Pneumatic tire for racing kart

Abstract

To provide a pneumatic tire 2 for a racing cart superior in traction performance, brake performance, and steering stability.SOLUTION: A tire 2 includes a carcass 10 and a reinforcement layer 14. The carcass 10 includes a bias structure. The reinforcement layer 14 contains topping rubber and a plurality of cords. An absolute value of an angle to a circumferential direction of each of the cords is 0° or more and 15° or less. The width Wr of the reinforcement layer 14 is 25 mm or less. The height Hi of a radially inward end Pi of the reinforcement layer 14 is 20 mm or more. The height Ho of a radially outward end Po of the reinforcement layer 14 is 50 mm or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pneumatic tire mounted on a racing kart.

Background Art

[0002] In kart racing, a racing kart runs on a circuit course. Kart racing plays a role in the popularization of motorsports, the training of drivers, etc. A so-called bias structure is adopted for the tires mounted on racing karts.

[0003] In recent years, the performance of the engines and chassis of racing karts has been remarkably improved. There is also a demand for improved performance in tires for racing karts. Japanese Patent Application Laid-Open No. 2017-137008 discloses a kart tire having a filler. This filler is located inside the sidewall. This filler contains a plurality of cords.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The filler disclosed in Japanese Patent Application Laid-Open No. 2017-137008 contributes to the front-rear rigidity of the tire. Tires with high front-rear rigidity are excellent in traction performance and braking performance. In the tire having this filler, the longitudinal rigidity is also high. High longitudinal rigidity may inhibit the handling stability performance of the tire.

[0006] An object of the present invention is to provide a pneumatic tire for a racing kart that is excellent in the balance of traction performance, braking performance, and handling stability performance.

Means for Solving the Problems

[0007] The pneumatic tire for a racing cart according to the present invention has a tread, a pair of sidewalls, a pair of beads, a carcass, and a pair of reinforcing layers. Each sidewall extends substantially inward in the radial direction from the edge of the tread. Each bead is located axially inward of the sidewall. The carcass extends along the inner sides of the tread and the sidewalls, spans between one bead and the other bead, and has a bias structure. Each reinforcing layer is located axially inward of the sidewall. The width of the reinforcing layer is 25 mm or less. The reinforcing layer includes a plurality of cords. The absolute value of the angle of each cord with respect to the circumferential direction is 0° or more and 15° or less.

[0008] Preferably, the height Hi of the radially inner end of the reinforcing layer is 20 mm or more. Preferably, the height Ho of the radially outer end of the reinforcing layer is 50 mm or less.

[0009] The bead may have a core and an apex extending radially outward from the core. Preferably, the height Hi of the inner end of the reinforcing layer is smaller than the height Ha of the outer end of the apex. Preferably, the height Ho of the outer end of the reinforcing layer is larger than the height Ha of the outer end of the apex. Preferably, the ratio ((Ha - Hi) / Ht) of the difference (Ha - Hi) between the height Ha and the height Hi to the tire height Ht is 0.05 or more and 0.30 or less. Preferably, the ratio ((Ho - Ha) / Ht) of the difference (Ho - Ha) between the height Ho and the height Ha to the tire height Ht is 0.05 or more and 0.30 or less.

[0010] The carcass may have a first ply and a second ply. The first ply may include a plurality of cords each inclined in a negative direction with respect to the circumferential direction and a topping. The second ply may include a plurality of cords each inclined in a positive direction with respect to the circumferential direction and a topping. The angle of the cords of the reinforcing layer with respect to the circumferential direction is zero or a positive value. Preferably, the absolute value of the angle of the cords of the reinforcing layer with respect to the cords of the second ply is 10° or more and 40° or less.

[0011] The first ply may include a plurality of cords each inclined in a positive direction with respect to the circumferential direction, and a topping. The second ply may include a plurality of cords each inclined in a negative direction with respect to the circumferential direction, and a topping. The angle of the cords of the reinforcing layer with respect to the circumferential direction is zero or a positive value. Preferably, the absolute value of the angle of the cords of the reinforcing layer with respect to the cords of the first ply is 10° or more and 40° or less.

