Heavy-duty tires

Abstract

To provide a heavy-duty tire 2 that achieves improved block chipping resistance while balancing wet performance and quietness. [Solution] The tire 2 comprises a tread 4. The tread 4 comprises one or more center circumferential grooves 16. The center portion 28 of the tread 4 comprises a center land portion 22. The center land portion 22 comprises lateral grooves 32. In the center portion 28, the lateral grooves 32 are arranged such that a reference lateral groove located on one side in the circumferential direction and a corresponding lateral groove located on the other side constitute a pair of lateral grooves. In the pair of lateral grooves, the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are in the same position in the circumferential direction. One or more center circumferential grooves 16 include at least one circumferential narrow groove 44. When the tread 4 contacts the road surface and deforms, a pair of wall surfaces 44S of the circumferential narrow groove 44 contact each other in the narrow groove portion 48.

Description

Technical Field

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

Background Art

[0002] In the tread of a tire, in addition to grooves extending in the circumferential direction, transverse grooves or transverse sipes (hereinafter referred to as transverse grooves) that cross the land portions are provided to improve drainage performance and wet performance. Transverse grooves are related to the generation of noise. There is a concern that the noise increases when transverse grooves are provided. For example, in the heavy-duty tire disclosed in Patent Document 1, in order to suppress the generation of noise and enhance quietness while maintaining good wet performance, transverse grooves arranged in the circumferential direction are arranged so that the transverse grooves do not break in the circumferential direction. In other words, arranging the transverse grooves arranged in the circumferential direction in a seamless manner has been studied.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a heavy-duty tire that can achieve both wet performance and quiet performance while improving the resistance to block chipping.

Means for Solving the Problems

[0005] The heavy-duty tire according to the present invention comprises a tread that contacts the road surface. The tread comprises a plurality of circumferential grooves arranged in the axial direction. The plurality of circumferential grooves comprises two shoulder circumferential grooves located on the outermost axial side and one or more center circumferential grooves located between the two shoulder circumferential grooves. The portion of the tread between the two shoulder circumferential grooves is the center portion. The center portion comprises a plurality of center land portions separated by one or more center circumferential grooves. Each of the plurality of center land portions comprises a plurality of lateral grooves that traverse the center land portion. In each of the center land portions, the plurality of lateral grooves are arranged in the circumferential direction. Each of the plurality of lateral grooves has a first end located on one side in the circumferential direction and a second end located on the other side. In the center portion, the plurality of lateral grooves are arranged such that a reference lateral groove located on one side in the circumferential direction and a corresponding lateral groove located on the other side constitute a pair of lateral grooves. In the pair of lateral grooves, the second end of the reference lateral groove and the first end of the corresponding lateral groove are in the same position in the circumferential direction. At least one of the one or more center circumferential grooves is a circumferential narrow groove. The circumferential narrow groove has a body portion that includes the groove opening. The body portion has a narrow groove portion. When the tread contacts the road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other in the narrow groove portion. [Effects of the Invention]

[0006] According to the present invention, a heavy-duty tire can be obtained that achieves improved resistance to block chipping while simultaneously balancing wet performance and quietness. [Brief explanation of the drawing]

[0007] [Figure 1] This is an exploded view showing a portion of the tire tread according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line II-II in Figure 1. [Figure 3] This is an unfolded diagram showing a portion of the center section. [Figure 4] This is a cross-sectional view along the line IV-IV in Figure 1. [Figure 5] This is a cross-sectional view along the VV line in Figure 1. [Figure 6] This is a cross-sectional view along the line VI-VI in Figure 3. [Modes for carrying out the invention]

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

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

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

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

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

[0013] The normal internal pressure means the internal pressure defined in the standards relied on by the tire. The "maximum air pressure" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are the normal internal pressures.

[0014] The normal load means the load defined in the standards relied on by the tire. The "maximum load capacity" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are the normal loads.

[0015] In the present invention, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as portions, a tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion includes a tread as a component of the tire. The sidewall portion includes a sidewall as a component of the tire. The bead portion includes a bead as a component of the tire. The central portion of the tread portion is also called the crown portion. The end portion of the tread portion is also called the shoulder portion.

[0016] [Findings on which the present invention is based] The land portion having transverse grooves includes blocks separated by the transverse grooves. The inclination angle of the transverse grooves affects the lateral rigidity of the blocks.

[0017] As described above, in order to achieve both wet performance and quiet performance, arranging circumferentially aligned transverse grooves in a seamless manner has been considered. When arranging the transverse grooves in a seamless manner, the transverse grooves are arranged to be inclined with respect to the axial direction. Due to the large inclination angle of the transverse grooves, the lateral rigidity of the block is lower than that of the block constituted by the transverse grooves extending in the axial direction. Arranging the transverse grooves in a seamless manner may reduce the wear resistance performance and handling stability performance of the tire.

[0018] Sharp corners are formed on the block. The sharp corners increase the risk of chipping on the block. In the case of a heavy-duty tire, the load acting on the tire is larger than that of a passenger car tire. The concern about block chipping is significant. The ground contact pressure of the crown portion is high. The high ground contact pressure further increases the risk of block chipping. The risk of block chipping can be reduced by not providing the transverse grooves, but in this case, the wet performance deteriorates. Therefore, the inventor has intensively studied a technique capable of achieving improvement in block chipping resistance while achieving both wet performance and quiet performance, and has completed the present invention described below.

[0019] [Overview of Embodiments of the Present Invention] The present invention provides a tread that contacts the road surface, the tread having a plurality of circumferential grooves arranged in the axial direction, the plurality of circumferential grooves comprising two shoulder circumferential grooves located on the outermost axial side and one or more center circumferential grooves located between the two shoulder circumferential grooves, the portion of the tread between the two shoulder circumferential grooves being the center portion, the center portion comprising a plurality of center land portions separated by one or more center circumferential grooves, each of the plurality of center land portions having a plurality of transverse grooves that traverse the center land portion, in each of the center land portions the plurality of transverse grooves are arranged in the circumferential direction, and each of the plurality of transverse grooves is circumferentially A heavy-duty tire comprising a first end located on one side and a second end located on the other side, wherein a plurality of lateral grooves in the center portion are arranged such that a reference lateral groove located on one side in the circumferential direction and a corresponding lateral groove located on the other side constitute a pair of lateral grooves, the second end of the reference lateral groove and the first end of the corresponding lateral groove are in the same position in the circumferential direction in the pair of lateral grooves, at least one of the one or more center circumferential grooves is a circumferential narrow groove, the circumferential narrow groove comprises a body portion including the groove opening of the circumferential narrow groove, the body portion comprises a narrow groove portion, and when the tread contacts the road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other in the narrow groove portion.

[0020] The tire of the present invention achieves improved resistance to block chipping while simultaneously balancing wet performance and quietness. Although the mechanism by which the tire achieves these effects has not been fully elucidated, it is presumed to be as follows.

[0021] In this tire, the lateral grooves are seamlessly arranged in the center of the tread. This tire can improve quietness while maintaining good wet performance. The lateral grooves traverse the main land area. The main land area consists of blocks separated by the lateral grooves. Because the lateral grooves are arranged seamlessly, there is a risk of chipping occurring at the corners of the blocks where the lateral grooves merge with the circumferential grooves. Of the one or more center circumferential grooves provided in the center section, at least one of the center circumferential grooves is a circumferential narrow groove. As mentioned above, when the tread contacts the road surface and deforms, a pair of walls of the circumferential narrow groove come into contact with each other in the narrow groove section. As a result, the main land sections located on both sides of the circumferential narrow groove support each other. The rigidity of the blocks constituting the main land section is effectively increased. Deformation of the corners of the blocks is suppressed. This tire can reduce the risk of block chipping. This tire achieves a balance between wet performance and quietness while also improving resistance to block chipping.

[0022] Preferably, the reference lateral groove and the corresponding lateral groove constituting the pair of lateral grooves are provided in different parts of the center ridge. In this case, the inclination angle of the lateral grooves with respect to the axial direction can be set at a gentle angle while maintaining a seamless arrangement. The tire can increase the lateral rigidity of the blocks separated by the lateral grooves while maintaining good quietness. The tire can improve wear resistance and handling stability. The risk of block chipping is also reduced, so the tire can also improve block chipping resistance.

[0023] Preferably, the lateral grooves are inclined with respect to the circumferential direction, and the inclination angle of the lateral grooves with respect to the circumferential direction is between 55 degrees and 85 degrees. In this case, the tire can improve both its quietness and its resistance to block chipping.

[0024] Preferably, the tread has a tread pattern in which grooves including a plurality of circumferential grooves and a plurality of lateral grooves are carved into the tread, and the tread pattern has a plurality of pitch patterns arranged in the circumferential direction, and one lateral groove is arranged in each of the plurality of center land portions included in the pitch patterns. In this case, the tire can improve block chipping resistance while maintaining good wet performance.

[0025] Preferably, the lateral grooves provided on one of two adjacent center tread sections are arranged alternately in the circumferential direction. In this case, the tire can arrange the lateral grooves at a certain distance apart on one main tread section. The tire can increase the rigidity of the blocks separated by the lateral grooves. The tire can improve its resistance to block chipping.

