JP2002114010A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire realized in the low pattern noise without impairing other performance such as the draining performance and the operation stability. SOLUTION: In each tread half area 4a and 4b, central parts 5a and 5b in the cross direction have plural compound inclined grooves 10a and 10b respectively having each one circumferential main groove 7a and 7b extended along the tire circumferential direction 6, each steep inclined groove part 8a and 8b, and first and second gentle inclined groove parts 9a, 9b and 11a, 11b extended from the predetermined positions 12 and 14 of the steep inclined groove parts 8a and 8b. A pair of the compound inclined grooves 10a1 and 10b1 adjacent to each other on both sides of a pattern center 2 are arranged in the tire circumferential direction with the predetermined phase difference so that a positional relation of the first gentle inclined groove parts 9a and 9b to a first virtual line (m) is opposite to a positional relation of the second gentle inclined groove parts 11a and 11b relative to a second virtual line (n).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire having low pattern noise without sacrificing other performances such as drainage performance and steering stability performance, and more particularly to a so-called pneumatic tire having a low flatness and a wide tread width. It relates to high performance tires.

[0002]

2. Description of the Related Art In the case of a pneumatic tire, for example, a tire for a passenger car, its tread pattern is, as shown in FIG. 3, for example, a circumferential groove extending parallel to the tire equatorial plane and an opening in the circumferential groove. Generally, a plurality of inclined grooves extending from the equatorial plane toward the tread end are provided.

[0003] This tread pattern mainly imparts excellent drainage performance to the tire by draining the tire in the front-rear direction through a circumferential groove and draining the tire laterally through an inclined groove. it can.

In a tire having such a tread pattern, as a means for further improving the drainage performance, a groove area, that is, a so-called negative rate is increased by widening a groove width, or an inclined groove is formed in the tire circumferential direction. It is useful to arrange them as so-called high angle grooves arranged at a small angle.

[0005] However, if the negative rate is increased, the land rigidity of the tread becomes insufficient.
In addition, arranging the inclined groove as a high-angle groove is because the corner of the land portion divided by the inclined groove becomes an acute angle,
The rigidity of each land portion is insufficient, so that in any case, sufficient steering stability cannot be obtained.

The tread pattern for satisfying the drainage performance and the steering stability performance in a well-balanced manner is basically composed of a combination of a circumferential groove and an inclined groove. The center region and the side region are different, more specifically, the groove portion of the inclined groove located in the center region is formed as a steeply inclined groove portion that makes a small inclination with respect to the tire circumferential direction, It is preferable to form the groove portion of the inclined groove located at a gentle inclination groove portion which makes a large inclination with respect to the tire circumferential direction.

[0007] That is, by making the inclined groove extend as described above, the excellent drainage performance is maintained by the steeply inclined groove portion of the inclined groove located in the center region, while the inclined groove located in the side region is moderately inclined. Good steering stability can be obtained by securing the rigidity of the land portion defined by the inclined groove portion.

Means for improving the pattern noise include: (1) disposing the two groove portions of the inclined groove divided by the circumferential groove so as to be shifted from each other in the tire circumferential direction;
(2) Terminating the inclined groove in the land portion without opening the groove in the circumferential direction, and (3) Shifting a pair of inclined grooves adjacent to each other across the pattern center in the tire circumferential direction so as to provide a phase difference. Useful.

However, in the means (1), since the inclined groove is continuously extended from the pattern center side toward the tread end, it becomes impossible to smoothly drain water to the tire side. It is not preferable from the point of view.

The above-mentioned means (2) is not preferable from the viewpoint of drainage performance because drainage efficiency is inferior because part of water flowing in the circumferential groove cannot be diverted to the inclined groove.

For this reason, the present inventor has proposed a means for improving the pattern noise, in which one adjacent pattern center is interposed.
The means of the above (3), in which a pair of inclined grooves are shifted from each other in the tire circumferential direction to provide a phase difference, is adopted, and the magnitude of pattern noise of various tires having tread patterns having different phase differences is examined. The following findings were obtained.

First, when a steeply sloping groove portion and a gently sloping groove portion of a pair of sloping grooves adjacent to each other with a pattern center interposed therebetween are arranged at the same pitch number in the tire circumferential direction in the central region and the lateral region of the tread portion, respectively. However, since the corners of the land portions divided by the steeply inclined grooves are acute, the rigidity of the land portions located in the central region cannot be sufficiently obtained.

