JP4568099B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having a plurality of land portions defined on a tread surface by a plurality of circumferential grooves, and more particularly to a pneumatic tire having improved performance at the initial use of the tire.

  There is a so-called studless tire as a tire with improved performance on an icy and snowy road surface or a wet road surface. Studless tires are blended with various fillers to obtain an edge effect on the ice surface, and foam rubber is used to obtain the water absorption / edge effect of the foam layer during the period of use. There are things.

  However, in general, when rubber is vulcanized and cured, the filler and the foamed layer are not exposed on the surface of the tire that is in direct contact with the mold, and a film tends to be formed on the surface of the tire. As a result, in the initial use of the tire, the effect of the filler and the foam layer is not exhibited (or the effect is small).

  On the other hand, for example, Patent Document 1 and Patent Document 2 describe pneumatic tires for snowy and snowy roads that have improved braking / driving performance in the early stage of wear by forming narrow grooves on the tread surface. Patent Document 3 describes a pneumatic tire in which shallow grooves that form an angle of 0 ° to 40 ° with the tire circumferential direction are arranged side by side in the tire width direction at the ground contact portion of the tread.

On the other hand, however, there is a problem that the performance on the dry road surface is lowered due to the formation of the shallow groove.
JP 2004-34902 A JP 2004-34903 A Japanese Patent Laid-Open No. 7-186633

  In view of the above fact, an object of the present invention is to obtain a pneumatic tire capable of improving the performance in the initial stage of use and ensuring the performance on the dry road surface.

  The invention according to claim 1 is a pneumatic tire having a plurality of land portions partitioned by a plurality of main grooves on a tread surface, wherein the land portions are divided by at least one sipe to form sub-blocks. The tread pattern is asymmetrical between the outer half region located outside and the inner half region located inside when the tire is mounted on the tire equatorial plane. A plurality of shallow outer shallow grooves are formed, and a plurality of inner shallow grooves shallower than the sipe are formed in the inner half region of the land portion, and the inner shallow grooves are wider than the outer shallow grooves. It is characterized by satisfying at least one condition of a deep depth and a high formation density.

  Here, examples of the “land portion” include blocks and ribs partitioned by main grooves. In this pneumatic tire, main grooves, sipes, outer shallow grooves, and inner shallow grooves (hereinafter, the outer shallow grooves and the inner shallow grooves are collectively referred to as “shallow grooves”) are formed on the tread surface. Various magnitudes and levels of force are applied to the pneumatic tire, but the edge effect of the main groove is applied to a relatively large force, and the sipe is applied to a relatively small force that remains at the land deformation. The edge effect is exerted, and the edge effect of the shallow groove is exhibited for a further minute force. In addition, the water absorption effect is also exhibited mainly in sipes and shallow grooves. Thereby, various forces can be received in a wider range, and the frictional force of the pneumatic tire can be effectively improved.

  Further, the tread pattern of the present invention is asymmetric on both sides of the tire equatorial plane. That is, the land pattern is asymmetrical between the outer half region located outside the tire equator when mounted on the vehicle and the inner half region located inside.

  Usually, in the case of a tire having such an asymmetric pattern, in order to ensure tire performance on a dry road surface, it is effective to make the rigidity and ground contact area of the outer half region larger than that of the inner half region. On the other hand, it is also necessary to ensure drainage on icy and snowy road surfaces.

  Therefore, in the present invention, the relationship between the inner shallow groove and the outer shallow groove satisfies at least one of the conditions that the inner shallow groove is wider, deeper, and has a higher formation density than the outer shallow groove. To.

  When the inner shallow groove satisfies the above-described conditions, the outer shallow groove satisfies at least one of the following conditions: narrower width, smaller depth, and lower formation density than the inner shallow groove. The rigidity can be ensured, the contact area can be increased, and the tire performance on the dry road surface can be ensured.

  On the other hand, the inner shallow groove formed in the inner half region satisfies at least one of the following conditions: wider, deeper, and higher density than the outer shallow groove. Can be improved.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the outer shallow groove and the inner shallow groove are linear in the tire circumferential direction.

  According to the above configuration, the outer shallow groove and the inner shallow groove having different widths can be easily formed. In addition, the formation density can be easily changed simply by changing the formation pitch.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the difference between the width of the outer shallow groove and the width of the inner shallow groove is 0.1 mm to 0.9 mm. And

  In consideration of the suppression of deformation of the micro land portion, the water removal effect, and the balance between the two, it is preferable that the difference in width between the two is 0.1 mm to 0.9 mm as described above.