Advantages of the Invention

[0012] In the pneumatic tire for a racing cart according to the present invention, the front and rear rigidity is large and the longitudinal rigidity is not excessive. This tire is excellent in the balance of traction performance, braking performance, and handling stability performance.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail based on preferred embodiments while referring to the drawings as appropriate.

[0015] In FIGS. 1 and 2, a pneumatic tire 2 is shown. In FIGS. 1 and 2, arrow X represents the axial direction of the tire 2, and arrow Y represents the radial direction of the tire 2. In FIGS. 1 and 2, the direction perpendicular to the plane of the paper is the circumferential direction of the tire 2. In FIG. 1, the dashed-dotted line CL represents the equatorial plane of the tire 2. In this FIG. 1, the virtual line BL represents the baseline. The baseline BL is a line that defines the diameter (refer to JATMA) of the standard rim on which the tire 2 is mounted. This baseline BL extends in the axial direction.

[0016] This tire 2 has a tread 4, a pair of sidewalls 6, a pair of beads 8, a carcass 10, an inner liner 12, and a pair of reinforcing layers 14. This tire 2 is of a tubeless type. This tire 2 is mounted on a racing cart.

[0017] The tread 4 has a shape that is convex radially outward. The tread 4 forms a tread surface 16 that contacts the road surface. No grooves are engraved on this tread 4. This tire 2 is of a slick type. Grooves may be engraved on this tread 4. The tread 4 is made of a crosslinked rubber that is excellent in wear resistance and grip. In FIG. 1, arrow Ht is the height of the tire 2. The height Ht is the height from the baseline BL to the intersection Pe of the tread surface 16 and the equatorial plane CL.

[0018] Each sidewall 6 extends substantially radially inward from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber that is excellent in cut resistance and weather resistance. This sidewall 6 prevents damage to the carcass 10. The sidewall 6 may include a clinch in a part thereof. This clinch is made of a crosslinked rubber with high hardness.

[0019] Each bead 8 is located axially inward of the sidewall 6. The bead 8 has a core 18 and an apex 20. The core 18 is ring-shaped. The core 18 includes a wound non-stretchable wire. A typical material of the wire is steel. The apex 20 extends radially outward from the core 18. The apex 20 tapers radially outward. In FIG. 2, reference numeral Pa represents the outer end of the apex 20 in the radial direction.

[0020] The carcass 10 has a first ply 22 and a second ply 24. The number of plies in this carcass 10 is 2. The number of plies may be 1. The carcass 10 may have three or more plies.

[0021] In this tire 2, the second ply 24 is laminated with the first ply 22. The first ply 22 and the second ply 24 are spanned between the beads 8 on both sides. The first ply 22 and the second ply 24 are along the inside of the tread 4 and the sidewall 6.

[0022] The first ply 22 is spanned between the beads 8 on both sides. The first ply 22 is folded around each core 18. By this folding, as shown in FIG. 2, a first main portion 26 and a pair of first folded portions 28 are formed on the first ply 22.

[0023] The second ply 24 is spanned between the beads 8 on both sides. The second ply 24 is folded around each core 18. By this folding, as shown in FIG. 2, a second main portion 30 and a pair of second folded portions 32 are formed on the second ply 24.

[0024] Although not shown, each of the first ply 22 and the second ply 24 includes a plurality of cords arranged in parallel and topping rubber. Each cord is inclined with respect to the equatorial plane CL. The absolute value of the preferred inclination angle is 25° or more and 40° or less. The inclination direction of the cords of the first ply 22 with respect to the equatorial plane CL is opposite to the inclination direction of the cords of the second ply 24 with respect to the equatorial plane CL. The carcass 10 of this tire 2 has a so-called bias structure.