[0026] Preferably, the lateral grooves are sipes. In this case, the blocks formed on both sides of the lateral grooves support each other. The rigidity of the blocks is increased. Deformation of the corners of the blocks is suppressed. The tire can improve its resistance to block chipping.

[0027] Preferably, the center land portion comprises a plurality of blocks separated by a plurality of lateral grooves, and each of the plurality of blocks has an acute angle portion formed by the lateral grooves intersecting the circumferential grooves at an acute angle, and the acute angle portion has a slope that is connected to the top surface of the block and inclined with respect to the top surface. In this case, the tire can increase the rigidity of the acute angle portion of the corner portion of the main block, which is formed by the lateral grooves intersecting the circumferential grooves at an acute angle. The tire can improve its resistance to block chipping.

[0028] Preferably, the body of the tire has a tapered section including the groove, the narrow groove is located radially inward of the tapered section, and the tapered section narrows from the groove towards the narrow groove. In this case, the increase in ground pressure at the groove opening of the circumferential narrow groove is suppressed. The tire can improve its resistance to block chipping.

[0029] Preferably, the circumferential groove includes a widened section located radially inward of the body, where the circumferential groove exhibits its minimum width in the grooved section and its maximum width in the widened section. In this case, the widened section can help suppress the reduction in drainage performance caused by the adoption of circumferential grooves as circumferential grooves. The tire can maintain good wet performance.

[0030] Preferably, the depth of the body portion DHB, the depth of the lateral groove DGy, and the depth DHX from the groove opening to the position where the widened portion shows its maximum width satisfy the following formula. DHB ≤ DGy ≤ DHX In this case, there are lateral grooves that contribute to wet performance and quietness during the process of the widened section expanding, from the point where the widened section is exposed due to wear until the widest point of the widened section is exposed. The tire can maintain good wet performance and good quietness even when worn.

[0031] Thus, according to the present invention, a heavy-duty tire can be obtained that achieves improved block chipping resistance while simultaneously balancing wet performance and quietness. This will be explained in detail below.

[0032] [Details of the Embodiments of the Invention] [tire] Figure 1 is a plan view showing a portion of the tread 4 of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on vehicles such as trucks and buses. This tire 2 is a heavy-duty tire.

[0033] In Figure 1, the direction indicated by the double-headed arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2 (not shown). The direction indicated by the double-headed arrow CD is the circumferential direction of tire 2. The circumferential direction of tire 2 is also the rotation direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the radial direction of tire 2.

[0034] In Figure 1, the dashed line EL extending in the circumferential direction represents the equatorial plane of tire 2. In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2.

[0035] The direction indicated by arrow CD1 is the first circumferential side of tire 2, and the direction indicated by arrow CD2 is the second circumferential side of tire 2. If the first circumferential side is considered one side of the circumferential direction, then the second circumferential side is the other side of the circumferential direction. If the second circumferential side is considered one side, then the first circumferential side is the other side. In this specification, "first circumferential side" refers to one side in the circumferential direction, and "second circumferential side" refers to the other side in the circumferential direction.

[0036] Tire 2 has a tread 4. The tread 4 constitutes the internal structure of tire 2. In this invention, the internal structure of the tire 2 is not particularly limited. Although not described in detail, this tire 2 has an internal structure that is typical for heavy-duty tires.

[0037] The tread 4 is made of cross-linked rubber. The tread 4 is located on the radially outermost part of the tire 2. The tread 4 is in contact with the road surface. The tread 4 extends in the circumferential direction. The outer surface of the tread 4 is the tread surface 6. The tread 4 has a tread surface 6. The tread 4 is in contact with the road surface at the tread surface 6. Grooves 8 are cut into the tread 4. This forms the tread pattern. The portion of the tread surface 6 other than the grooves 8 is the land surface 10.

[0038] Figure 1 shows an example of a tread pattern formed on the tread 4. The tread pattern of the present invention will be explained using the tread pattern shown in Figure 1 as an example. The tread pattern shown in Figure 1 is the tread pattern of a new, unworn tire 2.

[0039] The intersection of the tread surface 6 and the equatorial surface is the equator. If a groove 8 is located on the equatorial surface, the equator is determined based on a hypothetical outer surface obtained by assuming that there is no groove 8 on the equatorial surface.

[0040] The dashed line indicated by the symbol TE represents the edge of the tread surface 6. In the case of a tire, if the edge of the tread surface is not identifiable by appearance, the position on the outer surface of the tire corresponding to the axial outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and bringing the tire into contact with a flat surface is used as the edge of the tread surface.

[0041] In this specification, one end TE of the tread surface 6 located to the left of the equatorial plane is called the first end TE1. The other end TE located to the right of the equatorial plane is called the second end TE2. Alternatively, the end TE located to the left of the equatorial plane may be called the second end TE2, and the end TE located to the right of the equatorial plane may be called the first end TE1.

[0042] In Figure 1, the length indicated by the symbol TW is the width of the tread surface 6. The width TW of the tread surface 6 is the axial distance from the first end TE1 to the second end TE2 of the tread surface 6. The width TW of the tread surface 6 is measured along the tread surface 6.

[0043] Figure 2 is a cross-sectional view along the line II-II in Figure 1. The direction indicated by the double arrow RD is the radial direction of tire 2. The direction indicated by arrow RD1 is the radially outward direction of tire 2, and the direction indicated by arrow RD2 is the radially inward direction of tire 2. Figure 2 shows a cross-section of the groove 8, more specifically, a cross-section of the shoulder circumferential groove along a plane perpendicular to the longitudinal direction of the shoulder circumferential groove, which will be described later. The main components of the groove 8 will be explained based on Figure 2. In this specification, the cross-section of the groove 8 is represented by the cross-section of the groove 8 along a plane perpendicular to the longitudinal direction of the groove 8.

[0044] The groove 8 comprises a pair of wall surfaces 8S including a groove opening 8M and a bottom surface 8B including a groove bottom 8T. The groove opening 8M is composed of a pair of edges 8E. In other words, the groove opening 8M comprises a pair of edges 8E. Each edge 8E is the boundary between the land surface 10 and the groove 8. The pair of wall surfaces 8S each span between the edges 8E and the bottom surface 8B. The groove bottom 8T is represented by the position where the distance from the reference plane RP to the bottom surface 8B is maximum. The distance from the reference plane RP to the bottom surface 8B is measured along the normal to the reference plane RP. Unless otherwise specified, the plane containing the groove opening 8M is used as the reference plane RP. If the bottom surface 8B is a plane, the groove bottom 8T is represented by the width center of the bottom surface 8B. If the bottom surface 8B has a projection, the groove bottom 8T is determined based on a virtual bottom surface obtained by assuming the absence of the projection. The normal to the reference plane RP, which connects the reference plane RP and the groove bottom 8T, is the reference normal RN, and the direction of this reference normal RN is the depth direction of the groove 8. The width of the groove 8 is expressed as the distance between one wall surface 8S and the other wall surface 8S (hereinafter referred to as the inter-wall distance). Unless otherwise specified, the inter-wall distance is measured along a line perpendicular to the reference normal RN. If the profile of the tread surface 6 can be confirmed, the profile of the tread surface 6 may be used as the reference surface RP to determine the groove bottom 8T and width of the groove 8.

[0045] In Figure 2, the length indicated by the double-headed arrow WG is the width of groove 8 at groove opening 8M. If the groove opening 8M portion of groove 8 is machined in a tapered manner, the width of groove 8 at groove opening 8M is expressed based on a virtual edge obtained assuming that it is not machined in a tapered manner. The length indicated by the double-headed arrow DG is the depth of groove 8. Unless otherwise specified, the depth DG of groove 8 is expressed as the distance from the reference surface RP to the groove bottom 8T of groove 8, measured along the reference normal RN. The position, width WG, and depth DG of groove 8 are determined as appropriate according to the specifications of tire 2.

[0046] When tire 2 presses against the road surface, the tread 4 deforms. In a new tire 2, grooves 8 that have a wide width and a pair of wall surfaces 8S that do not come into contact with each other even when the tread 4 deforms are also called main grooves. Grooves 8 that have a narrow width and a pair of wall surfaces 8S that come into contact with each other when the tread 4 deforms are also called contact grooves. Among the contact grooves, contact grooves where the width of the pair of wall surfaces 8S that come into contact with each other is 1.0 mm or less are called sipes. Contact grooves other than sipes are called fine grooves. Fine grooves have a width of more than 1.0 mm where the pair of wall surfaces 8S that come into contact with each other.

[0047] The tread 4 of this tire 2 is provided with a plurality of circumferential grooves 12. The plurality of circumferential grooves 12 are aligned in the axial direction. Each circumferential groove 12 is continuous in the circumferential direction. The circumferential grooves 12 of this tire 2 extend in a straight line in the circumferential direction. The circumferential grooves 12 may be configured to extend in a zigzag pattern in the circumferential direction.

[0048] As shown in Figure 1, the tread 4 of this tire 2 is provided with four circumferential grooves 12. Of the four circumferential grooves 12, the two circumferential grooves 12 located on the outermost axial side are shoulder circumferential grooves 14. The shoulder circumferential groove 14 located on the first end TE1 side (hereinafter referred to as the first end TE1 side) of the tread surface 6 is also called the first shoulder circumferential groove 14a, and the shoulder circumferential groove 14 located on the second end TE2 side (hereinafter referred to as the second end TE2 side) of the tread surface 6 is also called the second shoulder circumferential groove 14b.