  The invention according to claim 4 is the invention according to claims 1 to 3, wherein the difference between the width of the outer shallow groove and the depth of the inner shallow groove is 0.1 mm to 0.4 mm. To do.

  In consideration of the suppression of deformation of the micro land portion, the water removal effect, and the balance between the two, it is preferable that the difference in depth between the two is 0.1 mm to 0.9 mm as described above.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the shallow groove has a depth of 0.1 mm to 0.5 mm.

  In this way, by setting the depth of the outer shallow groove and the inner shallow groove to 0.5 mm or less, the deformation at the time of ground contact of the micro land portion defined by the outer shallow groove and the inner shallow groove is suppressed, and wear is reduced. Can be reduced. In addition, by setting the depth of the outer shallow groove and the inner shallow groove to 0.1 mm or more, it is possible to secure a sufficient amount of water that can be taken into the outer shallow groove and the inner shallow groove, and to obtain a high water removal effect. .

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the outer shallow groove and the inner shallow groove have a width of 0.1 mm to 1.0 mm. It is characterized by.

  As described above, by setting the width of the outer shallow groove and the inner shallow groove to 1.0 mm or less, it is possible to secure the tread area of the micro land portion and obtain high performance in the initial use. Moreover, the water | moisture content which can be taken in in a shallow groove is ensured by making the width | variety of an outer shallow groove and an inner shallow groove into 0.1 mm or more, and a high water removal effect can be acquired.

The invention of claim 7 is the invention according to any one of claims 1 to 6, a plurality of micro land portions partitioned by a plurality of the shallow grooves, 0.4mm ² ~30mm ² It is characterized by the tread surface area.

By setting the tread surface area of the micro land portion to 0.4 mm ² or more, it is possible to secure a ground contact area and obtain high performance in the initial use. In addition, by limiting to 30 mm ² or less, it is possible to secure a shallow groove region (negative rate) per unit area, so that a high water removal effect can be obtained by increasing the amount of water that can be taken into the shallow groove. Can do.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the rubber constituting the land portion includes a foamed rubber layer on a radially outer side of the tire and a radially inner side. And an unfoamed rubber layer.

  In the pneumatic tire having the above structure, when the ground contact surface is worn by use, the foamed portion (foamed layer) of the foamed rubber layer is exposed. Therefore, the water absorption effect generated between the foamed portion and the road surface, and the road surface Edge effect can be obtained. Therefore, changes in performance, such as the water absorption effect and the edge effect, from the state in which the foamed portion is not exposed to the exposure in the initial use of the pneumatic tire can be moderated.

  Since the present invention has the above configuration, it is possible to improve the performance in the initial stage of use and ensure the performance on the dry road surface.

  FIG. 1 shows a pneumatic tire 10 according to a first embodiment of the present invention. The pneumatic tire 10 has a predetermined rotational direction. In the drawing, this rotational direction is indicated by an arrow S, and the tire width direction orthogonal thereto is indicated by an arrow W. The circumferential direction of the pneumatic tire 10 is the rotational direction and the opposite direction.

  As shown in FIGS. 2 and 3, the tread 12 of the pneumatic tire 10 includes an inner rubber layer 34 on the inner side in the tire radial direction and an outer rubber layer 36 on the outer side in the tire radial direction.

  The outer rubber layer 36 is a foamed rubber layer in which a large number of bubbles are present. When the pneumatic tire 10 is used, moisture between the tread 12 and the road surface is absorbed into the bubbles. The Moreover, the edge effect caught on the road surface by air bubbles is also exhibited. However, in general, in the initial stage of use of the pneumatic tire 10, bubbles are not exposed on the tire surface (tread surface) in direct contact with the tire molding die.

  On the other hand, the inner rubber layer 34 is an unfoamed rubber layer in which such bubbles do not exist, and has higher rigidity than the outer rubber layer 36. Thereby, the shape of the tread 12 can be stably maintained.