[0025] Preferred cords in the carcass 10 are twisted yarns of organic fibers. Examples of preferred organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

[0026] The inner liner 12 is located inside the carcass 10. The inner liner 12 is joined to the inner surface of the carcass 10. The inner liner 12 is made of crosslinked rubber having excellent air barrier properties. A typical base rubber of the inner liner 12 is butyl rubber or halogenated butyl rubber. The inner liner 12 holds the internal pressure of the tire 2.

[0027] Each reinforcing layer 14 is located axially inside the sidewall 6. As is apparent from FIG. 2, in this embodiment, the position of the reinforcing layer 14 is sandwiched between the apex 20 and the second main portion 30. In other words, the reinforcing layer 14 is located axially inside the apex 20. The reinforcing layer 14 may be located inside the first main portion 26. The reinforcing layer 14 may be sandwiched between the first main portion 26 and the second main portion 30. The reinforcing layer 14 may be sandwiched between the apex 20 and the second folded portion 32. The reinforcing layer 14 may be sandwiched between the second folded portion 32 and the first folded portion 28. The reinforcing layer 14 may be sandwiched between the first folded portion 28 and the sidewall 6.

[0028] In FIG. 2, reference numeral Pi represents the inner end of the reinforcing layer 14 in the radial direction, and reference numeral Po represents the outer end of the reinforcing layer 14 in the radial direction. In FIG. 2, reference numeral VS represents a virtual surface. The virtual surface is a curved surface where the radial distance to the inner end Pi is the same as the radial distance to the outer end Po.

[0029] FIG. 3 is a partially cutaway cross-sectional view showing the tire 2 of FIG. 1. In FIG. 3, the reinforcing layer 14 exposed from the sidewall 6 by the cutout is shown. The reinforcing layer 14 includes a plurality of cords 34 and topping rubber 36. These cords 34 are arranged concentrically. Each cord 34 extends along the circumferential direction.

[0030] FIG. 4 is a cross-sectional view showing a part of the tire 2 of FIG. 1. In FIG. 4, a first main part 26, a second main part 30, and a reinforcing layer 14 are shown. The second main part 30 is laminated on the first main part 26. The reinforcing layer 14 is laminated on the second main part 30.

[0031] FIG. 5 is an exploded perspective view showing the tire 2 of FIG. 4. In FIG. 5, a first main part 26, a second main part 30, and a reinforcing layer 14 are shown. As is clear by also referring to FIG. 4, in FIG. 5, arrow X represents the axial direction of the tire 2, arrow Y represents the radial direction of the tire 2, and arrow Z represents the circumferential direction of the tire 2.

[0032] As described above, the first main part 26 includes a plurality of cords 38a and topping rubber 40a. Each cord 38a is inclined with respect to the circumferential direction. In the present embodiment, the cords 38a of the first main part 26 are inclined in the negative direction with respect to the circumferential direction. In FIG. 5, reference numeral θ1 represents the angle of this cord 38a with respect to the circumferential direction. The angle θ1 is measured on the virtual surface VS (see FIG. 2).

[0033] As described above, the second main part 30 includes a plurality of cords 38b and a topping rubber 40b. Each cord 38b is inclined with respect to the circumferential direction. In the present embodiment, the cords 38b of the second main part 30 are inclined in the positive direction with respect to the circumferential direction. The reference sign θ2 in FIG. 5 is the angle with respect to the circumferential direction of the direction of this cord 38b. The angle θ2 is measured on the virtual plane VS (see FIG. 2). In the present embodiment, the absolute value of the angle θ2 coincides with the absolute value of the angle θ1.

[0034] As described above, the reinforcing layer 14 includes a plurality of cords 34 and a topping rubber 36. Each cord 34 extends in the circumferential direction. The angle with respect to the circumferential direction of the direction of this cord 34 is zero. This angle is measured on the virtual plane VS (see FIG. 2).