[0049] The circumferential groove 12 located between the two shoulder circumferential grooves 14 is the center circumferential groove 16. The tread 4 of this tire 2 has two center circumferential grooves 16. The number of center circumferential grooves 16 provided in the tread 4 may be one or three or more. The number of center circumferential grooves 16 provided in the tread 4 is determined appropriately, taking into consideration the specifications of the tire 2. Typically, the number of center circumferential grooves 16 provided in the tread 4 is between one and three.

[0050] The tread 4 of this tire 2 is provided with one or more center circumferential grooves 16 arranged axially between two shoulder circumferential grooves 14. For convenience of explanation, in this specification, when multiple center circumferential grooves 16 are located between two shoulder circumferential grooves 14, the multiple center circumferential grooves 16 are referred to as the first center circumferential groove 16a, the second center circumferential groove 16b, the third center circumferential groove 16c (not shown), and so on, from the first end TE1 to the second end TE2. As mentioned above, the tread 4 shown in Figure 1 is equipped with two center circumferential grooves 16. The two center circumferential grooves 16 are also called the first center circumferential groove 16a and the second center circumferential groove 16b, respectively, from the first end TE1 side to the second end TE2 side.

[0051] The tread 4 is formed by cutting circumferential grooves 12 into it, creating a land area 18. The tread 4 has multiple land areas 18 separated by the circumferential grooves 12. As shown in Figure 1, the tread 4 of this tire 2 has five land areas 18.

[0052] Of the five land sections 18, the two land sections 18 located on the outermost axial side are the shoulder land sections 20. The shoulder land sections 20 include the edge TE of the tread surface 6. The shoulder land section 20 including the first edge TE1 of the tread surface 6 is also called the first shoulder land section 20a, and the shoulder land section 20 including the second edge TE2 is also called the second shoulder land section 20b.

[0053] The land portion 18 located between the two shoulder land portions 20 is the center land portion 22. The tread 4 of this tire 2 has three center land portions 22. The number of center land portions 22 provided on the tread 4 may be two or four or more. The number of center land portions 22 is determined by the number of center circumferential grooves 16 provided on the tread 4.

[0054] The tread 4 of this tire 2 is provided with a plurality of center land portions 22. For the sake of explanation, in this specification, the plurality of center land portions 22 provided on the tread 4 are referred to as the first center land portion 22a, the second center land portion 22b, the third center land portion 22c, and so on, from the first end TE1 side to the second end TE2 side. As mentioned above, the tread 4 has three center sections 22. The three center sections 22 are also called the first center section 22a, the second center section 22b, and the third center section 22c, starting from the first end TE1 and moving towards the second end TE2.

[0055] As shown in Figure 1, the second center land area 22b is located between the two center circumferential grooves 16. The first center land area 22a is located between the center circumferential groove 16 and the shoulder circumferential groove 14. The third center land area 22c is also located between the center circumferential groove 16 and the shoulder circumferential groove 14. In the present invention, the center land portion 22 located between the two center circumferential grooves 16 is also called the main center land portion 24, and the center land portion 22 located between the center circumferential groove 16 and the shoulder circumferential groove 14 is also called the sub-center land portion 26. In this tire 2, the second center land area 22b is also called the main center land area 24, and the first center land area 22a and the third center land area 22c are also called the sub-center land area 26. The first center land area 22a, located on the first end TE1 side, is also called the first sub-center land area 26a, and the third center land area 22c, located on the second end TE2 side, is also called the second sub-center land area 26b.

[0056] In this tire 2, the portion of the tread 4 between the two shoulder circumferential grooves 14 is the center portion 28. The center section 28 is provided with one or more center circumferential grooves 16. As a result, multiple center land sections 22 are formed in the center section 28. In other words, the center section 28 is provided with multiple center land sections 22 separated by one or more center circumferential grooves 16. In the tread 4 shown in Figure 1, the center section 28 is provided with three center land sections 22 separated by two center circumferential grooves 16. Of the three center land sections 22, the second center land section 22b is located on the equatorial plane, the first center land section 22a is located on the first end TE1 side of the second center land section 22b, and the third center land section 22c is located on the second end TE2 side of the second center land section 22b.

[0057] The axially outer portion of the center portion 28 is the side portion 30. Each side portion 30 is provided with a shoulder land portion 20 separated by a shoulder circumferential groove 14.

[0058] In this tire 2, each of the multiple center land sections 22 provided on the center section 28 is equipped with multiple lateral grooves 32. In each center land section 22, the multiple lateral grooves 32 are arranged at predetermined intervals in the circumferential direction. Each of the multiple lateral grooves 32 crosses the center land portion 22. In other words, the lateral grooves 32 bridge the gap between the two circumferential grooves 12 that sandwich the center land portion 22. The lateral grooves 32 connect with the circumferential grooves 12 at their ends E. The lateral grooves 32 of this tire 2 connect with the circumferential grooves 12 on both sides. The multiple lateral grooves 32 provided in the center land portion 22 may include lateral grooves that connect with only one side of the circumferential groove 12. In the tread 4 shown in Figure 1, all lateral grooves 32 connect with the circumferential grooves 12 on both sides.

[0059] Figure 3 shows a portion of the center section 28. Based on Figure 3, the arrangement of the lateral grooves 32 in the center section 28 will be explained.

[0060] In this tire 2, the multiple lateral grooves 32 provided in the center section 28 are inclined with respect to the axial direction. The ends E of the lateral grooves 32 are spaced apart in the circumferential direction. For example, in the first center section 22a and the third center section 22c, the end E of the first lateral groove 32 on the TE1 side is located on the second side in the circumferential direction, and the end E of the second lateral groove 32 on the TE2 side is located on the first side in the circumferential direction. In the second center section 22b, the end E of the first lateral groove 32 on the TE1 side is located on the first side in the circumferential direction, and the end E of the second lateral groove 32 on the TE2 side is located on the second side in the circumferential direction.

[0061] In this specification, of the two ends E of the transverse groove 32, the end E located on the first side in the circumferential direction is the first end Ef, and the end E located on the second side in the circumferential direction is the second end Es. The lateral groove 32 of this tire 2 has a first end Ef located on the first circumferential side and a second end Es located on the second circumferential side.

[0062] As mentioned above, in each center land area 22, multiple transverse grooves 32 are arranged in the circumferential direction. For the sake of explanation, the multiple transverse grooves 32 provided in one center land area 22 are referred to as the first transverse groove 32a, the second transverse groove 32b, the third transverse groove 32c, and so on, from the first side to the second side in the circumferential direction. In this case, it is sufficient for one transverse groove 32 to be selected as the first transverse groove 32a from among the multiple transverse grooves 32 arranged in the circumferential direction, and there are no particular restrictions on the selection of the first transverse groove 32a. In Figure 3, one of the multiple transverse grooves 32 provided on a central land area 22 is selected as the first transverse groove and is represented as the first transverse groove 32a. Furthermore, the transverse grooves 32 provided on the central land area 22 are shown in order from the transverse groove 32 located on the second circumferential side of the first transverse groove 32a, as well as the second transverse groove 32b, the third transverse groove 32c, and so on.

[0063] In this invention, a combination of two adjacent transverse grooves 32 in the circumferential direction is also called a transverse groove pair. Of the two transverse grooves constituting a transverse groove pair, the transverse groove located on the first side in the circumferential direction is called the reference transverse groove, and the transverse groove located on the second side in the circumferential direction is called the corresponding transverse groove.

[0064] For example, in the center section 28 shown in Figure 3, the first transverse groove 32a of the second center land section 22b is located second circumferentially to the first transverse groove 32a of the third center land section 22c, and is a transverse groove 32 adjacent to this first transverse groove 32a. In other words, the combination of the first transverse groove 32a of the third center land section 22c and the first transverse groove 32a of the second center land section 22b constitutes a transverse groove pair, with the first transverse groove 32a of the third center land section 22c being the reference transverse groove and the first transverse groove 32a of the second center land section 22b being the corresponding transverse groove. The first transverse groove 32a of the first center land area 22a is located second circumferentially to the first transverse groove 32a of the second center land area 22b, and is a transverse groove 32 adjacent to this first transverse groove 32a. In other words, the first transverse groove 32a of the second center land area 22b and the first transverse groove 32a of the first center land area 22a form a transverse groove pair, with the first transverse groove 32a of the second center land area 22b being the reference transverse groove and the first transverse groove 32a of the first center land area 22a being the corresponding transverse groove. The second transverse groove 32b of the third center land area 22c is located second circumferentially to the first transverse groove 32a of the first center land area 22a, and is a transverse groove 32 adjacent to the first transverse groove 32a. In other words, the first transverse groove 32a of the first center land area 22a and the second transverse groove 32b of the third center land area 22c form a transverse groove pair, with the first transverse groove 32a of the first center land area 22a as the reference transverse groove and the second transverse groove 32b of the third center land area 22c as the corresponding transverse groove.