  As shown in FIG. 1, the tread 12 of the pneumatic tire 10 has a linear central circumferential groove 14 formed on the tire equator plane CL, and circumferential grooves 16 formed on both sides of the tire equator plane CL in the tire width direction. Has been. The central circumferential groove 14 divides the tread 12 of the tire 10 into two in the tire circumferential direction to form two tread half regions. Each tread half area is set as an outer half area OH arranged on the outer side OUT and an inner half area IH arranged on the inner side IN when mounted on the vehicle.

  A lateral groove 18 that curves toward the tire equatorial plane CL and intersects the circumferential groove 16 is formed from the outer side OUT of the outer half region OH of the pneumatic tire 10. The lateral groove 18 is bent in the rotational direction at an intermediate portion between the circumferential groove 16 and the central circumferential groove 14, and a lateral groove 24 continuous with the central circumferential groove 14 is formed from the substantially longitudinal center of the bent portion. Has been.

From the inner side IN of the inner half region IH of the pneumatic tire 10, a lateral groove 19 that curves in the direction opposite to the lateral groove 18 toward the tire equatorial plane CL and intersects the circumferential groove 16 is formed. The lateral groove 19 is bent toward the opposite side in the rotational direction at an intermediate portion between the circumferential groove 16 and the central circumferential groove 14, and further, the lateral groove 24 connected to the central circumferential groove 14 from the substantially longitudinal center of the bent portion. Is formed.
The central circumferential groove 14, the circumferential groove 16, and the lateral grooves 18, 19, 24 are the main grooves 38 according to the present invention, and a plurality of blocks 20 are provided in the tread 12 of the pneumatic tire 10 by the main grooves 38. (Likube) is defined.

  As described above, in the tread pattern of the tire 10 of the present embodiment, both sides of the central circumferential groove 14 are asymmetric and the pattern of the block 20 is also asymmetric.

The pneumatic tire 10 of the present embodiment is used as a winter studless tire, and the tread rubber forming the tread 12 has a hardness (0 ° C., JIS-A) of 50 degrees, The loss coefficient tan δ (peak position) is −45 ° C. and the dynamic elastic modulus (−20 ° C., 0.1% strain) is 180 kgf / cm ² , but the present invention is not limited to this.

The tread rubber used as a winter studless tire has a hardness (0 ° C., JIS-A) of 40 to 68 degrees, a loss coefficient tan δ (peak position) of −30 ° C. or less, and a dynamic elastic modulus ( −20 ° C., 0.1% strain) is preferably 300 kgf / cm ² or less.

Here, when the hardness of the tread rubber is less than 40 degrees, it is too soft and inferior in wear resistance, and when it is higher than 68 degrees, it is too hard and the contact area with the snowy and snowy road surface decreases, resulting in inferior braking performance and driving performance. Therefore, it is not preferable. Further, if the loss coefficient tan δ (peak position) is higher than −30 °, it is not preferable because it is too stiff on the snowy and snowy road surface and the contact area is reduced, resulting in poor braking performance and driving performance. Furthermore, if the dynamic elastic modulus is higher than 300 kgf / cm ² , it is not preferable because it is too stiff on the snowy and snowy road surface and the contact area is reduced, resulting in poor braking performance and driving performance.

  On the other hand, the central circumferential groove 14, the circumferential groove 16, and the lateral grooves 18, 19, and 24 are preferably set to a groove depth of 8 mm or more and a groove width of 3 mm or more from the viewpoint of drainage and life, and the negative ratio of the tread 12 tread surface. Is preferably 25 to 65% from the viewpoint of drainage and the rigidity of the block 20.

  Here, if the groove depth is less than 8 mm and the groove width is less than 3 mm, the drainage by the groove cannot be sufficiently exhibited, which is not preferable. Further, if the negative ratio is less than 25%, the drainage performance is lowered, which is not preferable. If the negative ratio is higher than 65%, the land block 20 becomes smaller and the rigidity is lowered, so that the braking performance and the driving performance are lowered. In some cases, wear resistance is also deteriorated, which is not preferable.

  As shown in FIGS. 4 and 5, linear sipe 22 extending in the tire width direction (arrow W direction) is provided on the treads of these blocks 20, and each of the blocks 20 has a main groove 38. -It is divided into a plurality of sub-blocks 28 between the sipes 22 or between the sipes 22 and the sipes 22.

