JP2016155395A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering stability performance on a dry road surface while maintaining travelling on an ice and snow road.SOLUTION: In a pneumatic tire 1, at a tread part 2 are provided at least four main grooves 3 continuously extending in a tire circumference direction and a plurality of lateral grooves 4 extending between main grooves 3 and 3 and between the main groove 3 and a tread grounding end Te, so that a plurality of block rows 5R, having blocks 5 partitioned by the main grooves 3 and the lateral grooves 4 arranged in a tire circumference direction, are formed and in the blocks 5 are provided sipings S. In a reference grounding surface FP where the tire is installed in a normal rim and grounded on a flat surface at a 1-degree camber angle by applying a normal load to a normal state of the tire filled with normal inner pressure are included a plurality of different types of block rows with different grounding lengths L in the tire circumference direction, where the block rows having larger grounding lengths L have smaller grounding widths W in a tire shaft direction of the block 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire that improves driving stability performance on a dry road surface while maintaining icy and snowy road running.

  A pneumatic tire having a plurality of block rows in which tread portions are divided into main grooves extending in the tire circumferential direction and lateral grooves extending in a direction intersecting the main grooves, and blocks provided with siping are arranged in the tire circumferential direction. It has been known. Such pneumatic tires have a snow column shearing force and snow removal performance secured by the main grooves and lateral grooves to improve the steering stability performance on snowy roads, and the edge effect due to siping is demonstrated, and steering on ice roads is achieved. Stability performance is improved.

  However, in the conventional pneumatic tire, the relationship between the contact width in the tire axial direction of each block row and the contact length in the tire circumferential direction is not considered, and there is room for further improvement in the handling stability performance on the dry road surface. there were.

JP 2008-201368 A

  The present invention has been devised in view of the above problems, and is based on defining the ground contact width and ground contact length of each block row formed in the tread portion within a certain range. The main purpose is to provide a pneumatic tire that improves driving stability on a dry road while maintaining traveling.

  In the present invention, at least four main grooves extending continuously in the tire circumferential direction and a plurality of lateral grooves extending between the main grooves and between the main groove and the tread grounding end are provided in the tread portion. Thus, a plurality of block rows in which the blocks divided by the main grooves and the lateral grooves are arranged in the tire circumferential direction are formed, and the blocks are pneumatic tires provided with siping, and the rim is attached to a regular rim. In the reference grounding surface that is assembled and loaded with a normal load in a normal state filled with normal internal pressure and grounded to a plane with a camber angle of 1 degree, a plurality of types with different ground contact lengths L in the tire circumferential direction are included, A block row having a larger ground contact length L has a smaller ground contact width W in the tire axial direction of the block.

  In the pneumatic tire according to the present invention, the ratio L1 / Ln between the ground contact length Ln of the block row Bn having the smallest ground contact length L and the ground contact length L1 of the block row B1 having the largest ground contact length L is It is desirable that the ratio is smaller than the ratio Wn / W1 between the ground width Wn of the block row Bn and the ground width W1 of the block row B1.

  In the pneumatic tire according to the present invention, the tread portion has an asymmetric pattern in which the direction of mounting on the vehicle is specified, and the main groove is disposed at the center of the tire equator most on the tire equator side than the tire equator. An inner main groove, a center outer main groove disposed on the outermost side of the tire equator than the tire equator, and a shoulder outer main groove disposed on the vehicle outer side of the center outer main groove. The center position in the tire axial direction of the center block row divided between the center outer main groove and the center outer main groove is preferably on the vehicle inner side than the tire equator.

  In the pneumatic tire according to the present invention, it is preferable that the groove width of the main groove gradually decreases from the center inner main groove toward the shoulder outer main groove.

  In the pneumatic tire of the present invention, at least four main grooves extending continuously in the tire circumferential direction in the tread portion, and a plurality of lateral grooves extending between the main grooves and between the main grooves and the tread grounding end, Is provided, a plurality of block rows in which the blocks divided by the main grooves and the lateral grooves are arranged in the tire circumferential direction are formed, and siping is provided in the blocks. In such a pneumatic tire, the snow drainage performance is enhanced by the main groove and the snow column shear force is exhibited by the lateral groove, so that the steering stability performance on the snowy road is improved and the edge effect of siping is exhibited. In addition, the stability of handling on icy roads is improved.

