JP6091885B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, in particular, a pneumatic tire for heavy loads, and relates to a pneumatic tire that prevents cracks in lug grooves and extends the life of the tire.

  In conventional pneumatic tires, repeated use over a long period of time may cause damage such as cracks on the outer surface. One of the causes is the tire rubber surface caused by oxygen, ozone, etc. in the atmosphere. Oxidation and degradation can be mentioned. As shown in the following patent documents, tires are proposed in which the tire surface is coated with a thin film according to various purposes.

  In Patent Document 1 below, a tread groove is formed on the surface of the tread portion, and a thin film having a uniform thickness of 0.1 mm to 1 mm is formed along the tread surface contour. It is a relatively soft rubber that is different from the rubber of the part and excellent in crack resistance, and has a JIS hardness of 45 to 55 degrees and is substantially the same quality as the side wall. Only the thin film on the tread groove surface remains, but this thin film is excellent in crack resistance, and therefore, there is a pneumatic tire that can effectively suppress the occurrence of cracks in the tread groove bottom due to repeated deformation during running. It is shown.

  However, since the pneumatic tire described in Patent Document 1 has a uniform thickness of 0.1 mm to 1 mm, the thin tire has a lug groove in the tire width direction in the shoulder portion that is the outermost side of the tire tread. Since the thickness of the thin film is insufficient, there is a possibility that groove cracks (cracks caused by concentration of strain at the groove bottom) may occur in the lug grooves.

  The following Patent Document 2 discloses a pneumatic tire in which a conductive thin film having a thickness of 0.5 mm or less is continuously disposed on the tread surface in the tire circumferential direction, and the conductive thin film is disposed on both sides of the tread. The conductive thin film provided on one side of the conductive thin film has a width (w) of 10% to 30% of the total tread width (W), and the thin film provided on the ground surface of the tread. Disappears due to wear after running a certain distance, the thin film disposed in the groove part of the tread remains, and the tread is composed of rubber with low rolling resistance, and by placing a conductive thin film on this, Pneumatic tires with low fuel consumption and good conductivity can be obtained, and conductive thin films are arranged only on both sides near the shoulder of the tread. Inherently It has been shown to a pneumatic tire which can exhibit a small rolling resistance is.

  However, since the pneumatic tire described in Patent Document 2 is intended to ensure conductivity, it does not eliminate groove cracks in the lug grooves. Moreover, since the thickness of a thin film is 0.5 mm or less and the thickness of the thin film in a lug groove is inadequate, there exists a possibility that a groove crack may generate | occur | produce in a lug groove.

  In the following Patent Document 3, in a pneumatic tire having a peripheral rubber tread having a lug and a groove shape, a thin tire is disposed to extend to a boundary between the tread and the tread wing on a part of the tread surface. A tire is shown having a tread composed of layer strips, with a thin outer tread strip covering less than 50% of the tire tread surface and a tread strip thickness of about 0.005 cm to about 0.08 cm. .

  However, since the tire described in Patent Document 3 is intended to ensure conductivity, it does not eliminate the groove crack in the lug groove in the tire width direction in the shoulder portion which is the outermost side of the tire tread. Moreover, although the thickness of a thin film is about 0.05 mm-about 0.8 mm, since the thickness of the thin film in a lug groove is inadequate, there exists a possibility that a groove crack may generate | occur | produce in a lug groove.

  In the following Patent Document 4, in a heavy duty pneumatic tire having a tread portion having a cap-base structure, a cap rubber is provided between main grooves located on both outer sides in the tire width direction among two or more main grooves. A thin cap part with a thickness of 2.4 mm or less is provided in 15% to 90% of the total width of the tread, and uneven wear-resistant rubber is placed at the places where uneven wear mainly occurs, resulting in low rolling resistance. Heavy load air that can achieve low fuel consumption while efficiently preventing uneven wear by placing it in the center surface layer where the amount of rubber is as large as possible and the amount of rubber deformation is large An inset tire is shown.