[0065] In the center section 28 shown in Figure 3, the combination of the transverse groove 32 of the third center land section 22c and the transverse groove 32 of the second center land section 22b, which is located on the second circumferential side of the transverse groove 32 of the third center land section 22c and is close to the transverse groove 32 of the third center land section 22c, constitutes a pair of transverse grooves, where the transverse groove 32 of the third center land section 22c is the reference transverse groove and the transverse groove 32 of the second center land section 22b is the corresponding transverse groove. The lateral groove 32 of the second center land area 22b and the lateral groove 32 of the first center land area 22a, which is located on the second circumferential side of the lateral groove 32 of the second center land area 22b and is adjacent to the lateral groove 32 of the second center land area 22b, form a pair of lateral grooves, with the lateral groove 32 of the second center land area 22b being the reference lateral groove and the lateral groove 32 of the first center land area 22a being the corresponding lateral groove. The lateral groove 32 of the first center land area 22a and the lateral groove 32 of the third center land area 22c, which is located on the second circumferential side of the lateral groove 32 of the first center land area 22a and is close to the lateral groove 32 of the first center land area 22a, form a pair of lateral grooves, with the lateral groove 32 of the first center land area 22a being the reference lateral groove and the lateral groove 32 of the third center land area 22c being the corresponding lateral groove. In the center section, multiple lateral grooves 32 are arranged such that a pair of lateral grooves is formed, consisting of a lateral groove 32 of one center land section 22 as a reference lateral groove, and a corresponding lateral groove 32 of another center land section 22 located on the second circumferential side of this lateral groove 32 of the first center land section 22 and adjacent to it.

[0066] In each central land section 22 included in the central section 28, a first transverse groove 32a and a second transverse groove 32b located on the second circumferential side of the first transverse groove 32a and adjacent to the first transverse groove 32a constitute a transverse groove pair, with the first transverse groove 32a as the reference transverse groove and the second transverse groove 32b as the corresponding transverse groove. A second transverse groove 32b and a third transverse groove 32c located on the second circumferential side of the second transverse groove 32b and adjacent to the second transverse groove 32b constitute a transverse groove pair, with the second transverse groove 32b as the reference transverse groove and the third transverse groove 32c as the corresponding transverse groove. In the central land section 22, which forms part of the central section 28, the multiple transverse grooves 32 are arranged such that one transverse groove 32, which serves as a reference transverse groove, and another transverse groove 32, which serves as a corresponding transverse groove, are located on the second circumferential side of this first transverse groove 32 and are close to it, thus forming a pair of transverse grooves.

[0067] Thus, in the center portion 28 of the tire 2, multiple lateral grooves 32 are arranged such that a reference lateral groove located on the first circumferential side and a corresponding lateral groove located on the second circumferential side constitute a single lateral groove pair.

[0068] In Figure 3, the dashed line L1 is a straight line extending in the axial direction, passing through the second end Es of the transverse groove 32 of the third center land section 22c, which forms the reference transverse groove of the transverse groove pair, and the first end Ef of the transverse groove 32 of the second center land section 22b, which forms the corresponding transverse groove of the same transverse groove pair. The circumferential position of the second end Es of the transverse groove 32 of the third center land section 22c, which serves as the reference transverse groove, coincides with the circumferential position of the first end Ef of the transverse groove 32 of the second center land section 22b, which serves as the corresponding transverse groove. The dashed line L2 is a straight line extending in the axial direction, passing through the second end Es of the transverse groove 32 of the second center land section 22b, which forms the reference transverse groove of the transverse groove pair, and the first end Ef of the transverse groove 32 of the first center land section 22a, which forms the corresponding transverse groove of the same transverse groove pair. The circumferential position of the second end Es of the transverse groove 32 of the second center land section 22b, which serves as the reference transverse groove, coincides with the circumferential position of the first end Ef of the transverse groove 32 of the first center land section 22a, which serves as the corresponding transverse groove. The dashed line L3 is a straight line extending in the axial direction, passing through the second end Es of the transverse groove 32 of the first center land section 22a, which forms the reference transverse groove of the transverse groove pair, and the first end Ef of the transverse groove 32 of the third center land section 22c, which forms the corresponding transverse groove of the same transverse groove pair. The circumferential position of the second end Es of the transverse groove 32 of the first center land section 22a, which serves as the reference transverse groove, coincides with the circumferential position of the first end Ef of the transverse groove 32 of the third center land section 22c, which serves as the corresponding transverse groove. In this center section 28, the reference lateral groove and the corresponding lateral groove constituting the lateral groove pair are provided on different center land sections 22, and the reference lateral groove provided on one center land section 22 and the corresponding lateral groove provided on the other center land section 22 are arranged such that the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are in the same position in the circumferential direction.

[0069] Although not shown in the figures, for example, in the third center land section 22c, the first transverse groove 32a and the second transverse groove 32b forming a transverse groove pair may be arranged such that the second end Es of the first transverse groove 32a and the first end Ef of the second transverse groove 32b are in the same position in the circumferential direction. Similarly, the second transverse groove 32b and the third transverse groove 32c forming a transverse groove pair may be arranged such that the second end Es of the second transverse groove 32b and the first end Ef of the third transverse groove 32c are in the same position in the circumferential direction. In other words, in one center land section 22 included in the center section 28, the reference transverse groove and the corresponding transverse groove of a transverse groove pair may be arranged such that the second end Es of the reference transverse groove and the first end Ef of the corresponding transverse groove are in the same position in the circumferential direction. In all center land portions 22 constituting the center portion 28, the reference lateral groove and the corresponding lateral groove of a pair of lateral grooves may be arranged such that the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are in the same position in the circumferential direction.

[0070] Thus, in the center portion 28 of the tire 2, the reference lateral groove and the corresponding lateral groove that constitute the lateral groove pair are arranged such that the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are in the same position in the circumferential direction.

[0071] Whether the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are in the same position circumferentially is determined using the groove width centerlines of the reference lateral groove and the corresponding lateral groove. The first and second ends Ef and Es of the reference lateral groove, and the first and second ends Ef and Es of the corresponding lateral groove, are identified by the ends of the groove width centerlines of each lateral groove. In light of the characteristics of a vulcanized rubber product such as a tire, the aforementioned "same position" includes a configuration in which the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are offset by a small distance in the circumferential direction of the tire, to the extent that manufacturing tolerances are permitted. In this case, the distance between the second end Es of the reference groove and the first end Ef of the corresponding groove, defined by the circumferential distance from the second end Es of the reference groove to the first end Ef of the corresponding groove, is 5% or less, preferably 3% or less, and more preferably 1% or less, of the sum of the circumferential length Lr of the groove width centerline of the reference groove and the circumferential length Lc of the groove width centerline of the corresponding groove (Lr + Lc). Most preferably, the distance between the second end Es of the reference groove and the first end Ef of the corresponding groove is 0.0 mm or less.

[0072] As mentioned above, the tread 4 of this tire 2 is provided with two shoulder circumferential grooves 14 and two center circumferential grooves 16 located between the two shoulder circumferential grooves 14. Figure 2 shows a cross-section of the shoulder circumferential groove 14. Figure 4 shows a cross-section of the center circumferential groove 16. The shoulder circumferential groove 14 is a circumferential main groove 42. The center circumferential groove 16 is a circumferential narrow groove 44. The circumferential grooves 12 provided in the tread 4 of this tire 2 consist of two types of circumferential grooves 12 with different shapes, namely a circumferential main groove 42 and a circumferential narrow groove 44.

[0073] The circumferential main groove 42 comprises a pair of wall surfaces 42S including a groove opening 42M and a bottom surface 42B including a groove bottom 42T. The circumferential main groove 42 is the main groove described above. The pair of wall surfaces 42S of the circumferential main groove 42 do not come into contact with each other even when the tread 4 is in contact with the road surface and deforms. The circumferential main groove 42 has a shape that is typical for grooves provided in the tread of heavy-duty tires. The width WGm of the groove opening 42M of the circumferential main groove 42 is preferably 2% to 10% of the width TW of the tread surface 6, from the viewpoint of contributing to drainage performance and traction performance. The depth DGm of the circumferential main groove 42 is, for example, 10 mm to 21 mm. From the viewpoint of enabling the tire 2 to exhibit good wet performance, the depth DGm is preferably 13 mm to 18 mm.

[0074] The circumferential groove 44 comprises a pair of wall surfaces 44S including a groove opening 44M and a bottom surface 44B including a groove bottom 44T. The dashed line LC is the groove width centerline of the circumferential groove 44. The circumferential groove 44 of this tire 2 has a cross-sectional shape symmetrical with respect to the groove width centerline LC. The groove width centerline LC extends in the depth direction of the circumferential groove 44 and passes through the groove bottom 44T. The circumferential groove 44 may have a cross-sectional shape asymmetrical with respect to the groove width centerline LC. In Figure 4, the length indicated by the double arrow DGh is the depth of the circumferential groove 44.

[0075] The depth DGh of the circumferential groove 44 of this tire 2 is the same as the depth DGm of the circumferential main groove 42, or the circumferential groove 44 is shallower than the circumferential main groove 42. Specifically, the ratio DGh / DGm of the depth DGh of the circumferential groove 44 to the groove depth DGm of the circumferential main groove 42 is between 0.75 and 1.00.