Therefore, in order to secure the rigidity of the land portion located in the central region, when the arrangement pitch number of the steeply inclined groove portion is set to half of that of the gentlely inclined groove portion, in other words, the first and second steeply inclined groove portions are moved from the steeply inclined groove portion. Considering the case where the arrangement pitch of the steeply inclined groove portion is made twice as large as that of the gentlely inclined groove portion by branching into the second gentlely inclined groove portion, the steeply inclined groove portions of the pair of inclined grooves and the gentlely inclined groove portions are connected to each other. Shifting the phase by a half pitch in the tire circumferential direction is effective for reducing pattern noise.

However, if the steeply inclined grooves of the pair of inclined grooves are shifted in phase by a half pitch of the arrangement pitch, the phase difference between the gentlely inclined grooves becomes the same phase, and a sufficient pattern noise reduction effect can be obtained. Could not be obtained.

Further, when the phases of the gentle inclined grooves of the pair of inclined grooves are shifted by a half pitch of the arrangement pitch, the phase difference between the steeply inclined grooves is half of the half pitch, that is, 1/4 pitch. Due to the phase difference, a sufficient pattern noise reduction effect cannot be obtained, and in addition, the symmetry of the pattern center is lost, and the rigidity of the land located in the center area of the tread is uniform. As a result, it is difficult to obtain a feeling of handling rigidity when the steering angle is sufficiently small, which is not preferable.

[0016]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a basic structure in which a circumferential groove is combined with a compound inclined groove having a steeply inclined groove and a gentle inclined groove. The steeply sloping grooves of the pair of compound sloping grooves are formed with a predetermined phase difference, and by optimizing the arrangement of the gently sloping grooves, other performances such as drainage performance and steering stability are sacrificed. SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic tire that realizes low pattern noise, especially a so-called high-performance tire having a low flatness and a wide tread width.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a tread half area divided by a pattern center and a tread edge, which is located at or near the width center of the tread half area, One circumferential main groove extending along the tire circumferential direction, a steeply inclined groove portion located between the pattern center and the circumferential main groove and inclined at a relatively small angle with respect to the tire circumferential direction, and a steeply inclined groove From the end position located on the tread end side of the groove and the middle position in the extending direction of the steeply inclined groove and from the groove wall position side on the tread end side, while bending, at the tread end at a relatively large angle with respect to the tire circumferential direction. A plurality of compound inclined grooves having first and second gentle inclined grooves extending obliquely until they are opened, and a pair of compound inclined grooves adjacent to each other across the pattern center are arranged at predetermined positions in the tire circumferential direction. The positional relationship of the first gentle slope groove with respect to the first imaginary line connecting the end position of the sharp slope groove and the opening position of the first gentle slope groove to the tread end with a straight line, A pneumatic tire characterized in that the position is opposite to the positional relationship of the second gentle slope groove with respect to a second imaginary line connecting the end side groove wall position and the opening position of the second gentle slope groove to the tread end with a straight line. is there.

When it is necessary to more effectively improve the pattern noise, the pair of compound inclined grooves adjacent to each other with the pattern center interposed therebetween is a phase difference of a half pitch in the tire circumferential direction between the steeply inclined grooves. It is preferable to form with.

Further, from the viewpoint of reducing the pattern noise without deteriorating the drainage performance, the inclination angle of the first gentle inclination groove portion with respect to the tire circumferential direction gradually increases, and the inclination angle of the second gentle inclination groove portion gradually decreases. It is preferable to configure.

Further, in order to obtain excellent drainage performance,
The steeply inclined groove portion of the compound inclined groove preferably extends at an inclination angle of 30 ° or less with respect to the tire circumferential direction. In addition, in order to secure the rigidity of the land portion located in the side region of the tread portion, It is preferable that the inclination angle of the second gentle inclined groove with respect to the tire circumferential direction is 60 to 85 ° and 80 to 60 °, respectively.

When it is necessary to effectively increase the drainage capacity and further reduce the pattern noise, the opening width of the first gentle slope groove should be wider than the opening width of the second gentle slope groove. Is preferred.

