Heavy-load tire

Abstract

To provide a heavy lord tyre 2 capable of suppressing accumulation of static electricity and achieving reduction in rolling resistance.SOLUTION: A tire 2 includes a tread 4. The tread 4 includes has a plurality of circumferential grooves 46. A plurality of land parts 48 constituted by the plurality of circumferential grooves 46 include a plurality of main land parts 64. The circumferential grooves 46 between the main land parts 64 adjacent to each other are circumferential fine grooves 54. The circumferential fine groove 54 includes a barrel part 66 and an expanded width part 68. A maximum width W2 of the expanded width part 68 is broader than a minimum width W1 of the barrel part 66. Each of the plurality of main land parts 64 has a traverse siping 78. The traverse siping 78 includes a sipe main body 80 and a tubular part 82. A maximum width W4 of the tubular part 82 is broader than a groove width W3 of the sipe main body 80. The tread 4 includes a conductive part 42. Either one main land parts 64 includes the conductive part 42.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Considering the impact on the environment, there is a strong demand for tires to have reduced rolling resistance. To reduce rolling resistance, the use of low-heat-generating rubber in the tread has been considered. Low-heat-generating rubber contains a lot of silica. The electrical resistance of a tread made of low-heat-generating rubber is higher than that of a tread made of rubber containing a lot of carbon black. When a tire having a tread made of low-heat-generating rubber is mounted on a vehicle, there is a concern that static electricity may accumulate on the vehicle. For this reason, as described in Patent Document 1, for example, a conductive bridge (hereinafter referred to as a conductive portion) made of conductive rubber is provided on the tread. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2006-502909 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a heavy-duty tire that can suppress the accumulation of static electricity and achieve a reduction in rolling resistance. [Means for solving the problem]

[0005] The heavy-duty tire according to the present invention comprises a pair of beads, a carcass spanning the pair of beads, a reinforcing layer located radially outward of the carcass, and a tread having an outer circumferential surface in contact with the road surface and an inner circumferential surface in contact with the reinforcing layer. The tread has a plurality of circumferential grooves extending continuously in the circumferential direction. The plurality of circumferential grooves define a plurality of land portions in the tread. The plurality of land portions include a plurality of main land portions located between adjacent circumferential grooves. The circumferential groove located between adjacent main land portions is a circumferential narrow groove. The circumferential narrow groove comprises a body portion and a widened portion located radially inward of the body portion. The widened portion has a maximum width W2 greater than a minimum width W1 of the body portion. When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other in the body portion. Each of the main land portions has a transverse sipe that crosses the main land portion. The transverse sipe includes a sipe body and a tubular portion located radially inward of the sipe body. The maximum width W4 of the tubular portion is greater than the groove width W3 of the sipe body. The tread includes a conductive portion connecting the outer circumferential surface and the inner circumferential surface. Any one of the main land portions includes the conductive portion. [Effects of the Invention]

[0006] According to the present invention, a heavy-duty tire can be obtained that can suppress the accumulation of static electricity and achieve a reduction in rolling resistance. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a development view showing a tread of a heavy duty tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged development view showing a part of FIG. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 3 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 4 is an enlarged cross-sectional view showing a part of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] The tire of the present invention is mounted on a rim. The inside of the tire is filled with air, and the internal pressure of the tire is adjusted. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly includes a rim and a tire mounted on the rim.

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

[0011] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part of the tire's meridian cross section, which cannot be measured when the tire is mounted on a regular rim, are measured on a cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads of the tire mounted on a regular rim. Note that the tire configuration, which cannot be confirmed when the tire is mounted on a regular rim, is confirmed on the cut surface.

[0012] A genuine rim is a rim specified 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 genuine rims.

[0013] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0014] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0015] In the present invention, crosslinked rubber is obtained by pressurizing and heating a rubber composition. Crosslinked rubber is a crosslinked product of a rubber composition. A rubber composition is a material obtained by mixing raw rubber components and chemicals in a kneader such as a Banbury mixer. In crosslinked rubber, the raw rubber components are crosslinked, but in rubber compositions, the raw rubber components are not crosslinked. Crosslinked rubber is also called vulcanized rubber, and rubber compositions are also called unvulcanized rubber.

[0016] Examples of raw rubber components include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Examples of chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of raw rubber components and chemicals, the content of the selected chemicals, etc., are determined appropriately depending on the specifications of the elements to which the rubber composition is applied, such as the tread and sidewall.

[0017] In the present invention, conductive rubber has a volume resistivity of 1.0×10 8 Non-conductive rubber means cross-linked rubber with a volume resistivity of less than 1.0×10 8 This refers to crosslinked rubber with a conductivity of Ω·cm or more. The conductivity of rubber is controlled by the carbon black content. In particular, when the main component of the reinforcing agent is carbon black, crosslinked rubber can become conductive. When the main component of the reinforcing agent is silica, crosslinked rubber can become non-conductive.

[0018] In the present invention, when the rubber composition contains silica and carbon black as reinforcing agents, if the content of silica in 100 parts by mass of the reinforcing agent exceeds 50 parts by mass, silica is the main component of the reinforcing agent, and if the content of carbon black in 100 parts by mass of the reinforcing agent exceeds 50 parts by mass, carbon black is the main component of the reinforcing agent.

[0019] In the present invention, the volume resistivity of an element made of crosslinked rubber among elements constituting a tire is measured in accordance with the double ring electrode method specified in JIS K6271 under conditions of an applied voltage of 500 V, a temperature of 25°C, and a humidity of 50%. A sheet (thickness = 2 mm) is used for this measurement.

[0020] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0021] [Findings that form the basis of the present invention] The use of low-heat-generating rubber in the tread of not only passenger vehicle tires but also heavy-duty tires is being considered to reduce rolling resistance. In this case, the aforementioned conductive portion is provided in the tread to suppress the accumulation of static electricity on the vehicle, for example. The conductive part is made of conductive rubber. As mentioned above, when the main component of the reinforcing agent is carbon black, the crosslinked rubber can become conductive rubber. Such rubber has a high heat-generating property. The conductive part generates heat as the tire moves. Heavy-duty tires have thicker treads than passenger car tires. Heat tends to accumulate in the treads of heavy-duty tires. There is concern that providing a conductive part in the tread of a heavy-duty tire will increase the temperature around the conductive part. Localized increases in temperature affect tire durability. There are concerns that providing conductive parts in the tread of heavy-duty tires will reduce durability. Reducing the heat generation properties of the conductive parts from a compositional perspective may prevent the reduction in durability due to heat generation in the conductive parts. However, there are concerns that reducing the heat generation properties of the conductive parts from a compositional perspective could widen the gap between the conductive parts and the surrounding rubber in terms of physical properties, increasing the risk of uneven wear and chipping. Grooving the periphery of the conductive area would promote heat dissipation and potentially reduce the deterioration of durability due to heat generation in the conductive area. However, this would reduce the rigidity of the tread, which would increase rolling resistance. Therefore, in order to obtain a heavy-duty tire that can suppress the accumulation of static electricity and achieve reduced rolling resistance, the inventors conducted extensive research into the shape of the grooves to be carved around the conductive portion, and discovered that by carving narrow grooves around the conductive portion, each having a body portion with a narrow groove width and a widened portion located radially inward of the body portion and having a groove width wider than the groove width of the body portion, it is possible to suppress the decrease in durability due to heat generation in the conductive portion without increasing rolling resistance, and have thus completed the present invention, which is described below.

[0022] [Outline of the embodiment of the present invention] The present invention relates to a tire comprising a tread having a pair of beads, a carcass spanning the pair of beads, a reinforcing layer located radially outward of the carcass, an outer circumferential surface in contact with a road surface, and an inner circumferential surface in contact with the reinforcing layer, wherein the tread has a plurality of circumferential grooves extending continuously in a circumferential direction, the plurality of circumferential grooves constituting a plurality of land portions in the tread, the plurality of land portions including a plurality of main land portions located between adjacent circumferential grooves, the circumferential grooves located between adjacent main land portions being circumferential narrow grooves, the circumferential narrow groove having a body portion and an expanded portion located radially inward of the body portion, The maximum width W2 of the widened portion is wider than the minimum width W1 of the body portion, and when the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other in the body portion, and each of the main land portions has a transverse sipe that crosses the main land portion, and the transverse sipe comprises a sipe body and a tubular portion located radially inside the sipe body, and the maximum width W4 of the tubular portion is wider than the groove width W3 of the sipe body, and the tread comprises a conductive portion connecting the outer circumferential surface and the inner circumferential surface, and any one of the main land portions comprises the conductive portion. This is a heavy-duty tire.

[0023] The heavy duty tire of the present invention can suppress the accumulation of static electricity and achieve a reduction in rolling resistance. The mechanism by which this effect is achieved has not been clarified, but is presumed to be as follows.

[0024] The conductive portion connecting the outer peripheral surface and the inner peripheral surface of the tread is provided in the main land portion. The circumferential narrow groove is located between adjacent main land portions. The circumferential narrow groove is provided around the conductive portion. The circumferential narrow groove has a widened portion on the radially inner side of the body portion. The widened portion contributes to increasing the surface area of ​​the circumferential narrow groove. The surface area of ​​this circumferential narrow groove is larger than that of a circumferential narrow groove consisting only of the body portion. This circumferential narrow groove can promote the dissipation of heat generated in the conductive portion. The increase in temperature around the conductive portion due to heat generation in the conductive portion is suppressed. This tire can suppress the decrease in durability caused by providing a conductive portion in the tread. The body of the circumferential narrow groove has a groove width narrower than the groove width of the widened portion. When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other at the body. The two main land portions located on both sides of the circumferential narrow groove support each other, suppressing tread deformation. This tread has higher rigidity than conventional treads that do not have circumferential narrow grooves. This circumferential narrow groove can contribute to increasing the rigidity of the tread. This tire can reduce rolling resistance. The tire has transverse sipes in the main land portion. The transverse sipes are also located around the conductive portion. The transverse sipes have tubular portions radially inward of the sipe body. The tubular portions contribute to increasing the surface area of ​​the transverse sipes. The sipe bodies of the transverse sipes can contribute to suppressing deformation of the main land portion. By combining the transverse sipes with the circumferential narrow grooves, the tire effectively dissipates heat generated in the conductive portion, effectively suppressing deformation of the tread. This tire can suppress a decrease in durability due to heat generation in the conductive portion without increasing rolling resistance. In this tire, even if a low-heat-generating rubber containing a large amount of silica is used in the tread to reduce rolling resistance, the conductive part can fully perform its function. This tire can suppress the accumulation of static electricity. Furthermore, by using a low-heat-generating rubber in the tread, this tire can further reduce rolling resistance. This tire can suppress the accumulation of static electricity and achieve a reduction in rolling resistance.