  In addition, the tire of the present invention is configured such that a tire is grounded in a circumferential direction on a reference ground surface in which a normal load is loaded in a normal state in which a normal rim is assembled and a normal internal pressure is filled and a normal load is applied to the plane with a camber angle of 1 degree. A plurality of types having different lengths L are included, and a block row having a larger ground contact length L has a smaller ground contact width W in the tire axial direction of the block. In such tires, the sum of the ground contact areas of each block row in the ground contact surface tends to be uniform as compared with conventional tires. Even if the tire equator changes from the tire equator to the inside or outside of the vehicle, the contact pressure acting on the block row where the maximum contact pressure acts is equalized, and the behavior of the block row where the maximum contact pressure acts greatly affects the behavior of the vehicle Can be stabilized and a phenomenon such as local slip can be suppressed. Therefore, the tire of the present invention can improve the grip performance when turning, and the steering stability performance on the dry road is improved. It is also useful for suppressing uneven wear.

It is an expanded view of the tread part which shows the pneumatic tire of one Embodiment of this invention. It is a top view of the reference ground plane of FIG. It is the elements on larger scale of FIG. It is a top view of the reference ground plane of the tire of an example and a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a pneumatic tire (hereinafter, simply referred to as “tire”) 1 of the present embodiment is suitably used as a studless tire for a passenger car, for example. Further, the tire 1 of the present embodiment has an asymmetric tread pattern in which the mounting direction to the vehicle is specified. In addition, the direction of mounting the tire 1 on the vehicle is displayed by characters or the like on, for example, a sidewall portion (not shown).

  The tread portion 2 of the tire 1 is provided with at least four main grooves 3 extending continuously in the tire circumferential direction. The main groove 3 of the present embodiment is a center inner main groove 3A arranged on the tire equator C side most inside the vehicle from the tire equator C, and a center arranged on the tire equator C side most outside the vehicle from the tire equator C. Four of an outer main groove 3B, a shoulder outer main groove 3C disposed on the vehicle outer side than the center outer main groove 3B, and a shoulder inner main groove 3D disposed on the vehicle inner side than the center inner main groove 3A. It consists of a main groove 3.

  The tread portion 2 is provided with a plurality of lateral grooves 4 extending between the main grooves 3 and 3 and between the main groove 3 and the tread grounding end Te. The lateral groove 4 of the present embodiment has a plurality of center lateral grooves 4A extending between the center inner main groove 3A and the center outer main groove 3B, and between the center inner main groove 3A and the shoulder inner main groove 3D. A plurality of middle inner lateral grooves 4B extending between the center outer main groove 3B and the shoulder outer main groove 3C, and a plurality of middle outer lateral grooves 4C extending between the shoulder inner main groove 3D and the tread grounding end Te. And a plurality of shoulder outer lateral grooves 4E extending between the shoulder outer main groove 3C and the tread grounding end Te.

  The tread portion 2 is formed with a plurality of block rows 5R in which the blocks 5 divided by the main grooves 3 and the lateral grooves 4 are arranged in the tire circumferential direction. In the present embodiment, a plurality of center blocks 6 divided by the center inner main groove 3A, the center outer main groove 3B, and the center lateral groove 4A are arranged in the center block row 6R, the center inner main groove 3A, and the shoulder inner side. A plurality of inner middle blocks 7 divided by the main groove 3D and the middle inner lateral groove 4B are arranged by the inner middle block row 7R arranged in the tire circumferential direction, the center outer main groove 3B, the shoulder outer main groove 3C, and the middle outer lateral groove 4C. A plurality of inner shoulder blocks 9 divided by the outer middle block row 8R in which the divided outer middle blocks 8 are arranged in the tire circumferential direction, the shoulder inner main groove 3D, the tread grounding end Te, and the shoulder inner lateral grooves 4D are arranged in the tire circumferential direction. Inner shoulder block row 9R and shoulder outer main groove 3C lined up with Outer shoulder block row 10R is provided with a plurality of outer shoulder blocks 10 are partitioned by a de grounding end Te and the shoulder outer lateral grooves 4E are arranged in the tire circumferential direction. Further, each of the blocks 6 to 10 of the present embodiment is provided with a plurality of sipings S that are inclined with respect to the tire axial direction and extend in a zigzag manner.

