 12 on the radially inner side of the tread 4. The outer belt ply 48 is laminated to the inner belt ply 46. The end of the outer belt ply 48 is located axially inward of the end of the inner belt ply 46. The outer belt ply 48 is narrower than the inner belt ply 46. The end of the inner belt ply 46 is the end of the belt 14.

[0053] The belt plies 44 that make up the belt 14 include a number of parallel belt cords 50. In Figure 2, for ease of explanation, the belt cords 50 are represented by solid lines, but the belt cords 50 are covered with topping rubber 52. Belt cord 50 is a steel cord. There are no particular restrictions on belt cord 50; any steel cord commonly used as a tire belt cord is used as belt cord 50. Each belt cord 50 included in the belt 14 is inclined with respect to the circumferential direction. As shown in Figure 2, the direction of inclination of the belt cord 50 included in the outer belt ply 48 (hereinafter referred to as the outer belt cord 50s) and the direction of inclination of the belt cord 50 included in the inner belt ply 46 (hereinafter referred to as the inner belt cord 50u) are opposite to each other. The belt 14 is made of steel cord and includes a belt cord 50 that is inclined with respect to the circumferential direction.

[0054] The band 16 is laminated on the belt 14 on the radially inner side of the tread 4. The band 16 is located radially between the tread 4 and the belt 14. The ends of the band 16 are located axially outward from the ends of the belt 14. The band 16 covers the belt 14. The band 16 of this tire 2 is a full band 54. This band 16 may be a pair of edge bands arranged axially apart on the equatorial plane and configured to cover the end portion of the belt 14. This band 16 may consist of a full band 54 and a pair of edge bands. Although not shown, in this case the pair of edge bands are arranged axially apart on the equatorial plane and configured to cover the end portion of the full band 54 from the radially outward direction.

[0055] The full band 54 that makes up band 16 includes a helically wound band cord 56. In Figure 2, for ease of explanation, the band cord 56 is represented by a solid line, but the band cord 56 is covered with topping rubber 58. In band 16, the band cord 56 extends substantially in the circumferential direction. More specifically, the angle that the band cord 56 makes with respect to the circumferential direction is 5° or less. Band 16 has a jointless structure. The band cord 56 is an organic fiber cord. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. There are no particular restrictions on the band cord 56; any organic fiber cord commonly used as a tire band cord can be used as the band cord 56. The band 16 comprises an organic fiber cord, a band cord 56 that extends substantially circumferentially.

[0056] Each chafer 18 is located radially inward of the bead 10. The chafer 18 is in contact with the rim R. The chafer 18 of this tire 2 consists of cloth and rubber impregnated into this cloth.

[0057] The inner liner 20 is located inside the carcass 12. The inner liner 20 constitutes the inner surface 2N of the tire 2. The inner liner 20 is made of cross-linked rubber with excellent air shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

[0058] Each insulation 22 is located axially inward of the sidewall 6. More specifically, the insulation 22 is laminated onto the second ply body 42a on the axial inward side of the sidewall 6. In other words, the insulation 22 of this tire 2 is laminated onto the outermost ply body of at least one ply body of the carcass 12 on the axial inward side of the sidewall 6. One end of the insulation 22 is located axially inward of the end of the belt 14. The other end of the insulation 22 is located radially inward of the outer end of the apex 36. The insulation 22 is located radially inward of the end of the first folded portion 40b, between the second ply body 42a and the first folded portion 40b, and radially inward of the outer end of the apex 36, between the second ply body 42a and the apex 36. The insulation 22 is made of cross-linked rubber. The insulation 22 is harder than the sidewall 6. In the tire 2 of the present invention, the insulation 22 is not an essential element. The tire 2 does not need to be provided with insulation 22.

[0059] Figure 3 shows a portion of the outline of the outer surface 2G of tire 2 in a meridional cross-section of tire 2. The outline of the outer surface 2G is represented by a virtual outer surface obtained by assuming that there are no grooves, patterns, letters, or other decorations. Although not described in detail here, in this invention the outline of the outer surface 2G is obtained, for example, by measuring the outer surface shape of tire 2 using a displacement sensor, with tire 2 assembled on rim R, air filled inside tire 2, and the internal pressure of tire 2 adjusted. The outline of the outer surface 2G shown in Figure 3 represents the outer surface shape of tire 2 under standard conditions. The outline of the outer surface 2G represented by the outline has a shape symmetrical with respect to the equatorial plane.