[0025] Preferably, the maximum width W2 of the widened portion is greater than the maximum width WX of the conductive portion. In this case, dissipation of heat generated in the conductive portion is promoted. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0026] Preferably, the maximum width W4 of the tubular portion is wider than the minimum width WN of the conductive portion. In this case, dissipation of heat generated in the conductive portion is promoted. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0027] Preferably, the land ratio, as defined below, is 75% or more. Land ratio: The ratio of the total area of ​​the contact area of ​​the multiple land portions included in the contact area to the area of ​​the entire contact area, obtained by mounting the tire on a regular rim, adjusting the internal pressure to the regular internal pressure, and applying a load of 100% of the regular load with a camber angle of 0 degrees and bringing the tire into contact with a flat road surface. In this case, the main land portions are more likely to support each other, effectively increasing the rigidity of the tread. The tire can effectively reduce rolling resistance and improve wear resistance. The circumferential narrow grooves effectively promote heat dissipation, effectively suppressing the deterioration of durability due to heat generation in the conductive parts.

[0028] Preferably, the groove bottom of the circumferential narrow groove is located radially inward of the radial center of the conductive portion. In this case, dissipation of heat generated in the conductive portion is promoted. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0029] Preferably, the groove bottom of the transverse sipe is located radially inward of the radial center of the conductive portion. In this case, dissipation of heat generated in the conductive portion is promoted. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0030] Preferably, the circumferential groove includes a plurality of the circumferential narrow grooves, the main land portion located between adjacent circumferential narrow grooves is an inner main land portion, and the main land portion having the conductive portion is the inner main land portion. In this case, the conductive portion can effectively function as a conductive path. Since the circumferential narrow grooves are located on both sides of the inner main land portion, dissipation of heat generated in the conductive portion is effectively promoted. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0031] Preferably, the conductive portion is disposed on the inner main land portion away from the axial center of the inner main land portion. In this case, the conductive portion is disposed near the circumferential narrow groove. This promotes dissipation of heat generated in the conductive portion. This tire can effectively suppress deterioration in durability due to heat generation in the conductive portion.

[0032] Preferably, the axial center of the inner main land portion coincides with the tire equatorial plane. In this case, the conductive portion can effectively function as a conductive path. This tire can effectively suppress the accumulation of static electricity. Moreover, since the conductive portion is disposed near the circumferential narrow groove, the dissipation of heat generated in the conductive portion is effectively promoted. This tire can effectively suppress a decrease in durability due to heat generation in the conductive portion.

[0033] [Details of the embodiment of the present invention] Fig. 1 is a developed view showing a part of a tread 4 of a tire 2 according to one embodiment of the present invention, and Fig. 2 is an enlarged developed view showing a part of Fig. 1. This tire 2 is mounted on vehicles such as trucks, buses, etc. This tire 2 is a heavy-duty tire.

[0034] The direction indicated by the double-headed arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis (not shown) of the tire 2. The direction indicated by the double-headed arrow CD is the circumferential direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the radial direction of the tire 2. The dashed dotted line EL extending in the circumferential direction represents the equatorial plane of the tire 2. The direction indicated by arrow AD1 is the first axial direction side of the tire 2, and the direction indicated by arrow AD2 is the second axial direction side of the tire 2. The direction toward the equatorial plane in the axial direction is the axially inner side, and the direction toward the edge of the tread surface described later is the axially outer side. The direction indicated by the arrow CD1 is the first circumferential direction side of the tire 2, and the direction indicated by the arrow CD2 is the second circumferential direction side of the tire 2.

[0035] Fig. 3 shows a part of a cross section of the tire 2 taken along line III-III in Fig. 1. Line III-III in Fig. 1 is included in a plane including the rotation axis (not shown) of the tire 2. The cross section shown in Fig. 3 is also called a meridian cross section.

[0036] The tire 2 is mounted on a rim R. The inside of the tire 2 is filled with air, for example, and the internal pressure is adjusted. Although not described in detail, the rim R is a regular rim.

[0037] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of chafers 8 , a pair of beads 10 , a carcass 12 , a reinforcing layer 14 , a pair of cushion layers 16 , and an inner liner 18 .

[0038] The tread 4 is located radially outward of the carcass 12. The tread 4 comes into contact with the road surface at its outer peripheral surface 20. The outer peripheral surface 20 of the tread 4 comes into contact with the road surface. The inner peripheral surface 22 of the tread 4 comes into contact with the reinforcing layer 14. The tread 4 has the outer peripheral surface 20 that comes into contact with the road surface and the inner peripheral surface 22 that comes into contact with the reinforcing layer 14.

[0039] The portion of the outer peripheral surface 20 that comes into contact with the road surface is also called a tread surface 24 . The position indicated by the symbol Eq is the equator of this tire 2. The equator Eq is the intersection of the tread surface 24 and the equatorial plane. When a groove, which will be described later, is located on the equatorial plane, the equator is identified based on a virtual tread surface obtained by assuming that there are no grooves on the equatorial plane. The position indicated by the symbol TE is the edge of the tread surface 24 . In the present invention, the position on the outer surface of the tire corresponding to the axially 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 contacting the tire with a flat surface is represented as the edge of the tread surface. In the tire 2, an edge TE of the tread surface 24 coincides with an edge 20e of the outer circumferential surface 20.

[0040] 1, one end TE of the tread surface 24 located on the left side of the equatorial plane is called a first end TE1, and the other end TE located on the right side of the equatorial plane is called a second end TE2.

[0041] 1 is the width of the tread surface 24. The width TW of the tread surface 24 is the axial distance from a first end TE1 to a second end TE2 of the tread surface 24. The width TW of the tread surface 24 is represented by the length measured along the tread surface 24.

[0042] Each sidewall 6 is continuous with an edge of the tread 4. The sidewalls 6 are located axially outward of the carcass 12. The sidewalls 6 are made of conductive crosslinked rubber. The sidewalls 6 may also be made of non-conductive crosslinked rubber.

[0043] Each chafer 8 is located radially inward of the sidewall 6. The chafers 8 contact the rim R. The chafers 8 are made of conductive crosslinked rubber.

[0044] Each bead 10 is located axially inside the chafer 8. The beads 10 are located radially inside the sidewall 6. Each bead 10 includes a core 26 and an apex 28. Although not shown, the core 26 includes a steel wire wound circumferentially. The apex 28 is located radially outside the core 26. The apex 28 is tapered. The apex 28 is made of hard cross-linked rubber. The beads 10 are electrically conductive.

[0045] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of chafers 8. The carcass 12 bridges between the pair of beads 10. The carcass 12 includes at least one carcass ply 30. The carcass 12 of the tire 2 is made up of one carcass ply 30. The carcass ply 30 is turned up from the axially inner side to the axially outer side at each bead 10. The end of the turned up carcass ply 30 is located radially inward of the outer end of the chafer 8. Although not shown, the carcass ply 30 includes a large number of parallel carcass cords. These carcass cords are covered with topping rubber and intersect with the equator plane. The carcass 12 has a radial structure. The carcass cords are steel cords. The topping rubber is a conductive crosslinked rubber. The carcass ply 30, i.e., the carcass 12, is conductive.

[0046] The reinforcing layer 14 is located radially outside the carcass 12. The reinforcing layer 14 is located radially between the tread 4 and the carcass 12. The reinforcing layer 14 of the tire 2 is laminated on the carcass 12. The reinforcing layer 14 is covered with the tread 4.

[0047] The reinforcing layer 14 includes a belt 32. The reinforcing layer 14 of the tire 2 is the belt 32. The belt 32 includes a plurality of belt plies 34 arranged in the radial direction. The belt 32 of the tire 2 is configured with four belt plies 34. The four belt plies 34 are a first belt ply 34A, a second belt ply 34B, a third belt ply 34C, and a fourth belt ply 34D. The first belt ply 34A is located at the innermost side in the radial direction. The second belt ply 34B has the widest width, and the fourth belt ply 34D, located at the outermost side in the radial direction, has the narrowest width.

[0048] Although not shown, each belt ply 34 includes a number of parallel belt cords. These belt cords are covered with topping rubber and are inclined with respect to the equatorial plane. The belt cords are steel cords. The topping rubber is a conductive cross-linked rubber. The belt ply 34, i.e., the belt 32, is conductive.

[0049] The reinforcing layer 14 may further include a band including a spirally wound band cord. In this case, the band cord included in the band extends substantially in the circumferential direction.

[0050] Each cushion layer 16 is located at an end of the reinforcing layer 14 (specifically, the belt described later) between the reinforcing layer 14 and the carcass 12. The cushion layer 16 is made of a soft crosslinked rubber. The cushion layer 16 is electrically conductive.

[0051] The inner liner 18 is positioned inside the carcass 12. The inner liner 18 forms the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber that has excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0052] The tread 4 of the tire 2 includes a cap portion 36 and a base portion 38 . The cap portion 36 includes the outer peripheral surface 20 of the tread 4. The cap portion 36 is made of cross-linked rubber that takes into consideration wear resistance and grip performance. This cap portion 36 may be made of cross-linked rubber that takes into consideration not only wear resistance and grip performance but also low heat buildup. In this case, the cap portion 36 may be made of non-conductive rubber. The base portion 38 is located radially inward of the cap portion 36. The base portion 38 is entirely covered by the cap portion 36. The base portion 38 is made of cross-linked rubber that is designed to have low heat generation properties. The base portion 38 may also be made of non-conductive rubber. The portion consisting of the cap portion 36 and the base portion 38 is the main body 40 of the tread 4. The tread 4 further includes a conductive portion 42 that penetrates the main body 40. The conductive portion 42 is made of conductive cross-linked rubber.