[0035] When the racing cart accelerates or decelerates, shear stress in the rotational direction is generated in the tire 2. Since the cords 34 of the reinforcing layer 14 are oriented in the circumferential direction, the tension of this cord 34 suppresses the shear deformation of the tire 2. In this tire 2, the reinforcing layer 14 contributes to the longitudinal rigidity of the tire 2. A tire 2 with high longitudinal rigidity is excellent in traction performance and braking performance. Since the cord 34 extends in the circumferential direction, this reinforcing layer 14 does not significantly affect the longitudinal rigidity. In this tire 2, the longitudinal rigidity is not excessive. This tire 2 is also excellent in handling stability performance.

[0036] The arrow Wr in FIG. 2 is the width of the reinforcing layer 14. The width Wr is the straight-line distance between the inner end Pi and the outer end Po. From the viewpoints of traction performance and braking performance, the width Wr is preferably 10 mm or more, more preferably 13 mm or more, and particularly preferably 15 mm or more. From the viewpoint that a tire 2 excellent in uniformity and thus excellent in handling stability performance can be obtained, the width Wr is preferably 25 mm or less, more preferably 22 mm or less, and particularly preferably 20 mm or less.

[0037] In FIG. 2, arrow Hi represents the height of the inner end Pi from the baseline BL. The height Hi is measured along the radial direction. The height Hi is preferably 20 mm or more. The longitudinal rigidity in the vicinity of the core 18 is sufficiently large regardless of the presence or absence of the reinforcing layer 14. Moreover, since the radius of rotation in the vicinity of the core 18 is small, even if the reinforcing layer 14 is disposed in the vicinity of the core 18, its effect is small. In the tire 2 where the height Hi is 20 mm or more, the reinforcing layer 14 is sufficiently separated from the core 18 (or the rim). In this tire 2, the reinforcing layer 14 can be effectively disposed while the width Wr is suppressed. From this viewpoint, the height Hi is more preferably 23 mm or more, and particularly preferably 25 mm or more.

[0038] In FIG. 2, arrow Ho represents the height of the outer end Po from the baseline BL. The height Ho is measured along the radial direction. The height Ho is preferably 50 mm or less. In the vicinity of the outer end 42 (see FIG. 1) of the sidewall 6, the tire 2 is thin. In the tire 2 where another layer is located in the vicinity of this outer end 42, the longitudinal rigidity is excessive. In the tire 2 where the height Ho is 50 mm or less, the reinforcing layer 14 is sufficiently separated from the outer end 42 of the sidewall 6. This reinforcing layer 14 does not inhibit the handling stability performance. From this viewpoint, the height Ho is more preferably 47 mm or less, and particularly preferably 45 mm or less.

[0039] In FIG. 2, arrow Ha represents the height of the outer end Pa of the apex 20 from the baseline BL. The height Ha is measured along the radial direction. The height Ha is larger than the height Hi. In other words, the position of the inner end Pi of the reinforcing layer 14 does not coincide with the position of the outer end Pa of the apex 20 in the radial direction. The inner end Pi is a point where the rigidity changes significantly, and the outer end Pa is also a point where the rigidity changes significantly. The tire 2 in which the two do not coincide is excellent in handling stability performance.

[0040] The ratio ((Ha - Hi) / Ht) of the difference (Ha - Hi) between the height Ha and the height Hi to the height Ht of the tire 2 is preferably 0.05 or more and 0.30 or less. The tire 2 with this ratio of 0.05 or more is excellent in handling stability performance. From this viewpoint, this ratio is more preferably 0.08 or more, and particularly preferably 0.10 or more. The tire 2 with this ratio of 0.30 or less is excellent in uniformity. From this viewpoint, this ratio is more preferably 0.25 or less, and particularly preferably 0.22 or less.

