Patent Publication Number: US-2022219491-A1

Title: Pneumatic Tire

Description:
TECHNICAL FIELD 
     The present technology relates to a pneumatic tire. 
     BACKGROUND ART 
     Studless tires are required to have good running performance on ice and snow. To increase the adhesive friction force, a flexible rubber is used in the studless tire, and to increase performance on ice and snow, a groove formed in a tread portion has a special configuration. For example, the pneumatic tire described in Japan Unexamined Patent Publication No. 2015-20465 is designed to have improved performance on icy roads, steering stability performance, and wear resistance performance in a well-balanced manner. The pneumatic tire includes a center land portion defined by a pair of center main grooves, a central narrow groove extending in a zigzag-manner in the tire circumferential direction on a tire equator line on the center land portion, and center lug grooves extending from the center main grooves to the zigzag vertices of the central narrow groove. 
     In addition, the pneumatic tire described in Japan Patent No. 5770834 is designed to have improved traction performance and steering stability on snow-covered road surfaces. The pneumatic tire includes edge land portion rows formed outward of two circumferential main grooves in the tire lateral direction, main lug grooves formed in the edge land portion rows inclined with respect to the tire lateral direction, and a first auxiliary groove inclined in the opposite direction to the main lug grooves, the first auxiliary groove extending across a central land portion row located between the two circumferential main grooves and the edge land portion row. The pneumatic tire described in Japan Unexamined Patent Publication No. 2015-229461 is designed to have enhanced performance on ice and performance on snow in a well-balanced manner. The pneumatic tire includes, in a tread portion, three small grooves that meet with the center lines offset from one another and a triangular portion defined by the center lines of the small grooves formed in the portion where the small grooves meet. 
     In recent years, in the development of studless tires, importance has increasingly been placed on obtaining performance on snow and steering stability on snow and ice in a compatible manner. In particular, in terms of the steering stability, the demand of improvements in braking ability and turnability on snow and ice has increased. Generally, decreasing the groove area of the tread pattern is an effective way of improving the steering stability. However, increasing the groove area is an effective way of improving performance on snow. Thus, it is very difficult to achieve both performances in a compatible manner. 
     SUMMARY 
     The present technology provides a pneumatic tire that can achieve performance on snow and steering stability in a compatible manner. 
     A pneumatic tire according to an embodiment of the present technology includes: 
     a first main groove extending in a tire circumferential direction; 
     a first land portion defined by the first main groove; 
     a second land portion located adjacent to the first land portion across the first main groove; and 
     a second land portion lug groove extending from the first main groove toward the second land portion in a tire lateral direction and defining the second land portion together with the first main groove; 
     the first main groove including a first land portion side edge portion corresponding to an edge portion on the first land portion side, the first land portion side edge portion including a bent portion formed bent in a direction outwards in a groove width direction of the first main groove with an acute bend angle θ; and 
     the second land portion lug groove including an opening portion to the first main groove connected to the first main groove at a position opposing the bent portion. 
     In the pneumatic tire described above, preferably the bend angle θ of the bent portion is within a range of 40°≤θ≤85°. 
     In the pneumatic tire described above, preferably a groove depth Ds of the first main groove and a groove depth Dg of a wear detection main groove extending in the tire circumferential direction and including a tread wear indicator have a relationship within a range of 0.25Dg≤Ds≤Dg. 
     In the pneumatic tire described above, preferably a groove width W of the first main groove is within a range of 3 mm≤W≤10 mm. 
     In the pneumatic tire described above, preferably 
     a first land portion lug groove is connected to the first main groove and extends inwards from the first main groove in the tire lateral direction; 
     a plurality of the second land portion lug grooves are provided, and at least one of the plurality of second land portion lug grooves includes an opening portion to the first main groove connected at a position that at least partially overlaps in the tire circumferential direction with an opening portion of the first land portion lug groove to the first main groove; 
     the plurality of second land portion lug grooves are connected to the first main groove at a plurality of intersection points; and 
     the plurality of intersection points include a three-direction intersection point where the bent portion is formed on the first land portion side edge portion side of the first main groove, and a four-direction intersection point where the first land portion lug groove is connected to the first main groove on the first land portion side edge portion side, the three-direction intersection point and the four-direction intersection point being alternately disposed in the tire circumferential direction. 
     In the pneumatic tire described above, preferably the second land portion is provided with a circumferential narrow groove extending in the tire circumferential direction, the circumferential narrow groove including an end connected to the second land portion lug groove and an end terminating within the second land portion. 
     In the pneumatic tire described above, preferably the circumferential narrow groove has a length in the tire circumferential direction ranging from 50% to 90% of an entire length of the second land portion in the tire circumferential direction. 
     In the pneumatic tire described above, preferably the circumferential narrow groove has a wider groove width at an end portion on a side connected to the second land portion lug groove than at an end portion on a side where the circumferential narrow groove terminates within the second land portion. 
     In the pneumatic tire described above, preferably the second land portion lug groove includes an edge on a side where the circumferential narrow groove is connected, the edge is offset in a groove width direction of the second land portion lug groove at either side in the tire lateral direction of a position where the circumferential narrow groove is connected. 
     A pneumatic tire according to an embodiment of the present technology can achieve the effects of providing performance on snow and steering stability in a compatible manner. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view illustrating a tread surface of a pneumatic tire according to an embodiment. 
         FIG. 2  is a cross-sectional view of a center main groove and a second main groove illustrated in  FIG. 1 . 
         FIG. 3  is a detailed view of portion A of  FIG. 1 . 
