Racing tires

Abstract

The racing tire (2) provided by the present invention can suppress the influence on durability and achieve the improvement of wear resistance. The tire (2) has a pair of reinforcing layers (16) arranged in the axial direction across the equatorial plane. In the radial direction, the reinforcing layer (16) is located on the inner side of the tread (4) and is stacked on the outer side of the carcass (10). In the axial direction, the inner end (34) of the reinforcing layer (16) is located on the inner side than the end (TE) of the tread surface (18). In the axial direction, the position of the outer end (36) of the reinforcing layer (16) is consistent with the position of the end (TE) of the tread surface (18), or the outer end (36) of the reinforcing layer (16) is located on the outer side than the end (TE) of the tread surface (18). The reinforcing layer (16) is a cord reinforcement layer (40) including a plurality of reinforcing cords (38) arranged side by side in the circumferential direction.

Description

Technical Field

[0001] The present invention relates to tires for racing cars. Background Art

[0002] In recent years, the performance of racing cars has been significantly improved. In response to this, further performance improvements are required in racing tires mounted on racing cars. Various studies have been conducted to meet this requirement (for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2001-47810

[0004] The tread of a tire wears out due to use. If a thick tread is used, the service life of the tire can be extended. However, a tire with a thick tread is heavier and will affect the vehicle's sports performance.

[0005] If the thickness of the tread can be reduced, the tire can be made lighter. Light tires help improve the vehicle's sports performance. Therefore, in racing tires, it is required to improve wear resistance and reduce the thickness of the tread.

[0006] In order to improve the wear resistance, the use of cross-linked rubber with high modulus in the tread has been studied. Cross-linked rubber with high modulus has a small elongation at break. Therefore, when the tread is made of cross-linked rubber with high modulus, the tread of the shoulder part stretched in the axial direction during cornering may be damaged by cracks, breakage, etc., and the durability may be reduced. Summary of the invention

[0007] The present invention has been made in view of such actual circumstances, and an object of the present invention is to provide a racing tire capable of suppressing the influence on durability and achieving improved wear resistance.

[0008] A racing tire according to one embodiment of the present invention comprises: a tread having a tread surface in contact with a road surface; a pair of sidewalls connected to the ends of the tread and located radially inward of the tread; a pair of beads located radially inward of the sidewalls; a carcass spanning between the beads of one side and the beads of the other side; and a pair of reinforcing layers arranged axially across an equatorial plane. The reinforcing layer is located radially on the inner side of the tread and is stacked on the outer side of the carcass. The inner end of the reinforcing layer is located axially inward of the end of the tread surface. The outer end of the reinforcing layer is axially aligned with the end of the tread surface, or the outer end of the reinforcing layer is located outward of the end of the tread surface. The reinforcing layer is a rubber reinforcing layer harder than the tread, or a cord reinforcing layer including a plurality of reinforcing cords arranged circumferentially.

[0009] Preferably, in the racing tire, a ratio of an axial distance from the equatorial plane to an inner end of the reinforcing layer to an axial distance from the equatorial plane to an end of the tread surface is 0.60 or more and 0.80 or less.

[0010] Preferably, in the racing tire, a ratio of an axial distance from the end of the tread surface to the outer end of the reinforcing layer to an axial distance from the equatorial plane to the end of the tread surface is 0.15 or less.

[0011] Preferably, in the racing tire, the stress of the tread at 200% elongation at a temperature of 100° C. is 6.5 MPa or more.

[0012] Preferably, in the racing tire, the reinforcement layer is a cord reinforcement layer including a plurality of reinforcement cords arranged in a circumferential direction, and the angle formed by the reinforcement cords with respect to the equatorial plane is 70° or more and 90° or less.

[0013] Preferably, in the racing tire, the carcass includes at least two carcass plies, the carcass plies include a plurality of carcass cords arranged side by side, and the angle formed by the reinforcing cord and the carcass cord included in the carcass ply stacked with the cord reinforcing layer is greater than 50° and less than 70°.

[0014] Preferably, in the racing tire, the reinforcing layer is a rubber reinforcing layer harder than the tread, and the hardness of the rubber reinforcing layer at a temperature of 23° C. is 80 or more and 95 or less.

[0015] In the racing tire, preferably, the difference between the hardness of the reinforcing layer and the hardness of the tread at a temperature of 23° C. is 10 or more and 30 or less.

[0016] According to the present invention, a racing tire capable of suppressing the influence on durability and achieving improved wear resistance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing a portion of a racing tire according to an embodiment of the present invention.

[0018] Figure 2 A schematic diagram illustrating the structure of a carcass and a reinforcing layer.

[0019] Figure 3 This is a schematic diagram for explaining the structure of a reinforcing layer of a racing tire according to another embodiment of the present invention.

[0020] Explanation of the reference numerals: 2, 52…tire; 4…tread; 6…sidewall; 8…bead; 10…carcass; 16, 54…reinforcing layer; 18…tread surface; 24…carcass cord; 30…carcass cord; 34…inner end of reinforcing layer 16; 36…outer end of reinforcing layer 16; 38…reinforcing cord; 40…cord reinforcing layer; 56…inner end of reinforcing layer 54; 58…outer end of reinforcing layer 54; 60…rubber reinforcing layer. DETAILED DESCRIPTION

[0021] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0022] In the present invention, the state where the tire is assembled 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 referred to as the regular state. In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the regular state.

[0023] A regular rim is a rim defined in the standard to 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 regular rims.

[0024] The normal internal pressure refers to the internal pressure determined in the standard to which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" in the "TIRE LOAD LIMITS AT VARIATION COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures. In the case of tires for passenger cars, the normal internal pressure is 180 kPa unless otherwise specified.

