JP2009202722A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing crack-resistance and eccentric wear-resistance of the tire. <P>SOLUTION: In the pneumatic tire 1, a thin groove 71 is positioned at an outer side in a tire width direction from a linear line L. Further, a distance d of the thin groove 71 and the linear line L has a relationship of 0≤d/TDW≤0.015 relative to tread development width TDW. Further, a distance c in a tire ground-contact surface normal direction from a tire ground-contact end to a groove bottom of the thin groove 71 has a relationship of 0.5≤c/g≤1.2 and 0.1≤b/c≤0.3 relative to groove depth g of a circumferential main groove 52 on the outermost side in a tire width direction and the maximum value b of the groove width of the thin groove 71. Even further, a distance between a groove wall and non-grounding rib 72 on the side opposing to the non-grounding rib 72 out of groove walls of the thin groove 71 has a relationship of 0.6≤a/b≤0.9 relative to the maximum value b of the groove width of the thin groove 71. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire capable of improving the crack resistance performance of the tire while maintaining the uneven wear resistance performance of the tire.

  In recent pneumatic tires, a narrow groove is formed on the wall surface of the shoulder portion on the side wall portion, and non-ground ribs are defined by the narrow groove. In such a configuration, the narrow groove is in an open state when the tire is not grounded. When the tire contacts the ground, the shoulder is deformed by the load and the narrow groove is closed. As a result, the peak contact pressure of the shoulder portion is reduced when the tire contacts the ground, and uneven wear (shoulder fall wear) of the shoulder portion is suppressed. At this time, the non-grounding rib contacts the groove wall surface of the narrow groove (opposing groove wall surface), thereby supporting the tire load. Thereby, the rigidity of the shoulder part at the time of tire grounding is ensured appropriately.

  The technique described in Patent Document 1 is known as a conventional pneumatic tire employing such a configuration. A conventional pneumatic tire (a pneumatic radial tire) is a pneumatic radial tire in which a plurality of main grooves extending in the tire circumferential direction and ribs divided into the main grooves are formed on the tread surface. A narrow groove extending obliquely inwardly on the lateral side surface of the shoulder portion is provided along the tire circumferential direction, a non-grounding rib that is divided into the narrow groove radially inward from the narrow groove and projects from the lateral side surface, and The lateral side surface is formed by a straight line having an angle α of 20 ° to 60 ° with respect to the normal direction of the surface S including the tread surface, and the narrow groove has an angle β with respect to the normal direction of the surface S of 10 ° to 50 °. Further, when the vertical distance from the surface S of the groove bottom of the narrow groove is h, the groove depth of the main groove is d, and the vertical distance from the surface S of the top surface of the non-grounding rib is h, /D=0.5-1.2, g / h = 0.5-0.8 It was in the relationship.

Japanese Patent No. 3344794

  An object of the present invention is to provide a pneumatic tire capable of improving the crack resistance performance of the tire while maintaining the uneven wear resistance performance of the tire.

  In order to achieve the above object, a pneumatic tire according to the present invention is formed in a plurality of circumferential main grooves formed in a tread portion and extending in a tire circumferential direction, and a wall surface on a side wall portion side of a shoulder portion. A pneumatic tire having a narrow groove defined by the narrow groove and a non-grounding rib defined by the narrow groove, the tire from a point A defining a tread deployment width TDW in a cross-sectional view in the tire meridian direction in a no-load state When a straight line L perpendicular to the ground contact surface is drawn, the narrow groove is positioned on the outer side in the tire width direction with respect to the straight line L, and the distance d between the narrow groove and the straight line L is 0 with respect to the tread deployment width TDW. ≦ d / TDW ≦ 0.015, and the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove is the outermost circumferential main groove in the tire width direction. Groove depth g and A groove wall of the fine groove having a relationship of 0.5 ≦ c / g ≦ 1.2 and 0.1 ≦ b / c ≦ 0.3 with respect to the maximum value b of the groove width of the fine groove; The distance a between the groove wall on the side facing the non-grounding rib and the non-grounding rib has a relationship of 0.6 ≦ a / b ≦ 0.9 with respect to the maximum value b of the groove width of the narrow groove. It is characterized by having.