  However, the heavy-duty pneumatic tire described in Patent Document 4 is intended to reduce fuel consumption and tan δ, and does not eliminate groove cracks in the lug groove in the tire width direction at the shoulder portion which is the outermost side of the tire tread. Absent. Further, since the thin cap portion is not arranged at the groove bottom, there is a possibility that a groove crack may occur in the lug groove.

  In Patent Document 5 below, the outer surface of the tread including the groove wall and the groove bottom of the tire body is covered with a thin layer made of rubber containing EPT or butyl halide, and the thickness of the thin layer is 0. 1 to 2.0 mm, a tire that can prevent the occurrence of cracks on the outer surface without deteriorating the dynamic performance of the tire and extends its life is shown.

  However, although the tire described in Patent Document 5 contains EPT or butyl halide, it is difficult to say that it is effective for groove cracks.

Japanese Utility Model Publication No. 61-39604 JP-A-8-244409 JP-A-10-203114 JP 2000-52713 A JP-A-2-45202

  As described above, the present situation is that no proposal has been made that a sufficient effect can be achieved for the occurrence of cracks in the lug groove and the shoulder groove in the outermost shoulder portion of the tire tread.

  Therefore, as a result of intensive research, the inventor formed a thin rubber layer having a lower modulus than the tread rubber layer on the tire tread instead of the thin rubber layer of the special composition in the pneumatic tire, and the lug groove A pneumatic tire has been devised in which the thickness of the thin rubber layer is made thicker than that of the other thin rubber layers, thereby preventing cracks in the lug grooves and extending their life.

The pneumatic tire according to claim 1 of the present invention is a pneumatic tire having two rows of shoulder portions that are circumferentially arranged on the outermost side in the width direction of the tire tread and have lug grooves in the tire width direction. The first thin rubber layer and the second thin rubber layer having a 300% modulus of 9.0 MPa or less, which is lower than that of the tread rubber layer, are partially or entirely formed on the surface including the unevenness of the tire tread, The first thin rubber layer is thicker than the second thin rubber layer, the thickness of the first thin rubber layer is 1.0 mm to 2.0 mm, and the lug groove in the shoulder portion is covered with the first thin rubber layer. It is characterized by being.

  The test method for 300% modulus (MPa) is in accordance with JIS K 6251. The lower the number, the less the force to return, so the distortion can be reduced.

  A pneumatic tire according to a second aspect of the present invention is the pneumatic tire according to the first aspect, wherein the entire peripheral surface of the shoulder portion including the lug groove is covered with a first thin rubber layer. is there.

  A pneumatic tire according to a third aspect of the present invention is the pneumatic tire according to the first or second aspect, wherein the shoulder portion is defined by a shoulder groove in a tire circumferential direction, and the shoulder groove is covered with a first thin rubber layer. It is characterized by being.

By configuring as in the first to third aspects, the tire ground contact surface is worn away by running so that the thin rubber layer disappears, but the groove wall and the groove bottom do not wear, so the thin rubber layer remains, Since the strain is reduced by arranging the low modulus material, the relaxation of the strain leads to the improvement of the groove crack of the lug groove, and the occurrence of the groove crack is suppressed. Groove cracks usually occur in the order of the lug groove in the tire width direction at the shoulder portion, the shoulder groove in the tire circumferential direction, and the center main groove in the tire circumferential direction, but the thickness of the thin rubber layer of the lug groove should be increased. This enhances the effect of suppressing the occurrence of groove cracks in the lug grooves. Since the center groove is less prone to groove cracks, it is possible to meet the needs in the market and usage environment by making the thickness equal to the thickness of the shoulder groove instead of the thickness of the thin rubber layer.

  By configuring the pneumatic tire of the present invention as described above, a sufficient effect can be exhibited in suppressing the occurrence of cracks in the lug grooves and shoulder grooves in the outermost shoulder portion of the tire tread.