[0053] The conductive portion 42 connects between the outer peripheral surface 20 and the inner peripheral surface 22 of the tread 4. An outer end surface 42s of the conductive portion 42 forms part of the outer peripheral surface 20 of the tread 4. In other words, the outer end surface 42s is included in the outer peripheral surface 20. The outer end surface 42s contacts the road surface. An inner end surface 42u of the conductive portion 42 forms part of the inner peripheral surface 22 of the tread 4. In other words, the inner end surface 42u is included in the inner peripheral surface 22. The inner end surface 42u contacts the reinforcing layer 14.

[0054] The conductive portion 42 of the tire 2 extends continuously in the circumferential direction. Although not shown, the conductive portion 42 may be configured by arranging a plurality of conductive elements at predetermined intervals in the circumferential direction. In this case, the conductive portion 42 extends discontinuously in the circumferential direction.

[0055] As shown in Fig. 1, grooves 44 are formed in the tread 4 of the tire 2. The grooves 44 form a tread pattern. The tread pattern of the present invention will be described using the tread pattern shown in Fig. 1 as an example.

[0056] Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 1. Fig. 4 shows a cross-section of a groove 44, more specifically, a shoulder circumferential groove, which will be described later. The main configuration of the groove 44 will be described based on Fig. 4. In the present invention, the cross section of the groove 44 is expressed as a cross section along a plane perpendicular to the longitudinal direction of the groove 44 .

[0057] The groove 44 has a pair of groove walls 44W that bridge between the groove mouth 44M and the groove bottom 44T. The pair of groove walls 44W, the first groove wall 44W and the second groove wall 44W, face each other. The groove width of the groove 44 is represented by the distance between the opposing first groove wall 44W and second groove wall 44W, i.e., the groove wall distance. 4, the length indicated by the double-headed arrow WG is the groove width of the groove 44 at the groove opening 44M. The groove width WG is expressed as the shortest distance between a pair of edges 44E that form the groove opening 44M. If the groove opening 44M of the groove 44 is tapered, the groove width at the groove opening 44M of the groove 44 is expressed based on a virtual edge obtained by assuming that the groove opening 44M is not tapered. The length indicated by the double-headed arrow DG is the depth of the groove 44. The depth DG of the groove 44 is expressed as the shortest distance from the line segment connecting the left and right edges 44E to the groove bottom 44T of the groove 44. The position, groove width WG, and groove depth DG of the groove 44 are determined appropriately according to the specifications of the tire 2.

[0058] The groove bottom 44T is the deepest position in the cross section of the groove 44. The distance from the line segment connecting the left and right edges 44E that make up the groove opening 44M to the groove 44 is measured along the normal to this line segment. The position where the distance from this line segment to the groove 44 is greatest is the groove bottom 44T. Of the groove 44, the portion including the groove bottom 44T is also referred to as a bottom surface 44B. In this case, the portion between the bottom surface 44B and the edge 44E is also referred to as a wall surface. 4 is a curved surface. The bottom surface 44B may be a flat surface. In this case, the width center of the flat surface that constitutes the bottom surface 44B is used as the groove bottom 44T.

[0059] A groove 44 having a groove width WG of less than 1.0 mm at the groove mouth 44M is called a sipe. A groove 44 other than a sipe is also called a normal groove, and has a groove width WG of 1.0 mm or more at the groove mouth 44M. The sipe may include a portion having a groove width of 1.0 mm or more between the groove mouth 44M and the groove bottom 44T (hereinafter referred to as a portion equivalent to a normal groove). In this case, as the tread 4 wears and the portion equivalent to a normal groove becomes exposed, the sipe changes into a normal groove. The normal groove may include a portion (a portion corresponding to a sipe) having a groove width of less than 1.0 mm between the groove mouth 44M and the groove bottom 44T. In this case, the normal groove changes into a sipe when the tread 4 wears and the portion corresponding to the sipe becomes exposed. Even among normal grooves, normal grooves that have a narrow groove width and allow a pair of groove walls 44W to come into contact with each other when the tread 4 comes into contact with the road surface and deforms are also called narrow grooves. Narrow grooves have a pair of groove walls 44W that come into contact with each other when the tread 4 comes into contact with the road surface and deforms. In contrast, normal grooves that have a wide groove width and do not allow a pair of groove walls 44W to come into contact with each other even when the tread 4 comes into contact with the road surface and deforms are also called wide grooves. Wide grooves have a pair of groove walls 44W that do not come into contact with each other even when the tread 4 comes into contact with the road surface and deforms.

[0060] The length indicated by the double-headed arrow DGC in Fig. 4 is the groove depth of the circumferential groove, which will be described later. The groove depth DGC of the circumferential groove is, for example, 10 mm or more and 21 mm or less. From the viewpoint of enabling the tire 2 to exhibit good wet performance, the groove depth DGC is preferably 13 mm or more and 18 mm or less.

[0061] As shown in Fig. 1, the tread 4 of this tire 2 has circumferential grooves 46 that extend continuously in the circumferential direction. The tread 4 has a plurality of circumferential grooves 46 formed therein, and a plurality of land portions 48 aligned in the axial direction are defined. In other words, the tread 4 has a plurality of circumferential grooves 46. The plurality of circumferential grooves 46 define a plurality of land portions 48 in the tread 4.

[0062] In the present invention, of the multiple circumferential grooves cut in the tread, the circumferential groove located at the outermost position in the axial direction is a shoulder circumferential groove. A circumferential groove located on the equatorial plane is a center circumferential groove. When no circumferential groove is provided on the equatorial plane, the circumferential groove closest to the equatorial plane is the center circumferential groove. When a circumferential groove is located between the center circumferential groove and the shoulder circumferential groove, the circumferential groove located between the center circumferential groove and the shoulder circumferential groove is called a middle circumferential groove.

[0063] The tread 4 shown in Fig. 1 has four circumferential grooves 46 aligned in the axial direction. Of the four circumferential grooves 46, the circumferential groove 50 located on the outermost side in the axial direction is the shoulder circumferential groove. The circumferential groove 52 closest to the equatorial plane is the center circumferential groove. This tread 4 has a pair of center circumferential grooves 52 and a pair of shoulder circumferential grooves 50 located axially outward of the center circumferential grooves 52. 1, the length indicated by the double-headed arrow WGCc is the groove width at the groove opening 52M of the center circumferential groove 52. The length indicated by the double-headed arrow WGCs is the groove width at the groove opening 50M of the shoulder circumferential groove 50.

[0064] The ratio (WGCc / TW) of the groove width WGCc of the central circumferential groove 52 to the width TW of the tread surface 24 is 2.0% or less. 1, the groove width WGCs of the shoulder circumferential groove 50 is wider than the groove width WGCc of the center circumferential groove 52. The ratio (WGCs / TW) of the groove width WGCs of the shoulder circumferential groove 50 to the width TW of the tread surface 24 exceeds 2.0%. Specifically, the ratio (WGCs / TW) is preferably 4.0% or more and 10% or less.

[0065] As shown in FIG. 1 , the shoulder circumferential groove 50 of the tire 2 includes an outer vertex 50s close to the edge TE of the tread surface 24 and an inner vertex 50u close to the equatorial plane. The outer vertices 50s and the inner vertices 50u are arranged alternately in the circumferential direction. The shoulder circumferential groove 50 extends circumferentially, alternately passing through the outer vertices 50s and the inner vertices 50u. The shoulder circumferential groove 50 extends in a zigzag manner in the circumferential direction. The shoulder circumferential groove 50 may also extend straight in the circumferential direction.

[0066] The shoulder circumferential groove 50 has a wide groove width. A pair of groove walls 50W of the shoulder circumferential groove 50 do not come into contact with each other even when the tread 4 comes into contact with the road surface and deforms. The shoulder circumferential groove 50 is a wide groove that extends continuously in the circumferential direction, i.e., a wide circumferential groove 56.

[0067] In the present invention, the land portion located at the outermost position in the axial direction among the multiple land portions configured in the tread is called a shoulder land portion. A land portion located on the equatorial plane is called a center land portion. If no land portion is provided on the equatorial plane, the land portion closest to the equatorial plane is called a center land portion. If a land portion is located between a center land portion and a shoulder land portion, this land portion between the center land portion and the shoulder land portion is called a middle land portion.

[0068] The tread 4 shown in FIG. 1 has five land portions 48 aligned in the axial direction. Of the five land portions 48, the land portion 58 located at the outermost position in the axial direction is the shoulder land portion. The land portion 60 located on the equatorial plane is the center land portion. The land portion 62 located between the center land portion 60 and the shoulder land portions 58 is the middle land portion. This tread 4 includes the center land portion 60, a pair of middle land portions 62 located axially outward of the center land portion 60, and a pair of shoulder land portions 58 located axially outward of the middle land portions 62. Although not described in detail, the width of each land portion 48 is determined appropriately according to the specifications of the tire 2.

[0069] In the present invention, among the plurality of land portions formed in the tread, the land portion between adjacent circumferential grooves is a main land portion.

[0070] As shown in Figure 2, the center land portion 60 of the tire 2 is located between two center circumferential grooves 52. The middle land portion 62 is located between the center circumferential groove 52 and the shoulder circumferential groove 50. The center land portion 60 and the middle land portion 62 are each a land portion 48 between adjacent circumferential grooves 46, i.e., a main land portion 64. The five land portions 48 formed in the tread 4 include three main land portions 64 located between adjacent circumferential grooves 46. The tread 4 of this tire 2 is configured with a plurality of land portions 48 aligned in the axial direction, and the plurality of land portions 48 includes a plurality of main land portions 64 positioned between adjacent circumferential grooves 46.

[0071] In the present invention, among the plurality of main land portions, the main land portion located on the outermost side in the axial direction is an outer main land portion, and the main land portion located between two outer main land portions is an inner main land portion.

[0072] As described above, the center land portion 60 and the middle land portion 62 are main land portions 64. Of these main land portions 64, the center land portion 60 and the middle land portion 62, the main land portion 64 located axially outermost is the middle land portion 62. The middle land portion 62 is an outer main land portion 64s. The center land portion 60 is located between the two middle land portions 62, which are outer main land portions 64s. The center land portion 60 is an inner main land portion 64u.

