Heavy-duty tires

Abstract

To provide a tire for heavy load which can be excellently adapted for both of an abrasion resistance and a heat generation resistance.SOLUTION: In a tire 1 for heavy load, a tread rubber 7 has a cap layer 7c, and a base layer 7b disposed closer to a tire inner periphery than the cap layer. The cap layer includes a cap top layer 7c1 and a cap intermediate layer 7c2. A tanδ of the cap top layer in a tensile test in a condition of the ambient temperature of 24°C, the amplitude of 2%, and 50 Hz is larger than that of the cap intermediate layer. A difference between the tanδ of the cap top layer in the tensile test in the condition of the ambient temperature of 24°C, the amplitude of 2%, and 50 Hz, and the tanδ of the cap intermediate layer in the tensile test in the condition of the ambient temperature of 24°C, the amplitude of 2%, and 50 Hz is 0.03 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heavy duty tire. [Background technology]

[0002] BACKGROUND ART Conventionally, there are heavy-duty tires in which the tread rubber includes a cap layer and a base layer (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-137411 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, heavy-duty tires are required to have two main performance characteristics: wear resistance and heat resistance (and therefore durability). However, these performance characteristics are in a trade-off relationship, and it is not easy to achieve both. In conventional heavy duty tires, there is room for improvement in terms of both wear resistance and heat resistance.

[0005] An object of the present invention is to provide a heavy-duty tire that can achieve both wear resistance and heat resistance at a higher level. [Means for solving the problem]

[0006] The above object can be achieved by the following means.

[0007] [1] Tread rubber is a cap layer; a base layer disposed closer to the tire inner circumferential side than the cap layer; and and The cap layer is A cap surface layer; a cap intermediate layer; Equipped with the cap surface layer has a larger tan δ than the cap intermediate layer in a tensile test under conditions of room temperature 24°C, 2% amplitude, and 50 Hz; A heavy-duty tire, wherein the difference between the tan δ of the cap surface layer in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz and the tan δ of the cap intermediate layer in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz is 0.03 or more. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0008] [2] The heavy-duty tire according to [1], wherein the base layer has a tan δ in a tensile test under conditions of room temperature 24°C, 2% amplitude, and 50 Hz that is 0.03 or more lower than that of the cap intermediate layer. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0009] [3] A heavy-duty tire according to [1] or [2], wherein the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in the portion of the cap layer between the tire widthwise positions of a pair of ground contact edges is 75% or less. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0010] [4] A heavy-duty tire according to any one of [1] to [3], wherein the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in a portion of the cap layer between the tire width direction positions of a pair of ground contact edges is 30% or more. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0011] [5] A heavy-duty tire according to any one of [1] to [4], wherein the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in a portion of the cap layer between the tire width direction positions of a pair of ground contact edges is 30 to 75%. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0012] [6] In the cap layer, the average value of the ratio of the thickness of the cap surface layer to the thickness of the cap layer in a portion between a pair of 1 / 4 points that are spaced apart by 1 / 4 times the contact width from the tire equatorial plane is 30 to 60%, [1] to [5], wherein the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in a pair of portions of the cap layer between the pair of quarter points and the pair of ground contact edges in the tire width direction is 50 to 75%. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0013] [7] A heavy-duty tire according to any one of [1] to [6], wherein the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in a portion of the cap layer between a pair of 1 / 4 points that are 1 / 4 times the contact width from the tire equatorial plane is lower than the average ratio of the thickness of the cap surface layer to the thickness of the cap layer in a pair of portions of the cap layer between the pair of 1 / 4 points and the tire width direction positions of a pair of contact edges. This allows for both wear resistance and heat resistance to be achieved at a higher level.

[0014] [8] A heavy-duty tire according to any one of [1] to [7], wherein the cap surface layer, the cap intermediate layer, and the base layer are each present over the entire tire width direction region between the tire width direction positions of a pair of ground contact edges. This allows for both wear resistance and heat resistance to be achieved at a higher level. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a heavy-duty tire that can achieve both wear resistance and heat resistance at a higher level. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a cross-sectional view in the tire width direction, schematically showing a heavy-duty tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view showing a part of the heavy-duty tire of FIG. 1. [Figure 3] 1 is a diagram showing analysis results for a plurality of tire models. DETAILED DESCRIPTION OF THE INVENTION

[0017] The heavy-duty tire according to the present invention can be suitably used for any kind of heavy-duty tire, and can be suitably used in particular for tires for construction and mining vehicles (off-the-road tires).

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a heavy duty tire according to the present invention will be described by way of example with reference to the drawings. In each drawing, the same members and parts are designated by the same reference numerals. For convenience, in this specification, heavy duty tires and the like are also referred to simply as "tires." In this specification, tires are pneumatic tires.