  In this pneumatic tire, (1) the narrow groove is positioned outside the straight line L in the tire width direction, and the distance d between the narrow groove and the straight line L is optimized with respect to the tread deployment width TDW (0 ≦ d / TDW ≦ 0.015). (2) The distance c in the normal direction of the tire ground contact surface from the tire ground contact edge to the groove bottom of the narrow groove is the groove depth g of the circumferential main groove on the outermost side in the tire width direction and the groove width of the narrow groove. The maximum value b is optimized (0.5 ≦ c / g ≦ 1.2 and 0.1 ≦ b / c ≦ 0.3). Further, the distance a between the groove wall of the narrow groove facing the non-grounding rib and the non-grounding rib is optimized with respect to the maximum groove width b (0.6 ≦ a / b). ≦ 0.9). In such a configuration, deformation of the connecting portion between the rib of the tread shoulder region and the non-grounding rib is suppressed when the tire is in contact with the ground, and the peak contact pressure of the shoulder is appropriately reduced when the tire is in contact with the ground. Thereby, there is an advantage that the crack resistance performance of the tire is improved, and there is an advantage that the uneven wear resistance performance (shoulder wear of the shoulder portion) of the tire is maintained.

  In the pneumatic tire according to the present invention, the angle α formed by the straight wall L and the wall surface of the shoulder portion on the side wall portion side is 20 [deg] ≦ α ≦ 60 [deg] in a sectional view in the tire meridian direction. The angle β formed by the groove depth direction of the narrow groove and the straight line L is within a range of 10 [deg] ≦ β ≦ 50 [deg], and the tire ground contact edge is connected to the non-ground rib. The relationship of 0.5 ≦ f / c ≦ 0.8 between the distance f in the tire contact surface normal direction to the top surface and the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove. Have

  In this pneumatic tire, the inclination angle (angle α) of the wall surface on the side wall portion of the shoulder portion, the groove depth direction (angle β), and the top surface position of the non-grounding rib are optimized. Therefore, there is an advantage that the crack resistance performance and uneven wear resistance performance of the tire are further improved.

  In the pneumatic tire according to the present invention, the non-grounding rib is disposed on the inner side in the tire radial direction with respect to the narrow groove.

  In this pneumatic tire, the tire molding die can be removed better than the configuration in which the non-grounding rib is disposed on the inner side in the tire radial direction with respect to the narrow groove. Thereby, there exists an advantage by which manufacture of a tire is made easy.

  In the pneumatic tire according to the present invention, (1) the narrow groove is positioned outside the straight line L in the tire width direction, and the distance d between the narrow groove and the straight line L is optimized with respect to the tread deployment width TDW (0 ≦ d /TDW≦0.015). (2) The distance c in the normal direction of the tire ground contact surface from the tire ground contact edge to the groove bottom of the narrow groove is the groove depth g of the circumferential main groove on the outermost side in the tire width direction and the groove width of the narrow groove. The maximum value b is optimized (0.5 ≦ c / g ≦ 1.2 and 0.1 ≦ b / c ≦ 0.3). Further, the distance a between the groove wall of the narrow groove facing the non-grounding rib and the non-grounding rib is optimized with respect to the maximum groove width b (0.6 ≦ a / b). ≦ 0.9). In such a configuration, deformation of the connecting portion between the rib of the tread shoulder region and the non-grounding rib is suppressed when the tire is in contact with the ground, and the peak contact pressure of the shoulder is appropriately reduced when the tire is in contact with the ground. Thereby, there is an advantage that the crack resistance performance of the tire is improved, and there is an advantage that the uneven wear resistance performance (shoulder wear of the shoulder portion) of the tire is maintained.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. 2 to 4 are an enlarged cross-sectional view (FIGS. 2 and 4) and an operation explanatory view (FIG. 3) showing a narrow groove in the shoulder portion of the pneumatic tire shown in FIG. 5 and 6 are charts showing the results of the performance test of the pneumatic tire according to the example of the present invention.