It is a schematic sectional drawing of the pneumatic tire of this invention. 1 is a schematic partial plan view of a pneumatic tire according to the present invention. It is a principal part perspective view of the tire tread which concerns on Example 1 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 1 of Example 1 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 2 of Example 1 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 3 of Example 1 of this invention. It is a principal part perspective view of the tire tread which concerns on Example 2 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 1 of Example 2 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 2 of Example 2 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 3 of Example 2 of this invention. It is a principal part perspective view of the tire tread which concerns on the modification 4 of Example 2 of this invention. 3 is a perspective view of a main part of a tire tread according to Comparative Example 1. FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the drawings. In describing each example, first, an outline of a pneumatic tire will be described with reference to FIGS. 1 and 2.

  In FIG. 1, T is a pneumatic tire, and the pneumatic tire T has a carcass 2 that is bent and locked at both ends of the bead core 1, a belt layer 3 that is disposed outside the crown portion of the carcass 2, and unevenness. A formed tire tread 4 is provided. The convex shape in the circumferential direction on the outermost side in the width direction of the tire tread 4 is a shoulder portion 5, and a concave lug groove 6 is formed in the shoulder portion 5 in the tire width direction as shown in FIG. The part 5 includes a convex lug 7 and a lug groove 6. On the inner side of the shoulder portion 5, a concave shoulder groove 8 that defines the shoulder portion 5 is formed. A convex mediate portion 9 is formed on the inner side of the shoulder groove 8, and a convex center portion 11 is formed on the inner side of the mediate portion 9 via a concave center sub-groove 10. A center main groove 12 is formed between the center portions 11. The pneumatic tire T shown in FIG. 1 and FIG. 2 is an exemplification, and the essential configuration in the present invention is a pneumatic tire provided with a shoulder portion 5 having lug grooves 6 with respect to Examples 1 and 2. Good.

Figure 3 shows a first embodiment, FIGS. 4 to 6 is a modification of Example 1, the lug grooves of Example 1 containing, as essential this to the lug grooves in the shoulder portion covered by the first thin rubber layer It is an illustration of the variation regarding arrangement | positioning of thin rubber layers other than . The tire is premised on left-right symmetry with respect to the equator (circumferential line passing through the center of the tire width), and FIGS. 3 to 6 each show a half cross section of the tire. Each groove includes a groove wall and a groove bottom. Moreover, also present in some portions not thin rubber layer is formed.

  In the pneumatic tire of Example 1 shown in FIG. 3, the first thin rubber layer 20 is formed on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5, and the shoulder groove 8 is also formed on the surface thereof. A first thin rubber layer 20 is formed. A second thin rubber layer 21 is formed on the surfaces of the mediate portion 9, the center sub-groove 10, the center portion 11, and the center main groove other than that.

  Each of the first thin rubber layer 20 and the second thin rubber layer 21 is made of a rubber material having a 300% modulus of 9.0 MPa. The first thin rubber layer and the second thin rubber layer are not limited to rubber materials having a 300% modulus of 9.0 MPa, and may be rubber materials having a 300% modulus of 9.0 MPa or less. Further, the ratio of the thickness of the first thin rubber layer 20 to the thickness of the second thin rubber layer 21 is 2: 1, and in this embodiment, the thickness of the first thin rubber layer 20 is 2.0 mm. . The first thin rubber layer only needs to be thicker than the second thin rubber layer. The thickness of the first thin rubber layer is preferably in the range of 1.0 mm to 2.0 mm.

The pneumatic tire of the first modification shown in FIG. 4 is a first thin rubber layer having a thickness of 2.0 mm on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5 and the surface of the shoulder groove 8. The point 20 is formed is the same as that of the first embodiment. In the first modification, Mediate unit 9, the second thin rubber layer 21 having a thickness of 1.0mm is formed on the surface of the center minor groove 10, one in the center portion 11 and the center main groove thin rubber No layer is formed .

The pneumatic tire of Modification 2 of Example 1 shown in FIG. 5 includes a first thin rubber layer having a thickness of 2.0 mm on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5 and the surface of the shoulder groove 8. The point 20 is formed is the same as that of the first embodiment. In the modified example 2, the mediate portion 9 is not formed with any thin rubber layer, and the second thin rubber layer 21 having a thickness of 1.0 mm is formed on the surface of the center sub-groove 10, the center portion 11, and the center main groove. Is formed.