  In such a tire 1, the snow removal performance and snow column shearing force are enhanced by the main groove 3 and the lateral groove 4, and the steering stability performance on the snowy road is improved, and the edge effect of the siping S is demonstrated, and the ice 1 The steering stability performance is improved.

  Here, the “tread grounding end” Te is applied to the tire 1 in a normal state in which the rim is assembled to the normal rim and filled with the normal internal pressure, and a normal load is applied to the flat tire with a camber angle of 0 degree. Is defined as the contact position on the outermost side in the tire axial direction. A distance in the tire axial direction between the tread ground contact Te and Te is determined as a tread ground contact width TW. Further, the dimensions and the like of each part of the tire are values in the normal state unless otherwise specified.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA and “Design Rim” for TRA. For ETRTO, use "Measuring Rim".

  The “regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based, and is “maximum air pressure” for JATMA and table for TRA. The maximum value described in TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES is "INFLATION PRESSURE" for ETRTO, but 180 kPa for tires for passenger cars.

  Furthermore, “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “Maximum load capacity” for JATMA, “TIRE” for TRA The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is “LOAD CAPACITY” in the case of ETRTO.

  FIG. 2 shows that the tire 1 of the present invention is loaded with a normal load in a normal state in which a rim is assembled on a normal rim (not shown) and filled with a normal internal pressure, and a camber angle of 1 degree (however, the direction of mounting on the tire) If there is a negative camber, a reference ground plane FP which is a ground plane when grounded on a plane is shown. (However, the lateral groove 4 is omitted.) As is apparent from FIG. 2, the reference row FP has a plurality of types of block rows 5R having different contact lengths L in the tire circumferential direction (five types in the figure). ) Is included. In the reference ground contact surface FP, the block contact width W in the tire axial direction of the block is set to be smaller in the block row having a greater ground contact length L. That is, in this example, when the block rows are arranged in descending order of the contact length L, the center block row 6R, the inner middle block row 7R, the outer middle block row 8R, the inner shoulder block row 9R, and the outer shoulder block row 10R. When the blocks are arranged in order from the smallest contact width W in the tire axial direction, the same as described above is obtained.

  Thus, the tire 1 of the present invention has a tendency that the total sum of the contact area of each block row 5R within the contact surface tends to be uniform as compared with the conventional tire, and therefore changes from straight travel to turning travel, Even if the maximum contact pressure position fluctuates from the tire equator C of the tread portion 2 to the inside and outside of the vehicle, the contact pressure acting on the block row 5R to which the maximum contact pressure acts is made uniform, and the maximum greatly affects the behavior of the vehicle. The behavior of the block row 5R to which the contact pressure acts is stabilized, and a phenomenon such as a local slip can be suppressed. Therefore, the tire 1 of the present invention can improve the grip performance when turning, and the steering stability performance on the dry road is improved. It is also useful for suppressing uneven wear.

  The contact length L is represented by an average value of the contact lengths Lr and Ls on both sides in the tire axial direction in the contact surface shape of each block row 5R.

Further, assuming that the block rows are B1, B2,..., Bn−1, Bn in order from the largest ground contact length L, the tire 1 of the present embodiment has a block row Bn with the smallest ground contact length L. The ratio L1 / Ln between the ground contact length Ln (corresponding to 10R in FIG. 2) and the ground contact length L1 of the block row B1 having the largest ground contact length L (corresponding to 6R in FIG. 2). Is formed smaller than the ratio Wn / W1 between the ground width Wn of the block row Bn and the ground width W1 of the block row B1.
In general, a rib having a small contact length increases the contact pressure when turning compared to a rib having a large contact length. Since the lateral force acts on the rib on the grounding end Te side in addition to the longitudinal force and the severity is increased, the effect of the present invention can be further improved by setting the grounding width of the rib at a ratio larger than the ratio L1 / Ln. Can be demonstrated.