[0019] 1 and 2 are drawings for explaining a heavy-duty tire 1 according to one embodiment of the present invention. Fig. 1 is a cross-sectional view in the tire width direction that schematically shows a heavy-duty tire 1 according to one embodiment of the present invention. Fig. 2 is an enlarged view that shows an enlarged portion of the tire 1 in Fig. 1. The heavy duty tire 1 of the embodiment shown in Figures 1 and 2 is configured as a tire for construction and mining vehicles (off-the-road tire). However, the heavy duty tire 1 may be configured as any type of heavy duty tire.

[0020] Unless otherwise specified, the positional relationship and dimensions of each element are measured in a standard state in which the tire 1 is mounted on an applicable rim, inflated to a specified internal pressure, and no load is applied. In addition, when tire 1 is mounted on an applicable rim, inflated to the specified internal pressure, and subjected to a maximum load, the width of the contact surface in the tire width direction that comes into contact with the road surface is called the "contact width (TW)," and the end of the contact surface in the tire width direction is called the "contact edge (TE)."

[0021] In this specification, the term "applicable rim" refers to the standard rim (called "Measuring Rim" in the ETRTO Standards Manual and "Design Rim" in the TRA Year Book) for the applicable size, which is an industrial standard valid in the region where the pneumatic tire is produced and used, and which is described or will be described in the future, such as the JATMA Year Book of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the European Tyre and Rim Technical Organization (ETRTO) Standards Manual in Europe, and the Tire and Rim Association, Inc. (TRA) Year Book in the United States. However, for sizes not described in these industrial standards, the term refers to a rim with a width corresponding to the bead width of the pneumatic tire. "Applicable rim" includes not only current sizes but also sizes that will be described in the aforementioned industrial standards in the future. An example of a "size to be described in the future" is the size described as "FUTURE DEVELOPMENTS" in the 2013 edition of the ETRTO Standards.

[0022] In this specification, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating as set forth in the aforementioned industrial standards, such as the JATMA Yearbook, or, in the case of a size not set forth in the aforementioned industrial standards, refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is to be mounted. Furthermore, in this specification, "maximum load" refers to the load corresponding to the maximum load capacity of the tire for the applicable size as set forth in the aforementioned industrial standards, or, in the case of a size not set forth in the aforementioned industrial standards, the load corresponding to the maximum load capacity specified for each vehicle on which the tire is to be mounted.

[0023] First, the overall structure of the tire 1 will be described. 1, the tire 1 includes a tread portion 1a, a pair of sidewall portions 1b extending radially inward from both ends of the tread portion 1a in the tire width direction, and a pair of bead portions 1c provided at the radially inner ends of each sidewall portion 1b. When the tire 1 is mounted on a rim, the bead portions 1c are configured to contact the rim on the radially inner side and the tire widthwise outer side. The tire 1 also includes a pair of bead cores 4 a , a pair of bead fillers 4 b , a carcass 5 , a belt 6 , a tread rubber 7 , a side rubber 8 , and an inner liner 9 .

[0024] Each bead core 4a is embedded in a corresponding bead portion 1c. Each bead core 4a includes a plurality of bead wires covered with rubber. The bead wires are preferably made of metal (e.g., steel). The bead wires may be made of, for example, monofilament or stranded wire.

[0025] Each bead filler 4b is located radially outward of the corresponding bead core 4a. The bead fillers 4b extend radially outward in a tapered shape. The bead fillers 4b are made of rubber. Generally, the bead filler is sometimes called a "stiffener."

[0026] The carcass 5 straddles the pair of bead cores 4a and extends in a toroidal shape. The carcass 5 is made up of one or more carcass plies 5a (one in the example of FIG. 1). Each carcass ply 5a includes one or more carcass cords and a covering rubber that covers the carcass cords. The carcass cords can be formed of monofilaments or twisted wires. The carcass 5 is preferably of radial construction, but may also be of bias construction.

[0027] The belt 6 is disposed radially outward of the crown portion of the carcass 5. The belt 6 includes one or more belt layers 6a (six layers in the example of FIG. 1). Each belt layer 6a includes one or more belt cords and a coating rubber that covers the belt cords. The belt cords may be formed of monofilaments or twisted wires. The belt cords are preferably made of metal (e.g., steel), but may also be made of organic fibers such as polyester, nylon, rayon, or aramid.