  Further, the tread surface of the block 20 is provided with an outer shallow groove 26 and an inner shallow groove 27 that can absorb moisture generated between the block 20 and the water film to be removed or reduced. The outer shallow groove 26 and the inner shallow groove 27 of the present embodiment are linear along the circumferential direction of the tire 10, and the sub-block is a micro land portion 30 by the outer shallow groove 26 and / or the inner shallow groove 27. It is divided into. The outer shallow groove 26 is formed in the outer half region OH on the outer side OUT from the central circumferential groove 14, and the inner shallow groove 27 is formed in the inner half region IH on the inner side IN from the central circumferential groove 14.

  The width W2 of the inner shallow groove 27 is wider than the width W1 of the outer shallow groove 26, and the depth D2 of the inner shallow groove 27 is deeper than the depth D1 of the outer shallow groove 26. The formation pitch of the inner shallow grooves 27 is narrower than the formation pitch of the outer shallow grooves 26. As a result, the formation density of the inner shallow grooves 27 is larger than the formation density of the outer shallow grooves 26.

  The difference between the width W1 of the outer shallow groove 26 and the width W2 of the inner shallow groove 27 is in the range of 0.1 mm to 0.00 in consideration of the suppression of the deformation of the micro land portion, the water removal effect, and the balance between the two. It is preferable to be 9 mm. Further, the difference between the depth D1 of the outer shallow groove 26 and the depth D2 of the inner shallow groove 27 is also 0.1 mm to considering the suppression of the deformation of the micro land portion, the water removal effect, and the balance between the two. It is preferable to be 0.4 mm.

  As shown in FIG. 6, the width W1 of the outer shallow groove 26 and the width W2 of the inner shallow groove 27 are formed to be at least narrower than the width W3 of the sipe 22 (see FIG. 3). W1 and the width W2 of the inner shallow groove 27 are preferably in the range of 0.1 mm to 1.0 mm. By setting the widths W1 and W2 to be equal to or less than 1.0 mm, the deformation of the micro land portion 30 at the time of ground contact can be suppressed and wear can be reduced. Further, by setting the widths W1 and W2 to 0.1 mm or more, it is possible to secure a sufficient amount of water that can be taken into the outer shallow groove 26 and the inner shallow groove 27 and to obtain a high water removal effect.

  As shown in FIG. 6, the outer shallow groove 26 and the inner shallow groove 27 have a substantially rectangular cross section, and the depths D1 and D2 are preferably in the range of 0.1 mm to 0.5 mm. By setting the depths D1 and D2 to 0.1 mm or more, it is possible to secure an amount of moisture that can be taken into the outer shallow groove 26 and the inner shallow groove 27 and to obtain a high water removal effect. Further, by setting the depths D1 and D2 to 0.5 mm or less, it is possible to suppress the deformation at the time of the ground contact of the micro land portion 30 and reduce the wear.

As the tread area of the small land portion 30, it is preferable to 0.4mm ² ~30mm ^2. By setting the tread surface area to 0.4 mm ² or more, it is possible to secure a ground contact area and obtain high performance in the initial use of the pneumatic tire 10. Further, by limiting to 30 mm ² or less, it is possible to secure an amount of moisture that can be taken into the outer shallow groove 26 and the inner shallow groove 27 and to obtain a high water removal effect.

  The outer shallow groove 26 and the inner shallow groove 27 can be formed on the inner surface of a mold for vulcanizing the pneumatic tire 10 by cutting, electric discharge machining, etching, or the like.

  In addition, the outer shallow groove 26 and the inner shallow groove 27 can be formed on a molded tire or a tire whose surface is worn to some extent by running, in such a tire, by knife cutting or sandpaper. It can be formed by a surface buff or the like.

  Next, the effect | action of the pneumatic tire 10 of this embodiment is demonstrated.

  The tread 12 of the pneumatic tire 10 includes an inner rubber layer 34 (unfoamed rubber layer) on the inner side in the tire radial direction and an outer rubber layer 36 (foamed rubber layer) on the outer side in the tire radial direction. In the initial stage of use, the bubbles of the outer rubber layer 36 are not exposed on the tread.

  When the pneumatic tire 10 in the initial use state travels on an icy and snowy road, water is generated due to pressure, friction, and the like when the tread 12 contacts the ice or snow. This water that causes a reduction in frictional force is taken into the outer shallow groove 26 and the inner shallow groove 27 provided on the tread surface of the block 20, and through this groove portion (or further via the sipe 22), the center. Since it is discharged to the circumferential groove 14, the circumferential groove 16, and the lateral grooves 18, 19, and 24, the water film between the tread surface and the road surface is removed.