         FIG. 4  is a detailed view of portion B of  FIG. 3 . 
         FIG. 5  is a detailed view of portion C of  FIG. 3 . 
         FIG. 6  is a detailed view of a second land portion illustrated in  FIG. 3 . 
         FIG. 7A  is a table showing the results of performance tests of pneumatic tires. 
         FIG. 7B  is a table showing the results of performance tests of pneumatic tires. 
         FIG. 7C  is a table showing the results of performance tests of pneumatic tires. 
     
    
    
     DETAILED DESCRIPTION 
     Pneumatic tires according to embodiments of the present technology are described in detail below with reference to the drawings. However, the technology is not limited to these embodiments. Constituents of the following embodiments include elements that are essentially identical or that can be substituted or easily conceived by one skilled in the art. 
     Herein, “tire lateral direction” refers to the direction that is parallel with a rotation axis of a pneumatic tire. “Inward in the tire lateral direction” refers to the direction toward the tire equator line in the tire lateral direction. “Outward in the tire lateral direction” refers to the direction opposite the direction toward the tire equator line in the tire lateral direction. “Tire radial direction” refers to the direction orthogonal to the tire rotation axis. “Tire circumferential direction” refers to the direction of rotation about the tire rotation axis. 
       FIG. 1  is a plan view of a tread surface of a pneumatic tire according to an embodiment. The pneumatic tire  1  illustrated in  FIG. 1  is provided with a tread portion  2  in the outermost portion in the tire radial direction. The surface of the tread portion  2 , i.e., the portion that comes into contact with the road surface when a vehicle (not illustrated) mounted with the pneumatic tire  1  travels, is formed as a tread surface  3 . A plurality of circumferential main grooves  20  extending in the tire circumferential direction and a plurality of lug grooves  40  extending in the tire lateral direction are formed in the tread surface  3 . A plurality of land portions  10  defined by the circumferential main grooves  20  and the lug grooves  40  are formed in the tread surface  3 . 
     Specifically, four circumferential main grooves  20  are formed side by side in the tire lateral direction. The four circumferential main grooves  20  include two center main grooves  21  located on either side of a tire equator line CL in the tire lateral direction and two second main grooves  22  located outward of the two center main grooves  21  in the tire lateral direction. The lug grooves  40  include center lug grooves  41  located between the two center main grooves  21 , second lug grooves  45  located between an adjacent center main groove  21  and second main groove  22 , and shoulder lug grooves  48  located outward of the second main grooves  22  in the tire lateral direction. The circumferential main grooves  20  herein have a groove width ranging from 3.0 mm to 10.0 mm and a groove depth ranging from 8.0 mm to 9.5 mm. Moreover, the lug grooves  40  have a groove width ranging from 1.5 mm to 8.0 mm and a groove depth ranging from 5.0 mm to 9.0 mm. 
       FIG. 2  is a cross-sectional view of a center main groove and a second main groove illustrated in  FIG. 1 . Of the plurality of circumferential main grooves  20 , the center main grooves  21  are provided as first main grooves, and the second main grooves  22  are provided as wear detection main grooves provided with a tread wear indicator  23  indicating the terminal stages of wear. The tread wear indicator  23  has a short length in the tire lateral direction and is formed projecting from the groove bottom of the second main groove  22 . The tread wear indicator  23  is provided at a plurality of sections around the tire circumference of the second main groove  22 . A groove depth Ds of the center main groove  21  and a groove depth Dg of the second main groove  22  including the tread wear indicator  23  have a relationship within the range of 0.25Dg≤Ds≤Dg. Note that the groove depth Dg of the second main groove  22  is the depth at a position without the tread wear indicator  23 , and preferably the relationship is within the range of 0.50Dg≤Ds≤Dg. 
     In addition, the center main groove  21  has a groove width W within the range 3 mm≤W≤10 mm. Preferably, the groove width W of the center main groove  21  is within the range of 3.5 mm≤W≤7.0 mm. 
     Of the plurality of lug grooves  40 , the center lug grooves  41  are provided as first land portion lug grooves that define a center land portion  11 . The center lug grooves  41  extending in the tire lateral direction are formed between the two center main grooves  21  and are connected to the center main grooves  21  at both ends. The second lug grooves  45  are formed between an adjacent center main groove  21  and second main groove  22  and extending in the tire lateral direction. The second lug grooves  45  each include an end connected to the center main groove  21  and an end connected to the second main groove  22 . That is, the second lug grooves  45  are provided as second land portion lug grooves that define second land portions  12  and extend from the center main groove  21  toward the second land portion  12  in the tire lateral direction. The shoulder lug grooves  48  are formed at a position outward of the second main grooves  22  in the tire lateral direction and extend in the tire lateral direction. The shoulder lug grooves  48  each include an inner end portion in the tire lateral direction connected to the second main groove  22 . Moreover, these lug grooves  40  extend in the tire lateral direction and are inclined or curved in the tire circumferential direction. The configuration of the lug grooves  40  inclined or curved in the tire circumferential direction with respect to the tire lateral direction is set as appropriate depending on the target tread pattern. 