[0073] The tread 4 of this tire 2 has three main land portions 64. The three main land portions 64 include an inner main land portion 64u and a pair of outer main land portions 64s located axially outward of the inner main land portion 64u. The inner main land portion 64u is the main land portion 64 located at the center of the three main land portions 64 lined up in the axial direction. In particular, the inner main land portion 64u of this tire 2 is located on the equatorial plane.

[0074] The shoulder land portion 58 is located axially outward of the shoulder circumferential groove 50 that is located axially outermost among the multiple circumferential grooves 46 that the tread 4 has. This shoulder land portion 58 includes the edge TE of the tread surface 24. The shoulder land portion 58 is not a land portion 48 that is located between adjacent circumferential grooves 46. The shoulder land portion 58 is not a main land portion 64. The plurality of land portions 48 formed in the tread 4 of this tire 2 include two shoulder land portions 58 located at the outermost sides in the axial direction, and a plurality of main land portions 64 located between the two shoulder land portions 58.

[0075] In the present invention, the circumferential grooves located between adjacent main land portions are circumferential narrow grooves.

[0076] The center circumferential groove 52 is located between the center land portion 60 and the middle land portion 62. As described above, the center land portion 60 and the middle land portion 62 are the main land portions 64. The center circumferential groove 52 is located between the adjacent main land portions 64. The center circumferential groove 52 is a circumferential narrow groove 54. The circumferential narrow groove 54 of this tire 2 is located between the outer main land portion 64s and the inner main land portion 64u.

[0077] Fig. 5 is a cross-sectional view taken along line VV in Fig. 2. Fig. 5 shows a cross-section of the center circumferential groove 52, that is, the circumferential narrow groove 54.

[0078] The circumferential narrow groove 54 includes a body portion 66 and an expanded width portion 68. The body portion 66 includes a groove mouth 54M of the circumferential narrow groove 54. The expanded width portion 68 is located radially inward of the body portion 66. The expanded width portion 68 includes a groove bottom 54T of the circumferential narrow groove 54.

[0079] The body portion 66 includes a tapered portion 70 and a body portion main body 72. The groove opening 54M of the circumferential narrow groove 54 is machined to have a tapered shape.

[0080] The tapered portion 70 includes the groove opening 54M of the circumferential narrow groove 54. The tapered portion 70 tapers inward from the groove opening 54M. The contour of the groove wall of the tapered portion 70 shown in Fig. 5 is represented by a straight line. This contour may also be represented by a curved line. 5, the length indicated by the double-headed arrow WA is the groove width at the groove opening 54M of the tapered portion 70. The groove width WA of the tapered portion 70 is preferably 0.15 to 0.45 times the groove width WGCs of the shoulder circumferential groove 50, in other words, the circumferential wide groove 56.

[0081] The barrel body 72 is located radially inside the tapered portion 70. The barrel body 72 is continuous with the tapered portion 70. The barrel body 72 extends straight in the depth direction of the circumferential narrow groove 54. In the cross section shown in FIG. 5, the contour of the groove wall of the barrel body 72 is represented by a straight line. The length indicated by the double-headed arrow W1 in FIG. 5 is the minimum width of the barrel body 72. The barrel body 72 has a uniform groove width W1 in the depth direction of the circumferential narrow groove 54.

[0082] As described above, when the groove opening 44M of the groove 44 is tapered, the groove width at the groove opening 44M of the groove 44 is expressed based on the virtual edge obtained assuming that the groove is not tapered. The groove width at the groove opening 54M of the circumferential narrow groove 54 is expressed as the groove width W1 of the trunk main body 72. Tapered section 70 is wider than barrel body 72. The minimum width W1 of barrel body 72 is the minimum width of barrel 66. Barrel 66 has minimum width W1.

[0083] The position indicated by the symbol PU in Figure 5 is the boundary between the tapered portion 70 and the barrel body 72. The boundary PU is represented by the intersection of the groove wall contour line of the tapered portion 70 and the groove wall contour line of the barrel body 72. As shown in Figure 5, when the boundary between the tapered portion 70 and the barrel body 72 is rounded, the boundary PU is represented by the intersection of the extension of the groove wall contour line of the tapered portion 70 and the extension of the groove wall contour line of the barrel body 72.

[0084] The widened portion 68 is located radially inward of the body portion 66. The widened portion 68 is continuous with the body portion 66. The widened portion 68 has a groove width that is wider than the minimum width W1 of the body portion 66. 5, the length indicated by the double-headed arrow W2 is the maximum width of the widened portion 68. The position indicated by the symbol PN is the position where the widened portion 68 has the maximum width W2 (hereinafter referred to as the widened portion PN). The portion of the circumferential narrow groove 54 excluding the body portion 66, i.e., the widened portion 68 of the circumferential narrow groove 54, tapers outward from the widened portion PN and tapers inward from the widened portion PN.

[0085] The widened portion 68 includes an inflection portion 74 and a bottom portion 76. The inflection portion 74 is located radially inward of the barrel main body 72. The bottom portion 76 is located radially inward of the inflection portion 74.

[0086] The inflection portion 74 connects the trunk main body 72 and the bottom portion 76. The groove width of the inflection portion 74 gradually increases from the trunk main body 72 side toward the bottom portion 76 side. The inflection portion 74 curves so as to recess inward from its outer side. In this tire 2, the outline of the inflection portion 74 is represented by an arc. In FIG. 5, arrow Rc indicates the radius of the arc representing the outline of the inflection portion 74.

[0087] The bottom portion 76 includes the groove bottom 54T. The bottom portion 76 has a rounded contour. The bottom portion 76 is curved so as to bulge outward from its inner side. The contour of the bottom portion 76 of the circumferential narrow groove 54 shown in FIG. 5 is represented by a circular arc. In FIG. 5, an arrow Rt indicates the radius of the circular arc representing the contour of the bottom portion 76. The radius Rt of this circular arc is, for example, not less than 1.5 mm and not more than 3.5 mm.

[0088] The position indicated by the symbol PR is the boundary between the inflection portion 74 and the bottom portion 76. The arc representing the contour of the inflection portion 74 and the arc representing the contour of the bottom portion 76 are in contact at the boundary PR. 5, the maximum width position PN of the widened portion 68 is included in the bottom portion 76. In other words, the maximum width position PN is located radially inward of the boundary PR. The maximum width WN of the widened portion 68 is equal to twice the radius Rt of the arc that defines the outline of the bottom portion 76.

[0089] In the tire 2, the radius Rc of the arc that defines the outline of the inflection portion 74 is larger than the radius Rt of the arc that defines the outline of the bottom portion 76. This allows the circumferential narrow groove 54 to fully exhibit its function. From this viewpoint, it is preferable that the ratio Rc / Rt of the radius Rc of the arc that defines the outline of the inflection portion 74 to the radius Rt of the arc that defines the outline of the bottom portion 76 be 1.5 or greater and 20.0 or less.

[0090] The position indicated by the symbol PS in FIG. 5 is the boundary between the body portion 66 and the widened portion 68. In the present invention, the position where the groove wall contour line of the widened portion 68 converges to the groove wall contour line of the trunk main body 72 (in the circumferential narrow groove 54 shown in FIG. 5, this is the boundary between the straight line representing the contour of the trunk main body 72 and the arc representing the contour of the inflection portion 74) is the boundary PS between the trunk portion 66 and the widened portion 68. If the boundary PS cannot be identified based on differences in contour, the position showing a groove width that is 1.1 times the minimum width W1 in the groove width from the position where the trunk portion 66 shows the minimum width W1 to the maximum width position PN of the widened portion 68 is shown as the boundary PS between the trunk portion 66 and the widened portion 68.

[0091] The circumferential narrow groove 54 does not have to be provided with the tapered portion 70. In other words, the body portion 66 may be composed of only the body portion main body 72. In this case, the cross-sectional shape of the circumferential narrow groove 54 is adjusted so that the groove wall of the body portion main body 72 shown in Fig. 5 extends outward and the intersection of the extension line of this groove wall and the extension line of the tread surface 24 corresponds to the groove opening of the body portion main body 72, i.e., the groove opening 54M of the circumferential narrow groove 54. From the viewpoint of being able to effectively suppress the concentration of strain on the edges of the main land portion 64 while ensuring the groove volume of the circumferential narrow groove 54, it is preferable that the circumferential narrow groove 54 be provided with a tapered portion 70 as shown in FIG. 5.

[0092] 5, the length indicated by the double-headed arrow HM is the groove depth of the circumferential narrow groove 54. The length indicated by the double-headed arrow HH is the groove depth of the trunk portion 66. The length indicated by the double-headed arrow HT is the groove depth of the tapered portion 70.

[0093] The groove depth HM of the circumferential narrow groove 54 of this tire 2 is approximately the same as the groove depth DGCs of the shoulder circumferential groove 50, i.e., the circumferential wide groove 56. Specifically, the groove depth HM of the circumferential narrow groove 54 is 0.95 to 1.05 times the groove depth DGCs of the circumferential wide groove 56.

[0094] From the viewpoint that the tire 2 can effectively suppress the concentration of strain on the edge of the main land portion 64 while ensuring the groove volume of the circumferential narrow groove 54, it is preferable that the ratio (HT / HM) of the groove depth HT of the tapered portion 70 to the groove depth HM of the circumferential narrow groove 54 is 0.12 or more and 0.14 or less.

[0095] For example, as shown in FIG. 2 , each of the multiple main land portions 64 formed in the tread 4 has multiple transverse sipes 78. The multiple transverse sipes 78 are aligned in the circumferential direction. Each of the transverse sipes 78 crosses the main land portion 64. The transverse sipes 78 connect two circumferential grooves 46.

[0096] Figure 6 is a cross-sectional view taken along line VI-VI in Figure 2. Figure 6 shows a cross-section of the transverse sipe 78. Figure 6 shows a cross-section of the transverse sipe 78 taken along a plane perpendicular to the longitudinal direction of the transverse sipe 78.

[0097] 6 shows a cross section of a transverse sipe 78 provided in the center land portion 60, in other words, the inner main land portion 64u. In this tire 2, the transverse sipe 78 is also provided in the middle land portion 62, in other words, the outer main land portion 64s. The cross-sectional shape of the transverse sipe 78 in the outer main land portion 64s is the same as that of the transverse sipe 78 in the inner main land portion 64u. A description of the cross-sectional shape of the transverse sipe 78 in the outer main land portion 64s will be omitted.