  For this reason, the pneumatic tire 10 of the present embodiment has improved braking performance and driving performance on the icy and snowy road surface in the initial use compared to a tire in which the outer shallow groove 26 and the inner shallow groove 27 are not formed on the tread. Also on the wet road surface, the wet performance is improved by the drainage effect of the outer shallow groove 26 and the inner shallow groove 27.

  In particular, in the present embodiment, the tread pattern is asymmetric on both sides of the central circumferential groove 14, and the width of the outer shallow groove 26 formed in the outer half region OH is reduced, the depth is reduced, and the formation density is reduced. Yes. Usually, in order to ensure performance such as steering stability on a dry road surface, the rigidity of the outer half region OH and the width of the ground contact area are required more than the rigidity of the inner half region IH and the width of the ground contact area. By setting it as the said structure, the performance on a dry road surface can be ensured efficiently.

  In this embodiment, the width of the inner shallow groove 27 formed in the inner half region IH is wide, the depth is deep, and the formation density is increased. Usually, since it is necessary to ensure drainage in an icy and snowy road, drainage can be improved efficiently by having the inner shallow groove 27 configured as described above.

  In the present embodiment, the inner shallow groove 27 is wider, deeper, and larger than the outer shallow groove 26 in all three elements of the width, depth, and formation density of the outer shallow groove 26 and the inner shallow groove 27. Although the example made to become was demonstrated, it is sufficient that at least one of the three elements is satisfied.

  Further, the shallow groove according to the present invention is not limited to the linear outer shallow groove 26 and the inner shallow groove 27 described above, but a zigzag outer shallow groove 50 extending in the tire circumferential direction S as shown in FIG. Even the inner shallow groove 52 may be a corrugated outer shallow groove 54 and an inner shallow groove 56 extending in the tire circumferential direction, as shown in FIG.

  Further, in the present embodiment, the pneumatic tire 10 in which the sipe 22 is formed in the block 20 has been described as an example. However, the present invention is applied to a pneumatic tire in which the sipe 22 is not formed, and the outer shallow groove 26 and the inner side. It is also possible to form the shallow groove 27 in the block 20. In this case, if the shallow groove is shallower and narrower than at least the central circumferential grooves 14 and 16 and the lateral grooves 18, 19 and 24, the outer shallow groove 26 and the inner shallow groove 27 are included in the basic performance of the pneumatic tire. The water removal effect which is the original effect of the outer shallow groove 26 and the inner shallow groove 27 can be maintained.

  Further, not only the pneumatic tire 10 in which the block 20 is formed by the main groove 38 but also a pneumatic tire in which a rib is formed, for example, a pneumatic tire according to the present invention is formed by forming a shallow groove in the rib. Is possible.

  Moreover, it replaces with the outer rubber layer comprised with the foamed rubber layer as the block 20 (or rib), and may be comprised with the rubber with which the filler was filled in order to improve on-ice performance. Even in this configuration, it is assumed that the filler is not exposed on the tread at the initial use of the pneumatic tire, but by using the shallow groove as in this embodiment, the initial use of the pneumatic tire The performance at can be improved.

  Next, the present invention will be described in more detail with reference to examples.

  In this example, the pneumatic tire 10 of the present embodiment shown in FIGS. 1 to 5 was mounted on a passenger car, and the on-ice performance in the initial use was evaluated. The width W1 of the outer shallow groove 26 is 0.2 mm, the width W2 of the inner shallow groove 27 is 0.4 mm, the depth D1 of the outer shallow groove 26 is 0.1 mm, and the depth D2 of the inner shallow groove 27 is 0. It is 3 mm.

  Further, as a comparative example, the performance on ice in the initial use was similarly evaluated using a pneumatic tire 70 shown in FIG. In this pneumatic tire 70, straight shallow grooves 72 along the tire circumferential direction S are formed at equal intervals, and the widths of the formed shallow grooves 72 are all 0.3 mm and the depth is all. It is set to 0.2 mm. .

  Table 1 shows the basic configuration of the pneumatic tires 10 and 70 and the evaluation of the performance on ice.