In order to make the above-described action more effective, the grounding length Li and grounding width Wi of the block row Bi having the i-th largest grounding length L, and the grounding length of the block row B1 having the maximum grounding length L are described. It is desirable that L1 and the grounding width W1 are defined by the following relationship.
When 1.00 <L1 / Li ≦ 1.05, 1.05 <Wi / W1 ≦ 1.20
When 1.05 <L1 / Li ≦ 1.15, 1.20 <Wi / W1 ≦ 1.45
When 1.15 <L1 / Li ≦ 1.35, 1.45 <Wi / W1 ≦ 1.75
When 1.35 <L1 / Li ≦ 1.60, 1.75 <Wi / W1 ≦ 2.00

  Thus, by setting the ratio Wi / W1 of the grounding width W to be larger than the ratio L1 / Li of the grounding length L of the block row B1 and the block row Bi, a lateral force is applied to each of the blocks B1 to Bn. In addition, the contact pressure due to the vertical force acts in a well-balanced manner, and the steering stability performance on the dry road is further improved. When the Wi / W1 is too large compared to the ratio L1 / Li (for example, when 1.00 <L1 / Li ≦ 1.05, Wi / W1 is larger than 1.2). The lateral rigidity of the block row Bn becomes excessive, and the grip during cornering may be lowered, which may deteriorate the steering stability performance.

  As shown in FIG. 2, in the ground contact shape of the tire 1 of the present embodiment, the block row B1 is arranged on the tire equator C, and the block row Bn is arranged on the vehicle outer end. Then, the block row Bn-1 having the largest ground contact width W next to the block row Bn is disposed at the vehicle inner end. As a result, the lateral rigidity of the blocks B arranged at both ends in the axial direction of the tire, where the lateral force acts greatly during turning, etc., is enhanced, and the ground pressure of the block B on the tire equator C where the ground contact pressure is greatest during straight traveling is increased. The rigidity in the tire circumferential direction can be increased. Therefore, such a tire 1 is further improved in steering stability performance.

  Furthermore, in the tire 1 of the present embodiment, the main groove 3 and the lateral groove 4 are formed as follows in addition to the ground contact shape of the block row 5R as described above. That is, as well shown in FIG. 3, the center inner main groove 3A has a linear shape along the tire circumferential direction. Since the center inner main groove 3A can smoothly discharge the drainage in the groove to the rear in the tire rotation direction, it can exhibit excellent drainage performance.

  The center outer main groove 3B is connected to the long piece portion 3B1 extending obliquely with respect to the tire circumferential direction and between the long piece portions 3B1 and 3B1 adjacent in the tire circumferential direction, and is smaller than the long piece portion 3B1. The short piece portions 3B2 are formed in zigzag grooves alternately arranged. Such a center outer main groove 3B increases the edge component in the tire axial direction, increases the frictional force during driving and braking on an icy road, and has a tire axial direction component, so that a large snow column shear force acts. To do.

  Further, the center outer main groove 3B has a sawtooth shape because the short piece portion 3B2 is inclined in the same direction as the long piece portion 3B1, so the groove length and the groove volume are increased, and the edge component and the tire axial direction component are increased. In addition to the increase, the snow can be firmly pressed at the intersection between the short piece 3B2 and the long piece 3B1 to obtain a larger snow column shear force.

  Further, in the tire 1 of the present embodiment, the center position 6RC of the center block row 6R in the tire axial direction is on the vehicle inner side than the tire equator C. As a result, the tire 1 helps to secure a large ground contact area of the outer middle block row 8R and the outer shoulder block 10R outside the vehicle, where the ground pressure during turning is higher than that inside the vehicle, and increases rigidity. Therefore, the tire 1 of this embodiment improves the rigidity balance between the vehicle inner side and the vehicle outer side, and further improves the steering stability performance. The center position 6RC is the amplitude center of the zigzag when the center block row 6R is formed in a zigzag shape. In addition, if the center position 6RC is disposed on the vehicle inner side more excessively than the tire equator, the rigidity of the inner middle block 7 becomes small, and the steering stability performance tends to deteriorate. For this reason, the distance Lt in the tire axial direction between the tire equator C and the center position 6RC is preferably 1 to 4% of the tread contact width TW.