[0098] The transverse sipe 78 has a sipe body 80 and a tubular portion 82. The sipe body 80 includes the groove mouth 78M of the transverse sipe 78. The tubular portion 82 includes the groove bottom 78T of the transverse sipe 78.

[0099] As shown in FIG. 2, the sipe body 80 extends in a zigzag pattern in the length direction of the transverse sipe 78. As shown in FIG. 6, the sipe body 80 extends in a zigzag pattern in the depth direction of the transverse sipe 78. This sipe body 80 is a three-dimensional sipe. Although not shown, the sipe body 80 may be a two-dimensional sipe that spreads like a flat plate. In this case, the sipe body 80 extends straight in the length direction and straight in the depth direction.

[0100] The tubular portion 82 is located radially inward of the sipe body 80. The tubular portion 82 extends in the length direction of the transverse sipe 78.

[0101] 6, a solid line LM is the boundary line between the sipe body 80 and the tubular portion 82. The length indicated by the double-headed arrow WM is the groove width of the transverse sipe 78 measured along this boundary line LM. The boundary line LM is set at a position where the groove width WM is 1.0 mm. The transverse sipe 78 has a groove width W3 at its groove mouth 78M that is less than 1.0 mm. The portion outside the boundary line LM, i.e., the sipe body 80, has a uniform groove width W3 in the depth direction of the transverse sipe 78. The groove width W3 of the sipe body 80 is less than 1.0 mm. The sipe body 80 is a sipe. The groove width of the inner portion of the boundary line LM, i.e., the tubular portion 82, is 1.0 mm or more. The groove width of the tubular portion 82 is wider than the groove width W3 of the sipe body 80.

[0102] The tubular portion 82 extends inward from the position of the boundary line LM. The length indicated by the double arrow W4 in FIG. 6 is the maximum width of the tubular portion 82. The position indicated by the symbol PT is the position where the tubular portion 82 exhibits the maximum width W4. The tubular portion 82 tapers outward from the portion exhibiting the maximum width W4. The tubular portion 82 tapers inward from the portion exhibiting the maximum width W4. The maximum width W4 of the tubular portion 82 is equal to or narrower than the maximum width W2 of the widened portion 68 of the circumferential narrow groove 54. The maximum width W4 is equal to or wider than the minimum width W1 of the body portion 66 of the circumferential narrow groove 54.

[0103] The cross-sectional shape of the tubular portion 82 may be circular or elliptical. This cross-sectional shape may be a shape in which the portion showing the maximum width W4 is represented by a straight line, and the sipe main body 80 side and the groove bottom 78T side of this straight line are represented by arcs (hereinafter, this shape is also referred to as a track shape).

[0104] 6, the length indicated by the double arrow DA is the groove depth of the transverse sipe 78. The length indicated by the double arrow DC is the groove depth of the sipe main body 80. In the tire 2, the groove depth DA of the transverse sipes 78 is the same as the groove depth DGC of the circumferential grooves 46, more specifically, the groove depth DGCs of the wide circumferential grooves 56, or the transverse sipes 78 are shallower than the wide circumferential grooves 56. Specifically, the groove depth DA of the transverse sipes 78 is 0.80 to 1.00 times the groove depth DGCs of the wide circumferential grooves 56. As described above, the groove depth HM of the circumferential narrow groove 54 is approximately the same as the groove depth DGCs of the circumferential wide groove 56. The groove depth DA of the transverse sipe 78 is the same as the groove depth HM of the circumferential narrow groove 54, or the transverse sipe 78 is shallower than the circumferential narrow groove 54.

[0105] In the tire 2, the center land portion 60 has the aforementioned conductive portion 42. The conductive portion 42 may be provided in the middle land portion 62. The conductive portion 42 may be provided in each of the center land portion 60 and the middle land portion 62. As described above, the center land portion 60 and the middle land portion 62 are main land portions 64. In the tire 2, any one of the main land portions 64 formed in the tread 4 includes the conductive portion .

[0106] As shown in FIG. 3, the rim R contacts the chafer 8. The chafer 8 contacts the carcass 12. The carcass 12 contacts the belt 32. The belt 32 contacts the conductive portion 42. The conductive portion 42 contacts the road surface. As described above, the chafer 8, carcass 12, belt 32, and conductive portion 42 are conductive. The chafer 8, carcass 12, belt 32, and conductive portion 42 form a conductive path connecting the rim R and the road surface. Static electricity generated in the vehicle and tire 2 flows from the rim R to the road surface through this conductive path. This tire 2 can suppress the accumulation of static electricity.

[0107] The conductive path that is the subject of the present invention is not limited to the conductive path shown in Fig. 3, as long as it passes through the conductive portion 42 formed in the tread 4. The conductive path shown in Fig. 3 is one example of the conductive path that is the subject of the present invention.

[0108] As mentioned above, the conductive portion 42 is made of conductive cross-linked rubber. When the tire 2 runs, the conductive portion 42 generates heat. Although not described in detail, the tread 4 of this tire 2 is thicker than that of tires for passenger cars. Heat tends to accumulate in this tread 4. When the conductive portion 42 generates heat, the ambient temperature of the conductive portion increases, and depending on the degree of this increase, there is a concern that durability may decrease.

[0109] However, the conductive portion 42 of this tire 2 is provided in the main land portion 64. As described above, the circumferential narrow groove 54 is provided between adjacent main land portions 64. The circumferential narrow groove 54 is located next to the main land portion 64 on which the conductive portion 42 is provided. The circumferential narrow groove 54 is provided around the conductive portion 42. The circumferential narrow groove 54 has a widened portion 68 on the radially inner side of the body portion 66. As described above, the maximum width W2 of the widened portion 68 is wider than the minimum width W1 of the body portion 66. The widened portion 68 contributes to increasing the surface area of ​​the circumferential narrow groove 54. The surface area of ​​this circumferential narrow groove 54 is larger than that of a circumferential narrow groove formed only in the body portion 66. This circumferential narrow groove 54 can promote the dissipation of heat generated in the conductive portion 42. An increase in temperature around the conductive portion 42 due to heat generation in the conductive portion 42 is suppressed. The tire 2 can suppress a decrease in durability caused by providing the conductive portion 42 in the tread 4.

[0110] As described above, the circumferential narrow groove 54 of the tire 2 has a trunk portion 66 with a minimum width W1. When the tread surface 24 comes into contact with the road surface, the tread 4 deforms. In the tire 2, the minimum width W1 is adjusted so that the opposing groove walls 54W of the circumferential narrow groove 54 come into contact with each other in the trunk portion 66 due to the deformation of the tread 4. In other words, when the tread 4 comes into contact with the road surface and deforms, the pair of groove walls 54W of the circumferential narrow groove 54 come into contact with each other in the trunk portion 66. As a result, the two main land portions 64 located on both sides of the circumferential narrow groove 54 support each other, suppressing deformation of the tread 4. The tread 4 has higher rigidity than a conventional tread that does not have a circumferential narrow groove 54. The circumferential narrow groove 54 can contribute to increasing the rigidity of the tread 4. The tire 2 can reduce rolling resistance.

[0111] As described above, each of the main land portions 64 formed in the tread 4 has a plurality of transverse sipes 78. In the tire 2, not only the circumferential narrow grooves 54 but also the transverse sipes 78 are provided around the conductive portion 42.

[0112] In the transverse sipe 78, the maximum width W4 of the tubular portion 82 is wider than the groove width W3 of the sipe body 80. The tubular portion 82 contributes to increasing the surface area of ​​the transverse sipe 78. The surface area of ​​this transverse sipe 78 is larger than that of a transverse sipe formed only by the sipe body 80. The tubular portion 82 can contribute to the dissipation of heat generated in the conductive portion 42. In the sipe body 80, the groove walls come into contact with each other and support each other. The sipe body 80 can contribute to suppressing deformation of the main land portion 64. In this tire 2, by using the transverse sipes 78 in addition to the circumferential narrow grooves 54 described above, heat generated in the conductive portions 42 is effectively dissipated, and deformation of the tread 4 is effectively suppressed. The tire 2 can suppress a decrease in durability due to heat generation in the conductive portion 42 without increasing the rolling resistance. In this tire 2, even if a low heat buildup rubber containing a large amount of silica is used in the tread 4 to reduce rolling resistance, the conductive portion 42 can fully demonstrate its function. This tire 2 can suppress the accumulation of static electricity. Furthermore, by using a low heat buildup rubber in the tread 4, this tire 2 can further reduce rolling resistance. The tire 2 can suppress the accumulation of static electricity and achieve a reduction in rolling resistance.

[0113] As described above, the widened portion 68 has a groove width wider than the minimum width W1 of the body portion 66. The maximum width W2 of the widened portion 68 is wider than the minimum width W1 of the body portion 66. The portion of the circumferential narrow groove 54 other than the tapered portion 70 has the minimum width W1 in the body portion 66 and the maximum width W2 in the widened portion 68. From the viewpoint that the widened portion 68 can effectively contribute to the dissipation of heat generated in the conductive portion 42, the maximum width W2 of the widened portion 68 is preferably at least two times, and more preferably at least three times, the minimum width W1 of the body portion 66. From the viewpoint that the influence of the widened portion 68 on the rigidity of the tread 4 can be suppressed and the tire 2 can maintain good resistance to uneven wear, the maximum width W2 of the widened portion 68 is preferably no more than eight times, and more preferably no more than seven times, the minimum width WD of the body portion 66.

[0114] The ratio (HH / HM) of the groove depth HH of the body portion 66 to the groove depth HM of the circumferential narrow groove 54 is preferably 0.30 or more and 0.70 or less. By setting the ratio (HH / HM) to be equal to or greater than 0.30, the tire 2 can suppress the effect of the widened portion 68 on the rigidity of the tread 4 and reduce the rolling resistance. From this viewpoint, the ratio (HH / HM) is more preferably equal to or greater than 0.35. By setting the ratio (HH / HM) to be equal to or less than 0.70, the widened portion 68 can effectively contribute to dissipating heat generated in the conductive portion 42. From this viewpoint, it is more preferable that the ratio (HH / HM) be equal to or less than 0.65.