[0028] The tread rubber 7 is located on the radially outer side of the belt 6 in the tread portion 1a. The tread rubber 7 constitutes a tread surface 2, which is the radially outer surface of the tread portion 1a. A tread pattern is formed on the tread surface 2 by grooves and / or sipes. However, for simplicity, the grooves and / or sipes provided on the tread surface 2 are not shown in FIG. 1. For reference, an example of a groove g that may be provided on the tread surface 2 is indicated by a dashed line in FIG. 2. Further details of the tread rubber 7 will be described later.

[0029] The side rubber 8 is located on the sidewall portion 1b. The side rubber 8 forms an outer surface of the sidewall portion 1b on the outer side in the tire width direction. The side rubber 8 is located further outward in the tire width direction than the carcass 5. The side rubber 8 is located further outward in the tire width direction than the bead filler 4b. The side rubber 8 is formed integrally with the tread rubber 7.

[0030] The inner liner 9 is disposed on the tire inner side of the carcass 5, and may be laminated on the tire inner side of the carcass 5, for example. The inner liner 9 is made of, for example, a butyl-based rubber having low air permeability. Butyl-based rubbers include, for example, butyl rubber and its derivative, halogenated butyl rubber. The inner liner 9 is not limited to butyl-based rubber, and may be made of other rubber compositions, resins, or elastomers.

[0031] The tread rubber 7 will be described in more detail below. 1 and 2, the tread rubber 7 has a cap layer 7c and a base layer 7b. The base layer 7b is disposed closer to the inner periphery of the tire than the cap layer 7c. The cap layer 7c includes two layers, a cap surface layer 7c1 and a cap intermediate layer 7c2, and in this embodiment, these two layers are used. The cap intermediate layer 7c2 is disposed closer to the tire inner periphery than the cap surface layer 7c1. The outer periphery of the tire surface of the cap surface layer 7c1 forms the tread surface 2. The tread rubber 7 is made up of three layers: a cap surface layer 7c1, a cap intermediate layer 7c2, and a base layer 7b.

[0032] The cap surface layer 7c1, the cap intermediate layer 7c2, and the base layer 7b are each present over the entire region in the tire width direction between the tire width direction positions D of the pair of ground contact edges TE.

[0033] The cap surface layer 7c1 has a larger tan δ than the cap intermediate layer 7c2 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz, and the difference between the tan δ of the cap surface layer 7c1 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz and the tan δ of the cap intermediate layer 7c2 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz is 0.03 or more. As a result, the cap surface layer 7c1 has higher abrasion resistance than the cap intermediate layer 7c2. Furthermore, the cap intermediate layer 7c2 has higher heat resistance than the cap surface layer 7c1.

[0034] As described above, the tire 1 has a cap layer 7c of the tread rubber 7 that has two layers: a cap surface layer 7c1 and a cap intermediate layer 7c2. The cap surface layer 7c1 has a larger tan δ than the cap intermediate layer 7c2 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz, and the difference between the tan δ of the cap surface layer 7c1 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz and the tan δ of the cap intermediate layer 7c2 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz is 0.03 or more. Through various studies and analyses, the inventors of the present invention have newly discovered that it is possible to provide higher wear resistance than conventional tires while ensuring heat resistance (and therefore durability) by configuring the tire 1. Furthermore, with this configuration, even if the tire 1 wears out and the cap intermediate layer 7c2 becomes exposed, the cap intermediate layer 7c2 still has a certain degree of wear resistance, so that the rapid progression of wear can be suppressed. In this way, the tire 1 can achieve both wear resistance and heat resistance at a higher level.

[0035] Preferably, the base layer 7b has a tan δ that is at least 0.03 lower than that of the cap intermediate layer 7c2 in a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50 Hz, thereby achieving both high levels of abrasion resistance and heat resistance.