これら実施例及び比較例では、共通の条件として、
・タイヤサイズ：１９５／６５Ｒ１６
・使用リム ：６Ｊ−１５
・使用内圧 ：２１０ｋＰａ（フロント、リヤ同じ）
とした。

In these examples and comparative examples, as common conditions,
・ Tire size: 195 / 65R16
・ Rim used: 6J-15
・ Internal pressure: 210 kPa (same for front and rear)
It was.

<Test method and evaluation method>
-Acceleration on ice The time required to accelerate from 5 km / h to 15 km / h on ice was measured, and a comparative example was taken as a comparative example and index evaluation was relatively performed. The larger the value, the better the acceleration performance.

-Braking distance The braking distance required to decelerate to 0 km / h by brake lock while driving at a constant speed of 20 km / h on ice was measured. The smaller the value, the better the braking performance.

・ DRY stability (steering stability on dry road)
Steering stability on dry road surface was evaluated by feeling by a test driver. The larger the value, the better the turning stability.

  From Table 1, it can be seen that the present example is superior to the comparative example in all of the acceleration on ice, the braking distance, and the handling stability on the dry road surface. This is considered to be because the outer shallow groove 26 is narrower and shallower than the shallow groove 72 and the inner shallow groove 27 is wider and deeper than the shallow groove 72 in this embodiment.

It is a top view which shows the tread of the pneumatic tire of embodiment of this invention. It is sectional drawing which expands and shows the block of the outer side half area | region of the pneumatic tire of embodiment of this invention. It is sectional drawing which expands and shows the block of the inner half area | region of the pneumatic tire of embodiment of this invention. It is a top view which expands and shows partially the tread of the outside half field of the pneumatic tire of the embodiment of the present invention. It is a top view which expands and shows partially the tread of the inner half area of the pneumatic tire of the embodiment of the present invention. It is explanatory drawing which shows the depth and width | variety of the shallow groove | channel formed in the tread of the pneumatic tire of embodiment of this invention. It is a top view which shows the modification of the tread of the pneumatic tire of embodiment of this invention. It is a top view which shows the other modification of the tread of the pneumatic tire of embodiment of this invention. It is a top view which shows the tread of the pneumatic tire of a comparative example.

Explanation of symbols

10 tire 12 tread 14 central circumferential groove 16 circumferential groove 18 lateral groove 19 lateral groove 20 block 22 sipe 24 lateral groove 26 outer shallow groove 27 inner shallow groove 28 subblock 30 minute land portion 38 main groove 50 outer shallow groove 52 inner shallow groove 54 outer shallow Groove 56 Inner shallow groove IH Inner half area OH Outer half area

Claims (8)

In a pneumatic tire having a plurality of land portions partitioned by a plurality of main grooves on a tread surface, and the land portions are divided by at least one sipe to form sub-blocks,
The tread pattern is asymmetric between the outer half region located outside and the inner half region located inside when the vehicle is mounted on the tire equator plane,
A plurality of outer shallow grooves shallower than the sipe are formed in the outer half region of the land portion,
A plurality of inner shallow grooves shallower than the sipe are formed in the inner half region of the land portion,
The inner shallow groove satisfies at least one of the following conditions: a wider width, a deeper depth, and a higher formation density than the outer shallow groove;
Pneumatic tire characterized by.   The pneumatic tire according to claim 1, wherein the outer shallow groove and the inner shallow groove are linear along the tire circumferential direction.   The pneumatic tire according to claim 1 or 2, wherein a difference between a width of the outer shallow groove and a width of the inner shallow groove is 0.1 mm to 0.9 mm.   The pneumatic tire according to any one of claims 1 to 2, wherein a difference between the width of the outer shallow groove and the depth of the inner shallow groove is 0.1 mm to 0.4 mm.   The pneumatic tire according to any one of claims 1 to 4, wherein the outer shallow groove and the inner shallow groove have a depth of 0.1 mm to 0.5 mm.   The pneumatic tire according to any one of claims 1 to 5, wherein the outer shallow groove and the inner shallow groove have a width of 0.1 mm to 1.0 mm. A plurality of micro land portions partitioned by a plurality of the shallow grooves, according to any one of claims 1 to 6, characterized in that there is a tread area of 0.4mm ² ~30mm ² Pneumatic tire.   The rubber constituting the land portion is composed of a foamed rubber layer on the radially outer side of the tire and an unfoamed rubber layer on the radially inner side of the tire. The pneumatic tire according to item 1.

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