Further, when the tire is worn, the groove volume is reduced so that the pattern noise can be reduced, but the drainage performance deteriorates. However, when the tire is worn, it is necessary to increase the drainage performance without significantly deteriorating the pattern noise. In some cases, the groove width of the second gentle slope groove is preferably wider on the groove bottom side than on the tread opening side,
In addition, it is more preferable that the second mildly inclined groove has a flask-like cross-sectional shape.

[0023]

FIG. 1 shows a part of a tread pattern formed on a typical tread portion of a pneumatic tire according to the present invention.
Is the pattern center, 3a and 3b are the tread edges, 4a and 4b
Is the tread half section, 5a and 5b are the width center positions of the tread half section, 6 is the tire circumferential direction, 7a and 7b are circumferential main grooves, 8a and 8b are steeply inclined grooves, 9a and 9b are first gentle inclined grooves, 10a and
10b is a compound inclined groove, and 11a and 11b are second gentle inclined grooves.

The tire having the tread portion 1 shown in FIG. 1 has a width center position 5a at each tread half section 4a or 4b divided by the pattern center 2 and the tread edge 3a or 3b.
Or 5b or in the vicinity thereof, one circumferential main groove 7a or 7b extending along the tire circumferential direction 6, and between the pattern center 2 and the circumferential main groove 7a or 7b. A relatively small angle, preferably steeply inclined groove 8a extending at an angle of 30 ° or less with respect to the tire circumferential direction
Or 8b, and the tread end 3a or 3b at a relatively large angle with respect to the tire circumferential direction 6 from the terminal position of the steeply inclined groove portion 8a or 8b.
First gentle groove 9a or 9b extending inclining until it is opened
And a plurality of compound inclined grooves 10a or 10b having the following.

Although FIG. 1 shows a case where the pattern center 2 coincides with the tire equator position, the pattern center 2 may be slightly shifted from the tire equator position.

The steeply inclined grooves 8a, 8b located in the central areas of the compound inclined grooves 10a, 10b maintain excellent drainage performance, while the gentle inclined grooves located in the side areas of the compound inclined grooves 10a, 10b. The rigidity of the land section defined by 9a and 9b can be secured, and good steering stability can be obtained. The circumferential main groove 7a or 7b is arranged at the width center position 5a or 5b of each tread half section 4a or 4b or in the vicinity thereof, because sufficient shoulder land rigidity is obtained and excellent maneuvering is achieved. This is to achieve stability.

The inventor made various studies to reduce the pattern noise by making the tread pattern as a basic configuration and further improving the tread pattern. We have also succeeded in developing a pneumatic tire that realizes drainage performance and low pattern noise. Hereinafter, the process of completing the present invention will be described together with the operation.

First, in order to obtain a sufficient steering stability when the above-described tread pattern is used as a basic structure, the arrangement pitch of the steeply inclined groove portion is made wider than that of the gentlely inclined groove portion so that the central region of the tread portion 1 is formed. It is necessary to secure the rigidity of the land part located in the central area, but if the layout pitch of the steeply inclined groove part is optimized so as to secure the rigidity of the land part located in the central area,
Since the number of steeply sloping grooves and the number of gently sloping grooves are the same, the pitch of the gently sloping grooves is set substantially equal to the pitch of the steeply sloping grooves. Since the rigidity of the land located in the area tends to be too large, the rigidity of the land is reduced (in other words, the rigidity of the land is reduced).
From the viewpoint of groundability, it is preferable that the arrangement pitch of the gently inclined grooves is smaller than the arrangement pitch of the steeply inclined grooves, and more preferably, １ ／ of the arrangement pitch of the steeply inclined grooves. I understood.

Therefore, in the present invention, as means for narrowing the arrangement pitch of the gentle inclined grooves to be smaller than the arrangement pitch of the steeply inclined grooves, the compound inclined grooves 10a and 10b are combined into one steeply inclined groove 8a, 8b.
And two first gentle inclined grooves 9a, 9b and a second gentle inclined groove 1 extending from the terminal position of the steeply inclined grooves 8a, 8b and the groove wall position 12 on the tread end side toward the open end of the tread end, respectively.
1a and 11b.

Next, in order to improve the drainage performance, it is necessary to increase the groove width of the steeply inclined grooves 8a and 8b.
When the groove widths of a and 8b are widened, the groove volume tends to increase, so that pattern noise tends to worsen. Therefore, in order to reduce the pattern noise, a pair of composite inclined grooves 10a1 adjacent to each other with the pattern center 2 interposed therebetween. , 10b1 by a predetermined phase difference L in the tire circumferential direction 6, preferably 1 /
It has been found useful to shift the phase difference by two pitches.