[0115] The length indicated by the double-headed arrow HN in FIG. 5 is the groove depth from the groove opening 54M of the circumferential narrow groove 54 to the maximum width position PN. From the viewpoint that the widened portion 68 can effectively contribute to the dissipation of heat generated in the conductive portion 42, it is preferable that the ratio (HN / HM) of the groove depth HN from the groove opening 54M of the circumferential narrow groove 54 to the groove depth HM of the circumferential narrow groove 54 be 0.75 or more and 0.95 or less.

[0116] As described above, the maximum width W4 of the tubular portion 82 is wider than the groove width W3 of the sipe body 80. From the viewpoint of enabling the tubular portion 82 to effectively contribute to the dissipation of heat generated in the conductive portion 42, the ratio (W4 / W3) of the maximum width W4 of the tubular portion 82 to the groove width W3 of the sipe body 80 is preferably equal to or greater than 4, and more preferably equal to or greater than 5. From the viewpoint of suppressing the effect of the tubular portion 82 on the rigidity of the tread 4, this ratio (W4 / W3) is preferably equal to or less than 13, and more preferably equal to or less than 12.

[0117] The ratio (DC / DA) of the groove depth DC of the sipe body 80 of the transverse sipe 78 to the groove depth DA of the transverse sipe 78 is preferably 0.35 or greater and 0.80 or less. By setting the ratio (DC / DA) to be 0.35 or greater, the tire 2 can suppress the effect of the tubular portion 82 on the rigidity of the tread 4 and reduce rolling resistance. From this viewpoint, the ratio (DC / DA) is more preferably 0.40 or greater. By setting the ratio (DC / DA) to 0.80 or less, the tubular portion 82 can effectively contribute to dissipating heat generated in the conductive portion 42. From this viewpoint, it is more preferable that the ratio (DC / DA) be 0.75 or less.

[0118] As described above, the tubular portion 82 has a bottom surface that includes the groove bottom 78T of the transverse sipe 78. In the cross section shown in Figure 6, the contour of the bottom surface of the tubular portion 82 is represented by an arc that passes through the groove bottom 78T. Arrow Rb in Figure 6 indicates the radius of this arc.

[0119] The radius Rb of the arc that defines the contour of the bottom surface of the tubular portion 82 is preferably 1.5 mm or more and 3.5 mm or less. Setting the radius Rb to 1.5 mm or greater suppresses the occurrence of cracks at the groove bottom 78T. From this viewpoint, it is more preferable that the radius Rb be 2.0 mm or greater. Setting the radius Rb to 3.5 mm or less suppresses a decrease in rigidity of the main land portion 64 (specifically, the main block described later) caused by providing the tubular portion 82 in the transverse sipe 78. From this viewpoint, it is more preferable that the radius Rb be 3.0 mm or less.

[0120] 1, a plurality of lateral grooves 84 are cut into the land portions 48 formed in the tread 4, crossing the land portions 48. As a result, a plurality of blocks 86 arranged in the circumferential direction are formed in each land portion 48. The tread pattern of this tire 2 is a block pattern. Although not described in detail, the lateral grooves 84 have a groove width at their groove openings that is narrower than the groove width WGCs of the shoulder circumferential grooves 50. The groove width of the lateral grooves 84 at their groove openings is 0.50 to 0.80 times the groove width WGCs of the shoulder circumferential grooves 50. The lateral grooves 84 are shallower than the shoulder circumferential grooves 50. The groove depth of the lateral grooves 84 is 0.35 to 0.65 times the groove depth DGCs of the shoulder circumferential grooves 50.

[0121] The transverse sipes 78 are formed in blocks 86 by forming lateral grooves 84 in the main land portion 64. The main land portion 64 has a plurality of lateral grooves 84 aligned in the circumferential direction. The plurality of lateral grooves 84 form a plurality of blocks 86 in the main land portion 64. Each block 86 has a transverse sipe 78 that crosses the block 86. The tread 4 has a plurality of main land portions 64, and each main land portion 64 has a plurality of lateral grooves 84 connecting adjacent circumferential grooves 46. The plurality of lateral grooves 84 cut in the main land portion 64 constitute a plurality of blocks 86 arranged in the circumferential direction in the main land portion 64. Each of the plurality of blocks 86 has a transverse sipe 78 that crosses the block 86.

[0122] In this tire, a plurality of lateral grooves 84 are also formed in the shoulder land portion 58, and a plurality of blocks 86 are formed therein. To distinguish them from the lateral grooves 84 and blocks 86 of the shoulder land portion 58, the lateral grooves 84 formed in the main land portion 64 are also called main lateral grooves 88, and the blocks 86 formed in this main land portion 64 are also called main blocks 90. The blocks 86 formed in the inner main land portion 64u are also called inner main blocks 90u. The blocks 86 formed in the outer main land portion 64s are also called outer main blocks 90s.

[0123] Fig. 7 shows a part of the cross section of the tire 2 shown in Fig. 3. Fig. 7 shows a part of the tread portion, specifically, a portion where the conductive portion 42 is provided.

[0124] The length indicated by the double-headed arrow WD in Fig. 7 is the width of the conductive portion 42. The conductive portion 42 has a uniform width WD from its outer end surface 42s to its inner end surface 42u. The maximum width WX and minimum width WN of the conductive portion 42 shown in Fig. 7 are the same. The cross-sectional shape of the conductive portion 42 is not limited to the cross-sectional shape shown in FIG. The width WD of the conductive portion 42 may be configured so that the groove width WD gradually decreases from the outer end surface 42s toward the inner end surface 42u. In this case, the groove width WD of the conductive portion 42 has a maximum width WX at the outer end surface 42s and a minimum width WN at the inner end surface 42u. The width WD of the conductive portion 42 may be configured so that the groove width WD gradually increases from the outer end surface 42s toward the inner end surface 42u. In this case, the width WD of the conductive portion 42 has a minimum width WN at the outer end surface 42s and a maximum width WX at the inner end surface 42u. The cross-sectional shape of the conductive portion 42 may be configured so that the width WD of the conductive portion 42 has a maximum width WX at the center portion and gradually decreases from the center portion toward the outer end surface 42s or the inner end surface 42u. In this case, the groove width WD of the conductive portion 42 has a minimum width WN at the outer end surface 42s or the inner end surface 42u. The cross-sectional shape of the conductive portion 42 may be configured so that the width WD of the conductive portion 42 has a minimum width WN at the center and gradually increases from the center toward the outer end face 42s or the inner end face 42u. In this case, the groove width WD of the conductive portion 42 has a maximum width WX at the outer end face 42s or the inner end face 42u.

[0125] It is preferable that the maximum width W2 of the widened portion 68 is wider than the maximum width WX of the conductive portion 42. This allows the widened portion 68 to effectively contribute to the dissipation of heat generated in the conductive portion 42. Dissipation of heat generated in the conductive portion 42 is promoted. The tire 2 can effectively suppress a decrease in durability due to heat generation in the conductive portion 42. From this viewpoint, it is more preferable that the maximum width W2 of the widened portion 68 is 2.0 times or more the maximum width WX of the conductive portion 72. From the viewpoint of suppressing a decrease in rigidity due to the widened portion 68 and maintaining low rolling resistance, it is more preferable that the maximum width W2 of the widened portion 68 is 8.0 times or less the maximum width WX of the conductive portion 72.

[0126] It is preferable that the maximum width W4 of the tubular portion 82 is wider than the minimum width WN of the conductive portion 42. This allows the tubular portion 82 to effectively contribute to the dissipation of heat generated in the conductive portion 42. Dissipation of heat generated in the conductive portion 42 is promoted. The tire 2 can effectively suppress a decrease in durability due to heat generation in the conductive portion 42. From this viewpoint, it is more preferable that the maximum width W4 of the tubular portion 82 is 1.5 times or more the minimum width WN of the conductive portion 72. From the viewpoint of suppressing a decrease in rigidity due to the tubular portion 82 and maintaining low rolling resistance, it is more preferable that the maximum width W4 of the tubular portion 82 is 4.0 times or less the minimum width WN of the conductive portion 72.

[0127] The land ratio of this tire 2 is preferably 75% or more. This makes it easier for the main land portions 64 to support each other, effectively increasing the rigidity of the tread 4. The tire 2 can effectively reduce rolling resistance and also improve wear resistance. From this perspective, the land ratio is more preferably 80% or more. From the perspective that the circumferential narrow grooves 54 effectively promote heat dissipation and effectively suppress deterioration in durability due to heat generation in the conductive portion 42, the land ratio is preferably 90% or less.

[0128] The position indicated by the symbol PB in FIG. 7 represents the radial center of the conductive portion 42. As shown in FIG. 7, the groove bottom 54T of the circumferential narrow groove 54 is located radially inward of the radial center PB of the conductive portion 42. This allows the widened portion 68 of the circumferential narrow groove 54 to effectively contribute to the dissipation of heat generated in the conductive portion 42. Dissipation of heat generated in the conductive portion 42 is promoted. The tire 2 can effectively suppress a decrease in durability due to heat generation in the conductive portion 42. From this viewpoint, it is preferable that the groove bottom 54T of the circumferential narrow groove 54 is located radially inward of the radial center PB of the conductive portion 42. In this case, it is more preferable that the maximum width position PN of the widened portion 68 is located radially inward of the radial center PB of the conductive portion 42.

[0129] In the tire 2, the groove bottom 78T of the transverse sipe 78 is preferably located radially inward of the radial center PB of the conductive portion 42. This allows the tubular portion 82 of the transverse sipe 78 to effectively contribute to dissipation of heat generated in the conductive portion 42. Dissipation of heat generated in the conductive portion 42 is promoted. The tire 2 can effectively suppress a decrease in durability due to heat generation in the conductive portion 42. From this viewpoint, it is more preferable that the maximum width position PT of the tubular portion 82 is located radially inward of the radial center PB of the conductive portion 42.

[0130] As described above, the central land portion 60 has the conductive portion 42. In this tire 2, the central land portion 60 is the inner main land portion 64u. That is, the inner main land portion 64u has the conductive portion 42. Circumferential narrow grooves 54 are located on both sides of the inner main land portion 64u. When the tread 4 comes into contact with the road surface and deforms, deformation of the inner main land portion 64u is effectively suppressed. Moreover, the widened portions 68 of the circumferential narrow grooves 54 can effectively contribute to dissipating heat generated in the conductive portion 42. In this tire 2, a decrease in durability due to heat generation in the conductive portion 42 is effectively suppressed. Moreover, suppressing deformation of the inner main land portion 64u can also contribute to reducing rolling resistance. In this tire 2, rolling resistance can be reduced while suppressing a decrease in durability due to heat generation in the conductive portion 42. From this perspective, it is preferable that the main land portion 64 having the conductive portion 42 is the inner main land portion 64u.