     The land portions  10  are defined by the circumferential main grooves  20  and the lug grooves  40  and include the center land portion  11 , i.e., first land portion, located between the two center main grooves  21 , the second land portions  12 , i.e., second land portions, located between an adjacent center main groove  21  and second main groove  22 , and shoulder land portions  13 , i.e., third land portions, located outward of the second main grooves  22  in the tire lateral direction. Of these, the center land portion  11  is located on the tire equator line CL and is defined by the center main grooves  21  and the center lug grooves  41 . The second land portions  12  are formed adjacent to the center land portion  11  across the center main grooves  21  and are defined by the center main grooves  21 , the second main grooves  22 , and the second lug grooves  45 . The shoulder land portions  13  are formed adjacent to the second land portions  12  across the second main grooves  22  and are defined by the second main grooves  22  and the shoulder lug grooves  48 . A shoulder narrow groove  55  is formed in each shoulder land portion  13  extending in the tire circumferential direction. The shoulder narrow groove  55  includes an end connected to the shoulder lug groove  48  and an end that terminates within the shoulder land portion  13 . In this manner, the center land portion  11 , the second land portions  12 , and the shoulder land portions  13  are defined by the circumferential main grooves  20  and the lug grooves  40 , forming blocks. 
     A plurality of sipes  58  are formed in the tread surface  3 . The sipes  58  are formed in each land portion  10 , i.e., the center land portion  11 , the second land portions  12 , and the shoulder land portions  13 . The sipes  58  have a zigzag shape that extends in the tire lateral direction oscillating in the tire circumferential direction. 
     Note that the sipe  58  herein refers to a narrow groove formed in the tread surface  3  with a configuration such that when the pneumatic tire  1  is mounted on a regular rim, adjusted to regular internal pressure conditions, and is in an unloaded state, the wall surfaces of the narrow groove do not come into contact, however, when the pneumatic tire  1  is placed on a flat plate and loaded in the vertical direction with the narrow groove located at the contact patch formed on the flat plate or when the land portion including the narrow groove flexes, the wall surfaces of the narrow groove or at least a portion on the wall surfaces are brought into contact with one another by the deformation of the land portion. Here, “regular rim” refers to a “standard rim” defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a “design rim” defined by the Tire and Rim Association, Inc. (TRA), or a “measuring rim” defined by the European Tyre and Rim Technical Organisation (ETRTO). “Regular internal pressure” refers to a “maximum air pressure” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. In the present embodiment, the sipes  58  have a width ranging from 0.6 mm to 1.0 mm and a depth ranging from 6.0 mm to 8.0 mm. 
       FIG. 3  is a detailed view of portion A of  FIG. 1 . The center main groove  21  includes a center side edge portion  31 , i.e., first land portion side edge portion, which is an edge portion  30  on the center land portion  11  side. The center side edge portion  31  includes a bent portion  35  formed where the center side edge portion  31  bends. Specifically, the center main groove  21  is formed with its position shifted in the tire lateral direction an amount equal to the groove width of the center main groove  21  at a predetermined plurality of positions in the tire circumferential direction. That is, the center main groove  21  is formed extending in the tire circumferential direction and in a direction in the tire lateral direction, meaning that the center main groove  21  is inclined with respect to the tire circumferential direction. Thus, at a predetermined plurality of positions in the tire circumferential direction, the position of the center main groove  21  in the tire lateral direction is shifted in the opposite direction to the inclination direction of the center main groove  21 . As such, the center main groove  21  overall is formed with its position in the tire lateral direction within a predetermined range. In other words, the center main groove  21  extends in the tire circumferential direction and is formed in a zigzag shape that oscillates in the tire lateral direction. 
     Because the center main groove  21  is shifted in the tire lateral direction at a plurality of positions in this way, the center side edge portion  31  and a second side edge portion  32 , which is the edge portion  30  of the center main groove  21  on the second land portion  12  side, are offset from one another in the same tire lateral direction at the position in the tire circumferential direction where the center main groove  21  is shifted in the tire lateral direction. By the center side edge portion  31  bending in the tire lateral direction at a position in the tire circumferential direction where the center side edge portion  31  is shifted in the tire lateral direction, the bent portion  35 , formed in the center side edge portion  31 , connects other center side edge portions  31  with different positions in the tire lateral direction. 
       FIG. 4  is a detailed view of portion B of  FIG. 3 . At the bent portion  35  where the position in the tire lateral direction of the center side edge portion  31  differs, the center side edge portion  31  is formed with a bend in the direction outward with respect to the groove width direction of the center main groove  21 . Specifically, by the position in the tire lateral direction of the center main groove  21  being shifted at a predetermined position in the tire circumferential direction, the position in the tire lateral direction of the center side edge portion  31  is also shifted. At the position where the position in the tire lateral direction of the center main groove  21  is shifted, the center side edge portion  31  includes a portion located on the center land portion  11  side and a portion located on the second land portion  12  side. In other words, the center side edge portion  31  includes an inner center side edge portion  31   b  and an outer center side edge portion  31   a  at the position where the position in the tire lateral direction of the center main groove  21  is shifted. The inner center side edge portion  31   b  is the portion located on the center land portion  11  side, and the outer center side edge portion  31   a  is the portion located on the second land portion  12  side. The outer center side edge portion  31   a  and the inner center side edge portion  31   b  are arranged such that the inner center side edge portion  31   b  is positioned further inwards in the tire lateral direction than the outer center side edge portion  31   a  at the position where the center side edge portion  31  is shifted in the tire lateral direction. 
     The bent portion  35  bends from the outer center side edge portion  31   a  of the center side edge portion  31  in the direction outward in the groove width direction of the center main groove  21 . The portion of the center side edge portion  31  extending outwards in the groove width direction of the center main groove  21  corresponds to a bent portion edge portion  36 . That is, the outer center side edge portion  31   a  and the inner center side edge portion  31   b  of the center side edge portion  31  are connected by the bent portion edge portion  36 . 