[0060] The outer surface 2G of this tire 2 comprises a tread surface 60 and a pair of side surfaces 62 connected to the tread surface 60. The tread surface 60 is divided into seven parts arranged in the axial direction. The seven parts of the tread surface 60 are a crown portion 64, a pair of middle portions 66, a pair of shoulder portions 68, and a pair of corner portions 70.

[0061] The crown portion 64 is located in the axial center. The equatorial plane intersects the crown portion 64. The pair of middle portions 66 are each located axially outward from the crown portion 64. The position indicated by the symbol CM is the boundary between the crown portion 64 and the middle portion 66. The pair of shoulder portions 68 are each located axially outward from the middle portion 66. The position indicated by the symbol MS is the boundary between the middle portion 66 and the shoulder portion 68. The pair of corner portions 70 are each located axially outward from the shoulder portion 68. The position indicated by the symbol SC is the boundary between the shoulder portion 68 and the corner portion 70. The crown portion 64 is the part located in the axial center. The corner portion 70 is the part located on the outermost side in the axial direction. The middle portion 66 and the shoulder portion 68 are the parts located between the crown portion 64 and the corner portion 70.

[0062] As mentioned above, the corner section 70 is the outermost part in the axial direction. The corner section 70 connects to the side surface 62. The position indicated by the symbol CS is the boundary between the corner section 70 and the side surface 62. The boundary CS is also the edge of the tread surface 60. As shown in Figure 3, the boundary TS between the outer surface 4G of the tread 4 and the outer surface 6G of the sidewall 6 is included in the corner portion 70. In this tire 2, the outer surface 4G of the tread 4 is included in the tread surface 60. The outer surface 2G of the tire 2 may be configured such that the boundary TS between the outer surface 4G of the tread 4 and the outer surface 6G of the sidewall 6 coincides with the edge CS of the tread surface 60.

[0063] In this tire 2, the contours of the crown portion 64, middle portion 66, shoulder portion 68, and corner portion 70 are represented by arcs in its meridian cross-section.

[0064] The contour of the crown portion 64 is represented by a circular arc with its center on the equatorial plane. In Figure 3, arrow TR1 is the radius of the circular arc representing the contour of the crown portion 64. The contour of the middle section 66 is represented by an arc tangent to the arc representing the contour of the crown section 64. In Figure 3, arrow TR2 is the radius of the arc representing the contour of the middle section 66. The arc representing the contour of the middle section 66 is tangent to the arc representing the contour of the crown section 64 at boundary CM. Boundary CM is the point of tangency between the arc representing the contour of the middle section 66 and the arc representing the contour of the crown section 64. The contour of the shoulder portion 68 is represented by an arc tangent to the arc representing the contour of the middle portion 66. In Figure 3, arrow TR3 is the radius of the arc representing the contour of the shoulder portion 68. The arc representing the contour of the shoulder portion 68 is tangent to the arc representing the contour of the middle portion 66 at boundary MS. Boundary MS is the point of tangency between the arc representing the contour of the shoulder portion 68 and the arc representing the contour of the middle portion 66. The contour of the corner portion 70 is represented by an arc tangent to the arc representing the contour of the shoulder portion 68. In Figure 3, arrow TRc is the radius of the arc representing the contour of the corner portion 70. The arc representing the contour of the corner portion 70 is tangent to the arc representing the contour of the shoulder portion 68 at boundary SC. Boundary SC is the point of tangency between the arc representing the contour of the corner portion 70 and the arc representing the contour of the shoulder portion 68. The arc representing the contour of the corner portion 70 is tangent to the contour line of the side surface 62 at boundary CS. Boundary CS is the point of tangency between the arc representing the contour of the corner portion 70 and the contour line of the side surface 62.

