Patent Publication Number: US-2023135384-A1

Title: Heavy duty tire

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a heavy duty tire. 
     Background Art 
     Patent Document 1 below discloses a pneumatic tire used for heavy duty vehicles such as trucks and buses, wherein the tread portion is provided with three zigzag circumferential grooves, and thereby, four land portions extending in the tire circumferential direction are defined. 
     Patent Document 1: Japanese Patent Application Publication No. 2008-273306 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In a heavy duty vehicle that repeats sudden starts and stops at short intervals under relatively large tire loads, such as a garbage truck, there is a problem such that uneven wear is liable to occur on the tread portions of the tires used. 
     The present disclosure was made in view of the above circumstances, and a primary objective of the present disclosure is to provide a heavy duty tire of which uneven wear resistance is improved. 
     Means for Solving the Problems 
     According to the present disclosure, a heavy duty tire comprises: 
     a tread portion having tread edges and provided with circumferentially continuously extending circumferential grooves including a pair of shoulder circumferential grooves and a crown circumferential groove disposed therebetween, the tread portion axially divided by the circumferential grooves into land portions including a pair of shoulder land portions between the tread edges and the shoulder circumferential grooves and a pair of crown portions between the shoulder circumferential grooves and the crown circumferential groove, 
     wherein 
     the width in the tire axial direction of each of the shoulder land portions is 17% to 28% of the tread width between the tread edges, 
     each of the crown land portions is circumferentially divided by a plurality of crown shallow grooves into a row of crown blocks, 
     the groove depth of the crown shallow grooves is smaller than the groove depth of the crown circumferential groove, 
     the bottom of each of the crown shallow grooves is provided with a groove bottom sipe, 
     each of the crown blocks has a ground contacting top surface which has a maximum dimension in the tire axial direction and a maximum dimension in the tire circumferential direction which is 100% to 200% of the maximum dimension in the tire axial direction, and 
     the ground contacting top surface has a hexagonal shape of which width measured in parallel to the tire axial direction is continuously increased from both ends in the tire circumferential direction toward the center therebetween. 
     Effects of the Invention 
     By adopting the above configuration, the heavy duty tire according to the present disclosure can be improved in uneven wear resistance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a developed partial view of the tread portion of a heavy duty tire as an embodiment of present disclosure. 
         FIG.  2    is a cross-sectional view taken along line A-A of  FIG.  1   . 
         FIG.  3    is an enlarged view showing the shoulder circumferential grooves, the crown circumferential groove and the crown land portions shown in  FIG.  1   . 
         FIG.  4    is an enlarged view showing the shoulder circumferential groove and the shoulder land portion. 
         FIG.  5    is an enlarged view showing a part of the crown land portion divided into the crown blocks. 
         FIG.  6    is a cross-sectional view taken along line B-B of  FIG.  5   . 
         FIG.  7    is a developed partial view of the tread portion showing its worn state. 
         FIG.  8    is an enlarged view of the tread portion of a heavy duty tire as another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present disclosure will now be described in detail in conjunction with accompanying drawings. 
     Heavy Duty Tire (First Embodiment) 
       FIG.  1    shows a part of the tread portion  2  of a heavy duty tire  1  as an embodiment of present disclosure.  FIG.  2    is a schematic cross-sectional view of the tread portion  2  taken along line A-A of  FIG.  1   . 
     In the present embodiment, the tire  1  is a pneumatic tire for heavy duty vehicles such as trucks and buses, particularly suitable for a garbage truck that repeats sudden starts and stops at short intervals under relatively large tire loads. 
     As well known in the art, a pneumatic tire comprises a tread portion  2  whose radially outer surface defines the tread, a pair of axially spaced bead portions mounted on rim seats, a pair of sidewall portions extending between the tread edges and the bead portions, a carcass extending between the bead portions through the tread portion and the sidewall portions, and a tread reinforcing belt disposed radially outside the carcass in the tread portion. 
     In this application including specification and claims, various dimensions, positions and the like of the tire refer to those under a normally inflated unloaded condition of the tire unless otherwise noted. 
     The normally inflated unloaded condition is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load. 
     The undermentioned normally inflated loaded condition is such that the tire is mounted on the standard wheel rim and inflated to the standard pressure and loaded with the standard tire load. 
     The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&amp;RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used. 
     The standard pressure and the standard tire load are the maximum air pressure and the maximum tire load for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list. 
     For example, the standard wheel rim is the “standard rim” specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like. 
     The standard pressure is the “maximum air pressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA or the like. 
     The standard load is the “maximum load capacity” in JATMA, the “Load Capacity” in ETRTO, the maximum value given in the above-mentioned table in TRA or the like. 
     &lt;Tread Edges&gt; 
     The tread edges  3  are the axial outermost edges of the ground contacting patch of the tire which occurs under the normally inflated loaded condition when the tire  1  is placed on a flat horizontal surface at the camber angle of 0 degrees. 
     The tread width TW is the width measured under the normally inflated unloaded condition, as the axial distance between the tread edges  3  determined as above. 
     &lt;Tread Portion&gt; 
     The tread portion  2  is provided with a plurality of circumferential grooves  4  and thereby axially divided into a plurality of land portions  5 . 
     The tread portion  2  is provided with a tread pattern. In the present embodiment, the tread pattern is point symmetrical with respect to an arbitrary point on the tire equator C. But, the present disclosure is not limited to such point symmetrical tread pattern, and the tread pattern may be a line symmetrical pattern, for example. 
     &lt;Circumferential Grooves&gt; 
     The circumferential grooves  4  are located between the tread edges  3 , and extend continuously in the tire circumferential direction. 
     In the present embodiment, the circumferential grooves  4  include a pair of shoulder circumferential grooves  6 , and at least one (in this example, only one) crown circumferential groove  7  disposed between the shoulder circumferential grooves  6 . 
     &lt;Shoulder Circumferential Grooves&gt; 
       FIG.  3    shows the shoulder circumferential grooves  6 , the crown circumferential groove  7  and the crown land portions  10  of  FIG.  1   . 
     Each of the shoulder circumferential grooves  6  of the present embodiment has axially inwardly projecting vertices  6   a  and axially outwardly projecting vertices  6   b  as shown in  FIG.  3   . The vertices  6   a  are alternated with the vertices  6   b  in the tire circumferential direction. Thereby, each shoulder circumferential groove  6  has a zigzag shape. In the shoulder circumferential grooves  6  of the present embodiment, the groove segments between the vertices  6   a  and  6   b  extend linearly. 
     Since the shoulder circumferential grooves  6  are zigzag, the groove edges are increased in the component in the axial direction, namely, the direction crossing the tire circumferential direction. 