     As the bent portion edge portion  36  formed in this way extends outwards in the groove width direction of the center main groove  21  from the outer center side edge portion  31   a , i.e., toward the center land portion  11  side from the second land portion  12  side, the bent portion edge portion  36  is inclined in the tire circumferential direction with respect to the tire lateral direction toward the side in the tire circumferential direction where the outer center side edge portion  31   a  is located. In other words, the bent portion edge portion  36  includes an outer end portion  37 , which is the end portion connected to the outer center side edge portion  31   a , and an inner end portion  38 , which is the end portion connected to the inner center side edge portion  31   b , and the bent portion edge portion  36  is inclined such that the position in the tire circumferential direction of the inner end portion  38  is closer to the side where the outer center side edge portion  31   a  is located than the outer end portion  37 . Thus, the bent portion edge portion  36  has a bend angle θ which is an acute angle and is formed bent relative to the outer center side edge portion  31   a . That is, the bent portion  35  is formed so that the bend angle θ of the center side edge portion  31  is an acute angle. The bend angle θ of the bent portion  35  is preferably formed in the range of 40°≤θ≤85° and more preferably in the range of 60°≤θ≤75°. 
     At least one second lug groove  45  of the plurality of second lug grooves  45  extending outwards in the tire lateral direction from the center main groove  21  is connected to the center main groove  21  at a position at or near the bent portion  35 , that is, an opening portion  46  of the second lug groove  45  to the center main groove  21  is connected to the center main groove  21  at a position opposing the bent portion  35 . An intersection point  60  where the second lug groove  45  is connected to the center main groove  21  at a position at or near the bent portion  35  is formed as a three-direction intersection point  61  where grooves extend from the intersection point  60  in three directions including the two directions of the center main groove  21  and the one direction of the second lug groove  45 . 
     To explain the configuration of the three-direction intersection point  61  with the second lug groove  45  connected to the center main groove  21 , the center main groove  21  is shifted in the position in the tire lateral direction at a predetermined position in the tire circumferential direction. Thus, the position in the tire lateral direction of the second side edge portion  32  is also shifted, in a similar manner to the center side edge portion  31 . Accordingly, the second side edge portion  32  includes an inner second side edge portion  32   b  and an outer second side edge portion  32   a  at the position where the position in the tire lateral direction of the center main groove  21  is shifted. The inner second side edge portion  32   b  is the portion located on the center land portion  11  side and the outer second side edge portion  32   a  is the portion located on the second land portion  12  side. 
     The second lug groove  45  connected to the center main groove  21  at the three-direction intersection point  61  is connected to the second side edge portion  32  at a position where the position of the center main groove  21  in the tire lateral direction is shifted. Thus, the second lug groove  45  is configured such that one of two edges  47  of the second lug groove  45  on both sides in the groove width direction is connected to the outer second side edge portion  32   a  and the other edge  47  is connected to the inner second side edge portion  32   b . The positions in the tire lateral direction of the outer second side edge portion  32   a  and the inner second side edge portion  32   b  are different, thus the opening portion  46  of the second lug groove  45  to the center main groove  21 , with the edges  47  on both sides in the groove width direction separately connected to the outer second side edge portion  32   a  and the inner second side edge portion  32   b , is inclined with respect to the tire lateral direction. Accordingly, the opening portion  46  of the second lug groove  45  to the center main groove  21  is inclined towards the bent portion  35  formed on the center side edge portion  31  side of the center main grooves  21  and is formed at a position opposing the bent portion  35 . 
     Note that the opening portion  46  of the second lug groove  45  with such a configuration refers to a region connecting an intersection point between one of the edges  47  of the second lug groove  45  and the outer second side edge portion  32   a  of the center main groove  21  with an intersection point between the other edge  47  of the second lug groove  45  and the inner second side edge portion  32   b  of the center main groove  21 . Additionally, “the opening portion  46  of the second lug groove  45  with such a configuration opposing the bent portion  35 ” refers to a state in which at least a portion of the bent portion edge portion  36  of the bent portion  35  is located in the region orthogonal to the opening portion  46  in terms of the width of the opening portion  46 . 
     At least another one of the plurality of second lug grooves  45  is connected to the center main groove  21  at or near a portion where the center lug groove  41  extending from the center main groove  21  inwards in the tire lateral direction is connected to the center main groove  21 .  FIG. 5  is a detailed view of portion C of  FIG. 3 . The second lug groove  45 , connected to the center main groove  21  at or near a portion where the center lug groove  41  is connected to the center main groove  21 , is connected to the second side edge portion  32  of the center main groove  21 , in a similar manner to the second lug groove  45  connected to the center main groove  21  at the three-direction intersection point  61 . The intersection point  60 , where the center lug groove  41  is connected to the center main groove  21  on the center side edge portion  31  side and where the second lug grooves  45  is connected to the center main groove  21  on the second side edge portion  32  side, is formed as a four-direction intersection point  62  where grooves extend from the intersection point  60  in four directions including the two directions of the center main groove  21  and the one direction each of the center lug groove  41  and of the second lug groove  45 . 
     The opening portion  46  of the second lug groove  45  to the center main groove  21  connected to the center main groove  21  at the four-direction intersection point  62  and an opening portion  42  to the center main groove  21  of the center lug groove  41  are connected at positions that at least partially overlap in the tire circumferential direction. That is, the opening portion  46  of the second lug groove  45  to the center main groove  21  and the opening portion  42  of the center lug groove  41  to the center main groove  21 , when viewed in the tire lateral direction, overlap at least partially and are at least partially opposed to one another. 