[0025] The normal load refers to the load determined in the standard to which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" in the "TIRE LOAD LIMITS AT VARIOU s COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads. In the case of tires for passenger cars, unless otherwise specified, the normal load is a load equivalent to 88% of the above load.

[0026] In the present invention, the tread portion of the tire refers to the portion of the tire that contacts the road surface. The bead portion refers to the portion of the tire that fits into the rim. The sidewall portion refers to the portion of the tire that spans between the tread portion and the bead portion. The tire has a tread portion, a pair of bead portions, and a pair of sidewall portions as portions.

[0027] In the present invention, the hardness of the element composed of the crosslinked rubber among the elements constituting the tire is measured using a type A durometer at a temperature of 23° C. based on the provisions of JIS K6253.

[0028] In the present invention, the elongation at break and the stress at 200% elongation of the element composed of the crosslinked rubber among the elements constituting the tire are measured at a temperature of 100° C. in accordance with the provisions of JIS K6251.

[0029] In the present invention, crosslinked rubber refers to a molded body obtained by crosslinking a rubber composition. The crosslinked rubber is obtained, for example, by pressurizing and heating the rubber composition. The rubber composition is a rubber in an uncrosslinked state obtained by mixing a base rubber and a reagent in a mixer such as a Banbury mixer. Crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0030] As base rubber, natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR) and butyl rubber (IIR) are exemplified. As reagents, reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, sulfur and vulcanization accelerators are exemplified. Although not described in detail, the selection of base rubber and reagents, the content of the selected reagents, etc. can be appropriately set according to the specifications of the elements of the rubber composition.

[0031] In the present invention, the number of cords included in an element of a tire having a width of 5 cm, including parallel cords, is expressed as the density of the cords included in the element (unit: cords / 5 cm).

[0032] Figure 1 An example of a racing tire 2 (hereinafter, sometimes simply referred to as a "tire 2") according to an embodiment of the present invention is shown. Figure 1 , a portion of a cross section of the tire 2 along a plane including the rotation axis of the tire 2 is shown. Figure 1 In the figure, 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. Figure 1 The direction perpendicular to the paper surface is the circumferential direction of the tire 2. Figure 1 In FIG. 2 , a dashed line CL indicates the equatorial plane of the tire 2 .

[0033] exist Figure 1In the figure, the position indicated by the reference numeral PW is the axial outer end of the tire 2. The outer end PW is determined based on the contour of the outer surface of the tire 2. When the outer surface is decorated with patterns, characters, etc., the outer end PW is determined based on the contour of an imaginary outer surface obtained by assuming that there is no decoration.

[0034] The axial distance from one outer end PW to the other outer end PW is the maximum width, that is, the cross-sectional width (see JATMA, etc.) of the tire 2. The outer end PW is the position where the tire 2 shows the maximum width (hereinafter referred to as the maximum width position).

[0035] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of beads 8 , a carcass 10 , a pair of chafers 12 , an inner liner 14 , and a pair of reinforcing layers 16 as elements.

[0036] The tread 4 contacts the road surface at a tread surface 18. The tread 4 has a tread surface 18 that contacts the road surface. The tread surface 18 is convex toward the outside in the radial direction. The tread 4 is made of cross-linked rubber.

[0037] exist Figure 1 In the figure, the position indicated by the reference symbol TE is the end of the tread surface 18. The end TE of the tread surface 18 is a position on the outer surface of the tread 4 corresponding to the axial outer end of the contact surface (hereinafter, also referred to as the end of the contact surface). The end of the contact surface is determined based on the contact surface obtained by applying a normal load to the tire 2 in a normal state, setting the camber angle to 0°, and making the tread 4 contact with a flat surface. The tread surface 18 is a part of the outer surface of the tread 4.

[0038] exist Figure 1 , the length indicated by the double-headed arrow BW is the axial distance from the equatorial plane CL to the end TE of the tread surface 18. In the present invention, the axial distance BW is also referred to as a reference width of the tread surface 18.

[0039] Each sidewall 6 is connected to an end of the tread 4 and is located radially inward of the tread 4. The sidewall 6 is located axially outside the carcass 10. The sidewall 6 extends radially inward from the end of the tread 4 along the carcass 10.

[0040] The sidewall 6 is made of cross-linked rubber. In the tire 2, the hardness of the sidewall 6 at a temperature of 23°C is 40 or more and 95 or less. In the tire 2, when emphasis is placed on ride comfort, the hardness of the sidewall 6 at a temperature of 23°C is preferably 40 or more and preferably 55 or less. On the other hand, when emphasis is placed on sports performance, the hardness of the sidewall is preferably 80 or more and preferably 95 or less. In this case, the sidewall 6 is harder than the tread 4, and the difference between the hardness of the sidewall 6 and the hardness of the tread 4 at a temperature of 23°C is preferably 10 or more and preferably 30 or less.

[0041] Each bead 8 is located radially inward of the sidewall 6. The bead 8 includes a core 20 and an apex 22. Although not shown, the core 20 includes a steel wire. The apex 22 is located radially outward of the core 20. The apex 22 is made of cross-linked rubber.

[0042] The carcass 10 is located inside the tread 4 and the pair of sidewalls 6. The carcass 10 spans between one bead 8 and the other bead 8. The carcass 10 has a bias structure. The carcass 10 includes at least two carcass plies 24.

[0043] The carcass 10 of the tire 2 is composed of two carcass plies 24. Of the two carcass plies 24, the carcass ply 24 located on the inner side is referred to as a first ply 26, and the carcass ply 24 located on the outer side is referred to as a second ply 28.