[0076] The circumferential groove 44 comprises a body portion 46. The body portion 46 includes the groove opening 44M of the circumferential groove 44. In Figure 4, the length indicated by the double arrow WHN is the minimum width of the circumferential groove 44. The circumferential groove 44 shows its minimum width WHN in the body portion 46.

[0077] The body portion 46 is provided with a narrow groove portion 48. The circumferential narrow groove 44 exhibits a minimum width WHN in the narrow groove portion 48. The minimum width WHN is set so that when the tread 4 contacts the road surface and deforms, a pair of wall surfaces 44S of the circumferential narrow groove 44 come into contact with each other in the narrow groove portion 48. The minimum width WHN of the circumferential narrow groove 44 is also the minimum width of the narrow groove portion 48.

[0078] As mentioned above, the center portion 28 of the tread 4 is provided with one or more center circumferential grooves 16. In this tire 2, at least one of the one or more center circumferential grooves 16 is a circumferential narrow groove 44. As shown in Figure 3, all of the center circumferential grooves 16 in the center portion 28 may be circumferential narrow grooves 44.

[0079] As described above, in each center land area 22, multiple transverse grooves 32 are arranged in the circumferential direction at predetermined intervals. As a result, multiple blocks 34 are formed in the circumferential direction within the center land area 22. The center land area 22 comprises multiple blocks 34 separated by multiple transverse grooves 32. The top surface 35 of the block 34 forms part of the land surface 10.

[0080] Block 34 has four corners 36. Each corner 36 is located where the lateral groove 32 merges with the circumferential groove 12. The corners 36 are formed when the lateral groove 32 merges with the circumferential groove 12. When the lateral groove 32 merges with the circumferential groove 12 at an angle, an acute corner 36 (hereinafter referred to as acute corner 38) is formed on the block 34 located on one side of the lateral groove 32, and an obtuse corner 36 (hereinafter referred to as obtuse corner 40) is formed on the block 34 located on the other side of the lateral groove 32. In other words, the acute corner 38 is formed when the lateral groove 32 intersects the circumferential groove 12 at an acute angle, and the obtuse corner 40 is formed when the lateral groove 32 intersects the circumferential groove 12 at an obtuse angle. Block 34 of this tire 2 has two acute corners 38 and two obtuse corners 40.

[0081] The tread 4 of this tire 2 is provided with circumferential grooves 12, which include a circumferential main groove 42 and a circumferential narrow groove 44. Of the acute angles 38 formed by the confluence of the lateral grooves 32 with the circumferential grooves 12, the acute angle 38 formed by the confluence of the lateral grooves 32 with the circumferential main groove 42 is also called the main groove acute angle 38m. The acute angle 38 formed by the confluence of the lateral grooves 32 with the circumferential narrow groove 44 is also called the narrow groove acute angle 38s. The blocks 34 that make up the subcenter land portion 26 are provided with a main groove acute angle 38m on the TE side of the tread surface 6 and a narrow groove acute angle 38s on the equatorial side as acute angles 38. The two acute angles 38 of the blocks 34 that make up the main center land portion 24 are both narrow groove acute angles 38s.

[0082] In this tire 2, in the center portion 28 of the tread 4, multiple lateral grooves 32 are arranged such that a reference lateral groove located on the first circumferential side and a corresponding lateral groove located on the second circumferential side form a single lateral groove pair. In the lateral groove pair, the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are at the same position in the circumferential direction. In other words, multiple lateral grooves 32 are arranged seamlessly in the center portion 28 of the tread 4. As a result, multiple lateral grooves 32 that are intermittently arranged in the circumferential direction create a groove that appears to extend continuously in the circumferential direction. This tire can improve quietness while maintaining good wet performance.

[0083] As mentioned above, the center land section 22 is provided with blocks 34 separated by transverse grooves 32. Because the transverse grooves 32 are arranged seamlessly, there is a risk of chipping occurring at the corners 36 (especially the acute corners 38) of the blocks 34 where the transverse grooves 32 merge with the circumferential grooves 12.

[0084] As described above, of the one or more center circumferential grooves 16 provided in the center portion 28 of the tread 4, at least one center circumferential groove 16 is a circumferential narrow groove 44. When the tread 4 contacts the road surface and deforms, the pair of wall surfaces 44S of the circumferential narrow groove 44 come into contact with each other in the narrow groove portion 48. As a result, the center land portions 22 located on both sides of the circumferential narrow groove 44 support each other. The rigidity of the blocks 34 that make up the center land portion 22 appears to increase. Deformation of the corners 36 of the blocks 34 is suppressed. As a result, the occurrence of chipping at the corners 36 of the blocks 34 (especially the acute corners 38) is suppressed. This tire 2 can reduce the risk of block chipping.

[0085] This tire 2 achieves an improved resistance to block chipping while balancing wet performance and quietness.

[0086] As described above, in the center section 28, the reference lateral groove and the corresponding lateral groove that constitute the lateral groove pair are provided on different center land sections 22, and the reference lateral groove provided on one center land section 22 and the corresponding lateral groove provided on the other center land section 22 are arranged such that the second end Es of the reference lateral groove and the first end Ef of the corresponding lateral groove are at the same position in the circumferential direction. This allows the inclination angle of the lateral grooves 32 with respect to the axial direction to be set at a gentle angle while maintaining a seamless-like arrangement of lateral grooves 32. The tire 2 can increase the lateral rigidity of the blocks 34 separated by the lateral grooves 32 while maintaining good quietness. The tire 2 can improve wear resistance and handling stability. The risk of block chipping is also reduced, so the tire 2 can also improve block chipping resistance. From this perspective, each of the multiple transverse grooves 32 has a first end Ef located on the first circumferential side and a second end Es located on the second circumferential side, and in the center portion 28, the multiple transverse grooves 32 are arranged such that a reference transverse groove located on the first circumferential side and a corresponding transverse groove located on the second circumferential side constitute one transverse groove pair, and in the transverse groove pair, if the second end Es of the reference transverse groove and the first end Ef of the corresponding transverse groove are in the same position in the circumferential direction, it is preferable that the reference transverse groove and the corresponding transverse groove constituting the transverse groove pair are provided in different center land portions 22.

[0087] As mentioned above, the transverse grooves 32 are inclined with respect to the axial direction in each center land section 22. In other words, the transverse grooves 32 are inclined with respect to the circumferential direction. In Figure 3, angle θ represents the angle that the transverse groove 32 makes with respect to the circumferential direction. As mentioned above, the transverse groove 32 merges with the circumferential groove 12 at an angle. The inclination angle θ of the transverse groove 32 with respect to the circumferential direction is represented by the angle made between the edge 12E of the circumferential groove 12 and the edge 32E of the transverse groove 32 at the point where the transverse groove 32 merges with the circumferential groove 12, more specifically, at the point where the acute-angle portion 38 of the block 34 is formed. If the circumferential groove 12 is inclined with respect to the circumferential direction at the point where the transverse groove 32 merges with the circumferential groove 12, the inclination angle θ can be determined by assuming that the circumferential groove 12 extends straight in the circumferential direction at this point.

[0088] The inclination angle θ of the transverse groove 32 with respect to the circumferential direction is preferably between 55 degrees and 85 degrees. By setting the inclination angle θ to 55 degrees or more, the rigidity of the acute-angle portion 38 of the block 34 is increased. The occurrence of block chipping at the acute-angle portion 38 is suppressed. This tire 2 can improve its resistance to block chipping. From this viewpoint, an inclination angle θ of 65 degrees or more is more preferable. By setting the inclination angle θ to 85 degrees or less, the generation of noise caused by the lateral grooves 32 is suppressed. This tire 2 can improve its quietness. From this viewpoint, it is preferable that the inclination angle θ be 80 degrees or less.

[0089] As mentioned above, the tread 4 of this tire 2 is provided with circumferential grooves 12, which include a circumferential main groove 42 and a circumferential narrow groove 44. The acute angles 38 of the block 34 include a main groove acute angle 38m, which is formed when the lateral groove 32 merges with the circumferential main groove 42, and a narrow groove acute angle 38s, which is formed when the lateral groove 32 merges with the circumferential narrow groove 44. The narrow groove acute angle 38s includes a sub-narrow groove acute angle 38ss, which is formed in the block 34 of the sub-center land portion 26 located between the circumferential main groove 42 and the circumferential narrow groove 44, and a main narrow groove acute angle 38sm, which is formed in the block 34 of the main center land portion 24 located between the two circumferential narrow grooves 44. As shown in Figure 3, the circumferential narrow groove 44 is located axially inward of the circumferential main groove 42. The circumferential narrow groove 44 is included in the center portion 28, which exhibits high ground pressure when the tread 4 contacts the road surface. There is a concern that the narrow groove sharp-angle portion 38s of block 34 is more prone to chipping than the main groove sharp-angle portion 38m of block 34.