[0131] The inner main land portion 64u having the conductive portion 42 of this tire 2 is the center land portion 60. As described above, the center land portion 60 is located on the equatorial plane. The dashed dotted line EL representing the equatorial plane is the axial center of the center land portion 60. As shown in FIG. 2 , the conductive portion 42 is not located on the equatorial plane, but is located between the equatorial plane and the circumferential narrow groove 54 on the second axial direction side, i.e., on the second end TE2 side of the tread surface 24. The conductive portion 42 is disposed in the inner main land portion 64u so as to be offset from the axial center of the inner main land portion 64u. This positions the conductive portion 42 close to the circumferential narrow groove 54 on the second end TE2 side of the tread surface 24. In the tire 2, heat generated in the conductive portion 42 is more effectively dissipated through the circumferential narrow groove 54. The tire 2 can more effectively suppress deterioration in durability due to heat generation in the conductive portion 42. From this viewpoint, when the main land portion 64 having the conductive portion 42 is the inner main land portion 64u, the conductive portion 42 is preferably disposed in the inner main land portion 64u so as to be offset from the axial center of the inner main land portion 64u. Furthermore, from the viewpoint of increasing the frequency with which the conductive portion 42 comes into contact with the road surface and effectively suppressing the accumulation of static electricity, it is more preferable that the axial center of the inner main land portion 64u having the conductive portion 42 coincides with the equatorial plane.

[0132] 5, the groove width of the circumferential narrow groove 54 gradually increases from the body portion 66 to the maximum width position PM of the widened portion 68. As shown in FIG. 6, in the transverse sipe 78, there is a large difference between the groove width of the sipe main body 80 and the groove width of the tubular portion 82. The change in rigidity when the exposed portion of the circumferential narrow groove 54 changes from the body portion 66 to the widened portion 68 is smaller than the change in rigidity when the exposed portion of the transverse sipe 78 changes from the sipe body 80 to the tubular portion 82. From the viewpoint of effectively suppressing a sudden change in rigidity due to wear, it is preferable that the groove depth HH of the body portion 66 is shallower than the groove depth DC of the sipe body 80. Specifically, the ratio (HH / DC) of the groove depth HH of the body portion 66 to the groove depth DC of the sipe body 80 is preferably 0.50 or greater and 0.95 or less, and more preferably 0.60 or greater and 0.90 or less.

[0133] The ratio (DC / HM) of the groove depth DC of the sipe body 80 of the transverse sipe 78 to the groove depth HM of the circumferential narrow groove 54 is preferably 0.60 or greater and 0.80 or less. This allows the tubular portion 82 of the transverse sipe 78 and the widened portion 68 of the circumferential narrow groove 54 to effectively contribute to dissipating heat generated in the conductive portion 42. In the tire 2, a decrease in durability due to heat generation in the conductive portion 42 is effectively suppressed. From this viewpoint, the ratio (DC / HM) is more preferably 0.65 or greater and 0.75 or less.

[0134] 2, the circumferential narrow groove 54 extends in a circumferential direction in a meandering manner rather than in a straight line. In particular, the circumferential narrow groove 54 of the tire 2 includes a first narrow groove 92 close to a first end TE1 of the tread surface 24, a second narrow groove 94 close to a second end TE2 of the tread surface 24, and a connecting narrow groove 96 connecting the first narrow groove 92 and the second narrow groove 94. Of the connecting narrow grooves 96, the connecting narrow groove 96 that connects the first narrow groove 92 located on the leading side and the second narrow groove 94 located on the trailing side is also called a first connecting narrow groove 96a. The connecting narrow groove 96 that connects the second narrow groove 94 located on the leading side and the first narrow groove 92 located on the trailing side is also called a second connecting narrow groove 96b. When a groove unit is formed by connecting the first narrow groove 92, the first connecting narrow groove 96a, the second narrow groove 94, and the second connecting narrow groove 96b in this order, the circumferential narrow groove 54 is formed by connecting a plurality of such groove units in the circumferential direction. The first narrow grooves 92 and the second narrow grooves 94 are arranged alternately in the circumferential direction.

[0135] When the tread surface 24 comes into contact with the road surface and the tread 4 deforms, the opposing groove walls 54W of the circumferential narrow grooves 54 come into contact with each other in the trunk body 72. The circumferential narrow grooves 54 extend in a serpentine manner in the circumferential direction, so the groove walls mesh effectively with each other. The main land portions 64 located on both sides of the circumferential narrow grooves 54 constrain each other. The rigidity of the main land portions 64 is apparently increased. Deformation of the main land portions 64 is effectively suppressed. This tire 2 can effectively reduce rolling resistance and also improve wear resistance. From this perspective, it is preferable that the circumferential narrow groove 54 includes a first narrow groove 92, a second narrow groove 94, and a connecting narrow groove 96 connecting the first narrow groove 92 and the second narrow groove 94, and that the first narrow grooves 92 and the second narrow grooves 94 be arranged alternately in the circumferential direction.

[0136] The tire 2 includes a pair of central circumferential grooves 52, that is, a first central circumferential groove 521 and a second central circumferential groove 522, disposed on either side of the equatorial plane. As described above, the central circumferential groove 52 of this tire 2 is the circumferential narrow groove 54. The first central circumferential groove 521 is a first circumferential narrow groove 541 , and the second central circumferential groove 522 is a second circumferential narrow groove 542 .

[0137] The first narrow groove 92 and the second narrow groove 94 of the circumferential narrow groove 54 extend in the circumferential direction. The first narrow groove 92 and the second narrow groove 94 have a constant length in the circumferential direction. The second narrow groove 94 of the second circumferential narrow groove 542 has the same length as the first narrow groove 92 of the first circumferential narrow groove, and the first narrow groove 92 of the second circumferential narrow groove 542 has the same length as the second narrow groove 94 of the first circumferential narrow groove 541. The first narrow groove 92 of the first circumferential narrow groove 541 and the second narrow groove 94 of the second circumferential narrow groove 542 are located on the end TE side of the tread surface 24, and the second narrow groove 94 of the first circumferential narrow groove 541 and the first narrow groove 92 of the second circumferential narrow groove 542 are located on the equatorial plane side. Hereinafter, for ease of explanation, the second narrow groove 94 of the first circumferential narrow groove 541 and the first narrow groove 92 of the second circumferential narrow groove 542 will be referred to as an inner narrow groove 98, and the first narrow groove 92 of the first circumferential narrow groove 541 and the second narrow groove 94 of the second circumferential narrow groove 542 will be referred to as an outer narrow groove 100. The first connecting narrow groove 96a of the first circumferential narrow groove 541 and the second connecting narrow groove 96b of the second circumferential narrow groove 542 are referred to as outer connecting narrow grooves 102. The outer connecting narrow groove 102 connects the outer narrow groove 100 on the leading side with the inner narrow groove 98 on the trailing side. The second connecting narrow groove 96b of the first circumferential narrow groove 541 and the first connecting narrow groove 96a of the second circumferential narrow groove 542 are referred to as inner connecting narrow grooves 104. The inner connecting narrow groove 104 connects the inner narrow groove 98 on the leading side with the outer narrow groove 100 on the trailing side.

[0138] The inner narrow groove 98 of the first circumferential narrow groove 541 (hereinafter referred to as the first inner narrow groove 981) is located further rearward than the inner narrow groove 98 of the second circumferential narrow groove 542 (hereinafter referred to as the second inner narrow groove 982), but the first inner narrow groove 981 and the second inner narrow groove 982 partially overlap with each other in the axial direction. The outer narrow groove 100 of the first circumferential narrow groove 541 (hereinafter referred to as the first outer narrow groove 1001) is located further rearward than the outer narrow groove 100 of the second circumferential narrow groove 542 (hereinafter referred to as the second outer narrow groove 1002), but the first outer narrow groove 1001 and the second outer narrow groove 1002 partially overlap with each other in the axial direction.

[0139] 1, the length indicated by the double arrow LS is the circumferential length of the inner narrow groove 98. The length indicated by the double arrow LL is the circumferential length of the outer narrow groove 100. In this tire 2, the outer narrow groove 100 is longer than the inner narrow groove 98. Specifically, the circumferential length LL of the outer narrow groove 100 is preferably 1.1 to 1.5 times the circumferential length LS of the inner narrow groove 98.

[0140] The first circumferential narrow groove 541 and the second circumferential narrow groove 542 approach each other where the first inner narrow groove 981 and the second inner narrow groove 982 face each other, and separate from each other where the first outer narrow groove 1001 and the second outer narrow groove 1002 face each other. The axial distance between the first circumferential narrow groove 541 and the second circumferential narrow groove 542 varies in the circumferential direction. This axial distance is short between the first inner narrow groove 981 and the second inner narrow groove 982 and is long between the first outer narrow groove 1001 and the second outer narrow groove 1002. The main lateral grooves 88 (hereinafter referred to as inner main lateral grooves 88u) formed in the inner main land portion 64u connect the first inner narrow groove 981 and the second inner narrow groove 982, which have a short axial distance between them. The inner main lateral grooves 88u are disposed in portions where adjacent circumferential narrow grooves 54 are close to each other. As described above, the first outer narrow groove 1001 is located further rearward than the second outer narrow groove 1002. The end of the inner main lateral groove 88u located on the first end TE1 side of the tread surface 24 is located further rearward than the end of the inner main lateral groove 88u located on the second end TE2 side. In other words, the inner main lateral groove 88u is inclined with respect to the axial direction.