     A plurality of the four-direction intersection points  62  and the three-direction intersection points  61  formed in this manner are provided on the center main groove  21 , with the plurality of four-direction intersection points  62  and the plurality of three-direction intersection points  61  being alternately disposed in the tire circumferential direction. 
       FIG. 6  is a detailed view of the second land portion illustrated in  FIG. 3 . The plurality of second lug grooves  45  formed between the center main groove  21  and the second main groove  22  extend in the tire lateral direction and are inclined in the tire circumferential direction. The inclination angle is the same for each second lug groove  45 . Thus, the second land portion  12  is defined on both sides in the tire circumferential direction by the second lug grooves  45  and defined on both sides in the tire lateral direction by the center main groove  21  and the second main groove  22  and is formed in a generally parallelogram shape. 
     A circumferential narrow groove  50  is formed in the second land portion  12  formed in this manner. The circumferential narrow groove  50  extends in the tire circumferential direction and includes an end connected to the second lug groove  45  and an end that terminates within the second land portion  12 . The circumferential narrow groove  50  is formed in or near a central region of the second land portion  12  in the tire lateral direction. The circumferential narrow groove  50  is connected to and extends in the tire circumferential direction from one of the second lug grooves  45  that define the second land portion  12  on both sides in the tire circumferential direction. Additionally, the circumferential narrow grooves  50  formed in the plurality of second land portions  12  are all connected to the second lug groove  45  located on the same side in the tire circumferential direction and extend from this second lug groove  45  into the second land portion  12 . 
     In this way, the circumferential narrow groove  50  extending in the tire circumferential direction has a length L in the tire circumferential direction ranging from 50% to 90% of an entire length LB of the second land portion  12  in the tire circumferential direction. In other words, the relationship between the length L of the circumferential narrow groove  50  and the entire length LB of the second land portion  12  in the tire circumferential direction is in the range of 0.5≤(L/LB)≤0.9. The length L of the circumferential narrow groove  50  with such a configuration is the distance in the tire circumferential direction from an end portion  53  of the circumferential narrow groove  50  on the side terminating within the second land portion  12  to a portion of an end portion  52  of the circumferential narrow groove  50  on the side connected to the second lug grooves  45  that is distanced furthest away in the tire circumferential direction from the end portion  53  on the side terminating within the second land portion  12 . Additionally, the entire length LB of the second land portion  12  in the tire circumferential direction is the distance in the tire circumferential direction from one end portion of the second land portion  12  in the tire circumferential direction to the other end portion. Furthermore, the length L of the narrow groove  50  is preferably from 60% to 80% of the entire length LB of the second land portion  12 . 
     The circumferential narrow groove  50  has a groove width that is wider at the end portion  52  on the side connected to the second lug groove  45  than at the end portion  53  on the side terminating within the second land portion  12 . That is, the groove width of the circumferential narrow groove  50  gradually increases from the end portion  53  on the side terminating within the second land portion  12  to the end portion  52  on the side connected to the second lug groove  45 , or the groove width gradually decreases from the end portion  52  on the side connected to the second lug groove  45  toward the end portion  53  on the side terminating within the second land portion  12 . In other words, the circumferential narrow groove  50  has a tapered shape. 
     The edge  47  of the second lug groove  45  on the side where the circumferential narrow groove  50  is connected is offset in the groove width direction of the second lug groove  45  at either side in the tire lateral direction of the position where the circumferential narrow groove  50  is connected. Specifically, the edge  47  on the side where the circumferential narrow groove  50  is connected to the second lug groove  45  includes a portion located on the second main groove  22  side and a portion located on the center main groove  21  side relative to the position where the circumferential narrow groove  50  is connected in the tire lateral direction. The portion located on the second main groove  22  side is offset from the portion located on the center main groove  21  side in the direction in which the groove width of the second lug groove  45  increases. Thus, groove walls  54  of the circumferential narrow groove  50  are offset from one another in the length direction at or near an opening portion  51  of the circumferential narrow groove  50  to the second lug groove  45 , and the opening portion  51  of the circumferential narrow groove  50  opens to the second lug groove  45  with the groove walls  54  of the circumferential narrow groove  50  on either side in the groove width direction being offset from one another. 
     The offset amount of the edge  47  of the second lug groove  45  is preferably in the range of 0.6≤(WL1/WL2)≤0.9, where WL1 is a groove width of the portion of the second lug groove  45  on the center main groove  21  side of the position where the circumferential narrow groove  50  is connected, and WL2 is a groove width of a portion of the second lug groove  45  on the second main groove  22  side. 
     When such a pneumatic tire  1  is mounted on a vehicle and the vehicle is driven, the pneumatic tire  1  rotates while the tread surface  3  of the tread surface  3  located at the bottom comes into contact with the road surface. When a vehicle mounted with the pneumatic tire  1  travels on a dry road surface, the vehicle is driven via driving forces and braking forces transferring to the road surface and turning forces being generated via the friction force between the tread surface  3  and the road surface. Additionally, when traveling on a wet road surface, the water between the tread surface  3  and the road surface enters the circumferential main grooves  20 , the lug grooves  40 , and the like and is drained via these grooves. Thus, the tread surface  3  can easily come into contact with the road surface, allowing the vehicle to be driven via the friction force between the tread surface  3  and the road surface. 