[0065] In the contour line of the outer surface 4G of the tread 4, the arc representing the contour of the crown portion 64 is represented by the arc that maximizes the overlap length with the contour line from the equator Eq. The arc representing the contour of the middle portion 66 is tangent to the end of the arc representing the contour of the crown portion 64, and is represented by the arc that maximizes the overlap length with the contour line from this end. The end of the arc representing the contour of the crown portion 64 is one end of the arc representing the contour of the middle portion 66, and is the boundary CM between the crown portion 64 and the middle portion 66. The arc representing the contour of the shoulder portion 68 is tangent to the other end of the arc representing the contour of the middle portion 66, and is represented by the arc that maximizes the overlap length with the contour line from this other end. The other end of the arc representing the contour of the middle portion 64 is one end of the arc representing the contour of the shoulder portion 68, and is the boundary MS between the middle portion 66 and the shoulder portion 68. The arc representing the contour of the corner portion 70 is tangent to the other end of the arc representing the contour of the shoulder portion 68, and is represented by the arc that maximizes the overlap length with the contour line from this other end. The other end of the arc representing the contour of the shoulder portion 68 is one end of the arc representing the contour of the corner portion 70, and is the boundary SC between the shoulder portion 68 and the corner portion 70. The other end of this arc representing the contour of the corner portion 70 is the edge CS of the tread surface 60, and is the boundary CS between the tread surface 60 and the side surface 62.

[0066] In this tire 2, the radius TR1 of the arc representing the contour of the crown portion 64 is greater than the radius TR2 of the arc representing the contour of the middle portion 66. The radius TR2 of the arc representing the contour of the middle portion 66 is greater than the radius TR3 of the arc representing the contour of the shoulder portion 68. And the radius TR3 of the arc representing the contour of the shoulder portion 68 is greater than the radius TRc of the arc representing the contour of the corner portion 70. Of the seven parts that make up the tread surface 60, the arc representing the contour of the crown portion 64 located in the axial center has the largest radius TR1, and the arc representing the contour of the corner portion 70 located on the outermost axial side has the smallest radius TRc. Radius TRc is smaller than radius TR1. Specifically, the ratio of radius TRc to radius TR1, TRc / TR1, is between 0.020 and 0.040. In two parts adjacent in the axial direction, the arc representing the contour of the part located axially outward has a smaller radius than the arc representing the contour of the part located axially inward.

[0067] Figure 4 schematically shows an example of the contact surface of tire 2. In Figure 4, the direction indicated by the double arrow ADe corresponds to the axial direction of tire 2. The direction indicated by the double arrow CDe corresponds to the circumferential direction of tire 2. For the sake of explanation, the dimensions of the contact surface will be expressed in terms of the dimensions of tire 2 below.

[0068] The contact surface is obtained by using a tire contact surface shape measuring device (not shown) to mount the tire 2 onto the rim R, fill the inside of the tire 2 with air, adjust the internal pressure of the tire 2, apply a predetermined load to the tire 2, and bring the tire 2 into contact with a flat surface. By tracing the contour of the contact surface, an image of the contact surface as shown in Figure 4 is obtained. The shape of the contact surface is determined based on this image. If the contact surface includes parts that are interrupted by grooves, these parts are connected with straight lines to trace the contour of the contact surface. To obtain contact with the road surface, tire 2 is positioned so that its axial direction is parallel to the road surface. The aforementioned load is applied to tire 2 in a direction perpendicular to the road surface. In other words, with the camber angle of tire 2 set to 0°, a longitudinal load is applied to tire 2.

[0069] In Figure 4, the position indicated by the symbol CE is the axial outer end of the contact surface (also called the contact end). In this invention, the axial outer end of the contact surface between the tire 2 and the plane is identified when a longitudinal load of 75% of the normal load is applied to the tire 2 in a standard state and the tire 2 is brought into contact with the plane. The position on the outer surface 2G of the tire 2 that corresponds to this contact end CE is the reference end of the contact surface. In Figure 3, the position indicated by the symbol PE is the reference end of the contact surface.

[0070] In Figure 4, the length indicated by the double arrow Wc represents the contact width of the contact surface. The contact width Wc is the axial distance from one contact end CE to the other contact end CE. In the meridian cross-section shown in Figure 3, the length measured along the tread surface 60 from one contact reference end PE to the other contact reference end PE coincides with the contact width Wc.

[0071] In Figure 3, the double arrow Wa represents the axial width of the contact patch on the tire 2. The axial width Wa is the axial distance from one contact reference end PE to the other contact reference end PE on the tire 2 in a standard state. The tread surface 60 is curved so as to bulge outwards. The axial width Wa of the contact patch is shorter than the contact width Wc mentioned above. As shown in Figure 3, the grounding reference end PE is located between the aforementioned position P70 and the boundary SC between the shoulder portion 68 and the corner portion 70 (in other words, the outer end SC of the shoulder portion 68). Position P70 is located between the boundary MS between the middle portion 66 and the shoulder portion 68 (in other words, the inner end MS of the shoulder portion 68) and the grounding reference end PE.