[0041] As shown in FIG. 2, the height Ho is larger than the height Ha. In other words, the position of the outer end Po of the reinforcing layer 14 does not coincide with the position of the outer end Pa of the apex 20 in the radial direction. The outer end Po is a point where the rigidity changes significantly, and the outer end Pa is also a point where the rigidity changes significantly. The tire 2 in which both do not coincide is excellent in handling stability performance.

[0042] The ratio ((Ho - Ha) / Ht) of the difference (Ho - Ha) between the height Ho and the height Ha to the height Ht of the tire 2 is preferably 0.05 or more and 0.30 or less. The tire 2 with this ratio of 0.05 or more and 0.30 or less is excellent in handling stability performance. From this viewpoint, this ratio is more preferably 0.08 or more, and particularly preferably 0.10 or more. This ratio is more preferably 0.25 or less, and particularly preferably 0.22 or less.

[0043] FIG. 6 is a cross-sectional view showing a rubber sheet 44 for the reinforcing layer 14 of the tire 2 of FIG. 1. This rubber sheet 44 includes a plurality of parallel cords 34 and a topping rubber 36. Each cord 34 is generally covered with the topping rubber 36. The cords 34 are spaced apart from adjacent cords 34. There is a topping rubber 36 between the cord 34 and the adjacent cord 34. The cross-section of FIG. 6 is perpendicular to the extending direction of the cord 34.

[0044] In FIG. 6, the arrow Tp represents the thickness of the rubber sheet 44, and the arrow Pc represents the pitch of the cord 34. The thickness Tp is preferably 0.5 mm or more and 2.0 mm or less. The pitch Pc is preferably 0.8 mm or more and 2.0 mm or less.

[0045] In the manufacture of this tire 2, the rubber sheet 44 shown in FIG. 6 is wound around the drum of the molding device. The direction of the cords 34 contained in the wound rubber sheet 44 coincides with the circumferential direction of the drum. This rubber sheet 44 is assembled with a plurality of other rubber members to obtain a local cover (uncured tire). This local cover is put into a mold. The local cover is pressurized within the mold. Due to this pressurization, the local cover is deformed. This deformation is called shaping. The local cover is further pressurized and heated within the mold. Due to the pressurization and heating, the rubber composition of the local cover flows. Due to the heating, the rubber undergoes a crosslinking reaction to obtain the tire 2. The reinforcing layer 14 is formed from the rubber sheet 44.

[0046] The preferred cord 34 in the reinforcing layer 14 is a twisted yarn of organic fibers. Due to shaping, the cord 34 is stretched. From the viewpoint of achieving sufficient stretching, examples of preferred organic fibers include polyester fibers, nylon fibers, and rayon fibers. A cord 34 twisted from two or three yarns is preferred. The fineness of each yarn is preferably 500 dtex or more and 1000 dtex or less.

[0047] In the present invention, the dimensions and angles of each member of the tire 2 are measured in a state where the tire 2 is incorporated into a standard rim and filled with air so as to have a standard internal pressure. During the measurement, no load is applied to the tire 2. As used herein, the standard rim means the rim defined in the standard on which the tire 2 depends. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are standard rims. As used herein, the standard internal pressure means the internal pressure defined in the standard on which the tire 2 depends. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are standard internal pressures.

[0048] FIG. 7 is a partially cut-away cross-sectional view showing a pneumatic tire 46 for a racing cart according to another embodiment of the present invention. In FIG. 7, a reinforcing layer 50 exposed from a sidewall 48 by a notch is shown. The reinforcing layer 50 includes a plurality of cords 52 and topping rubber 54. Each cord 52 is inclined with respect to the circumferential direction. The specifications of this tire 46 other than the inclination angle of the cords 52 of the reinforcing layer 50 are the same as those of the tire 2 shown in FIGS. 1-6.