[0044] The first ply 26 includes a first ply main body 26a that spans between one tire core 20 and the other tire core 20, and a pair of first folded portions 26b that are connected to the first ply main body 26a and folded from the axial inside to the outside around each tire core 20. In the tire 2, the end of the first folded portion 26b is located radially outward of the maximum width position PW.

[0045] The second fabric 28 includes a second fabric main body 28a that spans between one tire core 20 and the other tire core 20, and a pair of second folded portions 28b that are connected to the second fabric main body 28a and folded from the axial inner side to the outer side around each tire core 20. In the tire 2, the end of the second folded portion 28b is located radially inward of the maximum width position PW. The end of the second folded portion 28b is covered by the first folded portion 26b from the axial outer side.

[0046] Figure 2 The structure of the carcass 10 in the tire 2 is shown together with the structure of the reinforcing layer 16 described later. 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 .

[0047] In the tire 2, the first ply 26 and the second ply 28 each include a plurality of carcass cords 30 arranged side by side. Figure 2 For convenience of explanation, the carcass cords 30 are indicated by solid lines, but the carcass cords 30 are covered with a topping rubber 32. The first ply 26 and the second ply 28 are respectively composed of a plurality of carcass cords 30 and a topping rubber 32 covering the carcass cords 30. In each of the first ply 26 and the second ply 28, the density of the carcass cords 30 is set in the range of 20 cords / 5 cm or more and 60 cords / 5 cm or less.

[0048] In the tire 2, the carcass cords 30 are inclined relative to the equatorial plane. Figure 2 As shown, the inclination direction of the carcass cords 30 included in the first ply 26 and the inclination direction of the carcass cords 30 included in the second ply 28 are opposite to each other.

[0049] exist Figure 2 In the figure, the angle indicated by the reference numeral α is the angle (hereinafter referred to as the inclination angle) formed by the carcass cord 30 included in the first ply 26 relative to the equatorial plane. The inclination angle α of the carcass cord 30 is greater than 15° and less than 45°. The angle indicated by the reference numeral β is the inclination angle of the carcass cord 30 included in the second ply 28. The inclination angle β of the carcass cord 30 is greater than 15° and less than 45°. In the tire 2, the inclination angle α of the carcass cord 30 included in the first ply 26 and the inclination angle β of the carcass cord 30 included in the second ply 28 are set at the same angle.

[0050] In the tire 2, cords made of organic fibers generally used in the field of tires are used as carcass cords 30. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0051] Each chafer 12 is located radially inward of the bead 8. The chafer 12 is in contact with a rim (not shown). The chafer 12 of the tire 2 is composed of cloth and rubber impregnated in the cloth.

[0052] The inner liner 14 is located inside the carcass 10. The inner liner 14 constitutes the inner surface of the tire 2. The inner liner 14 maintains the internal pressure of the tire 2. The inner liner 14 is made of cross-linked rubber.

[0053] Each reinforcing layer 16 is included in the axially outer portion of the tread portion T (hereinafter also referred to as the shoulder portion Sh). The reinforcing layer 16 is located radially inside the tread 4 of the shoulder portion Sh. The reinforcing layer 16 is radially laminated on the carcass 10, more specifically, on the outer side of the second ply main body 28a. In the tire 2, no element such as a belt including belt cords extending obliquely with respect to the equatorial plane or a belt including belt cords wound in a spiral shape along a substantially circumferential direction is provided between the carcass 10 and the reinforcing layer 16.

[0054] In the tire 2, a pair of reinforcing layers 16 are arranged across the equatorial plane in the axial direction. The tread 4 is laminated on the carcass 10, more specifically, on the outer side of the second ply main body 28a, between the reinforcing layer 16 on one side and the reinforcing layer 16 on the other side. In the tire 2, no elements such as the above-mentioned belt or band are provided between the tread 4 and the carcass 10.

[0055] In the tire 2, the inner end 34 of the reinforcing layer 16 is located axially inwardly of the end TE of the tread surface 18. The outer end 36 of the reinforcing layer 16 is located axially outwardly of the end TE of the tread surface 18. Although not shown in the figure, in the tire 2, the position of the outer end 36 of the reinforcing layer 16 in the axial direction may also coincide with the position of the end TE of the tread surface 18. In the tire 2, the position of the outer end 36 of the reinforcing layer 16 in the axial direction coincides with the position of the end TE of the tread surface 18, or the outer end 36 of the reinforcing layer 16 is located outwardly of the end TE of the tread surface 18.

[0056] like Figure 2 As shown, the reinforcement layer 16 includes a plurality of reinforcement cords 38 arranged side by side in the circumferential direction. The reinforcement layer 16 is a cord reinforcement layer 40. Figure 2 Although the reinforcing cords 38 are indicated by solid lines for the sake of convenience, the reinforcing cords 38 are covered by the topping rubber 42. The cord reinforcement layer 40 is composed of a plurality of reinforcing cords 38 arranged side by side in the circumferential direction and the topping rubber 42 covering the reinforcing cords 38. The density of the reinforcing cords 38 included in the cord reinforcement layer 40 is set in the range of 30 cords / 5 cm or more and 70 cords / 5 cm or less.

[0057] In the tire 2, the material of the reinforcing cord 38 is not particularly limited. In the technical field of tires, a cord commonly used is used as the reinforcing cord 38. The reinforcing cord 38 may also be a steel cord. The reinforcing cord 38 may also be a cord composed of organic fibers. From the viewpoint of easy manufacture of the tire 2, the reinforcing cord 38 is preferably a cord composed of organic fibers. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber. From the viewpoint of easy manufacture of the tire 2, the organic fiber is preferably nylon fiber or polyester fiber.

[0058] In the tire 2, the reinforcing cords 38 are arranged at intervals in the circumferential direction. One end of the reinforcing cord 38 is located at the inner end 34 of the cord reinforcing layer 40, and the other end of the reinforcing cord 38 is located at the outer end 36 of the cord reinforcing layer 40. The reinforcing cord 38 extends substantially in the axial direction.