     Further, in the present embodiment, as shown in  FIG.  3   , the zigzag phase of one of the shoulder circumferential grooves  6  is shifted, in the tire circumferential direction, from the zigzag phase of the other of the shoulder circumferential grooves  6 . 
     Thereby, the shoulder circumferential grooves  6  can ensure the traction performance and braking performance of the tire. 
     The shoulder circumferential grooves  6  each have a groove width W 1  (shown in  FIG.  1   ) in a range from 3% to 10% of the tread width TW, and a groove depth D 1  (shown in  FIG.  2   ) in a range from 15 mm to 25 mm. Thereby, the shoulder circumferential grooves  6  bring out the wet performance, and the rigidity of the tread portion  2  is maintained. 
     &lt;Crown Circumferential Groove&gt; 
     As shown in  FIG.  3   , the crown circumferential groove  7  of the present embodiment has vertices  7   a  projecting toward one side in the tire axial direction, and vertices  7   b  projecting toward the other side in the tire axial direction. 
     The vertices  7   a  are alternated with the vertices  7   b  in the tire circumferential direction. Thereby, the crown circumferential groove  7  is formed in a zigzag shape. 
     In the crown circumferential groove  7  of the present embodiment, the groove segments between the vertices  7   a  and  7   b  extend linearly. 
     Since the crown circumferential groove  7  is zigzag, the groove edges are increased in the component in the axial direction, namely, the direction crossing the tire circumferential direction. 
     Further, as shown in  FIG.  3   , the zigzag phase of the crown circumferential groove  7  is shifted in the tire circumferential direction from the zigzag phase of each of the shoulder circumferential grooves  6 . 
     Thereby, the crown circumferential groove  7  can further improve the traction performance and braking performance in cooperation with the shoulder circumferential grooves  6 . 
     The crown circumferential groove  7  has a groove width W 2  (shown in  FIG.  1   ) in a range from 3% to 10% of the tread width TW, and a groove depth D 2  (shown in  FIG.  2   ) in a range from 15 mm to 25 mm. 
     Thereby, the crown circumferential groove  7  brings out the wet performance, while maintaining the rigidity of the tread portion  2 . 
     &lt;Land Portions&gt; 
     The land portions  5  are divided by the circumferential grooves  4  as shown in  FIG.  1   . The land portions  5  include a pair of shoulder land portions  9  and a pair of crown land portions  10 . 
     &lt;Shoulder Land Portions&gt; 
     The shoulder land portions  9  are defined between the tread edges  3  and the shoulder circumferential grooves  6 . 
     In the present embodiment, each of the shoulder land portions  9  is not provided with lateral grooves and the like extending from the shoulder circumferential groove  6  to the tread edge  3 . Thereby, the shoulder land portions  9  are each formed as a rib extending continuously in the tire circumferential direction. 
     Since the shoulder land portions  9  are formed as a rib as described above, their rigidity is sufficiently secured, so the deformation during braking, driving and turning is suppressed. Therefore, uneven wear of the shoulder land portions  9  such as shoulder wear can be suppressed. 
       FIG.  4    shows a part of the shoulder circumferential groove  6  and a part of the shoulder land portion  9 . 
     In the present embodiment, the axially inner edge  9   s  of the shoulder land portion  9  is formed by the zigzag-shaped shoulder circumferential groove  6 , therefore, the axially inner edge  9   s  has axially inner corners  9 A projecting axially inward and axially outer corners  9 B projecting axially outward. 
     The axially inner corners  9 A and the axially outer corners  9 B are alternately arranged in the tire circumferential direction, and the axially inner edge  9   s  is formed in a zigzag shape. Thereby, the shoulder land portion  9  is provided with an edge component in the axial direction, namely, a direction crossing the tire circumferential direction, so the traction performance and the braking performance can be improved. 
     The inner angle θ 1  of the axially inner corner  9 A is set to be larger than 90 degrees. Thereby, the rigidity of the axially inner corner  9 A is ensured, and it is possible to suppress the axially inner corner  9 A from becoming a starting point of uneven wear. In order to effectively derive such advantageous effect, the internal angle θ 1  is preferably set in a range from 120 to 160 degrees. 
     As shown in  FIG.  1   , the axial width W 3  of the shoulder land portion  9  is preferably set in a range from 17% to 28% of the tread width TW. 
     When the edge  9   s  (shown in  FIG.  4   ) of the shoulder land portion  9  is zigzag as in the present embodiment, the axial width W 3  of the shoulder land portion  9  is defined by the axial distance between the tread edge  3  and the midpoint  9   c  in the tire axial direction between the axially inner corner  9 A and the axially outer corner  9 B. 
     When the edge  9   s  of the shoulder land portion  9  is linear and extends in the tire circumferential direction, the width W 3  is defined by the maximum width of the shoulder land portion  9 . 
     By setting the width W 3  of each shoulder land portion  9  to 17% or more of the tread width TW, each shoulder land portion  9  can ensure sufficient rigidity. Thereby, in the tire  1  of the present embodiment, it is possible to reduce the deformation of the shoulder land portions  9  during braking, driving and turning, and thereby uneven wear of the shoulder land portions  9  such as shoulder wear can be suppressed. 
     By setting the width W 3  to 25% or less of the tread width TW, the crown land portion  10  can secure a sufficient axial width (in this example, the maximum axial dimension W 4  (shown in  FIG.  3   ) of the crown block  13 ). 
     Accordingly, in the tire  1  of the present embodiment, the rigidity of the crown land portion  10  is sufficiently ensured, and uneven wear (heel and toe wear and the like) is suppressed. From such a point of view, the width W 3  of each shoulder land portion  9  is preferably not less than 19% and preferably not more than 23% of the tread width TW. 
     &lt;Shoulder Sipes&gt; 
     As shown in  FIG.  4   , each of the shoulder land portions  9  is provided with shoulder sipes  11 . 
     In the present embodiment, the shoulder sipe  11  comprises a first portion  11 A extending in the tire circumferential direction, and a second portion  11 B extending from one end of the first portion  11 A while inclining to the axially inside of the tire. 
     The second portion  11 B ends without reaching the shoulder circumferential groove  6 . 
     By the first portion  11 A and the second portion  11 B, the shoulder sipe  11  has an L shape in its top view. 
     The shoulder sipes  11  are spaced apart from each other in the tire circumferential direction. 
     Such shoulder sipes  11  can enhance wet performance, while suppressing decrease in rigidity of the shoulder land portions  9  to suppress uneven wear of the shoulder land portion  9 . 
     The angle θ 5  formed between the first portion  11 A and the second portion  11 B is preferably an obtuse angle. Thereby, it is possible to alleviate strain, that tends to concentrate on the intersect portion  11 C where the first portion  11 A and the second portion  11 B intersect, when the shoulder land portion  9  is deformed, and the intersect portion  11 C is prevented from becoming a starting point of wear. 
     In order to effectively derive such advantageous effect, the angle θ 5  is preferably set in a range from 95 to 120 degrees. Further, the intersect portion  11 C is preferably formed in an arc shape. 
     The sipe width W 5  of the shoulder sipe  11  is preferably not less than 1.0 mm, more preferably not less than 1.2 mm, but preferably not more than 2.0 mm, more preferably not more than 1.8 mm. 
     By setting the sipe width W 5  to 2.0 mm or less, the rigidity of the shoulder land portion  9  is maintained, and thereby uneven wear is suppressed. 
     By setting the sipe width W 5  to 1.0 mm or more, the wet performance is ensured. 