[0049] FIG. 8 is an exploded perspective view showing the tire 46 of FIG. 7. This tire 46 has a carcass, similar to the tire 2 shown in FIG. 1. This carcass has a first ply and a second ply. In FIG. 8, a first main portion 56 of the first ply and a second main portion 58 of the second ply are shown. Further shown in FIG. 8 is the reinforcing layer 50. In FIG. 8, arrow X represents the axial direction of the tire 46, arrow Y represents the radial direction of the tire 46, and arrow Z represents the circumferential direction of the tire 46.

[0050] The first main portion 56 includes a plurality of cords 60a and topping rubber 62a. Each cord 60a is inclined with respect to the circumferential direction. In this embodiment, the cords 60a of the first main portion 56 are inclined in the negative direction with respect to the circumferential direction. Reference numeral θ1 in FIG. 8 is the angle of this cord 60a with respect to the circumferential direction. The angle θ1 is measured on a virtual plane VS (see FIG. 2).

[0051] The second main portion 58 includes a plurality of cords 60b and topping rubber 62b as described above. Each cord 60b is inclined with respect to the circumferential direction. In this embodiment, the cords 60b of the second main portion 58 are inclined in the positive direction with respect to the circumferential direction. Reference numeral θ2 in FIG. 8 is the angle of this cord 60b with respect to the circumferential direction. The angle θ2 is measured on a virtual plane VS (see FIG. 2). In this embodiment, the absolute value of the angle θ2 coincides with the absolute value of the angle θ1.

[0052] As described above, the reinforcing layer 50 includes a plurality of cords 52 and a topping rubber 54. Each cord 52 is inclined with respect to the circumferential direction. In the present embodiment, the cords 52 of the reinforcing layer 50 are inclined in the positive direction with respect to the circumferential direction. The reference symbol θr in FIG. 8 is the angle of the direction of this cord 52 with respect to the circumferential direction. The angle θr is measured on the virtual plane VS (see FIG. 2). As is clear from FIGS. 7 and 8, the absolute value of the angle θr is smaller than the absolute value of the angle θ1 and smaller than the absolute value of the angle θ2.

[0053] In the present embodiment, since the inclination direction of the cord 60a of the first main portion 56 is regarded as "negative", the inclination direction of the cord 60b of the second main portion 58 is "positive", and the inclination direction of the cord 52 of the reinforcing layer 50 is "positive". When the inclination direction of the cord 60a of the first main portion 56 is regarded as "positive", the inclination direction of the cord 60b of the second main portion 58 is "negative", and the inclination direction of the cord 52 of the reinforcing layer 50 is "negative".

[0054] When the racing cart accelerates or decelerates, a shear stress in the rotational direction is generated in the tire 46. Since the absolute value of the angle θr of the cord 52 of the reinforcing layer 50 is small, the tension of this cord 52 suppresses the shear deformation of the tire 46. In this tire 46, the reinforcing layer 50 contributes to the longitudinal rigidity of the tire 46. A tire 46 with high longitudinal rigidity is excellent in traction performance and braking performance. Since the absolute value of the angle θr is small, this reinforcing layer 50 does not have a great influence on the longitudinal rigidity. In this tire 46, the longitudinal rigidity is not excessive. This tire 46 is also excellent in handling stability performance.

[0055] From the viewpoints of traction performance, braking performance, and handling stability performance, the absolute value of the angle θr is preferably 15° (degree) or less, more preferably 12° or less, and particularly preferably 10° or less. The ideal absolute value of the angle θr from the viewpoints of traction performance, braking performance, and handling stability performance is zero. From the viewpoint that the shaping in the mold has little adverse effect on the homogeneity, the absolute value of the angle θr is preferably 2° or more, more preferably 4° or more, and particularly preferably 5° or more.