The pneumatic tire of Modification 3 of Example 1 shown in FIG. 6 includes a first thin rubber layer having a thickness of 2.0 mm on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5 and the surface of the shoulder groove 8. The point 20 is formed is the same as that of the first embodiment. In the modified example 3, none of the thin rubber layer is formed in the mediate portion 9, the center portion 11 and the center main groove, and the second thin rubber layer having a thickness of 1.0 mm is formed on the surface of the center sub groove 10. 21 is formed.

FIG. 7 shows the second embodiment, and FIGS. 8 to 11 are modifications of the second embodiment, and the lug of the second embodiment in which it is essential to cover the lug groove in the shoulder portion with the first thin rubber layer. It is an illustration of the variation regarding arrangement | positioning of thin rubber layers other than a groove | channel . Incidentally, the tire assumes symmetrical about the equatorial (circumferential line passing through the tire width center), 8 to 1 1, and each illustrate a half-section of the tire. Each groove includes a groove wall and a groove bottom. Moreover, also present in some portions not thin rubber layer is formed.

In the pneumatic tire of Example 2 shown in FIG. 7 , the first thin rubber layer 20 is formed on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5, and the thickness of the shoulder groove 8 is 1.0 mm. The second thin rubber layer 21 is formed, and the second thin rubber layer 21 is formed on the other surfaces of the mediate portion 9, the center sub-groove 10, the center portion 11, and the center main groove.

  Each of the first thin rubber layer 20 and the second thin rubber layer 21 is made of a rubber material having a 300% modulus of 9.0 MPa. The first thin rubber layer and the second thin rubber layer are not limited to rubber materials having a 300% modulus of 9.0 MPa, and may be rubber materials having a 300% modulus of 9.0 MPa or less. Further, the ratio of the thickness of the first thin rubber layer 20 to the thickness of the second thin rubber layer 21 is 2: 1, and in this embodiment, the thickness of the first thin rubber layer 20 is 2.0 mm. . The first thin rubber layer only needs to be thicker than the second thin rubber layer. The thickness of the first thin rubber layer is preferably in the range of 1.0 mm to 2.0 mm.

In the pneumatic tire according to the first modification of the second embodiment shown in FIG. 8 , the first thin rubber layer 20 having a thickness of 2.0 mm is formed on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5. The second thin rubber layer 21 having a thickness of 1.0 mm is formed on the surface of the groove 8 as in the second embodiment. In the first modification, Mediate unit 9, the second thin rubber layer 21 having a thickness of 1.0mm is formed on the surface of the center minor groove 10, one in the center portion 11 and the center main groove thin rubber No layer is formed .

In the pneumatic tire of the second modification of the second embodiment shown in FIG. 9 , the first thin rubber layer 20 having a thickness of 2.0 mm is formed on the entire surface in the tire tread 4 including the lug groove 6 of the shoulder portion 5, and the shoulder The second thin rubber layer 21 having a thickness of 1.0 mm is formed on the surface of the groove 8 as in the second embodiment. In the modified example 2, the mediate portion 9 is not formed with any thin rubber layer, and the second thin rubber layer 21 having a thickness of 1.0 mm is formed on the surface of the center sub-groove 10, the center portion 11, and the center main groove. Is formed.

The pneumatic tire of the third modification example 2 shown in FIG. 1 0, the first thin rubber layer 20 having a thickness of 2.0mm is formed on the circumferential entire surface including the lug groove 6 in the shoulder regions 5 in the tire tread 4, The second thin rubber layer 21 having a thickness of 1.0 mm is formed on the surface of the shoulder groove 8 as in the second embodiment. In the modified example 3, none of the thin rubber layer is formed in the mediate portion 9, the center portion 11 and the center main groove , and the second thin rubber layer having a thickness of 1.0 mm is formed on the surface of the center sub groove 10. 21 is formed.