[0072] In Figure 3, the double arrow RW1 represents the axial distance from the equatorial plane to the boundary CM between the crown portion 64 and the middle portion 66. The double arrow RW2 represents the axial distance from the boundary CM between the crown portion 64 and the middle portion 66 to the boundary MS between the middle portion 66 and the shoulder portion 68. The double arrow RW3 represents the axial distance from the boundary MS between the middle portion 66 and the shoulder portion 68 to the ground reference end PE.

[0073] Although not described in detail, the tire 2 shown in Figure 1 is manufactured by a known manufacturing method. Although not shown, components such as the tread 4 and sidewall 6 are combined to prepare an unvulcanized tire 2, i.e., a green tire. The green tire is pressurized and heated in a mold to obtain the tire 2. The outer surface 2G of the tire 2 is formed by the mold.

[0074] A band strip 72, shown in Figure 5, is used to form the band 16. The band strip 72 is strip-shaped. The band strip 72 contains one or more band codes 56. The band strip 72 shown in Figure 5 contains five band codes 56. These band codes 56 are arranged in the width direction of the band strip 72 and extend in the length direction of the band strip 72. The band strip 72 is a code array in which multiple band codes 56 are arranged.

[0075] The band strip 72 is wound spirally to form the band 16. Therefore, as described above, the band 16 includes a spirally wound band cord 56. In forming the band 16, the band cord 56 is wound in a helical shape while a predetermined load is applied to it. The tension generated by applying the load to the band cord 56 acts on the tire 2 as a restraining force, which will be described later.

[0076] In this tire 2, the radius TR1 of the arc representing the contour of the crown portion 64 is 5 times or more the axial width Wa of the contact surface in the tire 2. This results in a tread 4 having a flat outer surface 4G. The contact pressure in the crown portion 64 is reduced, and the mechanical fatigue of the tread 4 is reduced. This tread 4 has a favorable effect on rolling resistance. This tread 4 can contribute to suppressing the impact on rolling resistance. From this viewpoint, it is preferable that the radius TR1 is 5.5 times or more the axial width Wa. The radius TR1 is 7 times or less the axial width Wa. This prevents the crown portion 64 from being recessed radially inward and suppresses excessive pressure on the shoulder portion 68. This allows the tire 2 to maintain good wear resistance. From this viewpoint, it is preferable that the radius TR1 is 6.5 times or less the axial width Wa.

[0077] As mentioned above, flat treads are disadvantageous for high-speed durability. However, in this tire 2, the shrinkage rate of the band cord 56 in the shoulder portion of the tread T is taken into consideration. Specifically, the shrinkage rate SRs of the band cord 56 at position P70, which corresponds to 70% of the maximum width SW of tire 2 in its standard state, is between 70% and 130% of the shrinkage rate SRc of the band cord 56 at the equatorial plane of tire 2. In this tire 2, the shrinkage rate of the band cord 56 in the shoulder portion is set to be approximately the same as the shrinkage rate of the band cord 56 in the crown portion. The movement of the shoulder portion is sufficiently restrained. The band 16, together with the belt 14 which has steel cords as belt cords 50, can contribute sufficiently to restraining the movement of the tread T. The belts 14 and bands 16 of this tire 2 are particularly effective for tires intended for use at speeds of 270 km / h or higher, in other words, for tires with a speed rating of W or higher. This tire 2 can achieve improved high-speed durability. Restricting the movement of the tread section T can also contribute to reducing rolling resistance. This tire 2 can achieve improved high-speed durability while suppressing the impact on rolling resistance.

[0078] As mentioned above, the shrinkage rate SRs of the band cord 56 at position P70 is 70% to 130% of the shrinkage rate SRc of the band cord 56 at the equatorial plane of the tire 2. In other words, the ratio SRs / SRc of the shrinkage rate SRs of the band cord 56 to the shrinkage rate SRc of the band cord 56 is 70% to 130%. From the viewpoint that the band 16 can effectively contribute to the restraint of the tread portion T, the ratio SRs / SRc is preferably 80% to 120%, more preferably 90% to 110%, and even more preferably 95% to 105%.

[0079] In this invention, the contraction rate SRc of bandcode 56 in the equatorial plane is measured in bandcode 56 contained within a zone centered on the equatorial plane and having an axial width of 5% of the maximum width SW. The contraction rate SRs of bandcode 56 at position P70 is measured in bandcode 56 contained within a zone centered on position P70 and having an axial width of 5% of the maximum width SW.