[0056] The absolute value of the difference (θ1 - θr) between the angle θ1 and the angle θr represents the angle of the cord 52 of the reinforcing layer 50 with respect to the cord 60a of the first ply. The absolute value of the difference (θ2 - θr) between the angle θ2 and the angle θr represents the angle of the cord 52 of the reinforcing layer 50 with respect to the cord 60b of the second ply. As described above, the inclination direction of the cord 60a of the first main part 56 is "negative", the inclination direction of the cord 60b of the second main part 58 is "positive", and the inclination direction of the cord 52 of the reinforcing layer 50 is "positive". Therefore, the absolute value of the difference (θ2 - θr) is smaller than the absolute value of the difference (θ1 - θr). The absolute value of the difference (θ2 - θr) is preferably 10° or more and 40° or less. In this tire 46, the carcass and the reinforcing layer 50 can contribute to the traction performance, braking performance, and handling stability performance. From this viewpoint, the absolute value of the difference (θ2 - θr) is more preferably 15° or more, and particularly preferably 20° or more.

[0057] The inclination direction of the cord 60a of the first main part 56 may be "positive", the inclination direction of the cord 60b of the second main part 58 may be "negative", and the inclination direction of the cord 52 of the reinforcing layer 50 may be "positive". In this case, the absolute value of the difference (θ1 - θr) is smaller than the absolute value of the difference (θ2 - θr). The absolute value of the difference (θ1 - θr) is preferably 10° or more and 40° or less. In this tire 46, the carcass and the reinforcing layer 50 can contribute to the traction performance, braking performance, and handling stability performance. From this viewpoint, the absolute value of the difference (θ1 - θr) is more preferably 15° or more, and particularly preferably 20° or more. [Examples]

[0058] Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed in a limited manner based on the description of these examples.

[0059] [Example 1] A front tire for a racing cart shown in FIGS. 1 - 6 was manufactured. The size of this tire was "10×4.50 - 5". This tire had the following specifications. Height Ht of the tire: 60 mm Height Ha of the outer end Pa of the apex: 38 mm Angle θ1 of the first ply cord: -35° Angle θ2 of the second ply cord: 35° Angle θr of the cords in the reinforcing layer: 0° Width Wr of the reinforcing layer: 20 mm Height Hi of the inner end Pi of the reinforcing layer: 30 mm Height Ho of the outer end Po of the reinforcing layer: 45 mm

[0060] [Example 2 - 4] Tires of Example 2 - 4 were obtained in the same manner as in Example 1, except that the height Hi of the inner end Pi and the height Ho of the outer end Po of the reinforcing layer were as shown in Table 1 below.

[0061] [Examples 5 - 7 and Comparative Example 1] Tires of Examples 5 - 7 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the width Wr of the reinforcing layer was as shown in Table 2 below.

[0062] [Examples 8 - 10 and Comparative Example 2] Tires of Examples 8 - 10 and Comparative Example 2 were obtained in the same manner as in Example 1, except that the angle θr of the cords in the reinforcing layer was as shown in Table 3 below.

[0063] [Examples 11 and 12] Tires of Examples 11 and 12 were obtained in the same manner as in Example 1, except that the angle θ1 of the cords in the first ply and the angle θ2 of the cords in the second ply were as shown in Table 4 below.

[0064] [Comparative Example 3] A tire of Comparative Example 3 was obtained in the same manner as in Example 1, except that no reinforcing layer was provided.

[0065] [Sensory Evaluation] The tire was mounted on a rim with a size of 435, and the tire was filled with air so that the internal pressure became 70 kPa. This tire was installed on a racing kart with a displacement of 250 cc. The driver was made to drive this racing kart on a racing circuit to evaluate the traction performance and braking performance. Furthermore, the driver was made to evaluate the handling stability performance. These results are shown in Table 1-4 below as indices. The larger the numerical value, the more preferable.

[0066] [Comprehensive Evaluation] The average of the index of the traction and braking performance and the index of the handling stability performance was calculated. This result is shown in Table 1-4 below. The larger the numerical value, the more preferable.

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070]

Table 4

[0071] As shown in Table 1-4, the tires of each example are excellent in the balance of traction performance, braking performance, and handling stability performance. From this evaluation result, the superiority of the present invention is clear.