     As shown in  FIG.  2   , the depth D 5  of the shoulder sipe  11  is preferably not less than 70%, more preferably not less than 75%, but preferably not more than 90%, more preferably not more than 85% of the groove depth D 1  of the shoulder circumferential groove  6 . 
     By setting the depth D 5  to 90% or less of the groove depth D 1 , the rigidity of the shoulder land portion  9  is maintained, and uneven wear can be suppressed. 
     By setting the depth D 5  to be 70% or more of the groove depth D 1 , wet performance can be exhibited from the early stage to the late stage of the tread wear life. 
     &lt;Crown Land Portions&gt; 
     As shown in  FIG.  1   , each of the crown land portions  10  is defined between the shoulder circumferential groove  6  and the crown circumferential groove  7 . 
     Each of the crown land portions  10  is provided with crown shallow grooves  12 , and thereby, circumferentially divided into crown blocks  13  in a circumferential row. 
     &lt;Crown Blocks&gt; 
     Each of the crown blocks  13  has a ground contacting top surface which has a maximum dimension W 4  in the tire axial direction and a maximum dimension L 4  in the tire circumferential direction as shown in  FIG.  3   . The maximum dimension L 4  in the tire circumferential direction is not less than 100%, preferably not less than 130%, but not more than 200%, preferably not more than 150% of the maximum dimension W 4  in the tire axial direction. 
     By setting the maximum dimension L 4  to 100% or more of the maximum dimension W 4 , it is possible to secure the rigidity of the crown block  13  in the tire circumferential direction to suppress uneven wear (heel and toe wear). 
     By setting the maximum dimension L 4  to 200% or less of the maximum dimension W 4 , it is possible to prevent the lateral rigidity of the crown block  13  from becoming insufficient. Thereby, the deformation of the crown block  13  during turning can be prevented from becoming large to suppress uneven wear such as abrasive wear. 
     Further, it is possible to prevent the crown shallow grooves  12  and the undermentioned groove bottom sipes  20  from becoming less or insufficient, and drainage performance is maintained. 
     As shown in  FIG.  5   , the ground contacting top surface of each of the crown blocks  13  is formed in a hexagonal shape of which width measured in the tire axial direction increases continuously from its circumferential ends toward the center in the tire circumferential direction. 
     Such crown block  13  gradually increases its lateral rigidity from the circumferential ends toward the center. As a result, deformation of the crown block  13  during turning is reduced, and uneven wear of the crown block  13  can be suppressed. 
     As shown in  FIG.  3   , the ground contacting top surface of the crown block  13  has corners  14  projecting outward of the crown block and positioned between the adjacent two crown shallow grooves  12 . 
     The corners  14  include an axially inner corner  14 A on the crown circumferential groove  7  side and an axially outer corner  14 B on the shoulder circumferential groove  6  side. 
     As shown in  FIG.  5   , the inner angle θ 2  of the axially inner corner  14 A and the inner angle θ 3  of the axially outer corner  14 B are set to be larger than 90 degrees, that is, the angles θ 2  and θ 3  are obtuse angles, to ensure their rigidity, and thereby, to prevent the axially inner corner  14 A and the axially outer corner  14 B from becoming the starting points of uneven wear. 
     In order to effectively derive such advantageous effect, it is preferred that the inner angles θ 2  and θ 3  are set in a range from 120 to 160 degrees. 
     &lt;Crown Sipes&gt; 
     The crown blocks  13  are each provided with a crown sipe  15 . 
     The crown sipe  15  provides edges to the ground contacting top surface of the crown block  13 , and thereby, the traction performance and braking performance can be improved. Further, the crown sipe  15  in this example facilitates drainage of water existing between the tread surface and the road surface. 
     As shown in  FIG.  2   , the depth D 6  of the crown sipe  15  is preferably not less than 10%, more preferably not less than 12%, but preferably not more than 20%, more preferably not more than 18% of the groove depth D 2  of the crown circumferential groove  7 . 
     By setting the depth D 6  to 20% or less of the groove depth D 2 , the rigidity of the crown block  13  can be ensured, and uneven wear resistance can be maintained. 
     By setting the depth D 6  to 10% or more of the groove depth D 2 , it is possible to discharge the water, while providing the ground contacting top surface of the crown block  13  with effective sipe edges. 
     The crown sipe  15  extends across the crown blocks  13  generally in the tire axial direction. 
     The axial inner end  15   i  of the crown sipe  15  is positioned at the axially inner corner  14 A as shown in  FIG.  5   . Thereby, the axially inner corner  14 A where the ground contact pressure becomes relatively high during braking and driving, can be prevented from increasing in rigidity more than necessary. As a result, the force (ground contact pressure) acting on the crown block  13  can be prevented from concentrating on the axially inner corner  14 A, and thereby, the axially inner corner  14 A is prevented from becoming a starting point of uneven wear. 
     The axially outer end  15   o  of the crown sipe  15  is positioned between the axially outer corner  14 B and one of the adjacent two crown shallow grooves  12 . Thereby, the axially outer corner  14 B where the ground contact pressure is relatively high during turning secures rigidity and can be prevented from becoming a starting point of uneven wear. 
     The crown sipe  15  comprises a first portion  15 A and a second portion  15 B. The first portion  15 A extends axially outwardly from the axially inner end  15   i  of the crown sipe  15 . The second portion  15 B extends axially inwardly from the axially outer end  15   o  of the crown sipe  15 . The first portion  15 A and the second portion  15 B are inclined with respect to the tire axial direction. The first portion  15 A and the second portion  15 B are connected to each other via an bending position  15   c.  Thereby, the crown sipe  15  is formed in a V shape. 
     Such edges of the first portion  15 A and the second portion  15 B can provide an axial edge component and a circumferential edge component to the ground contacting top surface of the crown block  13  to improve the traction performance and the braking performance. 
     Further, as compared to a sipe (not shown) extending straight in parallel to the tire axial direction, the crown sipe  15  which is bent, can suppress the deformation of the crown block  13  during braking and driving, and thereby suppress the uneven wear (heel-and-toe wear and the like). 
     In order to effectively derive such advantageous effect, it is preferred that the angle θ 6  of the first portion  15 A with respect to the tire axial direction and the angle θ 7  of the second portion  15 B with respect to the tire axial direction are set in a range from 10 to 30 degrees. 
     As shown in  FIG.  3   , the sipe width W 6  of the first portion  15 A may be set larger than the sipe width W 7  of the second portion  15 B. Thereby, the first portion  15 A can prevent the rigidity from increasing more than necessary on the side of the axially inner corner  14 A where the ground contact pressure during braking and driving is relatively high. Therefore, it is possible to prevent the force (ground contact pressure) acting on the crown block  13  from concentrating on the axially inner corner  14 A, and the axially inner corner  14 A can be prevented from becoming a starting point of uneven wear. 
     On the other hand, since the sipe width W 7  of the second portion  15 B is smaller than the width W 6  of the first portion  15 A, the rigidity is secured on the side of the axially outer corner  14 B where the ground contact pressure is relatively high during turning. As a result, it is possible to prevent the axially outer corner  14 B from becoming a starting point of uneven wear. 