[0090] However, in this tire 2, the inclination angle θs of the lateral groove 32 with respect to the circumferential direction in the portion constituting the narrow groove acute angle section 38s is set to be equal to or greater than the inclination angle θm of the lateral groove 32 with respect to the circumferential direction in the portion constituting the main groove acute angle section 38m. This allows the tire 2 to further improve block chipping resistance while maintaining good quietness performance. In this case, from the viewpoint of improving block chipping resistance, it is preferable that the inclination angle θsm of the lateral groove 32 with respect to the circumferential direction in the portion constituting the main narrow groove acute angle section 38sm is set to be greater than the inclination angle θss of the lateral groove 32 with respect to the circumferential direction in the portion constituting the sub-narrow groove acute angle section 38ss. Specifically, the difference between the inclination angle θsm and the inclination angle θss (θsm-θss) is preferably 3.5 degrees or more, and more preferably 4.5 degrees or more. From the viewpoint of enabling tire 2 to achieve a good balance between quietness and block chipping resistance, it is preferable that this difference (θsm-θss) be 6.0 degrees or less, and more preferably 5.0 degrees or less. Furthermore, from the viewpoint of achieving both quietness and block chipping resistance, if the inclination angle θsm of the lateral groove 32 with respect to the circumferential direction in the portion constituting the main narrow groove acute angle 38sm is set to be greater than the inclination angle θss of the lateral groove 32 with respect to the circumferential direction in the portion constituting the sub-narrow groove acute angle 38ss, it is preferable that the inclination angle θss be set to be equal to the inclination angle θm of the lateral groove 32 with respect to the circumferential direction in the portion constituting the main groove acute angle 38m. Note that an equal relationship in inclination angles means that the difference in inclination angles is 3.0 degrees or less.

[0091] As mentioned above, the tread pattern is formed by cutting grooves 8 into the tread 4. The tread pattern of this tire 2 includes a plurality of circumferential grooves 12 and a plurality of lateral grooves 32 as grooves 8. The tread 4 has a tread pattern formed by cutting grooves 8, which include a plurality of circumferential grooves 12 and a plurality of lateral grooves 32, into the tread 4.

[0092] As shown in Figure 1, the tread pattern is divided into multiple pitch patterns 50 arranged in the circumferential direction. In other words, the tread pattern comprises multiple pitch patterns 50 arranged in the circumferential direction. In Figure 1, the solid line BP extending in the axial direction is the boundary between two adjacent pitch patterns 50. The tread pattern is composed of a combination of multiple pitch patterns 50. In this invention, the pitch pattern 50 refers to a unit pattern that is repeated in the circumferential direction.

[0093] As mentioned above, the tread 4 has multiple center land sections 22. Each of the multiple pitch patterns 50 that make up the tread pattern includes multiple center land sections 22. The tread 4 of this tire 2 has a first center land section 22a, a second center land section 22b, and a third center land section 22c. As shown in Figure 1, one pitch pattern 50 includes a first center land section 22a, a second center land section 22b, and a third center land section 22c. The first center land section 22a included in this pitch pattern 50 includes one lateral groove 32. The second center land section 22b included in this pitch pattern 50 also includes one lateral groove 32. The third center land section 22c included in this pitch pattern 50 also includes one lateral groove 32. In this tire 2, each of the multiple center land sections 22 included in one pitch pattern 50 includes one lateral groove 32. This allows the tire 2 to effectively place the lateral grooves 32 in the center land sections 22. This tire 2 can achieve both good wet performance and block chipping resistance while maintaining good quietness. From this viewpoint, it is preferable that one lateral groove 32 is arranged in each of the multiple center land portions 22 included in the pitch pattern 50 that constitutes the tread pattern.

[0094] As shown in Figure 1, between the first center land section 22a and the second center land section 22b, which are adjacent in the axial direction, the lateral grooves 32 provided on the first center land section 22a and the lateral grooves 32 provided on the second center land section 22b are arranged alternately in the circumferential direction. Similarly, between the second center land section 22b and the third center land section 22c, which are adjacent in the axial direction, the lateral grooves 32 provided on the second center land section 22b and the lateral grooves 32 provided on the third center land section 22c are arranged alternately in the circumferential direction. In this tire 2, the lateral grooves 32 provided on one of two adjacent center land sections 22 and the lateral grooves 32 provided on the other are arranged alternately in the circumferential direction. This allows the tire 2 to arrange the lateral grooves 32 at a certain distance from each other in a single center land section 22. The tire 2 can increase the rigidity of the blocks 34 separated by the lateral grooves 32. This tire 2 can improve block chipping resistance. From this perspective, it is preferable that the lateral grooves 32 provided on one of the two adjacent center land sections 22 and the lateral grooves 32 provided on the other are arranged alternately in the circumferential direction.

[0095] Figure 5 shows a cross-section of the transverse groove 32. Figure 5 shows a cross-section of the transverse groove 32 of the second center land area 22b. Although not shown, the transverse grooves 32 of the first center land area 22a and the third center land area 22c have the same cross-sectional shape as the transverse groove 32 of the second center land area 22b. The lateral groove 32 comprises a pair of wall surfaces 32S including a groove opening 32M and a bottom surface 32B including a groove bottom 32T. The lateral groove 32 of this tire 2 comprises a wide section 52 and a sipe section 54. The wide section 52 includes the groove opening 32M of the lateral groove 32. The wide section 52 of this tire 2 has a rectangular cross-section. The wide section 52 may have a cross-sectional shape that tapers from the groove opening 32M toward the sipe section 54. In Figure 5, the length indicated by the double arrow WGy is the width of the wide section 52 at the groove opening 32M. The wide section 52 has a width WGy of more than 1.0 mm. From the viewpoint of wet performance, it is preferable that the width WGy of the wide section 52 is 1.5 mm or more and 5.0 mm or less.

[0096] The sipe portion 54 is located radially inward of the wide portion 52. The sipe portion 54 includes the groove bottom 32T of the lateral groove 32. The sipe portion 54 extends straight in the depth direction of the lateral groove 32. In Figure 5, the length indicated by the double arrow WYS is the width of the sipe portion 54. The sipe portion 54 has a width WYS of 1.0 mm or less. When the tread 4 contacts the road surface and deforms, the pair of wall surfaces 32S of the lateral groove 32 come into contact with each other at the sipe portion 54. This lateral groove 32 has a width of 1.0 mm or less at the point where the pair of wall surfaces 32S come into contact with each other. This lateral groove 32 is a sipe. This lateral groove 32 may be composed only of the sipe portion 54 without the wide portion 52 being provided. In this tire 2, the blocks 34 formed on both sides of the lateral groove 32 support each other. The rigidity of the blocks 34 is apparently increased. Deformation of the corners 36 of the block 34 (especially the acute corners 38) is suppressed. The tire 2 can improve its resistance to block chipping.

[0097] In this tire 2, the lateral groove 32 does not have to be a sipe. The lateral groove 32 may be configured as a narrow groove having a narrow width and a width of more than 1.0 mm in the portion where a pair of wall surfaces 32S contact each other, or it may be configured as a main groove having a wide width and a pair of wall surfaces 32S that do not contact each other even when the tread 4 deforms. From the viewpoint of improving block chipping resistance, it is preferable that the lateral groove 32 is a sipe. When the lateral groove 32 is a sipe, from the viewpoint of achieving both wet performance and block chipping resistance, it is preferable that the lateral groove 32 comprises a wide portion 52 and a sipe portion 54 located radially inward of the wide portion, as shown in Figure 5, where the wide portion 52 includes the groove opening 32M of the lateral groove 32 and has a width of more than 1.0 mm, and the sipe portion 54 includes the groove bottom 32T of the lateral groove 32 and has a width of 1.0 mm or less. In this case, although not shown, the sipe portion 54 may be configured to extend in a zigzag pattern in the depth direction.

[0098] In Figure 5, the length indicated by the double arrow DGy is the depth of the lateral groove 32. The length indicated by the double arrow DYW is the depth of the wide section 52. From the viewpoint of enabling the lateral groove 32 to fully perform its function, the ratio DYW / DGy of the depth DYW of the wide portion 52 to the depth DGy of the lateral groove 32 is preferably 0.10 or more and 0.25 or less, and more preferably 0.15 or more and 0.20 or less.

[0099] As shown in Figure 1, the acute-angled portion 38 of the block 34 is provided with a slope 56. The slope 56 is connected to the top surface 35 of the block 34 and is inclined with respect to the top surface 35. Providing a slope 56 on the acute-angled portion 38 seemingly increases the rigidity of the acute-angled portion 38. This suppresses deformation of the acute-angled portion 38. The tire 2 can improve its resistance to block chipping. From this viewpoint, it is preferable that the acute-angled portion 38 is connected to the top surface 35 of the block 34 and is provided with a slope 56 that is inclined with respect to the top surface 35. In this case, it is preferable that the angle that the slope 56 makes with respect to the top surface 35, that is, the inclination angle of the slope 56, is between 40 degrees and 70 degrees.

[0100] As described above, the body 46 of the circumferential groove 44 includes a groove portion 48. As shown in Figure 4, the portion of the groove opening 44M of the circumferential groove 44 may be machined to be tapered. In this case, the body 46 further includes a tapered portion 58. The tapered portion 58 includes the groove opening 44M of the circumferential groove 44. The groove portion 48 is located radially inward of the tapered portion 58. The tapered portion 58 narrows from the groove opening 44M toward the groove portion 48.