[0059] During cornering, the shoulder Sh of the tire 2 is strongly acted on in such a way that the tread 4 of the shoulder Sh is stretched in the axial direction. The cross-linked rubber having a high modulus is advantageous for wear resistance, but has a low elongation at break. Therefore, when the tread 4 is made of such a cross-linked rubber, damage such as cracks and breakage may occur at the tread 4 of the shoulder Sh.

[0060] In the tire 2, the reinforcing layer 16 located radially inward of the tread 4 at the shoulder portion Sh is a cord reinforcing layer 40 including reinforcing cords 38 extending substantially in the axial direction. Therefore, during cornering, even if a force is applied to the shoulder portion Sh in such a manner that the tread 4 is stretched in the axial direction, the reinforcing layer 16 acts in such a manner as to overcome the force. In the tire 2, the stretching of the tread 4 during cornering is suppressed. Even if the tread 4 is made of a cross-linked rubber having a low elongation when cut, the occurrence of damage caused by the tread 4 stretching in the axial direction can be suppressed. In the tire 2, the tread 4 can be made of a cross-linked rubber having a high modulus.

[0061] The tire 2 can suppress the influence on durability and improve the wear resistance. Since a thinner tread 4 can be used, the tire 2 can also reduce the mass. The tire 2 can also help improve the sports performance. In addition, by forming the sidewall 6 with a cross-linked rubber having a hardness of 80 to 95 at a temperature of 23°C, the occurrence of damage such as cracks can be effectively suppressed. When a cross-linked rubber having a hardness of 80 to 95 at a temperature of 23°C is applied to the sidewall 6, the tire 2 can not only improve the sports performance, but also improve the durability.

[0062] exist Figure 1 In FIG. 1 , the length indicated by the double-headed arrow NW is the axial distance from the equatorial plane to the inner end 34 of the reinforcing layer 16 .

[0063] In the tire 2 , the ratio NW / BW of the axial distance NW from the equatorial plane to the inner end 34 of the reinforcing layer 16 relative to the reference width BW of the tread surface 18 is preferably 0.60 or more and preferably 0.80 or less.

[0064] By setting the ratio of NW / BW to 0.60 or more, the influence of the reinforcing layer 16 on the rigidity of the tread 4 can be suppressed. In the tire 2, the tread 4 is in sufficient contact with the road surface. Since the grip performance is sufficiently ensured, good steering stability can be maintained. From this point of view, the ratio of NW / BW is more preferably 0.62 or more, and further preferably 0.65 or more.

[0065] By setting the ratio of NW / BW to 0.80 or less, the width of the reinforcing layer 16 is ensured. The reinforcing layer 16 effectively contributes to suppressing the stretching of the tread 4 during cornering, so that good durability is maintained in the tire 2. From this viewpoint, the ratio of NW / BW is more preferably 0.75 or less, and further preferably 0.73 or less.

[0066] exist Figure 1, the length indicated by the double-headed arrow GW is the axial distance from the end TE of the tread surface 18 to the outer end 36 of the reinforcing layer 16. When the outer end 36 of the reinforcing layer 16 is located axially outside the end TE of the tread surface 18, the axial distance GW is represented by a positive number.

[0067] As described above, in the tire 2, the position of the outer end 36 of the reinforcing layer 16 in the axial direction coincides with the position of the end TE of the tread surface 18, or the outer end 36 of the reinforcing layer 16 is located at a position outside the end TE of the tread surface 18. That is, the ratio GW / BW of the axial distance GW from the end TE of the tread surface 18 to the outer end 36 of the reinforcing layer 16 relative to the reference width BW of the tread surface 18 is 0.00 or more. Thus, the reinforcing layer 16 effectively contributes to suppressing the stretching of the tread 4 during cornering. In the tire 2, good durability is maintained. From this point of view, the GW / BW ratio is preferably 0.01 or more. From the point of view of being able to configure the reinforcing layer 16 directly below the end of the ground contact surface formed during rotation, the GW / BW ratio is more preferably 0.02 or more, and further preferably 0.03 or more.

[0068] In the tire 2, the ratio GW / BW of the axial distance GW from the end TE of the tread surface 18 to the outer end 36 of the reinforcing layer 16 to the reference width BW of the tread surface 18 is preferably 0.15 or less. Thus, the influence of the reinforcing layer 16 on the rigidity of the shoulder portion Sh can be suppressed. In the tire 2, good steering stability is maintained. From this viewpoint, the ratio GW / BW is more preferably 0.13 or less, and further preferably 0.10 or less.

[0069] In the tire 2, the stress at 200% elongation of the tread 4 at a temperature of 100°C (hereinafter also referred to as 200% modulus) is preferably 6.5 MPa or more. Thus, the tread 4 helps to improve wear resistance, and thus a thinner tread 4 can be used in the tire 2. A thinner tread 4 helps to reduce the weight of the tire 2, and a light tire 2 helps to improve sports performance. From this point of view, the 200% modulus of the tread 4 at a temperature of 100°C is more preferably 7.2 MPa or more, and further preferably 7.5 MPa or more. From the point of view of suppressing the influence of the tread 4 on the grip performance, the 200% modulus of the tread 4 at a temperature of 100°C is preferably 10 MPa or less, more preferably 9.0 MPa or less, and further preferably 8.5 MPa or less.