[Pneumatic tire]
The pneumatic tire 1 includes a bead core (not shown), a carcass layer 3, a belt layer 4, a tread rubber 5, and a sidewall rubber 6 (see FIG. 1). The bead core has an annular structure and is configured as a pair of left and right. The carcass layer 3 is bridged in a toroidal shape between the left and right bead cores to form a tire skeleton. The belt layer 4 includes a plurality of stacked belt members 41 to 43 and is disposed on the outer side in the tire radial direction of the carcass layer 3. The tread rubber 5 is disposed on the outer side in the tire radial direction of the carcass layer 3 and the belt layer 4 to constitute a tread portion of the tire. The sidewall rubber 6 is disposed on the outer side in the tire width direction of the carcass layer 3 to constitute a sidewall portion of the tire. In addition, a plurality of circumferential main grooves 51 and 52 extending in the tire circumferential direction are formed in the tread portion of the tire, and a plurality of ribs 53 to 55 are defined by the circumferential main grooves 51 and 52. The

[Thin groove and non-ground rib]
Further, narrow grooves 71 and non-grounding ribs 72 are formed on the wall surface of the shoulder portion on the side wall portion side (see FIGS. 1 and 2). These narrow grooves 71 and non-grounding ribs 72 are formed in the left and right sidewall portions of the tire, respectively. The narrow groove 71 inclines in the tire radial direction inner side and the tire width direction inner side (having a groove depth direction) in a sectional view in the tire meridian direction. The non-grounding rib 72 is defined by the narrow groove 71. Further, in this embodiment, the non-grounding rib 72 is positioned on the inner side in the tire radial direction with respect to the narrow groove 71 and constitutes the groove wall surface on the inner side in the tire radial direction of the narrow groove 71. The groove wall surface on the outer side in the tire radial direction of the narrow groove 71 is a flat surface and has a cross-sectional shape that is a straight line in a cross-sectional view in the tire meridian direction.

  In the pneumatic tire 1, the narrow groove 71 is in an open state when the tire is not grounded (see FIG. 3). When the tire contacts the ground, the shoulder portion is deformed by the load and the narrow groove 71 is closed. Thereby, since the peak ground contact pressure of the shoulder portion is reduced at the time of tire contact, uneven wear (shoulder fall wear) of the shoulder portion is suppressed. Further, at this time, the non-grounding rib 72 is in contact with the groove wall surface of the narrow groove 71 (opposing groove wall surface), whereby the tire load is supported. Thereby, the rigidity of the shoulder part at the time of tire grounding is ensured appropriately.

  Here, a straight line L perpendicular to the tire contact surface is drawn from a point A defining the tread development width TDW in a cross-sectional view in the tire meridian direction in an unloaded state (see FIG. 2). For example, in this embodiment, the point A that defines the tread development width TDW coincides with the tire ground contact end (the end of the tire ground contact surface in the tire width direction) in a sectional view in the tire meridian direction (see FIG. 3).

  At this time, (1) the narrow groove 71 is located outside the straight line L in the tire width direction. Further, the distance d between the narrow groove 71 and the straight line L has a relationship of 0 ≦ d / TDW ≦ 0.015 with respect to the tread development width TDW (see FIG. 2). For example, in this embodiment, the groove bottom (the innermost point in the tire width direction) of the narrow groove 71 is located on the outer side in the tire width direction with respect to the straight line L, and the groove bottom of the narrow groove 71 and the straight line L The distance d has a relationship of 0 ≦ d / TDW ≦ 0.015 with respect to the tread development width TDW.

  The tread development width TDW refers to a linear distance between both ends of the tread pattern portion of the tire when the tire is mounted on the applicable rim and applied with a specified internal pressure and is not loaded. Here, the applicable rim means “applied rim” defined in JATMA, “Design Rim” defined in TRA, or “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The specified load means “maximum load capacity” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO. However, in the case of a tire for a passenger car, the specified internal pressure is an air pressure of 180 [kPa], and the specified load is 88 [%] of the maximum load capacity.