[0101] In Figure 4, the straight line LTP represents the boundary position between the tapered section 58 and the narrow groove section 48. The boundary LTP between the tapered section 58 and the narrow groove section 48 is represented by the position at the boundary portion between the tapered section 58 and the narrow groove section 48 where the circumferential narrow groove 44 has a width Wd that is 1.1 times the minimum width WHN of the narrow groove section 48. In Figure 4, the length indicated by the double arrow DHT is the depth of the tapered section 58.

[0102] The tapered portion 58 can contribute to suppressing the increase in ground pressure at the groove opening 44M of the circumferential narrow groove 44. This tire 2 can improve block chipping resistance. The tapered portion 58 can also contribute to increasing the groove volume of the circumferential narrow groove 44. This tire 2 can also improve wet performance. From this viewpoint, it is preferable that the body portion 46 comprises a tapered portion 58 including the groove opening and a narrow groove portion 48 located radially inward of the tapered portion 58, and that the tapered portion 58 tapers from the groove opening 44M toward the narrow groove portion 48. In this case, from the viewpoint of achieving both wet performance and block chipping resistance, it is preferable that the ratio DHT / DGh of the depth DHT of the tapered portion 58 to the depth DGh of the circumferential narrow groove 44 is 0.10 or more and 0.15 or less.

[0103] The circumferential groove 44 of this tire 2 may have a widened section further provided on the radially inward side of the body 46. The circumferential groove 44 may comprise the body 46 and the widened section 60 located radially inward of the body 46. In this case, the widened section 60 includes the groove bottom 44T of the circumferential groove 44. The width of the widened section 60 is wider than the width of the groove 48 of the body 46.

[0104] In Figure 4, the position indicated by the solid line LPE is the boundary between the body portion 46 (specifically the narrow groove portion 48) and the widened portion 60. This boundary LPE is represented by the position where the circumferential narrow groove 44 has a width Wc that is 1.1 times the minimum width WHN of the narrow groove portion 48. If the portion with a width Wc that is 1.1 times the minimum width WHN has a constant length in the depth direction, the radial outer end of that portion is identified as the position of the boundary LPE. In Figure 4, the length indicated by the double arrow DHB is the depth of the body portion 46.

[0105] In this tire 2, the narrow groove 48 is the area between the LTP boundary between the tapered portion 58 and the narrow groove portion 48, and the LPE boundary between the narrow groove portion 48 and the widened portion 60. The narrow groove portion 48 includes a straight portion 62 that extends straight in the depth direction. The straight portion 62 has a uniform width WHN in the depth direction. In the cross-section of the circumferential narrow groove 44 shown in Figure 4, the contour of the straight portion 62 is represented by a straight line. Although not shown, the narrow groove portion 48 may be configured such that its width gradually widens from, for example, the position showing the minimum width WHN toward the groove opening 44M and the widened portion 60, respectively.

[0106] In Figure 4, the length indicated by the double arrow WHX is the maximum width of the circumferential groove 44. The position indicated by the symbol PX is the position where the circumferential groove 44 exhibits its maximum width WHX (hereinafter referred to as the maximum width position of the circumferential groove 44). If the portion exhibiting the maximum width WHX has a constant length in the depth direction, the radial outer end of that portion is identified as the maximum width position PX.

[0107] As shown in Figure 4, the widened section 60 includes the position of maximum width PX. The circumferential groove 44 exhibits a maximum width WHX in the widened section 60. The maximum width WHX of the circumferential groove 44 is also the maximum width of the widened section 60. The widened section 60 tapers radially outward from the portion exhibiting the maximum width WHX. The widened section 60 tapers radially inward from the portion exhibiting the maximum width WHX. In Figure 4, the length indicated by the double arrow DHX is the depth from the groove opening 44M of the circumferential groove 44 to the position where the widened section 60 exhibits the maximum width WHX.

[0108] The widened section 60 comprises a curved section 64 and a bottom section 66. The widened section 60 exhibits its maximum width WHX at the bottom section 66. In Figure 4, the position indicated by the symbol CB is the boundary between the curved section 64 and the bottom section 66.

[0109] The inflection section 64 connects the narrow groove section 48 and the bottom section 66. The width of the inflection section 64 gradually increases from the boundary LPE with the narrow groove section 48 towards the boundary CB with the bottom section 66. The inflection section 64 curves inward from its outside. Specifically, in the cross-section of the circumferential narrow groove 44, the contour of the inflection section 64 is represented by a circular arc. In Figure 4, the arrow RC is the radius of the circular arc representing the contour of the inflection section 64. The circular arc representing the contour of the inflection section 64 is tangent to the straight line representing the contour of the straight section 62 of the narrow groove section 48 at the boundary CS between the inflection section 64 and the straight section 62.

[0110] The bottom portion 66 is located radially inward of the curved portion 64. The bottom portion 66 includes the groove bottom 44T of the circumferential narrow groove 44. The bottom portion 66 curves outward from its inner side. The bottom portion 66 of this tire 2 comprises a straight portion 68 having a uniform width WHX in the depth direction, an outer portion 70 located radially outward of the straight portion 68, and an inner portion 72 located radially inward of the straight portion 68.

[0111] In the cross-section of the circumferential groove 44, the contour of the straight portion 68 is represented by a straight line. The outline of the outer portion 70 is represented by an arc. In Figure 4, arrows RBs are the radii of the arc representing the outline of the outer portion 70. The arc representing the outline of the outer portion 70 is tangent to the arc representing the outline of the inflection portion 64 at boundary CB. The arc representing the outline of the outer portion 70 is tangent to the straight line representing the outline of the straight portion 68 at boundary SS between the outer portion 70 and the straight portion 68. The contour of the inner portion 72 is represented by an arc. In Figure 4, arrow RBu is the radius of the arc representing the contour of the inner portion 72. The arc representing the contour of the inner portion 72 is tangent to the straight line representing the contour of the straight portion 68 at the boundary SU between the straight portion 68 and the inner portion 72. In this tire 2, the radius RBu of the arc representing the contour of the inner portion 72 is the same as the radius RBs of the arc representing the contour of the outer portion 70.

[0112] In this tire 2, a straight section 68 is not required on the bottom 66. In this case, the bottom 66 is composed of an outer section 70 and an inner section 72.

[0113] The circumferential narrow groove 44 exhibits a minimum width WHN at the narrow groove section 48 and a maximum width WHX at the widened section 60. The widened section 60 is located radially inward of the body section 46 (specifically, the narrow groove section 48). After the narrow groove section 48 disappears due to wear, the widened section 60 is exposed. The widened section 60 that is exposed after the narrow groove section 48 disappears can contribute to suppressing the decrease in drainage performance caused by adopting the circumferential narrow groove 44 as the circumferential groove 12. This tire 2 can maintain good wet performance. From this viewpoint, it is preferable that the circumferential narrow groove 44 has a widened section 60 located radially inward of the body section 46, and that the circumferential narrow groove 44 exhibits a minimum width WHN at the narrow groove section 48 and a maximum width WHX at the widened section 60.

[0114] In this tire 2, the radius RT of the arc representing the contour of the inflection portion 64 is preferably larger than the radius RBs of the arc representing the contour of the outer portion 70 of the bottom portion 66. This allows the circumferential grooves 44 to fully perform their function. From this viewpoint, the ratio RT / RBs of radius RT to radius RBs is preferably 1.1 or more and 2.5 or less, and more preferably 1.5 or more and 2.0 or less.

[0115] The ratio DHB / DGh of the depth DHB of the body portion 46 to the depth DGh of the circumferential groove 44 is preferably 0.20 or more and 0.60 or less. By setting the ratio DHB / DGh to 0.20 or higher, the groove depth DHB of the body 46 is appropriately maintained. As the tread 4 deforms in contact with the road surface, the pair of wall surfaces 44S of the circumferential narrow grooves 44 can make sufficient contact in the narrow groove section 48. This tire 2 can further improve its block chipping resistance. From this viewpoint, a ratio DHB / DGh of 0.25 or higher is more preferable, and a ratio of 0.30 or higher is even more preferable. By setting the ratio DHB / DGh to 0.60 or less, the tire 2 can form a widened section 60 with the necessary groove volume. The exposed widened section 60 can effectively contribute to suppressing a decrease in wet performance. From this viewpoint, a ratio DHB / DGh of 0.55 or less is more preferable, and 0.50 or less is even more preferable.

[0116] From the viewpoint of effectively contributing to suppressing a decrease in wet performance by the widened portion 60, the ratio DHX / DGh of the groove depth DHX from the groove opening 44M of the circumferential narrow groove 44 to the groove depth DGh of the circumferential narrow groove 44 is preferably 0.65 or more and 0.85 or less, and more preferably 0.70 or more and 0.80 or less.