[0080] In Figure 4, the dashed line LP extending in the circumferential direction is the centerline of the contact width Wc of the tire 2. This centerline LP of tire 2 corresponds to the equatorial plane of tire 2. The double arrow C100 is the length of the intersection line between the plane containing the centerline LP and the tire 2. This intersection line length C100 is the center contact length at the center of the contact width Wc of the tire 2. The solid line LM is a straight line passing through the contact end CE and parallel to the center line LP. The solid line L80 is a straight line located between the line LM and the center line LP, and is parallel to both the line LM and the center line LP. The double arrow A100 is the axial distance from the center line LP to the line LM. Distance A100 corresponds to half the contact width Wc of the contact surface. The double arrow A80 is the axial distance from the center line LP to the line L80. In Figure 4, the ratio of distance A80 to distance A100 is 80%. That is, the line L80 represents the position corresponding to 80% of the contact width Wc. The double arrow C80 is the length of the intersection line between the plane containing the line L80 and the contact surface. In this tire 2, the length of this intersection line C80 is the reference contact length at the position corresponding to 80% of the contact width Wc of the contact surface. In the contact patch of tire 2 in a standard state, the shape index F80 is the ratio C100 / C80 of the central contact length C100 at the center of the contact width Wc of the contact patch to the reference contact length C80 at a position corresponding to 80% of the contact width Wc of the contact patch.

[0081] The shape index F80 of tire 2 is preferably between 1.10 and 1.40. This results in a contact patch shape for tire 2 that suppresses the impact on high-speed durability and rolling resistance. This tire 2 can maintain good high-speed durability and low rolling resistance. Since wear on the crown portion is suppressed, this tire 2 can also maintain good wear resistance. From this viewpoint, the shape index F80 is more preferably between 1.15 and 1.35, and even more preferably between 1.20 and 1.30. A particularly preferred shape index F80 is 1.25.

[0082] The ratio TR2 / TR1 of the radius TR2 of the arc representing the contour of the middle section 66 to the radius TR1 of the arc representing the contour of the crown section 64 is preferably 0.35 or more and 0.40 or less. This results in a tread 4 having a flat outer surface 4G. The contact pressure at the crown section 64 is reduced, and the mechanical fatigue of the tread 4 is reduced. This tread 4 has a favorable effect on rolling resistance. This tread 4 can contribute to suppressing the influence on rolling resistance. From this viewpoint, a ratio TR2 / TR1 of 0.37 or more and 0.39 or less is more preferable.

[0083] The ratio TR3 / TR1 of the radius TR3 of the arc representing the contour of the shoulder portion 68 to the radius TR1 of the arc representing the contour of the crown portion 64 is preferably 0.09 or more and 0.13 or less. This results in a rounded shoulder portion 68. Local increases in ground pressure at the contact edge are suppressed. This tire 2 can suppress wear at the contact edge and a decrease in high-speed durability. This tire 2 can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance. From this viewpoint, it is more preferable that the ratio TR3 / TR1 is 0.10 or more and 0.12 or less.

[0084] Incidentally, when a flat tread is used for the tread, under conditions where high loads are applied to the shoulder area, such as during limit driving or high-speed driving, the contact pressure tends to increase locally in the shoulder area. In this case, there is a concern that the shoulder area will overheat abnormally, which may induce wear at the contact edge and reduce high-speed durability.

[0085] However, in this tire 2, as mentioned above, by setting the ratio TR2 / TR1 to 0.35 or more and 0.40 or less, a tread 4 with a flat outer surface 4G is formed, and this tread 4 can contribute to suppressing the effect on rolling resistance. By setting the ratio TR3 / TR1 to 0.09 or more and 0.13 or less, a rounded shoulder portion 68 is formed, and this shoulder portion 68 can contribute to suppressing wear at the contact edge and a decrease in high-speed durability. In particular, by setting the ratio TR2 / TR1 to 0.35 or more and 0.40 or less, and the ratio TR3 / TR1 to 0.09 or more and 0.13 or less, this tire 2 can set the radius TR3 of the arc representing the contour of the shoulder portion 68 to be smaller than that of a conventional tire. In other words, the shoulder portion 68 is rounder than a conventional shoulder portion. The increase in localized contact pressure at the contact edge is suppressed. This tire 2 can suppress wear at the contact edge and a decrease in high-speed durability. This tire 2 can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance. From this viewpoint, it is preferable that the ratio TR2 / TR1 is 0.35 or more and 0.40 or less, and the ratio TR3 / TR1 is 0.09 or more and 0.13 or less, and it is more preferable that the ratio TR2 / TR1 is 0.37 or more and 0.39 or less, and the ratio TR3 / TR1 is 0.10 or more and 0.12 or less.