[0036] FIG. 3 shows the results of FEM analysis performed on four types of tire models 1 to 4. As shown in FIG. 3, tire models 1 to 4 are different from one another in size. In all of tire models 1 to 4, as in the examples of FIGS. 1 and 2, tread rubber 7 has a cap layer 7c and a base layer 7b, and cap layer 7c is composed of a cap surface layer 7c1 and a cap intermediate layer 7c2 (excluding cases where the ratio of the thickness t7c1 of cap surface layer 7c1 to the thickness t7c of cap layer 7c is 0% or 100%). The physical properties used in the FEM calculations for the cap surface layer 7c1 are a tan δ of 0.25 in a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50 Hz, and the total filler amount (total amount of carbon and silica) is 65 parts. The cap intermediate layer 7c2 is made of rubber with a tan δ of 0.19 in a tensile test at room temperature of 24°C, 2% amplitude, and 50 Hz, as physical property values ​​used in the FEM calculation, and a total filler amount (total amount of carbon and silica added together) of 55 parts. In all of tire models 1 to 4, the ratio of the thickness t7c1 (FIG. 2) of the cap surface layer 7c1 to the thickness t7c (FIG. 2) of the cap layer 7c is approximately constant over the entire tire widthwise region between the tire widthwise positions D of a pair of ground contact edges TE. In the graph of FIG. 3, the horizontal axis represents the ratio (%) of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c of each tire model. In the graph of FIG. 3, the vertical axis represents the relative temperature (°C) relative to a predetermined reference temperature that occurred in the analysis target portion X (FIG. 2) of each tire model when each tire model was subjected to a predetermined operation. As shown in FIG. 2, the analysis target portion X is a portion of the belt 6 located approximately 3.5 mm toward the tire outer periphery from the outermost belt layer 6a of the tire and near the tire equatorial plane CL in the tire width direction. The predetermined reference temperature is the temperature (°C) that occurred in a portion of a tire corresponding to the analysis target portion X when the tire was subjected to the predetermined operation. The predetermined reference temperature is the temperature (°C) that occurred in a portion of the ... The predetermined reference temperature can be regarded as an index of the heat resistance of a conventional tire. Furthermore, the relative temperature of the analysis target portion X of the tire model can be regarded as an index of the heat resistance of the tire model. When the relative temperature of the analysis target portion X is 0°C, the heat resistance of the tire model can be said to be equivalent to that of a conventional tire. Furthermore, the lower the relative temperature of the analysis target portion X, the higher the heat resistance of the tire model. As can be seen from the analysis results in Figure 3, it is possible to adjust the degree of heat resistance and wear resistance of tire 1 by adjusting the ratio of the thickness t7c1 of cap surface layer 7c1 to the thickness t7c of cap layer 7c, and ultimately the ratio of the thickness t7c1 of cap surface layer 7c1 to the thickness t7c2 of cap intermediate layer 7c2.

[0037] In this specification, the "thickness t7c of the cap layer 7c," "thickness t7c1 of the cap outer layer 7c1," and "thickness t7c2 of the cap intermediate layer 7c2" are measured parallel to the tire radial direction as shown in FIG.

[0038] The ratio of the thickness t7c1 of the cap outer layer 7c1 to the thickness t7c of the cap layer 7c, and therefore the ratio of the thickness t7c1 of the cap outer layer 7c1 to the thickness t7c2 of the cap intermediate layer 7c2, may be constant along the tire width direction between the tire width direction positions D of a pair of ground contact ends TE, or may vary along the tire width direction.

[0039] In the tire 1, in the portion of the cap layer 7c between the tire widthwise positions D of a pair of ground contact ends TE (i.e., the portion from the tire widthwise position D of one ground contact end TE to the tire widthwise position D of the other ground contact end TE), it is preferable that the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c is 75% or less, more preferably 70% or less, and even more preferably 60% or less. As can be seen from the analysis results shown in Figure 3, this ensures the thickness t7c2 of the cap intermediate layer 7c2, which in turn makes it easier to ensure heat resistance at approximately the same level as in the past. Therefore, it is possible to achieve both wear resistance and heat resistance at a higher level.

[0040] In the tire 1, in the portion of the cap layer 7c between the tire width direction positions D of a pair of ground contact ends TE (i.e., the portion from the tire width direction position D of one ground contact end TE to the tire width direction position D of the other ground contact end TE), it is preferable that the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c is 30% or more, more preferably 40% or more, and even more preferably 50% or more. This ensures the thickness t7c1 of the cap surface layer 7c1, which in turn improves the wear resistance, thereby achieving both wear resistance and heat resistance at a higher level.

[0041] In this specification, as shown in FIG. 1, a pair of tire widthwise positions A that are 1 / 8 times the contact width TW from the tire equatorial plane CL are each referred to as the "1 / 8 point (A)," a pair of tire widthwise positions B that are 1 / 4 times the contact width TW from the tire equatorial plane CL are each referred to as the "1 / 4 point (B)," and a pair of tire widthwise positions C that are 3 / 8 times the contact width TW from the tire equatorial plane CL are each referred to as the "3 / 8 point (C)." The tire width direction position D of the ground contact edge TE can also be called the "half point" that is separated from the tire equatorial plane CL by half the ground contact width TW.