[0070] In the tire 2, the elongation of the tread 4 when cut at a temperature of 100°C is preferably 200% or more. This suppresses the occurrence of damage to the tread 4 caused by the stretching of the tread 4 during cornering. In the tire 2, good durability is ensured. From this point of view, the elongation of the tread 4 when cut at a temperature of 100°C is more preferably 210% or more, and further preferably 220% or more. From the viewpoint of being able to form a tread 4 that can contribute to improved wear resistance, the elongation of the tread 4 when cut at a temperature of 100°C is preferably 330% or less, more preferably 290% or less, and further preferably 270% or less.

[0071] The cross-linked rubber with high modulus, which can contribute to improving wear resistance, has a small elongation at cut. In the tire 2, the reinforcing layer 16 suppresses the stretching of the tread 4 during cornering, so that the cross-linked rubber with low elongation at cut and high modulus can be used for the tread 4. From this point of view, in the tire 2, the tread 4 can also be composed of a cross-linked rubber with an elongation at cut of 330% or less at a temperature of 100°C and a 200% modulus at a temperature of 100°C of 6.5 MPa or more. The tread 4 can also be composed of a cross-linked rubber with an elongation at cut of 290% or less at a temperature of 100°C and a 200% modulus at a temperature of 7.2 MPa or more. The tread 4 can also be composed of a cross-linked rubber with an elongation at cut of 270% or less at a temperature of 100°C and a 200% modulus at a temperature of 7.5 MPa or more.

[0072] In the tire 2, from the viewpoint of improving wear resistance, the cross-linked rubber constituting the tread 4 is preferably a cross-linked rubber having an elongation at cut of 330% or less at a temperature of 100°C and a 200% modulus at 100°C of 6.5 MPa or more, more preferably a cross-linked rubber having an elongation at cut of 290% or less at a temperature of 100°C and a 200% modulus at 100°C of 7.2 MPa or more, further preferably a cross-linked rubber having an elongation at cut of 270% or less at a temperature of 100°C and a 200% modulus at 100°C of 7.5 MPa or more.

[0073] exist Figure 1 In FIG. 1 , the length indicated by the double-headed arrow TB is the thickness of the tread 4 in the equatorial plane. The thickness TB of the tread 4 is indicated by the distance from the outer surface of the carcass 10 to the outer surface of the tread 4 measured along the equatorial plane.

[0074] In the tire 2, the thickness TB of the tread 4 at the equatorial plane is preferably 7 mm or less. The tread 4 is relatively thin. A thin tread 4 helps improve the sports performance. From this point of view, the thickness TB of the tread 4 is more preferably 6 mm or less, and further preferably 5 mm or less. From the point of view of ensuring the rigidity of the tread 4, the thickness TB of the tread 4 is preferably 2 mm or more, more preferably 3 mm or more, and further preferably 4 mm or more.

[0075] exist Figure 1 In the figure, the position indicated by the reference symbol PR is a position on the outer surface of the tread 4. In the tire 2, the distance from the outer surface of the reinforcing layer 16 to the outer surface of the tread 4 measured along the normal line of the outer surface of the reinforcing layer 16 is shown to be the largest when the normal line passes through the position PR on the outer surface of the tread 4. Figure 1 , the normal line of the outer surface of the reinforcing layer 16 passing through the position PR is indicated by a solid line LR. The distance from the outer surface of the reinforcing layer 16 to the outer surface of the tread 4 measured along the normal line LR is indicated by a double-headed arrow TR. In the tire 2, the distance TR is the thickness of the tread 4 at the shoulder portion Sh. The thickness TR of the tread 4 at the shoulder portion Sh is indicated by the maximum thickness.

[0076] In the tire 2, from the viewpoint of ensuring the service life, it is preferred that the tread 4 is configured so that the thickness TR of the tread 4 at the shoulder portion Sh is thicker than the thickness TB of the tread 4 at the equatorial plane. From this viewpoint, the difference TR-TB between the thickness TR of the tread 4 at the shoulder portion Sh and the thickness TB of the tread 4 at the equatorial plane is preferably 0.2 mm or more, and more preferably 0.5 mm or more. From the viewpoint of appropriately maintaining the side surface of the tread surface 18 and ensuring good running performance, the difference TR-TB between the thickness TR of the tread 4 at the shoulder portion Sh and the thickness TB of the tread 4 at the equatorial plane is preferably 2.0 mm or less, and more preferably 1.0 mm or less.

[0077] like Figure 1 As shown, in the tire 2, the outer end 36 of the reinforcing layer 16 is covered by the sidewall 6. When the sidewall 6 is harder than the tread 4, the sidewall 6 effectively restrains the reinforcing layer 16. Since the position of the reinforcing layer 16 relative to the ground contact surface is stably maintained, it can effectively help the reinforcing layer 16 to suppress the stretching of the tread 4 during cornering. From this point of view, when the sidewall 6 is harder than the tread 4, the outer end 36 of the reinforcing layer 16 is preferably covered by the sidewall 6.

[0078] exist Figure 1 , the length indicated by the double-headed arrow RS is the overlapping length of the sidewall 6 and the reinforcing layer 16. The overlapping length RS is indicated by the length from the end of the sidewall 6 to the outer end 36 of the reinforcing layer 16 measured along the boundary between the sidewall 6 and the reinforcing layer 16.

[0079] In the tire 2, from the viewpoint of suppressing the influence of the sidewall 6 on the rigidity of the tread portion T, the overlapping length between the sidewall 6 and the reinforcing layer 16 is preferably 10 mm or less, and more preferably 5 mm or less. When the sidewall 6 is harder than the tread 4, the outer end 36 of the reinforcing layer 16 is preferably covered by the sidewall 6, and thus the preferred lower limit of the overlapping length is not set.

[0080] exist Figure 2 In FIG. 8 , the angle indicated by the reference symbol γ is the angle formed by the reinforcing cords 38 included in the cord reinforcing layer 40 with respect to the equatorial plane (hereinafter referred to as the inclination angle).