[0086] The ratio RW1 / Wa of the axial distance RW1 from the equatorial plane to the boundary CM between the crown portion 64 and the middle portion 66, with respect to the axial width Wa of the contact surface, is preferably 0.15 or more and 0.25 or less. This allows the flat contour of the crown portion 64 to effectively contribute to reducing rolling resistance in the profile of the outer surface of the tread 4, i.e., the tread surface 60. From this viewpoint, a ratio RW1 / Wa of 0.18 or more and 0.22 or less is more preferable.

[0087] The ratio RW3 / Wa of the axial distance RW3 from the boundary MS between the middle section 66 and the shoulder section 68 to the ground reference end PE, with respect to the axial width Wa, is preferably 0.10 or more and 0.15 or less. This allows the rounded contour of the shoulder section 68 within the tread surface 60 profile to effectively contribute to suppressing localized increases in ground pressure at the ground contact end. From this viewpoint, a ratio RW3 / Wa of 0.10 or more and 0.13 or less is more preferable.

[0088] In this tire 2, it is preferable that the ratio RW1 / Wa is 0.15 or more and 0.25 or less, and the ratio RW3 / Wa is 0.10 or more and 0.15 or less. This allows the flat contour of the crown portion 64 of the tread surface 60 profile to effectively contribute to reducing rolling resistance, and the rounded contour of the shoulder portion 68 to effectively contribute to suppressing the increase in localized contact pressure at the contact edge. This tire 2 can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance. From this viewpoint, it is more preferable that the ratio RW1 / Wa is 0.18 or more and 0.22 or less, and the ratio RW3 / Wa is 0.10 or more and 0.13 or less.

[0089] Figure 6 shows a portion of the contour lines of Figure 3. The solid line AR1 in Figure 6 is an extension of the arc representing the contour of the crown portion 64. The extension line AR1 is an arc with radius TR1, centered on the equatorial plane and passing through the equator Eq. The solid line ARb is an arc with centered on the equatorial plane and passing through the equator Eq and the ground reference end PE. The arrow TRb in Figure 6 is the radius of the arc represented by the solid line ARb.

[0090] In the meridional cross-section of the tire 2 in its standard state, the ratio TR1 / TRb of the radius of the arc representing the contour of the crown portion 64 to the radius TRb of the arc passing through the equator Eq and the contact reference end PE of the tire 2, with its center on the equatorial plane of the tire 2, is preferably 1.66 or more and 1.96 or less. This allows the flat contour of the crown portion 64 to effectively contribute to reducing rolling resistance, and the rounded contour of the shoulder portion 68 to effectively contribute to suppressing localized increases in contact pressure at the contact end. This tire 2 can achieve improved high-speed durability while suppressing not only the impact on rolling resistance but also the impact on wear resistance. From this viewpoint, the ratio TR1 / TRb is more preferably 1.70 or more and 1.90 or less, and even more preferably 1.75 or more and 1.85 or less.

[0091] As is clear from the above description, the present invention provides a tire 2 that can achieve improved high-speed durability while suppressing the impact on rolling resistance. The present invention is particularly effective for tires 2 having a speed rating of W or higher. [Examples]

[0092] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0093] [Examples and Comparative Examples] We obtained tires for examples and comparative examples that have the basic configuration shown in Figure 1 and the specifications shown in Table 1 below. For each example, we prepared two types of tires with different sizes (tire sizes = 255 / 40ZR20 and 285 / 35R20). In the comparative example, a load was applied to the band cord on a flat drum, and the band cord was wound spirally to form a preliminary band shape. Then, the drum was shaped by expanding the diameter of the part corresponding to the crown and shrinking the diameter of the part corresponding to the shoulder. At position P70, the band cord was not stretched, and the shrinkage rate SRs was 0%. In contrast, in the embodiment, the band was formed by winding the band cord from end to end with constant tension using a drum having a certain profile that takes into account the shape of the band in the tire. As a result, the band was configured such that the shrinkage rate SRs of the band cord at position P70 was the same as the shrinkage rate SRc of the band cord at the equatorial plane. The shrinkage rate SRc of the band cord at the equatorial plane was the same as that of the comparative example.