     In order to effectively derive such advantageous effect, it is preferred that the width W 6  of the first portion  15 A is in a range from 150% to 250% of the sipe width W 7  of the second portion  15 B. The sipe width W 7  of the second portion  15 B is preferably set in the same range as the sipe width W 5  (shown in  FIG.  4   ) of the shoulder sipe  11 . 
     As shown in  FIG.  5   , the axial length L 7  of the second portion  15 B is preferably larger than the axial length L 6  of the first portion  15 A. As a result, the rigidity of the crown block  13  on the side of the axially outer corner  14 B is set to be relatively large, and thereby, the axially outer corner  14 B is prevented from becoming a starting point of uneven wear. 
     In order to effectively derive such advantageous effect, the axial length L 7  is preferably set in a range from 130% to 170% of the axial length L 6 . 
     &lt;Crown Shallow Grooves&gt; 
     As shown in  FIG.  3   , both ends of the crown shallow groove  12  are respectively connected to one of the vertices  6   a  of one of the shoulder circumferential grooves  6  projecting axially inwardly, and one of the vertices  7   a,    7   b  of the crown circumferential groove  7  projecting toward the above-said one of the shoulder circumferential grooves  6 . At the vertices  6   a  and  7   a  of the shoulder circumferential grooves  6  and the crown circumferential groove  7 , the force of water flowing in the grooves increases. By connecting the crown shallow grooves  12  to those vertices, the water in the grooves can be smoothly guided, and wet performance can be improved. 
     It is preferable that the crown shallow groove  12  extends linearly. As a result, the crown shallow groove  12  can smoothly discharge the water in the groove and improve the wet performance. 
       FIG.  6    is a cross-sectional view taken along line B-B in  FIG.  5   . 
     The crown shallow groove  12  has a groove bottom  16 , a first groove wall  17 , and a second groove wall  18 . 
     As shown in  FIG.  2   , the groove depth D 7  of the crown shallow groove  12  is set to be smaller than the groove depth D 2  of the crown circumferential groove  7 . Thereby, the rigidity of the crown land portion  10  can be secured, and uneven wear is suppressed. 
     The groove depth D 7  of the crown shallow groove  12  is preferably not less than 10%, more preferably not less than 12%, but preferably not more than 20%, more preferably not more than 18% of the groove depth D 2  of the crown circumferential groove  7 . 
     By setting the groove depth D 7  to 20% or less of the groove depth D 2 , the rigidity of the crown land portion  10  can be secured, and uneven wear resistance can be maintained. 
     By setting the groove depth D 7  to 10% or more of the groove depth D 2 , wet performance can be maintained. 
     From the same point of view, the groove width W 8  (shown in  FIG.  1   ) of the crown shallow groove  12  is preferably set in a range from 2% to 5% of the tread width TW. 
       FIG.  7    is a developed partial view of the tread portion  2  showing its worn state where the groove depth of the crown circumferential groove  7  is decreased to about 20% to 40% of the original groove depth D 2  as a result of the wear of the tread rubber. 
     As shown, the crown shallow grooves  12  (indicated by a chain double-dashed line) disappear earlier than the crown circumferential groove  7 , and each crown land portion  10  becomes a rib-like portion substantially continuous in the tire circumferential direction, therefore, the deformation during braking and driving is suppressed. 
     As a result, in the tire  1  of the present embodiment, uneven wear (heel-and-toe wear) in the crown land portions  10  which tends to occur as wear progresses, can be suppressed. 
     &lt;Groove Bottom Sipes&gt; 
     As shown in  FIGS.  1  and  2   , the groove bottom  16  of each of the crown shallow grooves  12  is provided with a groove bottom sipe  20 . 
     In the present embodiment, as shown in  FIG.  1   , the groove bottom sipe  20  is connected to the crown circumferential groove  7  and one of the shoulder circumferential grooves  6 . 
     The groove bottom sipe  20  can prevent the rigidity of the crown land portion  10  from increasing more than necessary while ensuring wet performance. 
     As a result, the groove bottom sipe  20  can prevent partial concentration of force acting on the crown land portion  10  during braking and driving, thereby suppressing uneven wear. 
     As shown in  FIG.  7   , the groove bottom sipes  20  remain even after the crown shallow grooves  12  disappear, so wet performance is maintained. 
     Further, after the crown shallow grooves  12  disappear, the crown blocks  13  adjacent to each other in the tire circumferential direction can support each other through the groove bottom sipes  20 . Thereby, the rigidity of the crown land portion  10  can be maintained, and uneven wear is suppressed. 
     In the tire  1  of the present embodiment, the groove bottom sipes  20  are provided as described above, and the groove depth D 7  of the crown shallow grooves  12  is smaller than the groove depth D 2  of the crown circumferential groove  7 . As a result, uneven wear of the crown land portions  10  of the tire  1  is effectively suppressed. 
     Further, in the tire  1  of the present embodiment, the width W 3  of each shoulder land portion  9  is limited to the range described above, and the ground contacting top surface of each of the crown blocks  13  is configured as described above. As a result, the deformation of the shoulder land portions  9  and the crown blocks  13  of the tire  1  can be reduced, and uneven wear thereof is suppressed. 
     Therefore, the tire  1  of the present embodiment can be improved in uneven wear resistance. 
     As shown in  FIG.  3   , the width W 9  of the groove bottom sipe  20  is preferably not less than 1.0 mm, more preferably not less than 1.2 mm, but preferably not more than 2.0 mm, more preferably not more than 1.8 mm. 
     By setting the width W 9  to 2.0 mm or less, the rigidity of the crown land portion  10  is maintained, thereby suppressing uneven wear. 
     By setting the width W 9  to 1.0 mm or more, wet performance and traction performance are ensured. 
     As shown in  FIG.  2   , the maximum depth D 8  of the groove bottom sipe  20  is preferably not less than 70%, but preferably not more than 90% of the groove depth D 2  of the crown circumferential groove  7 . 
     By setting the maximum depth D 8  to 70% or more of the groove depth D 2 , wet performance and traction performance can be exhibited while preventing uneven wear of the crown land portions  10  from the early stage to the late stage of wear. 
     If the maximum depth D 8  is more than 90% of the groove depth D 2 , the rigidity of the crown land portion  10  is liable to become insufficient, and uneven wear tends to occur. 
     As shown in  FIGS.  3  and  5   , in the present embodiment, the groove bottom sipe  20  is composed of a first portion  21 , a second portion  22  and a third portion  23 . 
     The first portion  21  is positioned at a first corner  24  between the groove bottom  16  and the first groove wall  17  of the crown shallow groove  12  as shown in  FIG.  6   , and extends in parallel with the longitudinal direction of the crown shallow groove  12  as shown in  FIG.  5   . 
     The second portion  22  is positioned at a second corner  25  between the groove bottom  16  and the second groove wall  18  of the crown shallow groove  12  as shown in  FIG.  6   , and extends in parallel with the longitudinal direction of the crown shallow groove  12  as shown in  FIG.  5   . 
     The third portion  23  connects one end of the first portion  21  and one end of the second portion  22  as shown in  FIG.  5   , therefore, the groove bottom sipe  20  has a crank shape in its top view. 
     As shown in  FIG.  7   , after the crown shallow grooves  12  disappear, the groove bottom sipes  20  allow the crown blocks  13  adjacent to each other in the tire circumferential direction to support each other when they are subjected to forces in the tire circumferential direction and tire axial direction. As a result, deformation of the crown blocks  13  is suppressed, so uneven wear such as abrasive wear thereof can be suppressed. 