Industrial Applicability

[0072] The pneumatic tire according to the present invention can be mounted on either the front rim or the rear rim of a racing kart. The pneumatic tire according to the present invention can be mounted on various grades of racing karts.

Explanation of Signs

[0073] 2 ··· Pneumatic tire 4 ··· Tread 6 ··· Sidewall 8 ··· Bead 10 ··· Carcass 14 ··· Reinforcing layer 18 ··· Core 20 ··· Apex 22 ··· First ply 24 ··· Second ply 26 ··· First main part 28 ··· First folded part 30 ··· Second main part 32 ··· Second folded part 34 ··· Cord of the reinforcing layer 36 ··· Topping rubber of the reinforcing layer 38a ··· Cord of the first ply 38b ··· Cord of the second ply 40a ··· Topping rubber of the first ply 40b ··· Topping rubber of the second ply 44 ··· Rubber sheet 46 ··· Pneumatic tire 48 ··· Sidewall 50 ··· Reinforcing layer 52 ··· Cord of the reinforcing layer 54 ··· Topping rubber of the reinforcing layer 56 ··· First main part 58 ··· Second main part 60a ··· Cord of the first main part 60b ··· Cord of the second main part 62a ··· Topping rubber of the first main part 62b ··· Topping rubber of the second main part

Claims

1. A pneumatic tire for a racing car, comprising a tread, a pair of sidewalls, a pair of beads, a carcass, and a pair of reinforcing layers, each sidewall extending substantially radially inward from an end of the tread, each bead being located axially inside the sidewall, the carcass extending along the inside of the tread and the sidewall, spanning between one bead and the other bead, and having a bias structure, each bead having a ring-shaped core and an apex extending radially outward from the core, each reinforcing layer being located axially inside the sidewall, a part of the reinforcing layer being sandwiched between the apex and the carcass axially inside the apex, the width of the reinforcing layer being 25 mm or less, the reinforcing layer including a plurality of cords, the height Hi of the radially inner end of the reinforcing layer being 20 mm or more, the height Hi being smaller than the height Ha of the radially outer end of the apex, the height Ho of the radially outer end of the reinforcing layer being larger than the height Ha of the outer end of the apex, and the absolute value of the angle of each cord with respect to the circumferential direction being 0° or more and 15° or less.

2. The tire according to claim 1, wherein the height Ho of the radially outer end of the reinforcing layer is 50 mm or less.

3. The tire according to claim 1, wherein the ratio ((Ha - Hi) / Ht) of the difference (Ha - Hi) between the height Ha and the height Hi to the height Ht of the tire is 0.05 or more and 0.30 or less.

4. The tire according to claim 1 or 3, wherein the ratio ((Ho - Ha) / Ht) of the difference (Ho - Ha) between the height Ho and the height Ha to the height Ht of the tire is 0.05 or more and 0.30 or less.

5. the carcass having a first ply and a second ply, the first ply including a plurality of cords and a topping, and each cord in the first ply being inclined in a negative direction with respect to the circumferential direction, the second ply including a plurality of cords and a topping, and each cord in the second ply being inclined in a positive direction with respect to the circumferential direction, and the angle of the cords of the reinforcing layer with respect to the circumferential direction being zero or a positive value. The tire according to any one of claims 1 to 4, wherein the absolute value of the angle of the cords of the reinforcing layer with respect to the cords of the second ply is 10° or more and 40° or less.

6. The carcass has a first ply and a second ply, The first ply includes a plurality of cords and a topping, and in this first ply, each cord is inclined in a positive direction with respect to the circumferential direction, The second ply includes a plurality of cords and a topping, and in this second ply, each cord is inclined in a negative direction with respect to the circumferential direction, The angle of the cords of the reinforcing layer with respect to the circumferential direction is zero or a positive value, The tire according to any one of claims 1 to 5, wherein the absolute value of the angle of the cords of the reinforcing layer with respect to the cords of the first ply is 10° or more and 40° or less.

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