[0094] [Rolling resistance] Using a rolling resistance tester, the rolling resistance coefficient (RRC) of a prototype tire (tire size = 285 / 35R20) was measured when it ran on a drum at a speed of 80 km / h under the following conditions. The results are shown in the "RRC" column of Table 1 below, with the comparative example set to 100. A higher value indicates lower tire rolling resistance. Rim width: 20 x 10.0J Internal pressure: 210kPa Vertical load: 6.28kN

[0095] [High speed durability] A prototype tire (tire size = 285 / 35R20) was mounted on a rim (size = 20 × 10.5J), and air was inflated to an internal pressure of 200kPa. This tire was mounted on a drum-type running test machine with a camber angle set to 2 degrees. A longitudinal load of 4.86kN was applied to the tire, and the tire was driven on a drum (drum diameter = 5.0m) while gradually increasing the speed until the tire became unable to move. The results are shown in the "High-Speed ​​Durability" column of Table 1 below, with Comparative Example 1 set to 100. A higher number indicates better high-speed durability.

[0096] [Abrasion resistance] A prototype tire (tire size = 255 / 40ZR20) was mounted on a rim (size = 20 × 10.0J), and air was inflated to an internal pressure of 220kPa. This tire was mounted on a drum-type running test machine. A longitudinal load of 7.20kN was applied to the tire, and the tire was driven at a speed of 100km / h on a drum (drum diameter = 5.0m) with a running surface made of asphalt. At the 30km mark, the tread surface profile was measured by laser scanning, and the amount of wear on the shoulder area was measured. The results are shown in the "Uneven Wear Resistance" column of Table 1 below, with Comparative Example 1 set to 100. A higher value indicates better high-speed durability.

[0097] [Ground pressure distribution] A prototype tire (tire size = 255 / 40ZR20) was mounted on a rim (size = 20 × 10.0J), and air was inflated to an internal pressure of 200 kPa. This tire was mounted on a ground pressure measurement test machine with a camber angle. The camber angle was set to 2 degrees. With a longitudinal load of 6.40 kN applied to the tire, the ground pressure distribution was measured. The total ground pressure in the width direction of the contact patch at the shoulder was obtained. The results are shown in the "Ground Pressure Distribution" column of Table 1 below, with Comparative Example 1 set to 100. A smaller value indicates lower total ground pressure.

[0098] [Table 1]

[0099] As shown in Table 1, the embodiments demonstrate improved high-speed durability while suppressing not only the impact on rolling resistance but also on wear resistance. The advantages of the present invention are clear from these evaluation results. [Industrial applicability]

[0100] The technology described above, which can improve high-speed durability while suppressing the impact on rolling resistance, can be applied to various types of tires.

[0101] [Note] The present invention includes the following embodiments.

[0102] [1] A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt, wherein the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 92% of the regular internal pressure, and no load is applied to the tire, and the outer surface of the tread comprises a crown portion located axially in the center, a pair of middle portions located axially outward of the crown portion, and a pair of shoulder portions located axially outward of the middle portions, and in the meridional cross-section of the tire in the standard state, The contour of the crown portion is represented by an arc centered on the equatorial plane, the contour of each middle portion is represented by an arc tangent to the arc representing the contour of the crown portion, the contour of each shoulder portion is represented by an arc tangent to the arc representing the contour of the middle portion, and the position on the outer surface of the tire corresponding to the axial outer end of the contact surface of the tire, obtained by applying a longitudinal load of 75% of the normal load to the tire in the standard state and bringing the tire into contact with a plane, is the contact reference end, and the axial distance from one contact reference end to the other of the tire is the contact A tire having an axial width Wa relative to the ground, a radius TR1 of an arc representing the contour of the crown portion being 5 to 7 times the axial width Wa, a belt comprising a belt cord inclined with respect to the circumferential direction, the belt cord being a steel cord, a band comprising a band cord substantially extending in the circumferential direction, the band cord being an organic fiber cord, and the shrinkage rate of the band cord at a position corresponding to 70% of the maximum width of the tire in its standard state being 70% to 130% of the shrinkage rate of the band cord at the equatorial plane of the tire. [2] The tire according to [1] above, wherein the ratio of the central contact length at the center of the contact width of the tire to the reference contact length at a position corresponding to 80% of the width of the contact width of the tire is a shape index F80, and the shape index F80 is 1.10 or more and 1.40 or less. [3] The tire as described in [1] or [2] above, wherein the ratio TR2 / TR1 of the radius TR2 of the arc representing the contour of the middle portion to the radius TR1 of the arc representing the contour of the crown portion is 0.35 or more and 0.40 or less, and the ratio TR3 / TR1 of the radius TR3 of the arc representing the contour of the shoulder portion to the radius TR1 of the arc representing the contour of the crown portion is 0.09 or more and 0.13 or less. [4] The tire according to any one of [1] to [3] above, wherein the ratio RW1 / Wa of the axial distance RW1 from the equatorial plane to the boundary between the crown portion and the middle portion to the axial width Wa of the contact surface is 0.15 or more and 0.25 or less, and the ratio RW3 / Wa of the axial distance RW3 from the boundary between the middle portion and the shoulder portion to the contact reference end to the axial width Wa is 0.10 or more and 0.15 or less. [5] The tire according to any one of [1] to [4] above, wherein in the meridional cross-section of the tire in the standard state, the ratio TR1 / TRb of the radius of the arc representing the contour of the crown portion to the radius TRb of the arc having its center on the equatorial plane of the tire and passing through the equator of the tire and the ground contact reference end is 1.66 or more and 1.96 or less. [Explanation of symbols]