     Furthermore, when traveling on snow-covered road surfaces, the tread surface  3  of the pneumatic tire  1  compacts the snow on the road surface and the snow on the road surface enters the circumferential main grooves  20  and the lug grooves  40 . Thus, snow also is compacted in the grooves. In this state, driving forces and braking forces and, when the vehicle turns, forces in the tire lateral direction act on the pneumatic tire  1 , generating a shear force in snow, i.e., a shear force that acts on the snow inside the grooves. The shear force in snow produces resistance between the pneumatic tire  1  and the road surface, which allows the vehicle to be driven on snow-covered road surfaces with driving forces and braking forces being transferred to the snow-covered road surface. 
     Additionally, when traveling on snow-covered or icy road surfaces, the circumferential main grooves  20 , the lug grooves  40 , and the sipes  58  exhibit an edge effect. In other words, when traveling on snow-covered or icy road surfaces, the edge portions  30  of the circumferential main grooves  20  and the edges of the sipes  58  bite into the snowy or icy surface producing resistance. Furthermore, when traveling on icy road surfaces, water on the surface of the icy road surface is taken in by the sipes  58 , and a water film between the icy road surface and the tread surface  3  is removed, allowing the icy road surface and the tread surface  3  to easily come into contact with one another. Thus, the resistance between the tread surface  3  and the icy road surface produced by the friction force and the edge effect is increased, allowing the running performance of the vehicle mounted with the pneumatic tire  1  to be ensured. 
     When traveling on snow-covered road surfaces, the shear force in snow is greatly displayed. Improving the shear force in snow is effective in improving performance on snow. To improve the shear force in snow, a region in which snow can be strongly compacted in the groove is ensured. Typically, a plurality of intersection points that open to grooves in four directions such as the four-direction intersection point  62  are provided. However, providing a tread pattern with only intersection points that open in four directions decreases the size of the land portions  10  and thus decreases block rigidity. This makes it difficult to ensure steering stability on snow and ice. On the other hand, to secure block rigidity, for example, a tread pattern may be provided with only intersection points that open in three directions by the end portions of the lug grooves  40  being connected to the circumferential main grooves  20 . This ensures block rigidity, however, the amount of snow that can enter the intersection points is small. This makes it difficult to improve the shear force in snow. 
     Performance on snow relating to the driving forces and braking forces transferring on snow and the steering stability on snow and ice have conflicting preferred configurations in terms of groove intersection points. However, in the pneumatic tire  1  according to the present embodiment, the bent portion  35  is provided on the center main groove  21  and the second lug groove  45  is connected to the center main groove  21  at a position where the opening portion  46  to the center main groove  21  opposes the bent portion  35 . Thus, the shear force in snow can be improved without reducing block rigidity. In other words, the bent portions  35  are formed where the position of the center main groove  21  in the tire lateral direction is offset in the tire lateral direction at a plurality of predetermined positions in the tire circumferential direction, and the second lug grooves  45  are connected to the center main grooves  21  with the opening portions  46  opening to the bent portions  35 . This allows the groove area of the three-direction intersection points  61  to be increased and thus allow a larger amount of snow to enter the three-direction intersection points  61 . As a result, the shear force in snow can be increased and performance on snow can be improved. 
     In addition, to increase the area into which snow can enter, by not increasing the number of grooves and instead forming the bent portions  35 , the area into which snow can enter is increased. Thus, the center land portion  11  defined by the center side edge portions  31 , i.e., the edge portions  30  of the center main grooves  21  on the side where the bent portions  35  are formed, can be prevented from decreasing in size. This can prevent a decrease in the block rigidity of the center land portion  11  and improve the steering stability on snow and ice. As a result, performance on snow and steering stability can be achieved in a compatible manner. 
     Furthermore, the bend angle θ of the bent portion  35  is in the range of 40°≤θ≤85°. Thus, the shear force in snow at the three-direction intersection point  61  can be ensured without a decrease in the block rigidity of the center land portion  11  around the bent portion  35 . In other words, when the bend angle θ is less than 40°, the angle between the bent portion edge portion  36  and the outer center side edge portion  31   a  is too small. This may likely result in a decrease in the block rigidity of the center land portion  11  around the bent portion  35 . When the bend angle θ is greater than 85°, the angle between the bent portion edge portion  36  and the outer center side edge portion  31   a  is too large. This may make it difficult to ensure the groove area of the three-direction intersection points  61  and ensure the shear force in snow. When the bend angle θ of the bent portion  35  is in the range of 40°≤θ≤85°, the shear force in snow at the three-direction intersection point  61  can be ensured and a decrease in the block rigidity around the bent portion  35  can be suppressed. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The groove depth Ds of the center main groove  21  and the groove depth Dg of the second main groove  22  including the tread wear indicator  23  have a relationship within the range of 0.25Dg ≤Ds≤Dg. Thus, the shear force in snow can be ensured without a decrease in block rigidity. In other words, when the relationship between the groove depth Ds of the center main groove  21  and the groove depth Dg of the second main groove  22  satisfies Ds&lt;0.25Dg, the volume of the center main grooves  21  that include the three-direction intersection points  61  decreases and the amount of snow that enters the three-direction intersection points  61  and the center main grooves  21  decreases. This may make it difficult to ensure the shear force in snow. When the relation between the groove depth Ds of the center main groove  21  and the groove depth Dg of the second main groove  22  satisfies Ds&gt;Dg, the groove depth Ds of the center main grooves  21  is too deep. As a result, the block rigidity of the center land portion  11  and the second land portions  12  may likely decrease. When the groove depth Ds of the center main groove  21  and the groove depth Dg of the second main groove  22  have a relationship within the range of 0.25Dg≤Ds≤Dg, the shear force in snow of the three-direction intersection points  61  and the center main grooves  21  can be ensured and a decrease in the block rigidity of the center land portion  11  and the second land portions  12  can be suppressed. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The groove width W of the center main grooves  21  is within the range of 3 mm≤W≤10 mm Thus, the shear force in snow can be ensured without reducing block rigidity. In other words, when the groove width W of the center main grooves  21  is less than 3 mm, the groove width W is too narrow. Thus, the amount of snow that enters the center main grooves  21  decreases, making it difficult to ensure the shear force in snow. When the groove width W of the center main grooves  21  is greater than 10 mm, the groove width W is too wide. As a result, the block rigidity of the center land portion  11  and the second land portions  12  may likely decrease. When the groove width W of the center main grooves  21  is within the range of 3 mm≤W≤10 mm, the shear force in snow of the center main grooves  21  can be ensured and a decrease in the block rigidity of the center land portion  11  and the second land portions  12  can be suppressed. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The three-direction intersection points  61  and the four-direction intersection points  62  are alternately disposed in the tire circumferential direction. Thus, the four-direction intersection points  62  can improve the shear force in snow, and a tread pattern can be formed with a good balance of block rigidity and shear force in snow. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     Additionally, the circumferential narrow groove  50  is formed in the second land portion  12 . The circumferential narrow groove  50  more reliably ensures the shear force in snow. Furthermore, the circumferential narrow groove  50  includes the end portion  53  that terminates within the second land portion  12 . This allows a decrease in block rigidity to be suppressed and the shear force in snow maintained. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The circumferential narrow groove  50  has the length L in the tire circumferential direction ranging from 50% to 90% of the entire length LB of the second land portion  12  in the tire circumferential direction. This allows the shear force in snow to be ensured and a decrease in block rigidity to be suppressed. In other words, when the length L of the circumferential narrow groove  50  is less than 50% of the entire length LB of the second land portion  12 , the length L of the circumferential narrow groove  50  to the second land portion  12  is too short. This may make it difficult for the circumferential narrow groove  50  to ensure the shear force in snow. When the length L of the circumferential narrow groove  50  is greater than 90% of the entire length LB of the second land portion  12 , the length L of the circumferential narrow groove  50  to the second land portion  12  is too long. As a result, the block rigidity of the second land portion  12  may likely decrease. When the length L of the circumferential narrow groove  50  ranges from 50% to 90% of the entire length LB of the second land portion  12 , the shear force in snow of the circumferential narrow groove  50  can be ensured and a decrease in the block rigidity of the second land portion  12  can be suppressed. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The circumferential narrow groove  50  has a groove width that is wider at the end portion  52  on the side connected to the second lug groove  45  than at the end portion  53  on the side terminating within the second land portion  12 . Thus, the shear force in snow of the portion of the circumferential narrow groove  50  on the side connected to the second land portion  12  can be ensured and a decrease in the block rigidity of the second land portion  12  can be suppressed. As a result, performance on snow and steering stability can be more reliably achieved in a compatible manner. 
     The edge  47  of the second lug groove  45  on the side where the circumferential narrow groove  50  is connected is offset in the groove width direction of the second lug groove  45  at either side in the tire lateral direction of the position where the circumferential narrow groove  50  is connected. Thus, the edge effect at the second lug grooves  45  and the circumferential narrow grooves  50  can be increased. In other words, the edge  47  of the second lug groove  45  is offset in the groove width direction of the second lug groove  45 . Thus, the ground contact position of the edge  47  in the tire circumferential direction is different on either side of the position where the circumferential narrow groove  50  is connected to the second lug groove  45 . This allows the edge effect in the tire circumferential direction to be increased. By the edge  47  of the second lug groove  45  being offset, one of the groove walls  54  on either side of the circumferential narrow groove  50  is easily exposed in the tire width direction. This allows the edge effect at the wall surface of the circumferential narrow groove  50  on the exposed side to be increased, and the edge effect in the tire width direction to be enhanced. As a result, steering stability can be more reliably improved. 
     Note that in the pneumatic tire  1  according to the embodiment described above, the bent portions  35  of the center main grooves  21  are provided on either side of the tire equator line CL in the tire lateral direction. That is, the three-direction intersection points  61  are provided on either side of the tire equator line CL in the tire lateral direction. However, the three-direction intersection point  61  may be provided on only one side in the tire lateral direction. In other words, relative to a vehicle mounted with the pneumatic tire  1 , the three-direction intersection points  61  each including the bent portion  35  may be provided only on a vehicle mounting direction inner side of the tire equator line CL or may only be provided on a vehicle mounting direction outer side of the tire equator line CL. 
     Additionally, in the pneumatic tire  1  according to the embodiment described above, the bent portion  35  is provided on the center side edge portion  31 , which is the edge portion  30  of the center main groove  21  located inwards in the tire lateral direction. However, the bent portion  35  may be provided on the edge portion  30  located outwards in the tire lateral direction. In a configuration in which the bent portion  35  is provided on the edge portion  30  of the center main groove  21  located outwards in the tire lateral direction, the center land portion  11  corresponds to the second land portion, the center lug grooves  41  correspond to the second land portion lug grooves, the center lug groove  41  is connected to the edge portion  30  on the opposite side to the edge portion  30  on the side of the center main groove  21  where the bent portion  35  is provided, and the opening portion is formed opposing the bent portion  35 . This allows a decrease in block rigidity to be suppressed and the shear force in snow to be ensured. 