[0042] As shown in the example of Figure 2, the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in the center side (the side closer to the tire equatorial plane CL) of the cap layer 7c may be lower than the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in the shoulder side (the side farther from the tire equatorial plane CL). More specifically, the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in the portion of the cap layer 7c between a pair of 1 / 4 points B (i.e., the portion from one 1 / 4 point B to the other 1 / 4 point B) may be lower than the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in a pair of portions of the cap layer 7c between the pair of 1 / 4 points B and the tire widthwise positions D of the pair of ground contact edges TE (i.e., the portions from the 1 / 4 points B to the tire widthwise positions D of the ground contact edges TE on both sides of the tire equatorial plane CL). For example, the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in the portion of the cap layer 7c between a pair of 1 / 4 points B (i.e., the portion from one 1 / 4 point B to the other 1 / 4 point B) may be 40 to 55%, and the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in a pair of portions of the cap layer 7c between a pair of 1 / 4 points B and a pair of tire widthwise positions D of the ground contact edges TE (i.e., the portion from the 1 / 4 points B to the tire widthwise positions D of the ground contact edges TE on both sides of the tire equatorial plane CL) may be 65 to 75%. Generally, the amount of heat generated during tire rolling tends to be greater in the center than in the shoulder. Therefore, in the above-described case, the thickness t7c2 of the cap intermediate layer 7c2 is made higher in the center than in the shoulder. This increases the proportion of the cap intermediate layer 7c2, which has relatively good heat resistance, in the area where the amount of heat generated is greater, thereby efficiently improving heat resistance. Furthermore, by increasing the proportion of the cap surface layer 7c1, which has good wear resistance, in the shoulder, this efficiently improves wear resistance. This allows for a high level of both wear resistance and heat resistance. In addition, the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in the portion of the cap layer 7c between a pair of 1 / 4 points B (i.e., the portion from one 1 / 4 point B to the other 1 / 4 point B) may be 30 to 60%, and the average ratio of the thickness t7c1 of the cap surface layer 7c1 to the thickness t7c of the cap layer 7c in a pair of portions of the cap layer 7c between a pair of 1 / 4 points B and a pair of tire widthwise positions D of the ground contact edges TE (i.e., the portion from the 1 / 4 points B to the tire widthwise positions D of the ground contact edges TE on both sides of the tire equatorial plane CL) may be 50 to 75%.

[0043] It should be noted that, among the grooves g (FIG. 2) provided in the tread rubber 7, the groove bottom (the innermost end of the groove g in the tire radial direction) of the deepest groove g is preferably located within the cap layer 7c, as shown in FIG. 2, and more preferably within the cap intermediate layer 7c2. The same applies to the sipes. [Industrial Applicability]

[0044] The heavy-duty tire according to the present invention can be suitably used for any kind of heavy-duty tire, and can be suitably used in particular for tires for construction and mining vehicles (off-the-road tires). [Explanation of symbols]

[0045] 1: Heavy duty tires (tires), 1a: tread portion, 1b: sidewall portion, 1c: bead portion, 2: Tread surface, 4a: Bead core, 4b: Bead filler, 5: carcass, 5a: carcass ply, 6: belt, 6a: belt layer, 7: tread rubber, 7c: cap layer, 7c1: cap surface layer, 7c2: cap middle layer, 7b: base layer, 8: Side rubber, 9: Inner liner, CL: tire equatorial plane, TW: contact width, TE: contact edge, A: 1 / 8 point, B: 1 / 4 point, C: 3 / 8 point, D: tire width direction position of contact edge, X: Analysis target part, g:Groove

Claims

1. The tread rubber a cap layer; a base layer disposed closer to the tire inner circumferential side than the cap layer; and and The cap layer is A cap surface layer; a cap intermediate layer; Equipped with the cap surface layer has a larger tan δ than the cap intermediate layer in a tensile test under conditions of room temperature 24°C, 2% amplitude, and 50 Hz; a difference between tan δ of the cap surface layer measured at room temperature of 24°C, 2% amplitude, and 50 Hz and tan δ of the cap intermediate layer measured at room temperature of 24°C, 2% amplitude, and 50 Hz is 0.03 or more; the average value of the ratio of the thickness of the cap surface layer to the thickness of the cap layer in a portion of the cap layer between a pair of quarter points spaced apart by a quarter of the contact width from the tire equatorial plane is 40 to 55%, In the heavy-duty tire, in a pair of portions of the cap layer between the pair of quarter points and the pair of ground contact edges in the tire width direction, the average value of the ratio of the thickness of the cap surface layer to the thickness of the cap layer is 65 to 75%.

2. 2. The heavy-duty tire according to claim 1, wherein the base layer has a tan δ in a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50 Hz that is 0.03 or more lower than that of the cap intermediate layer.

3. 3. The heavy-duty tire according to claim 1, wherein the cap surface layer, the cap intermediate layer, and the base layer are each present over an entire region in the tire width direction between positions of a pair of ground-contact edges in the tire width direction.

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