     It is preferable that, as shown in  FIG.  3   , the other end  21   a  of the first portion  21  is connected to the shoulder circumferential groove  6  at a position other than those of the zigzag vertices  6   a  and  6   b.    
     Here, being connected to a position other than those of the zigzag vertices  6   a  and  6   b  means that the zigzag vertices  6   a  and  6   b  do not exist on the extension line from the other end  21   a  of the first portion  21 . 
     In the present embodiment, after the crown shallow grooves  12  disappear as shown in  FIG.  7   , the groove bottom sipes  20  can prevent the axially outer corners  14 B and constrictions  26  of the crown land portion  10  formed by the vertices  6   a  and  6   b,  from being lowered in rigidity. Thereby, the rigidity of the crown land portion  10  (crown blocks  13 ) is ensured, so uneven wear thereof is suppressed. 
     From the same point of view, it is preferable that the other end  22   a  of the second portion  22  is connected to the crown circumferential groove  7  at a position other than the vertices  7   a  and  7   b.    
     In the present embodiment, the groove bottom sipe  20  is formed in a crank shape. But, the groove bottom sipe  20  is not limited to such a shape. 
     For example, it may be formed in an S shape by forming at least a portion of the first portion  21 , the second portion  22  and the third portion  23  as an arc shape. 
     After the crown shallow grooves  12  disappear as shown in  FIG.  7   , it is preferable that the ground contacting top surface of each crown block  13  has a maximum dimension W 10  in the tire axial direction, and a maximum dimension L 10  in the tire circumferential direction which is not less than 104%, preferably not less than 140%, but not more than 160%, preferably not more than 150% of the maximum dimension W 10  in the tire axial direction. 
     By setting the maximum dimension L 10  to 104% or more of the maximum dimension W 10 , the rigidity of the crown block  13  in the tire circumferential direction can be ensured, and uneven wear (heel and toe wear) can be suppressed. 
     By setting the maximum dimension L 10  to 160% or less of the maximum dimension W 10 , it is possible to prevent the lateral rigidity of the crown block  13  from becoming insufficient, thereby suppressing uneven wear such as abrasive wear. 
     Further, since it is possible to prevent the number of the crown sipes  15  from decreasing, the drainage performance is maintained. 
     Heavy Duty Tire (Second Embodiment) 
     In the above-described embodiment, the crown sipe  15  traverses the crown block  13  generally in the tire axial direction. But, the crown sipe  15  is not limited to such configuration. 
       FIG.  8    shows a part of the tread portion  2  of another embodiment of the present disclosure. The components of the present embodiment which are the same as those of the previous embodiment are assigned by the same reference numerals, and the redundant descriptions will be omitted. 
     Crown Sipes (Second Embodiment) 
     In the present embodiment, the crown sipe  15  has an axially inner end  15   i  which is connected to the crown circumferential groove  7 . Thereby, the crown sipe  15  can smoothly discharge water between the tread surface and the road surface. 
     The axially inner end  15   i  of the crown sipe  15  in this example is connected to a position between the axially inner corner  14 A and the crown shallow groove  12 . 
     As a result, the crown block  13  can secure the rigidity of the axially inner corner  14 A where the ground contact pressure becomes relatively high during braking and driving, thereby preventing the axially inner corner  14 A from becoming a starting point of uneven wear. 
     The crown sipe  15  has an axially outer end  15   o  connected to one of the crown shallow grooves  12 . As a result, the crown block  13  can secure the rigidity of the axially outer corner  14 B where the ground contact pressure is relatively high during turning, thereby preventing the axially outer corner  14 B from becoming a starting point of uneven wear. 
     In the present embodiment, the crown sipe  15  is composed of a first portion  15 A and a second portion  15 B. 
     The first portion  15 A extends axially outwardly from the axially inner end  15   i  of the crown sipe  15 . The second portion  15 B extends axially inwardly from the axially outer end  15   o  of the crown sipe  15 . The first portion  15 A and the second portion  15 B are inclined with respect to the tire axial direction. 
     The first portion  15 A and the second portion  15 B are connected to each other at a bending position  15   c.  As a result, the crown sipe  15  has a V shape in its top view. 
     Thereby, the crown sipe  15  in the present embodiment can ensure traction performance and braking performance, like the crown sipe  15  in the previous embodiment. 
     The crown sipe  15  in the present embodiment can prevent the deformation of the crown block  13  during braking and driving from becoming large compared to a sipe (not shown) extending parallel to the tire axial direction. Thus, it is possible to suppress uneven wear (heel-and-toe wear) and the like. 
     Further, the angle θ 7  of the second portion  15 B with respect to the tire axial direction is set larger than the angle θ 6  of the first portion  15 A with respect to the tire axial direction. As a result, the second portion  15 B can ensure rigidity of the axially outer corner  14 B where the ground contact pressure is relatively large during turning. As a result, it is possible to prevent the axially outer corner  14 B from becoming a starting point of uneven wear. 
     In order to effectively derive such advantageous effect, the angle θ 6  of the first portion  15 A with respect to the tire axial direction is preferably 10 to 30 degrees, and the angle θ 7  of the second portion  15 B with respect to the tire axial direction is preferably 50 to 70 degrees. 
     The width W 6  of the first portion  15 A may be set smaller than the sipe width W 7  of the second portion  15 B. As a result, the first portion  15 A can secure the rigidity of the axially inner corner  14 A where the ground contact pressure is relatively high during braking and driving, and can prevent the axially inner corner  14 A from becoming a starting point of uneven wear. 
     On the other hand, since the width W 7  of the second portion  15 B is set larger than the width W 6  of the first portion  15 A, water between the tread surface and the road surface can be smoothly discharged in the vicinity of the outer corner  14 B where the ground contact pressure is relatively high during turning. 
     In order to effectively derive such advantageous effect, the width W 6  of the first portion  15 A is preferably set in a range from 40% to 70% of the sipe width W 7  of the second portion  15 B. 
     In the present embodiment, the groove center lines (not shown) of two of the first portions  15 A adjacent to each other across the crown circumferential groove  7  are arranged on one straight line. As a result, the two first portions  15 A can form a large edge component in the direction crossing the tire circumferential direction in the vicinity of the tire equator C where the ground contact pressure is relatively high during braking and driving. Thereby, the traction performance and braking performance can be improved. 
     While detailed description has been made of preferable embodiments of the present disclosure, the present disclosure can be embodied in various forms without being limited to the illustrated embodiments. 
     Comparison Tests 
     &lt;&lt;Mode A&gt;&gt; 
     Based on the tread pattern shown in  FIG.  1   , heavy-duty tires having specifications listed in Table 1 were experimentally manufactured as test tires (working examples Ex. 1 to Ex. 6 and comparative examples Ref. 1 to Ref. 4), and tested for uneven wear resistance and wet performance. 
     In the comparative example Ref. 4, crown blocks thereof were configured to have the same shape as the crown blocks of Patent Document 1. 
     Common specifications to all the test tires are as follows.
     Tire size: 315/80R22.5   Rim size: 9×22.5   Tire inflation pressure: 900 kPa   Tire Load: 4000 kg   Tread width TW: 280 mm   Test vehicle: Garbage truck   