  (2) The distance c in the normal direction of the tire ground contact surface from the tire ground contact edge to the groove bottom of the narrow groove and the groove depth g of the outer circumferential main groove 52 at the outermost side in the tire width direction are 0.5. ≦ c / g ≦ 1.2 (see FIG. 2). Further, the distance c and the maximum value b of the narrow groove width have a relationship of 0.1 ≦ b / c ≦ 0.3.

  (3) The distance a between the groove wall of the narrow groove 71 on the side facing the non-grounding rib 72 and the non-grounding rib 72 is 0.6 relative to the maximum groove width b of the narrow groove 71. ≦ a / b ≦ 0.9. In this embodiment, the groove width of the narrow groove 71 is minimum at the opening of the narrow groove 71, and the groove width of the narrow groove 71 at this position is a distance a between the wall surface facing the non-grounding rib 72 a. It is equal to.

[effect]
As described above, in this pneumatic tire 1, (1) the narrow groove 71 is positioned on the outer side in the tire width direction with respect to the straight line L, and the distance d between the narrow groove 71 and the straight line L is relative to the tread deployment width TDW. It is optimized (0 ≦ d / TDW ≦ 0.015) (see FIG. 2). (2) The distance c in the normal direction of the tire ground contact surface from the tire ground contact end to the groove bottom of the narrow groove 71 is the groove depth g of the circumferential main groove 52 and the narrow groove 71 at the outermost side in the tire width direction. The maximum value b of the groove width is optimized (0.5 ≦ c / g ≦ 1.2 and 0.1 ≦ b / c ≦ 0.3). The distance a between the groove wall of the narrow groove 71 on the side facing the non-grounding rib 72 and the non-grounding rib 72 is optimized with respect to the maximum groove width b of the narrow groove 71 (0.6). ≦ a / b ≦ 0.9). In such a configuration, deformation of the connecting portion between the rib 55 in the tread shoulder region and the non-grounding rib 72 is suppressed when the tire is in contact with the ground, and the peak contact pressure of the shoulder is appropriately reduced when the tire is in contact with the ground. Thereby, there is an advantage that the crack resistance performance of the tire is improved, and there is an advantage that the uneven wear resistance performance (shoulder wear of the shoulder portion) of the tire is maintained. For example, when (1) d / TDW <0, the deformation amount (tensile stress shown in FIG. 3) of the connecting portion between the rib in the tread shoulder region and the non-grounding rib becomes excessive, and the crack resistance performance of the tire deteriorates. . In addition, when 0.015 <d / TDW, the peak contact pressure of the shoulder portion increases and the uneven wear resistance performance of the tire deteriorates. Similarly, when (2) c / g <0.5, the uneven wear resistance of the tire deteriorates, and when 1.2 <c / g, the crack resistance of the tire deteriorates. Further, when b / c <0.1, the crack resistance performance of the tire is deteriorated, and when 0.3 <b / c, the uneven wear resistance performance of the tire is deteriorated. Further, (3) when a / b <0.6, the uneven wear resistance of the tire deteriorates, and when 0.9 <a / b, the crack resistance of the tire deteriorates.

  In the pneumatic tire 1, the angle α formed by the wall surface on the side of the sidewall of the shoulder and the straight line L is in the range of 20 [deg] ≦ α ≦ 60 [deg] in a cross-sectional view in the tire meridian direction. The angle β formed by the groove depth direction of the narrow groove 71 and the straight line L is in the range of 10 [deg] ≦ β ≦ 50 [deg], and the top surface of the non-grounding rib 72 from the tire grounding end. The distance f in the tire ground contact surface normal direction and the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove 71 have a relationship of 0.5 ≦ f / c ≦ 0.8. It is preferable (see FIG. 4). In such a configuration, the inclination angle (angle α) of the wall surface of the shoulder portion on the side wall portion side, the groove depth direction (angle β) of the narrow groove 71 and the top surface position of the non-grounding rib 72 are optimized. There is an advantage that the anti-cracking performance and uneven wear-resistant performance are further improved.