The pneumatic tire of the fourth modification example 2 shown in FIG. 1 1 is a first thin rubber layer 20 having a thickness of 2.0mm is formed in the circumferential direction over the entire surface of the shoulder portion 5 in the tire tread 4, the surface of the shoulder groove 8 The second thin rubber layer 21 having a thickness of 1.0 mm is formed in the same manner as in Example 2. In the modified example 4, none of the thin rubber layers is formed on the surfaces of the mediate portion 9, the center sub-groove 10, the center portion 11, and the center main groove.

[Example 2-1]
Although the illustration of the pneumatic tire of Example 2-1 is omitted, Example 2 is the same as Example 2 except that the thickness of the first thin rubber layer 20 and the thickness of the second thin rubber layer 21 in Example 2 are changed. It is the same. That is, the thickness of the first thin rubber layer 20 is 1.0 mm, and the thickness of the second thin rubber layer 21 is 0.5 mm, which is a half of the thickness of the first thin rubber layer 20.

[Comparison test]
Next, with respect to the pneumatic tire according to the present invention, comparative tests were performed on the above Examples 1, 2 and 2-1, the following Comparative Examples 1 to 4 and the conventional example under the following conditions. The test methods are a groove crack test and a wear test.

  Groove crack test is a crack phenomenon of tread grooves and flex lines that occur in the market by applying predetermined internal pressure and predetermined load while irradiating ozone to a thermally deteriorated tire and pressing it against a rotating drum to continue repeated strain. Is reproduced and evaluated. The groove crack resistance in the table is the result of the groove crack test. The index of Comparative Example 1 is 100, and the higher the index, the better the groove crack resistance.

  With the wear test, tires are mounted on an actual vehicle, alignment is adjusted, and after running on a prescribed course, the amount of wear before the test is compared and evaluated. The wearability in the table is the result of the wear test, and is expressed as the wear index of Comparative Example 1 being 100. The higher the index, the better the wear.

[Configuration of Comparative Example 1]
The pneumatic tire of Comparative Example 1 shown in FIG. 1. 2, the circumferential direction over the entire surface including the lug groove 6 in the shoulder regions 5 in the tire tread 4, the shoulder groove 8, Mediate unit 9, the center minor groove 10, center portion 11 and the center Only the second thin rubber layer 21 is formed on the surface of the main groove, and the first thin rubber layer having a different thickness is not formed .

  The second thin rubber layer 21 is made of a rubber material having a 300% modulus of 9.0 MPa. The thickness of the second thin rubber layer 21 is 1.0 mm.

[Configuration of Comparative Example 2]
In the pneumatic tire of Comparative Example 2, although not shown, the first thin rubber layer is formed on the entire surface in the tire tread including the lug groove of the shoulder portion, and the second thin rubber layer is formed on the surface of the shoulder groove. It is a thing.

  The first thin rubber layer and the second thin rubber layer are made of a rubbery material having a 300% modulus of 10.0 MPa. The thickness of the first thin rubber layer is 2.0 mm, and the thickness of the second thin rubber layer is 1.0 mm.

[Configuration of Comparative Example 3]
In the pneumatic tire of Comparative Example 3, although not shown, the first thin rubber layer is formed on the entire surface in the tire tread including the lug groove of the shoulder portion, and the second thin rubber layer is formed on the surface of the shoulder groove. It is a thing.

  The first thin rubber layer and the second thin rubber layer are made of a rubber material having a 300% modulus of 9.0 MPa. The thickness of the first thin rubber layer is 0.5 mm, and the thickness of the second thin rubber layer is 0.25 mm.

[Configuration of Comparative Example 4]
In the pneumatic tire of Comparative Example 4, although not shown, the first thin rubber layer is formed on the entire surface in the tire tread including the lug groove of the shoulder portion, and the second thin rubber layer is formed on the surface of the shoulder groove. It is a thing.

  The first thin rubber layer and the second thin rubber layer are made of a rubber material having a 300% modulus of 9.0 MPa. The thickness of the first thin rubber layer is 2.5 mm, and the thickness of the second thin rubber layer is 1.25 mm.

[Conventional configuration]
Although not shown in the drawings, the conventional pneumatic tire is a pneumatic tire having a thin rubber layer thickness of 0.0 mm, that is, a thin rubber layer not formed on the surface of the tire tread.