[0103] 2... Tires 4. Tread 10...bead 12...Carcass 14. Belt 16 bands 44, 46, 48... Belt ply 50... Belt cord 54...Full Band 56... Band Code 60...Tread surface 64... Crown section 66...Middle Section 68... Shoulder section 70... Corner section

Claims

1. A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt, The standard condition of the tire is when the tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 92% of the standard internal pressure, and no load is applied to the tire. The outer surface of the tread comprises a crown portion located in the axial center, a pair of middle portions located axially outside the crown portion, and a pair of shoulder portions located axially outside the middle portions. In the meridian cross-section of the tire in the standard state, The outline of the crown portion is represented by a circular arc having its center on the equatorial plane. The contour of each middle section is represented by an arc tangent to the arc representing the contour of the crown section, The contour of each shoulder portion is represented by an arc tangent to the arc representing the contour of the middle portion, The tire, in the standard state, is subjected to a longitudinal load of 75% of the normal load, and the tire is brought into contact with a plane. The position on the outer surface of the tire corresponding to the axial outer end of the tire's contact surface is the contact reference end, and the axial distance from one of the contact reference ends of the tire to the other is the axial width Wa of the contact surface. The radius TR1 of the arc representing the contour of the crown portion is 5 times or more and 7 times or less the axial width Wa. The belt comprises a belt cord that is inclined with respect to the circumferential direction, and the belt cord is a steel cord. The band comprises a band cord that extends substantially in the circumferential direction, and the band cord is an organic fiber cord. The contraction rate of the band cord at a position corresponding to 70% of the maximum width of the tire in the standard state is 70% or more and 130% or less of the contraction rate of the band cord at the equatorial plane of the tire. tire.

2. In the contact surface of the tire, the ratio of the central contact length at the center of the contact width of the contact surface to the reference contact length at a position corresponding to 80% of the contact width of the contact surface is the shape index F80. The shape index F80 is 1.10 or more and 1.40 or less. The tire according to claim 1.

3. The ratio TR2 / TR1 of the radius TR2 of the arc representing the contour of the middle portion to the radius TR1 of the arc representing the contour of the crown portion is 0.35 or more and 0.40 or less. The ratio TR3 / TR1 of the radius TR3 of the arc representing the contour of the shoulder portion to the radius TR1 of the arc representing the contour of the crown portion is 0.09 or more and 0.13 or less. The tire according to claim 1.

4. The ratio RW1 / Wa of the axial distance RW1 from the equatorial plane to the boundary between the crown portion and the middle portion to the axial width Wa of the ground surface is 0.15 or more and 0.25 or less. The ratio RW3 / Wa of the axial distance RW3 from the boundary between the middle portion and the shoulder portion to the ground reference end to the axial width Wa is 0.10 or more and 0.15 or less. The tire according to claim 1.

5. In the meridian cross-section of the tire in the standard state, The ratio TR1 / TRb of the radius TR1 of the arc representing the contour of the crown portion to the radius TRb of the arc passing through the equator and the contact reference end of the tire, which has its center on the equatorial plane of the tire, is 1.66 or more and 1.96 or less. The tire according to claim 1.

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