  Moreover, in this pneumatic tire 1, it is preferable that the non-grounding rib 72 is arrange | positioned inside a tire radial direction with respect to the narrow groove 71 (refer FIG. 2). For example, in this embodiment, the non-grounding rib 72 is positioned on the inner side in the tire radial direction with respect to the narrow groove 71 and constitutes the groove wall surface on the inner side in the tire radial direction of the narrow groove 71. In such a configuration, the tire molding die can be removed more easily than the configuration in which the non-grounding rib is disposed on the inner side in the tire radial direction with respect to the narrow groove. Thereby, there exists an advantage by which manufacture of a tire is made easy.

[performance test]
In this example, performance tests on (1) crack resistance performance and (2) uneven wear resistance performance were performed on a plurality of pneumatic tires having different conditions (see FIGS. 5 and 6). In this performance test, a pneumatic tire having a tire size of 275 / 80R22.5 is assembled to a rim having a rim size of 22.5 × 7.50.

  (1) In the performance test related to crack resistance, a pneumatic tire is subjected to a load of 150% of the maximum load specified by JATMA and a maximum internal pressure. Then, after traveling 20,000 [km], the number of cracks generated in the narrow groove is observed. Based on this observation result, index evaluation is performed with the conventional example as a reference (100). This index evaluation is preferable as the numerical value increases.

  (2) In performance tests on uneven wear resistance, pneumatic tires are mounted on 2-D4 (two front wheels, four drive wheels, and four idle wheels) test vehicles. The maximum internal pressure specified by JATMA is applied to these pneumatic tires. And the maximum load is applied. And after this test vehicle travels 60,000 [km] on a general road, the wear amount difference between the shoulder ribs on the left and right sides of the tire is compared. Then, based on this comparison result, index evaluation is performed with the conventional example as a reference (100). In this index evaluation, the larger the numerical value, the smaller the uneven wear, which is preferable.

  In the pneumatic tire of Conventional Example 1, the narrow groove is located on the outer side in the tire width direction with respect to the straight line L (0 <d). In the pneumatic tire of Conventional Example 2, the narrow groove is located on the inner side in the tire width direction than the straight line L (d <0). In these pneumatic tires, the distance a between the groove wall of the fine groove and the non-grounding rib is a / b = 1.0 with respect to the maximum value b of the groove width of the fine groove.

  In the pneumatic tires 1 of the inventive examples 1 to 9, the narrow groove 71 is located on the outer side in the tire width direction with respect to the straight line L (see FIGS. 1 and 2). The distance d between the narrow groove 71 and the straight line L is optimized (0 ≦ d / TDW ≦ 0.015) with respect to the tread development width TDW. Further, the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove 71 is optimized with respect to the maximum value b of the groove width of the narrow groove 71 (0.1 ≦ b / c ≦ 0. 3) Has been done. The distance a between the groove wall of the narrow groove 71 on the side facing the non-grounding rib 72 and the non-grounding rib 72 is optimized with respect to the maximum groove width b of the narrow groove 71 (0.6). ≦ a / b ≦ 0.9).

  Further, in the pneumatic tires of Conventional Examples 1 and 2 and Invention Examples 1 to 9, the angle α formed between the wall surface of the shoulder portion on the side wall portion side and the straight line L is set to α = 30 [deg] (FIG. 4). Further, the angle β formed by the groove depth direction of the narrow groove 71 and the straight line L is set to β = 30 [deg]. Further, the ratio c / g of the distance c in the normal direction of the tire contact surface from the tire contact end to the groove bottom of the narrow groove 71 and the groove depth g of the outer circumferential main groove 52 in the tire width direction is c. /G=1.0. Further, the distance f in the tire contact surface normal direction from the tire contact end to the top surface of the non-ground rib 72 and the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove 71 are f /. c ≦ 0.65 is set.