     Shoulder Circumferential Grooves 
     Groove width W 1 : 5% of Tread width TW 
     Groove depth D 1 : 20.1 mm 
     Crown Circumferential Groove 
     Groove width W 2 : 5% of Tread width TW 
     Groove depth D 2 : 20.1 mm 
     Shoulder Land Portions 
     Inner angle θ 1  of Axially inner corner: 140 degrees 
     Crown Blocks 
     Maximum dimension L 4  in tire circumferential direction: 85 mm 
     Inner angle θ 2  of Axially inner corner: 140 degrees 
     Inner angle θ 3  of Axially outer corner: 140 degrees 
     Crown Shallow Grooves 
     Groove depth D 7 : 13.4% of Groove depth D 2   
     Groove width W 8 : 3.1% of Tread width TW 
     Shoulder Sipes 
     Width W 5 : 1.5 mm 
     Depth D 5 : 80% of Groove depth D 1   
     Crown Sipes 
     Depth D 6 : 15% of Groove depth D 2   
     First portion width W 6 : 200% of Second portion width W 7   
     Second portion length L 7 : 150% of First portion length L 6   
     First portion angle θ 6 : 20 degrees 
     Second portion angle θ 7 : 20 degrees 
     Groove Bottom Sipe: 
     width W 9 : 1.5 mm 
     Maximum depth D 8 : 80% of Groove depth D 2   
     Test methods are as follows. 
     &lt;Uneven Wear Resistance&gt; 
     Each test tire mounted on the above-mentioned rim and inflated to the above-mentioned pressure, was installed on all wheels of the above test vehicle. 
     After running for six months without tire rotation, uneven wear (heel and toe wear) of the crown land portions, and uneven wear (shoulder drop wear) of the shoulder land portions were visually inspected and evaluated. 
     The evaluation results are indicated in Table 1 by an index based on the working example Ex. 1 being 100, wherein the larger the value, the better the uneven wear resistance. 
     &lt;Wet Performance&gt; 
     Each test tire mounted on the above-mentioned rim and inflated to the above-mentioned pressure, was installed on all wheels of the above test vehicle. 
     Then, the braking distance was measured when the test vehicle running on a wet paved road surface at 80 km/h was suddenly braked. 
     The results are indicated in Table 1 by an index based on the working example Ex. 1 being 100, wherein the larger the number, the better the wet performance. When the index is 95 or higher, the wet performance is considered as being maintained. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Tire 
                 Ref. 1 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ref. 2 
               