[Results of comparative test]
For Example 1, the thin rubber layer of the lug groove was 2.0 mm compared to 1.0 mm of Comparative Example 1, so that the groove crack resistance in the lug groove was improved compared to Comparative Example 1. Yes. In addition, by making the thin rubber layer of the shoulder groove 2.0 mm compared to 1.0 mm of Comparative Example 1, the groove crack resistance in the shoulder groove is improved compared to Comparative Example 1.

  About the said Example 2, the groove-crack-proof property in a lag groove improved compared with the comparative example 1 by having made the thin rubber layer of the lag groove into 2.0 mm compared with 1.0 mm of the comparative example 1. Yes.

  About the said Example 2-1, the abrasion property of a shoulder part is improving by having made the thin rubber layer of the shoulder groove into 0.5 mm compared with 1.0 mm of the comparative example 1. FIG.

  About the said comparative example 2, the 300% modulus of the 1st thin rubber layer and the 2nd thin rubber layer was 10.0 Mpa or more and 10.0 Mpa, compared with Example 2, the groove crack resistance in a lug groove, and The groove crack resistance in the shoulder groove is lowered. However, the wear resistance is improved.

About the said comparative example 3, the groove crack resistance in a lug groove and a shoulder groove compared with Example 2-1 by having made the thickness of the 1st thin rubber layer of a lug groove into 0.5 mm of less than 1.0 mm. The groove crack resistance in the case is reduced. However, the wear resistance is improved.

About the said comparative example 4, compared with Example 2, the thickness of the 1st thin rubber layer of a lug groove was set to 2.5 mm exceeding 2.0 mm, compared with Example 2, the groove crack resistance in a lug groove, and the resistance in a shoulder groove Although the groove cracking property is improved, the wear resistance is greatly reduced.

  About the said prior art, since the thin rubber layer is not provided in a lug groove and a shoulder groove, both the groove crack resistance in a lug groove and the groove crack resistance in a shoulder groove are falling. However, the wear resistance is improved.

  From the above results, it was found that the thin rubber layer of the lug groove and the shoulder groove had a good result when the 300% modulus was 9.0 MPa or less. Further, the thickness of the thin rubber layer of the lug groove and the shoulder groove is preferably in the range of 1.0 mm to 2.0 mm, and if it is less than 1.0 mm, the wear resistance is improved, but the groove crack resistance in the lug groove is improved. It has been found that when the thickness exceeds 2.0 mm, the groove crack resistance in the lug groove is improved, but the wear resistance is greatly reduced. Therefore, good results were obtained for the configurations of Examples 1, 2, and 2-1 included in the scope of the present invention, but the results were obtained for Comparative Examples 1 to 4 and the conventional example not included in the scope of the present invention. Was not good.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

T: Pneumatic tire 1 ... Bead core 2 ... Carcass 3 ... Belt layer 4 ... Tire tread 5 ... Shoulder part 6 ... Lug groove 7 ... Lug 8 ... Shoulder groove 9 ... Mediate part 10 Center sub-groove 11 Center portion 12 Center main groove 20 First thin rubber layer 21 Second thin rubber layer

Claims (3)

A pneumatic tire having two rows of shoulder portions arranged circumferentially on the outermost side in the width direction of the tire tread and having lug grooves in the tire width direction,
Forming a first thin rubber layer and a second thin rubber layer having a 300% modulus lower than that of the tread rubber layer on the surface including the unevenness of the tire tread and having a pressure of 9.0 MPa or less partially or entirely;
The first thin rubber layer is thicker than the second thin rubber layer,
The thickness of the first thin rubber layer is 1.0 mm to 2.0 mm,
A pneumatic tire characterized in that a lug groove in a shoulder portion is covered with a first thin rubber layer.   2. The pneumatic tire according to claim 1, wherein the entire circumferential surface of the shoulder portion including the lug groove is covered with a first thin rubber layer.   The pneumatic tire according to claim 1 or 2, wherein a shoulder portion is partitioned by a shoulder groove in a tire circumferential direction, and the shoulder groove is covered with a first thin rubber layer.

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