  As shown in the test results, in the pneumatic tire 1 of Invention Examples 1 to 9, compared to the pneumatic tire of Conventional Example 1, the uneven wear resistance performance of the tire is maintained, and the crack resistance performance of the tire is improved. (See FIG. 6). Further, when comparing the pneumatic tires of Invention Examples 1 to 5 and Comparative Examples 1 and 2, the ratio d / TDW between the distance d from the straight line L to the narrow groove 71 and the tread development width TDW is optimized, It can be seen that the crack resistance performance of the tire is improved. Further, when comparing the pneumatic tires of Invention Examples 2, 6, and 7, the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove 71 and the maximum value b of the groove width of the narrow groove 71 It can be seen that the crack resistance performance of the tire is improved by optimizing the ratio b / c. Further, comparing the pneumatic tires of Invention Examples 2, 8, and 9, the ratio a / b between the distance a from the groove wall of the narrow groove 71 to the non-grounding rib 72 and the maximum value b of the groove width of the narrow groove 71 is It turns out that the crack resistance performance of a tire improves by optimizing.

  As described above, the pneumatic tire according to the present invention is useful in that it can improve the crack resistance performance and uneven wear resistance performance of the tire.

It is sectional drawing of the tire meridian direction which shows the pneumatic tire concerning the Example of this invention. It is an expanded sectional view which shows the narrow groove of the shoulder part of the pneumatic tire described in FIG. It is action explanatory drawing which shows the narrow groove of the shoulder part of the pneumatic tire described in FIG. It is an expanded sectional view which shows the narrow groove of the shoulder part of the pneumatic tire described in FIG. It is a graph which shows the result of the performance test of the pneumatic tire concerning the Example of this invention. It is a graph which shows the result of the performance test of the pneumatic tire concerning the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 3 Carcass layer 4 Belt layers 41-43 Belt material 5 Tread rubber 51, 52 Circumferential main groove 53-55 Rib 6 Side wall rubber 71 Narrow groove 72 Non-grounding rib

Claims (3)

A plurality of circumferential main grooves formed in the tread portion and extending in the tire circumferential direction, narrow grooves formed in the wall surface of the shoulder portion on the side wall portion side, and non-grounding ribs defined by the narrow grooves A pneumatic tire having
When a straight line L perpendicular to the tire contact surface is drawn from the point A that defines the tread development width TDW in a cross-sectional view in the tire meridian direction in an unloaded state,
The narrow groove is positioned on the outer side in the tire width direction from the straight line L, and the distance d between the narrow groove and the straight line L has a relationship of 0 ≦ d / TDW ≦ 0.015 with respect to the tread development width TDW. The distance c in the tire contact surface normal direction from the tire contact edge to the groove bottom of the narrow groove is the outermost groove depth g of the circumferential main groove and the maximum value of the narrow groove width. It has a relationship of 0.5 ≦ c / g ≦ 1.2 and 0.1 ≦ b / c ≦ 0.3 with respect to b, and faces the non-grounding rib in the groove wall of the narrow groove The distance a between the groove wall on the side and the non-ground rib has a relationship of 0.6 ≦ a / b ≦ 0.9 with respect to the maximum value b of the groove width of the narrow groove. .   In a cross-sectional view in the tire meridian direction, an angle α formed by the wall surface of the shoulder portion on the side wall portion side and the straight line L is in a range of 20 [deg] ≦ α ≦ 60 [deg], and the groove depth of the narrow groove The angle β formed by the vertical direction and the straight line L is in the range of 10 [deg] ≦ β ≦ 50 [deg], and the tire contact surface normal direction from the tire contact end to the top surface of the non-contact rib 2. The pneumatic tire according to claim 1, wherein the distance f and the distance c in the tire contact surface normal direction from the tire contact end to the groove bottom of the narrow groove have a relationship of 0.5 ≦ f / c ≦ 0.8. .   The pneumatic tire according to claim 1, wherein the non-grounding rib is disposed on the inner side in the tire radial direction with respect to the narrow groove.

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