[0141] The inner main block 90u formed between the first circumferential narrow groove 541 and the second circumferential narrow groove 542 is located circumferentially between the leading inner main lateral groove 88u and the trailing inner main lateral groove 88u, and is axially located between the first outer narrow groove 1001 and the second outer narrow groove 1002. Moreover, the outer narrow groove 100 is longer than the inner narrow groove 98, and the axial distance between the first outer narrow groove 1001 and the second outer narrow groove 1002 is longer than the axial distance between the first inner narrow groove 981 and the second inner narrow groove 982. An inner main block 90u formed between adjacent circumferential narrow grooves 54 is surrounded by two inner main lateral grooves 88u arranged in a portion where the adjacent circumferential narrow grooves 54 are close to each other, and two outer narrow grooves 100 as elements of the circumferential narrow grooves 54. This inner block 50u has an octagonal shape. The tire 2 can suppress an increase in ground pressure at the edges of the inner main block 90u. This allows the circumferential narrow grooves 54 to fully perform their functions. From this perspective, it is preferable that the inner main lateral groove 88u bridging the gap between adjacent circumferential narrow grooves 54 be arranged in a portion where the adjacent circumferential narrow grooves 54 are close to each other.

[0142] The inner vertices 50u of the shoulder circumferential grooves 50 serving as the wide circumferential grooves 56 include a first inner vertex 50uu that overlaps with the inner narrow groove 98 of the circumferential narrow groove 54 in the axial direction, and a second inner vertex 50us that overlaps with the outer narrow groove 100. The first inner vertices 50uu and the second inner vertices 50us are alternately arranged in the circumferential direction, with the outer vertex 50s sandwiched between them. The outer vertices 50s of the shoulder circumferential groove 50 include a first outer vertex 50sa that overlaps with a lateral groove 84 (hereinafter, shoulder lateral groove 84s) cut in the shoulder land portion 58, and a second outer vertex 50sb that overlaps with a block 86 (hereinafter, shoulder block 86s) formed in the shoulder land portion 58. The first outer vertices 50sa and the second outer vertices 50sb are arranged alternately in the circumferential direction, with the inner vertex 50u sandwiched between them. While the circumferential narrow groove 54 oscillates once, the shoulder circumferential groove 50, i.e., the circumferential wide groove 56 oscillates twice. When the tire 2 runs on a wet road surface, water easily flows through the circumferential wide groove 56. This circumferential wide groove 56 can contribute to improving wet performance.

[0143] The axial distance between the circumferential wide groove 56 and the circumferential narrow groove 54 varies in the circumferential direction. In the circumferential wide groove 56 on the first end TE1 side of the tread surface 24, this axial distance is short between the second inner apex 50us and the outer narrow groove 100 and long between the first outer apex 50sa and the inner narrow groove 98. In the circumferential wide groove 56 on the second end TE2 side of the tread surface 24, this axial distance is short between the second inner apex 50us and the outer narrow groove 100 and long between the second outer apex 50sb and the inner narrow groove 98. The main lateral grooves 88 (hereinafter referred to as outer main lateral grooves 88s) formed in the outer main land portion 64s connect the second inner apex 50us of the circumferential wide groove 56, which has a short axial distance, to the outer narrow groove 100. The outer main lateral groove 88s is disposed in a portion where the circumferential wide groove 56 and the circumferential narrow groove 54 are close to each other.

[0144] As shown in FIG. 2 , in the outer main land portion 64s, the outer main lateral grooves 88s are inclined with respect to the axial direction. The axially inner ends of the outer main lateral grooves 88s are located earlier than the axially outer ends. When the tire 2 travels, the axially inner ends of the outer main lateral grooves 88s contact the road surface earlier than the axially outer ends. The outer main lateral grooves 88s extend axially outward from their axially inner ends. When the tire 2 travels on a wet road surface, the outer main lateral grooves 88s can effectively drain water present between the tire 2 and the road surface from the contact patch. This tire 2 can improve wet performance. From this perspective, in the outer main land portion 64s, it is preferable that the outer main lateral grooves 88s are inclined with respect to the axial direction, and that the axially inner ends of the outer main lateral grooves 88s contact the road surface earlier than the axially outer ends.

[0145] As is clear from the above description, according to the present invention, a heavy duty tire can be obtained that can suppress the accumulation of static electricity and achieve a reduction in rolling resistance. [Industrial Applicability]

[0146] The above-described technology capable of suppressing static electricity accumulation and achieving a reduction in rolling resistance can be applied to various tires.

[0147] [Note] The present invention includes the following aspects.

[0148] [1] A tire comprising a pair of beads, a carcass spanning the pair of beads, a reinforcing layer positioned radially outward of the carcass, and a tread having an outer circumferential surface in contact with a road surface and an inner circumferential surface in contact with the reinforcing layer, The tread has a plurality of circumferential grooves extending continuously in the circumferential direction, The plurality of circumferential grooves define a plurality of land portions in the tread, the plurality of land portions include a plurality of main land portions located between adjacent ones of the circumferential grooves, the circumferential groove located between adjacent main land portions is a circumferential narrow groove, The circumferential narrow groove includes a body portion and an expanded portion located radially inside the body portion, The maximum width W2 of the widened portion is wider than the minimum width W1 of the body portion, When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other in the trunk portion, Each of the plurality of main land portions has a transverse sipe that crosses the main land portion, The transverse sipe includes a sipe body and a tubular portion located radially inward of the sipe body, The maximum width W4 of the tubular portion is wider than the groove width W3 of the sipe body, The tread includes a conductive portion connecting the outer circumferential surface and the inner circumferential surface, Any one of the main land portions includes the conductive portion. Heavy duty tires. [2] The heavy-duty tire according to the above-mentioned [1], wherein the maximum width W2 of the widened portion is greater than the maximum width WX of the conductive portion. [3] The heavy-duty tire according to the above [1] or [2], wherein the maximum width W4 of the tubular portion is greater than the minimum width WN of the conductive portion. [4] A heavy-duty tire according to any one of [1] to [3] above, wherein the land ratio, as defined below, is 75% or more. Land ratio: The ratio of the total area of ​​the contact area of ​​the multiple land portions included in the contact area to the area of ​​the entire contact area, obtained by mounting the tire on a regular rim, adjusting the internal pressure to the regular internal pressure, and applying a load of 100% of the regular load with a camber angle of 0 degrees and bringing the tire into contact with a flat road surface. [5] The heavy-duty tire according to any one of [1] to [4] above, wherein the groove bottom of the circumferential narrow groove is located radially inward of the radial center of the conductive portion. [6] The heavy-duty tire according to any one of [1] to [5] above, wherein the groove bottom of the transverse sipe is located radially inward of the radial center of the conductive portion. [7] The circumferential groove includes a plurality of the circumferential narrow grooves, the main land portion located between the adjacent circumferential narrow grooves is an inner main land portion, The heavy-duty tire according to any one of the above-mentioned [1] to [6], wherein the main land portion having the conductive portion is the inner main land portion. [8] The heavy-duty tire according to the above-mentioned [7], wherein the conductive portion is disposed on the inner main land portion away from the axial center of the inner main land portion. [9] The heavy-duty tire according to the above [7] or [8], wherein the axial center of the inner main land portion coincides with the tire equatorial plane. [Explanation of symbols]

[0149] 2. Tires 4. Tread 6. Sidewall 8. Chafer 10 Bead 12. Carcass 14. Reinforcement layer 20...Outer surface 22...Inner peripheral surface 24 Tread surface 30···Carcass ply 32 Belt 34, 34A, 34B, 34C, 34D... Belt plies 36 Cap part 38···Base 42 Conductive part 42s: Outer end surface of the conductive portion 42 42u: Inner end surface of the conductive portion 42 46...Circumferential groove 48... Rikubu 54, 541, 542... Circumferential narrow groove 56... Circumferential thick groove 64, 64s, 64u...Main land area 66...Torso 68 Widened section 70...Tapered section 72 Body 74...inflection section 76...bottom 78 Transverse sipes 80···Sipe body 82...Tubular part 88, 88u, 88s...Main lateral groove 90 Main block 92...first narrow groove 94...Second narrow groove 96, 96a, 96b...Connected narrow groove

Claims

1. a pair of beads; a carcass that spans between the pair of beads; a reinforcing layer located radially outward of the carcass; a tread having an outer peripheral surface that contacts the road surface and an inner peripheral surface that contacts the reinforcing layer; Equipped with The tread has a plurality of circumferential grooves extending continuously in the circumferential direction, The plurality of circumferential grooves define a plurality of land portions in the tread, the plurality of land portions include a plurality of main land portions located between adjacent ones of the circumferential grooves, the circumferential groove located between adjacent main land portions is a circumferential narrow groove, The circumferential narrow groove includes a body portion and an expanded portion located radially inside the body portion, The maximum width W2 of the widened portion is wider than the minimum width W1 of the body portion, When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other in the trunk portion, Each of the plurality of main land portions has a transverse sipe that crosses the main land portion, The transverse sipe includes a sipe body and a tubular portion located radially inward of the sipe body, The maximum width W4 of the tubular portion is wider than the groove width W3 of the sipe body, The tread includes a conductive portion connecting the outer circumferential surface and the inner circumferential surface, Any one of the main land portions includes the conductive portion. Heavy duty tires.

2. The maximum width W2 of the widened portion is wider than the maximum width WX of the conductive portion.

2. The heavy duty tire according to claim 1.

3. The maximum width W4 of the tubular portion is wider than the minimum width WN of the conductive portion.

2. The heavy duty tire according to claim 1.

4. The land ratio, as defined below, is 75% or more.

2. The heavy duty tire according to claim 1. Land ratio: The ratio of the total area of ​​the contact area of ​​the plurality of land portions included in the contact area to the area of ​​the entire contact area, obtained by mounting the tire on a regular rim, adjusting the internal pressure to the regular internal pressure, and applying a load of 100% of the regular load with a camber angle of 0 degrees to the tire contacting a flat road surface.

5. a groove bottom of the circumferential narrow groove is located radially inside the radial center of the conductive portion; 2. The heavy duty tire according to claim 1.

6. A groove bottom of the transverse sipe is located radially inward of a radial center of the conductive portion.

2. The heavy duty tire according to claim 1.

7. the circumferential groove includes a plurality of the circumferential narrow grooves, the main land portion located between the adjacent circumferential narrow grooves is an inner main land portion, the main land portion having the conductive portion is the inner main land portion; 2. The heavy duty tire according to claim 1.

8. the conductive portion is disposed on the inner main land portion away from the axial center of the inner main land portion, 8. A heavy duty tire according to claim 7.

9. an axial center of the inner main land portion coincides with the tire equatorial plane; 8. A heavy duty tire according to claim 7.

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