               
                   
               
               
                 W3/TW (%) 
                 15 
                  17 
                 23 
                 28 
                 30 
               
               
                 L4/W4 (%) 
                 142 
                 142 
                 142 
                 142 
                 142 
               
               
                 Crown block shape 
                 hexagon 
                 hexagon 
                 hexagon 
                 hexagon 
                 hexagon 
               
               
                 Uneven wear 
               
               
                 resistance 
               
               
                 Shoulder land portions 
                 93 
                 100 
                 105 
                 106 
                 106 
               
               
                 Crown land portions 
                 101 
                 100 
                 99 
                 97 
                 91 
               
               
                 Wet performance 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Tire 
                 Ref. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
                 Ref. 4 
               
               
                   
               
               
                 W3/TW (%) 
                 23 
                 23 
                 23 
                 23 
                 23 
               
               
                 L4/W4 (%) 
                 90 
                 100 
                 150 
                 200 
                 142 
               
               
                 Crown block shape 
                 hexagon 
                 hexagon 
                 hexagon 
                 hexagon 
                 dodecagon 
               
               
                 Uneven wear 
               
               
                 resistance 
               
               
                 Shoulder land portions 
                 100 
                 100 
                 100 
                 100 
                 105 
               
               
                 Crown land portions 
                 91 
                 97 
                 101 
                 103 
                 92 
               
               
                 Wet performance 
                 103 
                 102 
                 99 
                 98 
                 100 
               
               
                   
               
            
           
         
       
     
     From the test results, it was confirmed that, as compared to the comparative examples, the working examples were improved in the uneven wear resistance while maintaining the wet performance. 
     &lt;&lt;Mode B&gt;&gt; 
     Based on the tread pattern shown in  FIG.  1   , heavy-duty tires having specifications listed in Table 2 were experimentally manufactured as test tires (working examples Ex. 7 to Ex. 14), and tested for uneven wear resistance and wet performance. 
     Common specifications were the same as those of Mode A except for the following specifications and specifications listed in Table 2. 
     Shoulder Land Portions 
     Width W 3 : 23% of Tread width TW 
     Crown Blocks 
     Maximum dimension L 4 : 142% of Maximum dimension W 4  M 
     Shape: Hexagon 
     Test methods are the same as described above, and the test results are indicated in Table 2. In Table 2, the working example Ex. 2 is added as a reference. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Tire 
                 Ex. 7 
                 Ex. 8 
                 Ex. 2 
                 Ex. 9 
                 Ex. 10 
                 Ex. 11 
                 Ex. 12 
                 Ex. 13 
                 Ex. 14 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 D7/D2 (%) 
                 8 
                 10 
                 13.4 
                 20 
                 22 
                 13.4 
                 13.4 
                 13.4 
                 13.4 
               
               
                 W9 (mm) 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 0.8 
                 1.0 
                 2.0 
                 2.1 
               
               
                 Uneven wear 
               
               
                 resistance 
               
               
                 Shoulder land portions 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
               
               
                 Crown land portions 
                 101 
                 100 
                 99 
                 98 
                 96 
                 103 
                 102 
                 98 
                 96 
               
               
                 Wet performance 
                 97 
                 99 
                 100 
                 101 
                 102 
                 97 
                 98 
                 102 
                 103 
               
               
                   
               
            
           
         
       
     
     From the test results, it was confirmed that the working examples in which the groove depth D 7  of the crown shallow groove and the width W 9  of the groove bottom sipe were within the respective preferable ranges were improved in the uneven wear resistance while maintaining the wet performance, as compared to the working examples in which the groove depth D 7  and the width W 9  were outside the respective preferable ranges. 
     &lt;&lt;Mode C&gt;&gt; 
     Based on the tread pattern shown in  FIG.  1   , heavy-duty tires having specifications listed in Table 3 were experimentally manufactured as test tires (working examples Ex. 15 to Ex. 22), and tested for uneven wear resistance and wet performance. 
     Common specifications were the same as those of Mode A except for the following specifications and specifications listed in Table 3. 
     Shoulder Land Portions 
     Width W 3 : 23% of Tread width TW 
     Crown Blocks 
     Maximum dimension L 4 : 142% of Maximum dimension W 4   
     Shape: Hexagon 
     Test methods are the same as described above, and the test results are indicated in Table 3. In Table 3, the working example Ex. 2 is added as a reference. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Tire 
                 Ex. 15 
                 Ex. 16 
                 Ex. 2 
                 Ex. 17 
                 Ex. 18 
                 Ex. 19 
                 Ex. 20 
                 Ex. 21 
                 Ex. 22 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 D8/D2 (%) 
                 60 
                 70 
                 80 
                 90 
                 95 
                 80 
                 80 
                 80 
                 80 
               