[0117] Figure 6 shows a portion of the cross-section of the center section 28. Figure 6 shows a cross-section of the section where the main center land section 24 is located. The center foot portion 22 of this tire 2 is equipped with lateral grooves 32. As mentioned above, when the narrow groove portion 48 disappears due to wear, the wider portion 60 is exposed. The coexistence of the lateral grooves 32 and the wider portion 60 on the worn tread surface 6 may affect the balance between wet performance and quietness, especially after the widest position PX of the wider portion 60 is exposed. However, in this tire 2, the depth of the lateral groove 32 is adjusted such that the depth DHB of the body portion 46 of the circumferential groove 44, the depth DGy of the lateral groove 32, and the depth DHX from the groove opening 44M of the circumferential groove 44 to the position PX where the widened portion 60 shows its maximum width WHX satisfy the following equation. DHB ≤ DGy ≤ DHX As a result, during the process in which the width of the widened portion 60 expands from the time the widened portion 60 is exposed due to wear until the widened portion 60's maximum width position PX is exposed, the lateral grooves 32 can effectively contribute to achieving both wet performance and quietness. After the widened portion 60's maximum width position PX is exposed and the lateral grooves 32 disappear, the widened portion 60 can contribute to suppressing the deterioration of wet performance. Since the disappearance of the lateral grooves 32 appropriately maintains the rigidity of the center land portion 22, good quietness is also maintained. This tire 2 can maintain good wet performance and good quietness even when worn. From this viewpoint, it is preferable that the depths DHB, DGy, and DHX satisfy the above formula. From a similar viewpoint, it is more preferable that the depths DHB, DGy, and DHX satisfy the following equation. DHB≦DGy <DHX More preferably, the depths DHB, DGy, and DHX satisfy the following equation. DHB <DGy<DHX

[0118] As is clear from the above description, the present invention provides a heavy-duty tire that achieves improved block chipping resistance while simultaneously balancing wet performance and quietness. [Industrial applicability]

[0119] The technology described above, which achieves both wet performance and quietness while improving block chipping resistance, can be applied to various types of tires.

[0120] [Note] The present invention includes the following embodiments.

[0121] [1] A road surface having a tread that contacts the road surface, the tread having a plurality of circumferential grooves arranged in the axial direction, the plurality of circumferential grooves comprising two shoulder circumferential grooves located on the outermost axial side and one or more center circumferential grooves located between the two shoulder circumferential grooves, the portion of the tread between the two shoulder circumferential grooves being the center portion, the center portion comprising a plurality of center land portions separated by one or more center circumferential grooves, each of the plurality of center land portions comprising a plurality of transverse grooves that cross the center land portion, in each of the center land portions the plurality of transverse grooves are arranged in the circumferential direction, and each of the plurality of transverse grooves is located in one direction in the circumferential direction A heavy-duty tire comprising a first end located on one side and a second end located on the other side, wherein a plurality of lateral grooves in the center portion are arranged such that a reference lateral groove located on one side in the circumferential direction and a corresponding lateral groove located on the other side constitute a pair of lateral grooves, the second end of the reference lateral groove and the first end of the corresponding lateral groove are in the same position in the circumferential direction in the pair of lateral grooves, at least one of the one or more center circumferential grooves is a circumferential narrow groove, the circumferential narrow groove comprises a body portion including the groove opening of the circumferential narrow groove, the body portion comprises a narrow groove portion, and when the tread contacts the road surface and deforms, a pair of wall surfaces of the circumferential narrow groove contact each other in the narrow groove portion. [2] The heavy-duty tire according to [1] above, wherein the reference lateral groove and the corresponding lateral groove constituting the pair of lateral grooves are provided on different parts of the center land area. [3] The heavy-duty tire according to [1] or [2] above, wherein the lateral groove is inclined with respect to the circumferential direction, and the angle of inclination of the lateral groove with respect to the circumferential direction is 55 degrees or more and 85 degrees or less. [4] The heavy-duty tire according to any one of [1] to [3] above, wherein the tread has a tread pattern in which grooves including a plurality of circumferential grooves and a plurality of lateral grooves are engraved in the tread, the tread pattern has a plurality of pitch patterns arranged in the circumferential direction, and one lateral groove is disposed in each of the plurality of center land portions included in the pitch patterns. [5] A heavy-duty tire according to any of the above [1] to [4], wherein the lateral grooves provided on one of two adjacent center land sections and the lateral grooves provided on the other are arranged alternately in the circumferential direction. [6] A heavy-duty tire according to any of the above [1] to [5], wherein the lateral grooves are sipes. [7] The heavy-duty tire according to any one of [1] to [6] above, wherein the center land portion comprises a plurality of blocks separated by a plurality of lateral grooves, each of the plurality of blocks having an acute angle portion formed by the lateral grooves intersecting the circumferential grooves at an acute angle, and the acute angle portion has a slope that is connected to the top surface of the block and slopes with respect to the top surface. [8] The heavy-duty tire according to any one of [1] to [7] above, wherein the body portion comprises a tapered portion including the groove, the narrow groove portion is located radially inward of the tapered portion, and the tapered portion narrows from the groove towards the narrow groove portion. [9] The heavy-duty tire according to any one of the above [1] to [8], wherein the circumferential groove is provided with a widened portion located radially inward of the body, the circumferential groove exhibits a minimum width in the groove portion and a maximum width in the widened portion.

[10] The heavy-duty tire described in [9] above, wherein the depth of the body DHB, the depth of the lateral groove DGy, and the depth DHX from the groove opening to the position where the widened portion shows its maximum width satisfy the following formula. DHB ≤ DGy ≤ DHX [Explanation of symbols]

[0122] 2... Tires 4. Tread 12...Circumferential groove 14, 14a, 14b... Shoulder circumferential grooves 16, 16a, 16b, 16c... Center circumferential grooves 18... Rikube 22, 22a, 22b, 22c... Center Track and Field Club 28. Center Section 32, 32a, 32b, 32c... Yokomizo 34 blocks 35...Top surface 36...corner 38...Acute angle 42...Circumferential main groove 44... Circumferential narrow groove 46... Torso 48...Narrow groove part 50 pitch pattern 52... Wide section 54... Sipes 56...Slope 58...Tapered section 60... Widening section 64... Inflection 66...bottom

Claims

1. Equipped with a tread that makes contact with the road surface, The tread comprises a plurality of circumferential grooves arranged in the axial direction, The plurality of circumferential grooves comprises two shoulder circumferential grooves located on the outermost axial side and one or more center circumferential grooves located between the two shoulder circumferential grooves, The portion of the tread between the two shoulder circumferential grooves is the center portion. The center portion comprises a plurality of center land portions separated by one or more center circumferential grooves, Each of the multiple center land sections is provided with multiple transverse grooves that cross the center land section, In each of the aforementioned land areas of the center, a plurality of the aforementioned transverse grooves are arranged in the circumferential direction. Each of the aforementioned transverse grooves has a first end located on one side in the circumferential direction and a second end located on the other side, In the center portion, a plurality of transverse grooves are arranged such that a reference transverse groove located on one side in the circumferential direction and a corresponding transverse groove located on the other side constitute a pair of transverse grooves. In the aforementioned pair of transverse grooves, the second end of the reference transverse groove and the first end of the corresponding transverse groove are at the same position in the circumferential direction. Of the one or more of the aforementioned center circumferential grooves, at least one of the center circumferential grooves is a circumferential narrow groove. The circumferential groove comprises a body portion including the groove opening of the circumferential groove, The body portion is equipped with a narrow groove, When the tread comes into contact with the road surface and deforms, the pair of wall surfaces of the circumferential grooves come into contact with each other in the groove portion. Heavy-duty tires.

2. The reference lateral groove and the corresponding lateral groove that constitute the pair of lateral grooves are provided in different parts of the center land area. A heavy-duty tire according to claim 1.

3. The aforementioned transverse groove is inclined with respect to the circumferential direction, The inclination angle of the transverse groove with respect to the circumferential direction is 55 degrees or more and 85 degrees or less. A heavy-duty tire according to claim 1.

4. The tread comprises a tread pattern formed by cutting grooves in the tread that include a plurality of circumferential grooves and a plurality of transverse grooves, The tread pattern comprises a plurality of pitch patterns arranged in the circumferential direction, Each of the multiple center land portions included in the pitch pattern is provided with one of the transverse grooves. A heavy-duty tire according to claim 1.

5. The transverse grooves provided on one of two adjacent central land sections and the transverse grooves provided on the other are arranged alternately in the circumferential direction. A heavy-duty tire according to claim 1.

6. The aforementioned horizontal groove is a sipe. A heavy-duty tire according to claim 1.

7. The aforementioned center land area comprises a plurality of blocks separated by a plurality of the aforementioned transverse grooves, Each of the multiple blocks is provided with an acute-angle portion formed by the lateral groove intersecting the circumferential groove at an acute angle, The aforementioned acute angle is connected to the top surface of the block and has an inclined surface that slopes relative to the top surface. A heavy-duty tire according to claim 1.

8. The body portion includes a tapered portion including the groove, The aforementioned narrow groove portion is located radially inward of the tapered portion, The tapered portion narrows from the groove opening towards the narrow groove portion. A heavy-duty tire according to claim 1.

9. The circumferential narrow groove has a widened portion located radially inward of the body, The circumferential narrow groove exhibits its minimum width in the narrow groove portion and its maximum width in the widened portion. A heavy-duty tire according to claim 1.

10. The depth DHB of the body, the depth DGy of the lateral groove, and the depth DHX from the groove opening to the position where the widened portion shows its maximum width satisfy the following equation: The heavy-duty tire according to claim 9. DHB ≤ DGy ≤ DHX

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