  Furthermore, in order to exhibit the above-mentioned action more effectively, the distance Le between the groove center line 3Ag of the center inner main groove 3A and the tire equator C, and the zigzag amplitude center line 3Bg of the center outer main groove 3B and the tire equator. The ratio Lo / Le to the distance Lo to C is preferably 1.2 or more, more preferably 1.3 or more, and preferably 1.8 or less, more preferably 1.7 or less.

  In order to exert the above-described action, the distance Le is preferably 8.0% or more, more preferably 8.5% or more of the tread grounding width TW, preferably 12.0% or less, more preferably Is preferably 11.5% or less.

  The shoulder inner main groove 3D and the shoulder outer main groove 3C have a linear shape along the tire circumferential direction. Such a shoulder inner main groove 3D and a shoulder outer main groove 3C serve to increase the lateral rigidity of the inner shoulder block 9 and the outer shoulder block 10 on which a large lateral force acts.

  Further, the groove width Wg of the main groove 3 of this embodiment is gradually reduced from the center inner main groove 3A toward the shoulder outer main groove 3C on the vehicle outer side. That is, the groove width Wga of the center inner main groove 3A, the groove width Wgb of the center outer main groove 3B, and the groove width Wgc of the shoulder outer main groove 3C are Wga> Wgb> Wgc. As a result, even if the vehicle changes from straight running to turning and the maximum contact pressure position moves from the vicinity of the tire equator C to the outside of the vehicle, the contact pressure is easily equalized, so that uneven wear can be suppressed and grip can be improved. . Therefore, this tire 1 further improves the steering stability performance on the dry road.

  In order to effectively exhibit the above-described operation, the groove width Wga of the center inner main groove 3A (the groove width perpendicular to the longitudinal direction of the groove, hereinafter the same applies to other grooves) is, for example, tread grounding 4 to 8% of the width TW is desirable. Further, the groove width Wgb of the center outer main groove 3B (referred to as the groove width in the long piece portion 3B1) is preferably 2.5 to 6.5% of the tread ground contact width TW, for example. Furthermore, the groove width Wgc of the shoulder outer main groove 3C is desirably 1.0 to 3.0% of the tread ground contact width TW, for example.

  Further, although not particularly limited, for the groove width Wgd of the shoulder inner main groove 3D, in order to secure the rigidity of the inner shoulder block 9 and the inner middle block 7 in a well-balanced manner, for example, 3. 0 to 7.0% is desirable.

  In the present embodiment, the center lateral groove 4A has a widened portion 4A1 that inclines in the same direction as the short piece portion 3B2 and increases in groove width from the center inner main groove 3A toward the center outer main groove 3B. Further, the end 4Ae on the center outer main groove 3B side of the center lateral groove 4A is continuous with the intersection K1 between the long piece 3B1 and the short piece 3B2. Thereby, the tire axial direction component of the center lateral groove 4A is added to the short piece portion 3B2, and snow road performance is enhanced.

  Further, in the present embodiment, the middle inner lateral groove 4B extends in a zigzag shape from the tire equator C side to the tread ground contact end Te side. Such middle inner lateral grooves 4B are useful for increasing the groove volume and increasing the snow column shear force.

  The middle outer lateral groove 4C is inclined to one side with respect to the tire axial direction from the center outer main groove 3B, and is inclined to the other side at a substantially central portion of the length of the middle outer lateral groove 4C. The zigzag shape that is further inclined to one side and connected to the shoulder outer main groove 3C is formed. Such a middle outer lateral groove 4C increases the groove volume, and thus helps to improve the performance on ice and snowy roads.