[0081] As described above, in the tire 2, the cord reinforcement layer 40 including the reinforcing cords 38 extending substantially in the axial direction suppresses the occurrence of damage caused by the axial extension of the tread 4 during cornering. The cord reinforcement layer 40 contributes to improved durability and enables the use of a cross-linked rubber with a high modulus for the tread 4. From this viewpoint, the inclination angle γ of the reinforcing cords 38 is preferably 70° or more, more preferably 80° or more. The inclination angle γ is preferably 90° or less, more preferably 85° or less.

[0082] exist Figure 2 , the angle represented by the figure symbol η is the angle (hereinafter referred to as the crossing angle) formed by the reinforcing cord 3 included in the cord reinforcement layer 40 and the carcass cord 30 included in the carcass ply 24 (specifically, the second ply 28) stacked with the cord reinforcement layer 40.

[0083] In the tire 2, the crossing angle η between the reinforcing cord 38 and the carcass cord 30 is preferably 50° or more and preferably 70° or less. By setting the crossing angle η to 50° or more, the stretching of the tread 4 during cornering is effectively suppressed. In the tire 2, good durability is ensured and the wear resistance is improved. From this point of view, the crossing angle η is more preferably 55° or more. By setting the crossing angle η to 70° or less, the reinforcing layer 16 effectively restrains the carcass 10. In the tire 2, the movement of the shoulder portion Sh is suppressed, and thus in this case, the wear resistance is improved. From this point of view, the crossing angle η is more preferably 65° or less.

[0084] Figure 3 2 shows the structure of a reinforcing layer 54 included in a racing tire 52 according to another embodiment of the present invention. Figure 3 , the left-right direction is the axial direction of the tire 52 , and the up-down direction is the circumferential direction of the tire 52 .

[0085] Although not shown in the figure, the tire 52 includes a tread, a pair of sidewalls, a pair of beads, a carcass, a pair of chafers, and an inner liner in addition to the reinforcing layer 54. Figure 1The structure of the tire 2 shown is equivalent to the structure of the tire 2 shown. Figure 3 In the figure, the carcass is shown together with a pair of reinforcing layers 54, but the carcass is labeled with Figure 1 The same reference numerals are used for the carcass 10 and description thereof will be omitted.

[0086] In the tire 52, each reinforcing layer 54 is also included in the shoulder portion Sh. The reinforcing layer 54 is located radially inside the tread. The reinforcing layer 54 is radially laminated on the outside of the second cord main body 28a constituting a part of the carcass 10. In the tire 52, no element such as a belt or a band is provided between the carcass 10 and the reinforcing layer 54.

[0087] In the tire 52, a pair of reinforcing layers 54 are arranged across the equatorial plane in the axial direction. The tread is laminated on the carcass 10, more specifically, on the outer side of the second cord body 28a, between the reinforcing layer 54 on one side and the reinforcing layer 54 on the other side. In the tire 52, no elements such as the above-mentioned belt or band are provided between the tread and the carcass 10.

[0088] Although not shown in the figure, the tire 52 also has Figure 1 The same as the tire 2 shown, the inner end 56 of the reinforcing layer 54 is located axially inwardly of the end of the tread surface. In the axial direction, the position of the outer end 58 of the reinforcing layer 54 is consistent with the position of the end of the tread surface, or the outer end 58 of the reinforcing layer 54 is located in a position outwardly of the end of the tread surface.

[0089] In the tire 52, the reinforcing layer 54 is made of crosslinked rubber. The reinforcing layer 54 is a rubber reinforcing layer 60 that is harder than the tread. The rubber reinforcing layer 60 is located radially inward of the tread at the shoulder portion Sh of the tire 52.

[0090] In the tire 52, the rubber reinforcing layer 60 has high rigidity, so that even if a force is applied to the shoulder portion Sh in such a way that the tread of the shoulder portion Sh is stretched in the axial direction during cornering, the reinforcing layer 54 acts in such a way as to overcome the force. In the tire 52, the stretching of the tread during cornering is suppressed. Even if the tread is made of a cross-linked rubber having a low elongation when cut, the occurrence of damage caused by the tread stretching in the axial direction can be suppressed. In the tire 52, the tread can be made of a cross-linked rubber having a high modulus.

[0091] The tire 52 can suppress the influence on durability and improve the wear resistance. Since a thinner tread can be adopted, the tire 52 can also reduce the weight. The tire 52 can also contribute to improving the sports performance.

[0092] In the tire 52 , the hardness of the rubber reinforcing layer 60 at a temperature of 23° C. is preferably 80 or more and preferably 95 or less.

[0093] By setting the hardness of the rubber reinforcing layer 60 at a temperature of 23° C. to 80 or more, the rubber reinforcing layer 60 effectively suppresses the tread from being stretched in the axial direction during cornering. In the tire 52, the occurrence of damage caused by the tread stretching in the axial direction is suppressed. The rubber reinforcing layer 60 helps to improve durability, and a cross-linked rubber with a high modulus can be used for the tread. From this point of view, the hardness of the rubber reinforcing layer 60 is more preferably 82 or more, and more preferably 84 or more.

[0094] By setting the hardness of the rubber reinforcing layer 60 at a temperature of 23° C. to 95 or less, the occurrence of damage at the interface between the rubber reinforcing layer 60 and the tread is suppressed. In the tire 52, good durability is maintained. From this viewpoint, the hardness of the rubber reinforcing layer 60 is more preferably 93 or less, and further preferably 90 or less.

[0095] In the tire 52 , the difference between the hardness of the rubber reinforcing layer 60 and the hardness of the tread at a temperature of 23° C. is preferably 10 or more and preferably 30 or less.