               
                 D6/D2 (%) 
                 15 
                 15 
                 15 
                 15 
                 15 
                 5 
                 10 
                 20 
                 25 
               
               
                 Uneven wear 
               
               
                 resistance 
               
               
                 Shoulder land portions 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
                 105 
               
               
                 Crown land portions 
                 102 
                 100 
                 99 
                 98 
                 96 
                 103 
                 101 
                 98 
                 96 
               
               
                 Wet performance 
                 96 
                 99 
                 100 
                 101 
                 103 
                 97 
                 99 
                 101 
                 102 
               
               
                   
               
            
           
         
       
     
     From the test results, it was confirmed that the working examples in which the maximum depth D 8  of the groove bottom sipe and the depth D 6  of the crown sipe were within the respective preferable ranges. were improved in the uneven wear resistance while maintaining the wet performance, as compared to the working examples in which the maximum depth D 8  and the depth D 6  were outside the respective preferable ranges. 
     Statement of the Present Disclosure 
     
         
         The present disclosure is as follows: 
         Disclosure 1: A heavy duty tire comprising: 
         a tread portion having tread edges and comprising land portions axially divided by circumferential grooves extending continuously in the tire circumferential direction, the circumferential grooves include a pair of shoulder circumferential grooves and at least one crown circumferential groove disposed therebetween, 
         the land portions include a pair of shoulder land portions defined between the tread edges and the shoulder circumferential grooves, and a pair of crown land portions defined between the shoulder circumferential grooves and the crown circumferential groove, 
         the axial width of each of the shoulder land portions is 17% to 28% of the tread width between the tread edges, 
         each of the crown land portions is circumferentially divided by crown shallow grooves into a row of crown blocks, 
         the groove depth of each of the crown shallow grooves is smaller than the groove depth of the crown circumferential groove, 
         the groove bottom of each of the crown shallow grooves is provided with a groove bottom sipe, 
         each of the crown blocks has a ground contacting top surface which has a maximum dimension in the tire axial direction and a maximum dimension in the tire circumferential direction which is 100% to 200% of the maximum dimension in the tire axial direction, and 
         the ground contacting top surface of each of the crown blocks has a hexagonal shape of which width measured in the tire axial direction increases continuously from both ends in the tire circumferential direction toward the center therebetween. 
         Disclosure 2: The heavy duty tire according to Disclosure 1, wherein 
         the groove depths of the crown shallow grooves are in a range from 10% to 20% of the groove depth of the crown circumferential groove. 
         Disclosure 3: The heavy duty tire according to Disclosure 1 or 2, wherein 
         each of the crown shallow grooves is a straight groove. 
         Disclosure 4: The heavy duty tire according to Disclosure 1, 2 or 3, wherein 
         each of the shoulder circumferential grooves is a zigzag groove having axially inwardly projecting vertices ( 6   a ) and axially outwardly projecting vertices ( 6   b ), 
         the crown circumferential groove is a zigzag groove having vertices ( 7   a ) projecting toward one of the shoulder circumferential grooves, and vertices ( 7   b ) projecting toward the other of the shoulder circumferential grooves, and 
         each of the crown shallow grooves is connected to one of the axially inwardly projecting vertices ( 6   a ) of one of the shoulder circumferential grooves, and one of the vertices ( 7   a ) of the crown circumferential groove projecting toward said one of the shoulder circumferential grooves. 
         Disclosure 5: The heavy duty tire according to any one of Disclosures 1 to 4, wherein 
         the ground contacting top surface of each of the crown blocks is provided with a crown sipe. 
         Disclosure 6: The heavy duty tire according to Disclosure 5, wherein 
         the crown sipe traverses said ground contacting top surface in the tire axial direction. 
         Disclosure 7: The heavy duty tire according to Disclosure 6, wherein 
         the ground contacting top surface of each of the crown blocks has 
         an axially inner corner protruding toward the crown circumferential groove, and 
         an axially outer corner protruding toward the adjacent shoulder circumferential groove, and the crown sipe has an axially inner end connected to the axially inner corner. 
         Disclosure 8: The heavy duty tire according to Disclosure 7, wherein 
         the crown sipe has an axially outer end connected to the shoulder circumferential grooves at a position between the axially outer corner and one of the crown shallow grooves. 
         Disclosure 9: The heavy duty tire according to Disclosure 8, wherein 
         each of the crown sipes comprises a first portion extending axially outward from the axially inner end of the crown sipe, and a second portion extending axially inward from the axially outer end of the crown sipe, and the first portion and the second portion are inclined with respect to the tire axial direction. 
         Disclosure 10: The heavy duty tire according to Disclosure 9, wherein 
         the width of the first portion is larger than the width of the second portion. 
         Disclosure 11: The heavy duty tire according to Disclosure 5, wherein 
         the crown sipe has an axially inner end connected to the crown circumferential groove. 
         Disclosure 12: The heavy duty tire according to Disclosure 11, wherein 
         the crown sipe has an axially outer end connected to one of the crown shallow grooves. 
         Disclosure 13: The heavy duty tire according to Disclosure 12, wherein 
         each of the crown sipes comprises a first portion extending axially outward from the axially inner end of the crown sipe, and a second portion extending axially inward from the axially outer end of the crown sipe, and the first portion and the second portion are inclined with respect to the tire axial direction. 
         Disclosure 14: The heavy duty tire according to Disclosure 13, wherein 
         the width of the first portion is less than the width of the second portion. 
         Disclosure 15: The heavy duty tire according to any one of Disclosures 1 to 14, wherein 
         the groove bottom sipe has a width of 1.0 to 2.0 mm. 
         Disclosure 16: The heavy duty tire according to any one of Disclosures 1 to 15, wherein 
         the maximum depth of the groove bottom sipe is 70% or more of the groove depth of the crown circumferential groove. 
       
    
     DESCRIPTION OF THE REFERENCE SIGNS 
       6  Shoulder circumferential groove 
       7  Crown circumferential groove 
       9  Shoulder land portion 
       10  Crown land portion 
       12  Crown shallow groove 
       13  Crown block 
       20  Groove bottom sipe