  Further, the end 4Ce on the center outer main groove 3B side of the middle outer lateral groove 4C is connected to the intersection K2 (end of the short piece 3B2 on the vehicle outer side) of the long piece 3B1 and the short piece 3B2. Moreover, the short piece portion 3B2 side portion of the middle outer lateral groove 4C is inclined in the same direction as the short piece portion 3B2. As a result, a cross-shaped groove is formed by the center lateral groove 4A, the short piece portion 3B2 and the middle outer lateral groove 4C between the center inner main groove 3A and the short piece 3B2 portion of the shoulder outer main groove 3C. The column shear force is increased, and the steering stability performance on snowy roads is further improved.

  Further, in the present embodiment, the shoulder inner lateral grooves 4D and the shoulder outer lateral grooves 4E have one-side groove edges 4D1, 4E1 inclined in one direction with respect to the tire axial direction and extending in an arc shape. The other groove edges 4D2 and 4E2 have a zigzag shape. Thereby, in addition to helping to increase the rigidity of the inner shoulder block 9 and the outer shoulder block 10, it is useful for increasing the edge component in the tire axial direction and improving the ice road performance.

  The groove width of each of the lateral grooves 4A to 4E is preferably 25 to 70% of the groove width Wga of the center inner main groove 3A from the viewpoint of more exerting the above-described action.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

Pneumatic tires (size: 195 / 65R15) having the contact surface shape of FIG. 4 and based on the specifications of Table 1 were manufactured and tested for their respective performances. The main common specifications are as follows.
Tread contact width TW: 160mm
<Center inner main groove>
Groove width Wga / tread contact width TW: 11.2%
<Center outer main groove>
Groove width Wgb / tread contact width TW: 1.9%
<Shoulder inner main groove>
Groove width Wgc / tread contact width TW: 2.0%
<Shoulder outer main groove>
Groove width Wgd / tread contact width TW: 5.0%

<Operation stability on dry road>
Each sample tire is mounted on all wheels of a 2000cc rear-wheel drive vehicle with a rim (15x6JJ) and internal pressure (200kPa), and a driver rides on a dry road (asphalt road surface) test course. In addition, characteristics relating to steering wheel response, rigidity, grip, etc. were evaluated by sensory evaluation of the driver. A result is shown by the score which sets the comparative example 1 to 100. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it can be confirmed that the steering stability performance of the tire of the example is improved as compared with the comparative example. A similar test was performed on a 6-block pattern pneumatic tire, and the same tendency as in Table 1 was shown.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Main groove 4 Horizontal groove 5 Block 5R Block row | line | column FP Reference | standard grounding surface L Grounding length Te of tire circumferential direction Tread grounding end W Grounding width of tire axial direction

Claims (4)

The tread portion is provided with at least four main grooves extending continuously in the tire circumferential direction, and a plurality of lateral grooves extending between the main grooves and between the main groove and the tread grounding end. A plurality of block rows in which blocks divided by grooves and transverse grooves are arranged in the tire circumferential direction are formed, and the block is a pneumatic tire provided with siping,
In a reference ground plane that is assembled to a normal rim and loaded with a normal load in a normal state filled with normal internal pressure and grounded to a flat surface with a camber angle of 1 degree,
A pneumatic tire characterized in that a plurality of types having different ground contact lengths L in the tire circumferential direction are included, and a block row having a larger ground contact length L has a smaller ground contact width W in the tire axial direction of the block.   The ratio L1 / Ln between the ground length Ln of the block row Bn with the smallest ground length L and the ground length L1 of the block row B1 with the largest ground length L is the ground width Wn of the block row Bn. The pneumatic tire according to claim 1, wherein the pneumatic tire is smaller than a ratio Wn / W1 to a ground contact width W1 of the block row B1. The tread portion has an asymmetric pattern in which the direction of mounting on the vehicle is specified,
The main groove has a center inner main groove disposed on the tire equator side most inside the vehicle from the tire equator, a center outer main groove disposed on the tire equator side most on the vehicle outer side than the tire equator, and the center outer main groove. Including a shoulder outer main groove arranged on the vehicle outer side than the groove,
3. The pneumatic tire according to claim 1, wherein a center position in a tire axial direction of the center block row divided between the center inner main groove and the center outer main groove is on the vehicle inner side than the tire equator.   The pneumatic tire according to claim 3, wherein the groove width of the main groove gradually decreases from the center inner main groove toward the shoulder outer main groove.

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