[0096] By setting the difference between the hardness of the rubber reinforcing layer 60 and the hardness of the tread at a temperature of 23°C to be 10 or more, the rubber reinforcing layer 60 effectively suppresses the tread from being stretched in the axial direction during cornering. In the tire 52, the occurrence of damage caused by the tread stretching in the axial direction is suppressed. The rubber reinforcing layer 60 helps to improve durability, and a cross-linked rubber with a high modulus can be used for the tread. From this viewpoint, the difference between the hardness of the rubber reinforcing layer 60 and the hardness of the tread is more preferably 12 or more, and further preferably 15 or more.

[0097] By setting the difference between the hardness of the rubber reinforcing layer 60 and the hardness of the tread at a temperature of 23° C. to 30 or less, the occurrence of damage at the interface between the rubber reinforcing layer 60 and the tread is suppressed. In the tire 52, good durability is maintained. From this viewpoint, the difference between the hardness of the rubber reinforcing layer 60 and the hardness of the tread is more preferably 28 or less, and further preferably 25 or less.

[0098] The reinforcing layer 54 of the tire 52 is a rubber reinforcing layer 60 that is harder than the tread. Figure 1 The reinforcing layer 16 of the tire 2 shown in FIG. 1 is a cord reinforcing layer 40 including a plurality of reinforcing cords 38 arranged side by side in the circumferential direction. From the viewpoint of easy tire manufacturing, a rubber reinforcing layer 60 is preferably used as the reinforcing layer.

[0099] In the tire 52, the hardness of the sidewall is preferably 80 or more and preferably 95 or less. Thus, the sports performance is further improved. In this case, the sidewall is harder than the tread, and the difference between the hardness of the sidewall and the hardness of the tread at a temperature of 23° C. is preferably 10 or more and preferably 30 or less. In this case, the rubber reinforcing layer 60 may be made of a material different from that of the sidewall, or may be made of the same material as that of the sidewall.

[0100] As described above, according to the present invention, a racing tire that can suppress the influence on durability and achieve improved wear resistance can be obtained. In particular, the tire 2 and the tire 52 can suppress the influence on durability and achieve improved wear resistance, and can also achieve improved sports performance. In the tire 2 and the tire 52, the reduction in appearance quality and sports performance caused by use is suppressed. Compared with existing tires, the tire 2 and the tire 52 have excellent sports performance, and compared with existing tires, the service life of the tire 2 and the tire 52 is longer. The tire 2 and the tire 52 reduce the frequency of replacement of the tires of the racing car. In particular, in the rental racing tire, a longer service life is required. The tire 2 and the tire 52 are suitable for use as a rental racing tire.

[0101] [Example]

[0102] Hereinafter, the present invention will be described in further detail with reference to Examples and the like, but the present invention is not limited to these Examples.

[0103] [Example 1]

[0104] Get equipped Figure 1 A racing tire (tire size = 10×4.50-5) having the basic structure shown in and the specifications shown in the following Table 1. This tire is a front wheel tire.

[0105] In Example 1, the elongation at break (Elo.) of the tread at a temperature of 100° C. was 270%, and the 200% modulus (M200) of the tread was 7.5 MPa.

[0106] In this embodiment 1, the ratio NW / BW of the axial distance NW from the equatorial plane to the inner end of the reinforcing layer to the axial distance BW from the equatorial plane to the end of the tread surface is 0.70. The ratio GW / BW of the axial distance GW from the end of the tread surface to the outer end of the reinforcing layer to the axial distance BW is 0.06.

[0107] In this embodiment 1, there is Figure 2The cord reinforcement layer of the structure shown in Table 1 is used as a reinforcement layer. This is shown in the structure column of Table 1. The cords made of nylon fibers are used as reinforcement cords. The inclination angle γ of the reinforcement cord is 85° (degrees). In addition, the inclination angle α of the carcass cord included in the first cord and the inclination angle β of the carcass cord included in the second cord are 30° respectively.

[0108] In Example 1, the thickness TB of the tread at the equatorial plane is 6.0 mm, and the thickness TR of the tread at the shoulder is 7.0 mm. The hardness of the tread at a temperature of 23° C. is 70, and the hardness of the sidewall is 90. The outer end of the reinforcing layer is covered by the sidewall, and the overlap length RS is 5 mm.

[0109] [Comparative Examples 1 to 3]

[0110] Tires of Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 except that no reinforcing layer was provided and the elongation at break and the 200% modulus of the tread at a temperature of 100° C. were as shown in Table 1 below.

[0111] [Example 2]

[0112] A tire of Example 2 was obtained in the same manner as in Example 1 except that the elongation at break and the 200% modulus of the tread at a temperature of 100° C. were as shown in Table 1 below.

[0113] [Examples 3-4]

[0114] Tires of Examples 3 and 4 were obtained in the same manner as in Example 1 except that the ratio (GW / BW), the elongation at break of the tread at a temperature of 100° C., and the 200% modulus were as shown in Table 2 below.

[0115] [Example 5]

[0116] A tire of Example 5 was obtained in the same manner as in Example 1 except that the inclination angle γ of the reinforcing cords was set as shown in Table 2 below.

[0117] [Example 6]

[0118] In addition to having Figure 3 A tire of Example 6 was obtained in the same manner as in Example 1 except that a rubber reinforcing layer having the structure shown in was used as the reinforcing layer. In Example 6, the hardness of the rubber reinforcing layer at a temperature of 23° C. was 90.

[0119] [Installation of trial tires]

[0120] The trial tire was assembled on a rim (size = 4.5 × 5.0), filled with air and the internal pressure of the tire was adjusted to 120 kPa. The trial tire was mounted on the front wheel of the test vehicle (a racing vehicle equipped with a four-stroke engine with a displacement of 190 cc). A commercially available tire (size = 11 × 6.50-5) was assembled on a rim (size = 6.5 × 5.0), filled with air and the internal pressure of the tire was adjusted to 120 kPa. The tire was mounted on the rear wheel of the test vehicle.