     In the pneumatic tire  1  according to the embodiment described above, the bent portion  35  is provided in the center main groove  21 . However, the first main groove including the bent portion  35  may be a component other than the center main groove  21 . The first main groove provided with the bent portion  35  is only required to be a circumferential main groove extending in the tire circumferential direction, and there are no limitations on its relative positional relationship with other circumferential main grooves. 
     In the pneumatic tire  1  according to the embodiment described above, the three-direction intersection points  61  and the four-direction intersection points  62  are alternately disposed in the tire circumferential direction. However, the three-direction intersection points  61  and the four-direction intersection points  62  may not be alternately disposed. A plurality of three-direction intersection points  61  may be disposed between two four-direction intersection points  62  or alternatively a plurality of four-direction intersection points  62  may be disposed between two three-direction intersection points  61 . The three-direction intersection points  61  and the four-direction intersection points  62  are preferably appropriately arranged depending on the performance on snow and steering stability required for the pneumatic tire  1 . 
     Additionally, in the pneumatic tire  1  according to the embodiment described above, the end portions of the circumferential narrow grooves  50  on the side connected to the second lug groove  45  are all connected on the same side in the tire circumferential direction. However, the end portion of the circumferential narrow groove  50  that is connected to the second lug groove  45  may vary per circumferential narrow groove  50 . 
     Furthermore, the edge  47  on the side where the circumferential narrow groove  50  is connected to the second lug groove  45  includes a portion located on the second main groove  22  side and a portion located on the center main groove  21  side relative to the position where the circumferential narrow groove  50  is connected in the tire lateral direction. The portion located on the second main groove  22  side is offset from the portion located on the center main groove  21  side in the direction in which the groove width of the second lug groove  45  increases. However, the way the edge  47  is offset may be reversed. That is, the edge  47  on the side where the circumferential narrow groove  50  is connected to the second lug groove  45  includes a portion located on the second main groove  22  side and a portion located on the center main groove  21  side relative to the position where the circumferential narrow groove  50  is connected in the tire lateral direction, and the portion located on the center main groove  21  side may be offset in the direction in which the groove width of the second lug groove  45  increases. Regardless of the relative manner of the offset of the edge  47 , it is only required that the positions of the edge  47  in the groove width direction of the second lug groove  45  on either side in the tire lateral direction of the portion where the circumferential narrow groove  50  is connected are offset from one another. 
     Examples 
       FIGS. 7A to 7C  are tables showing the results of performance tests of pneumatic tires. In relation to the pneumatic tire  1  described above, performance evaluation tests conducted on a pneumatic tire of a Conventional Example and pneumatic tires  1  according to embodiments of the present technology will be described below. Performance evaluation tests were performed for braking on snow, which represents performance on snow, steering stability on snow, and steering stability on ice. 
     In the performance evaluation tests, the pneumatic tires  1  having a JATMA-specified nominal size of 195/65R15 91Q were mounted on the rim wheels of JATMA standard rims having a size of 15×6.0 J, the air pressure was adjusted to 210 kPa, and the tires were mounted on a test vehicle used for the test runs. The evaluation methods for the test items are as follows. For braking on snow, a braking test was conducted by a test driver on a test course with a snow-covered road surface. The reciprocal of the braking distances was expressed as index values and evaluated with the Conventional Example described below being assigned the nominal value of 100. Larger values indicate shorter braking distance and superior braking on snow. For steering stability on snow, a sensory evaluation was conducted by a test driver driving the test vehicle on a test course with a snow-covered road surface. The sensory evaluation scores were expressed as index values and evaluated with the Conventional Example described below being assigned the nominal value of 100. Larger values indicate superior steering stability on snow. For steering stability on ice, a sensory evaluation was conducted by a test driver driving the test vehicle on a test course with an ice-covered road surface. The sensory evaluation scores were expressed as index values and evaluated with the Conventional Example described below being assigned the nominal value of 100. Larger values indicate superior steering stability on ice. 
     The evaluation tests were conducted on a pneumatic tire of a Conventional Example, which is an example of a conventional pneumatic tire  1 , and pneumatic tires  1  of Examples 1 to 13, which are embodiments of the present technology. Of these pneumatic tires  1 , the pneumatic tire of the Conventional Example is not provided with the bent portion  35  in the center main groove  21 , and thus the second lug groove  45  does not open to the bent portion  35 . 
     In Examples 1 to 13, which are pneumatic tires  1  according to embodiments of the present technology, the opening portion  46  of the second lug groove  45  is disposed opposing the bent portion  35  of the center main groove  21 . Additionally, the bend angle θ of the bent portion  35 , the groove depth Ds of the center main groove  21  relative to the groove depth Dg of the second main groove  22 , the groove width W of the center main groove  21 , the arrangement of the three-direction intersection points  61  and the four-direction intersection points  62 , whether the circumferential narrow groove  50  of the second land portion  12  is provided, the length L of the circumferential narrow groove  50  relative to the entire length LB of the second land portion  12 , the configuration of the groove width of the circumferential narrow groove  50 , and whether the edge  47  of the second lug groove  45  is offset vary in the pneumatic tires  1  according to Examples 1 to 13. 
     As seen from the results of the evaluation tests for the pneumatic tires  1 , as indicated in  FIGS. 7A to 7C , the pneumatic tires  1  of Examples 1 to 13 all have better braking on snow, steering stability on snow, and steering stability on ice than the pneumatic tire of the Conventional Example. In other words, the pneumatic tires  1  of Examples 1 to 13 can achieve performance on snow and steering stability in a compatible manner.