[0121] [Lap time]

[0122] A driving test was conducted by having the driver drive the test vehicle 10 times on a 960m circular course. In the driving test, the lap time of the third lap and the lap time of the sixth lap were measured to obtain the fastest lap time. The difference between the fastest lap time of each example and the fastest lap time of Comparative Example 1 was calculated. The results are shown in Tables 1 and 2 below. The larger the value, the shorter the lap time.

[0123] [Handling stability]

[0124] In the driving test related to the lap time described above, the driver was asked to evaluate (sensory evaluation) the steering stability. The results are shown in the following Tables 1 and 2 as indexes. The larger the numerical value, the better the steering stability of the tire.

[0125] [Abrasion resistance]

[0126] The driver was asked to drive the above test vehicle 800 times on a 960m circular course. After driving, the wear amount was measured based on the wear indicator installed on the tire. The results are shown in the following Tables 1 and 2 as indexes. The larger the value, the better the wear resistance of the tire.

[0127] [crack]

[0128] The appearance of the tire after the above-mentioned running test related to wear resistance was observed to confirm whether cracks occurred, and if cracks occurred, the length of the cracks was measured. The results are shown in the following Tables 1 and 2 according to the following grades.

[0129] A···No cracks were generated.

[0130] B···The length of the crack is less than 5 mm.

[0131] C···The length of the crack is 5 mm or more and less than 10 mm.

[0132] D···The length of the crack is 10 mm or more.

[0133]

Table 1

[0134]

[0135]

Table 2

[0136]

[0137] As shown in Tables 1 and 2, it was confirmed that the Examples suppressed the influence on durability and achieved improvement in wear resistance, and that the Examples had lap times and steering stability equal to or greater than those of the Comparative Examples. The advantages of the present invention are apparent from these evaluation results.

[0138] Industrial Applicability

[0139] The above-described technology for improving wear resistance while suppressing the influence on durability can also be applied to various tires.

Claims

1. A racing tire, characterized in that: have: a tread having a tread surface that contacts a road surface; a pair of sidewalls connected to ends of the tread and located radially inward of the tread; a pair of beads located radially inward of the sidewalls; a carcass that spans between the beads on one side and the beads on the other side; and A pair of reinforcing layers are arranged axially across the equatorial plane. The reinforcing layer is located on the inner side of the tread in the radial direction and is stacked on the outer side of the carcass. The inner end of the reinforcing layer is located inwardly of the end of the tread surface in the axial direction. The position of the outer end of the reinforcing layer in the axial direction coincides with the position of the end of the tread surface, or the outer end of the reinforcing layer is located outside the end of the tread surface. The sidewall is harder than the tread, and the outer end of the reinforcing layer is covered by the sidewall. The reinforcing layer is a rubber reinforcing layer that is harder than the tread.

2. The racing tire according to claim 1, characterized in that: A ratio of an axial distance from the equatorial plane to an inner end of the reinforcing layer to an axial distance from the equatorial plane to an end of the tread surface is 0.60 or more and 0.80 or less.

3. The racing tire according to claim 1 or 2, characterized in that: A ratio of an axial distance from an end of the tread surface to an outer end of the reinforcing layer to an axial distance from the equatorial plane to the end of the tread surface is 0.15 or less.

4. The racing tire according to claim 1 or 2, characterized in that: The stress of the tread at 200% elongation at a temperature of 100° C. is 6.5 MPa or more.

5. The racing tire according to claim 1 or 2, characterized in that: The hardness of the rubber reinforcing layer at a temperature of 23° C. is 80 or more and 95 or less.

6. The racing tire according to claim 5, characterized in that: A difference between the hardness of the reinforcing layer and the hardness of the tread at a temperature of 23° C. is 10 or more and 30 or less.

7. A racing tire, characterized in that: have: a tread having a tread surface that contacts a road surface; a pair of sidewalls connected to ends of the tread and located radially inward of the tread; a pair of beads located radially inward of the sidewalls; a carcass that spans between the beads on one side and the beads on the other side; and A pair of reinforcing layers are arranged axially across the equatorial plane. The reinforcing layer is located on the inner side of the tread in the radial direction and is stacked on the outer side of the carcass. The inner end of the reinforcing layer is located inwardly of the end of the tread surface in the axial direction. The position of the outer end of the reinforcing layer in the axial direction coincides with the position of the end of the tread surface, or the outer end of the reinforcing layer is located outside the end of the tread surface. The carcass comprises at least two carcass cords, The carcass cord fabric comprises a plurality of carcass cords arranged side by side. The reinforcement layer is a cord reinforcement layer including a plurality of reinforcement cords arranged side by side in the circumferential direction, the angle formed by the reinforcement cords relative to the equatorial plane is greater than 70° and less than 90°, and the angle formed by the reinforcement cords and the carcass cords included in the carcass ply stacked with the cord reinforcement layer is greater than 50° and less than 70°.

8. The racing tire according to claim 7, characterized in that: A ratio of an axial distance from the equatorial plane to an inner end of the reinforcing layer to an axial distance from the equatorial plane to an end of the tread surface is 0.60 or more and 0.80 or less.

9. The racing tire according to claim 7 or 8, characterized in that: A ratio of an axial distance from an end of the tread surface to an outer end of the reinforcing layer to an axial distance from the equatorial plane to the end of the tread surface is 0.15 or less.

10. The racing tire according to claim 7 or 8, characterized in that: The stress of the tread at 200% elongation at a temperature of 100° C. is 6.5 MPa or more.

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