Therefore, according to the present invention, the steeply inclined grooves 8a and 8b of the pair of compound inclined grooves 10a1.10b1 adjacent to each other with the pattern center 2 interposed therebetween have a predetermined phase difference, preferably 1 / A configuration in which the phase difference is shifted by two pitches is adopted.

The steeply inclined grooves 8a and 8b of the pair of compound inclined grooves 10a1 and 10b1 adjacent to each other with the pattern center 2 interposed therebetween are separated by a predetermined phase difference L in the tire circumferential direction 6, for example, a half pitch. Considering the case of displacing by the phase difference,
The first gentle slope grooves 9a and 9b adjacent to the tire circumferential direction 6 and the second
The arrangement pitch of the gently inclined grooves 11a and 11b is the same pitch (in this case, approximately の of the arrangement pitch of the steeply inclined grooves 8a and 8b).
It becomes. ) Is preferable in terms of equalizing the rigidity of the land portion, but the first gentle slope grooves 9a and 9b and the second gentle slope groove 1
If the extending shapes of 1a and 11b are the same, the pattern center 2
The first gentle inclined groove 8a of one compound inclined groove 10a and the second gentle inclined groove 11b of the other compound inclined groove 10b that face each other have the same phase in the tire circumferential direction. Resulting in a line-symmetric pattern centered at
Pattern noise tends to worsen.

Therefore, according to the present invention, the composite inclined grooves 10a, 10a
b, the extending shapes of the first gently inclined grooves 9a, 9b and the second gently inclined grooves 11a, 11b are made different, more specifically, the steeply inclined grooves.
End position 12 of 8a, 8b and tread end 3 of first gentle slope groove 9a, 9b
The positional relationship of the first gentle inclined grooves 9a, 9b with respect to the first imaginary line m connecting the opening positions 13 to the a, 3b with straight lines is the steep inclined grooves 8a, 8b.
The groove wall position 14 on the tread end 3a, 3b side and the second gentle slope groove 11a,
The opening position 15 to tread ends 3a and 3b of 11b is connected by a straight line.
2 The position of the second gentle slope grooves 11a and 11b with respect to the imaginary line n is opposite to the positional relationship. More specifically, when the tire is rotated and grounded on the road surface in the direction of arrow 16 in FIG. When viewed on the line, the first gently inclined grooves 9a and 9b correspond to the first imaginary line m.
It is essential that the second gentle inclined grooves 11a and 11b be provided in an extended shape so as to be grounded earlier than the second imaginary line n. As a specific matter, the first gentle inclined groove portion 9 of one compound inclined groove 10a (located in the left tread half section 4a in FIG. 1) which is substantially line-symmetric with respect to the pattern center 2 as a center.
a or the second gentle inclined groove 11a and the ground impact timing of the second gentle inclined groove 11b or the first gentle inclined groove 9b of the other compound inclined groove 10b (located in the right tread half section 4b in FIG. 1). As a result, the effect of reducing the pattern noise can be achieved.

Further, from the viewpoint of drainage performance at the time of cornering and prevention of heel-and-toe wear of the land portion located in the side area, the first and second gentle slope grooves are curved from the steep slope grooves in the present invention. The opening at the tread edge is made at a relatively large angle with respect to the tire circumferential direction, preferably at 60 to 85 ° and 80 to 60 °, respectively.

Thus, the present invention employs the above-described configuration, and thereby succeeds in developing a pneumatic tire that achieves good steering stability, drainage performance, and low pattern noise.

In FIG. 1, the steeply inclined groove portions 8a1 of the pair of compound inclined grooves 10a1 and 10b1 adjacent to each other with the pattern center 2 interposed therebetween.
8b1 are formed with a phase difference L of a half pitch in the tire circumferential direction 6, and this is a tread pattern that emphasizes pattern noise among steering stability, drainage performance and pattern noise, When importance is placed on steering stability and drainage performance, the phase difference L
Can be changed as appropriate.

In another embodiment, the inclination angle of the first gentle inclination grooves 9a, 9b with respect to the tire circumferential direction 6 is gradually increased, and the inclination angle of the second gentle inclination grooves 11a, 11b is gradually decreased. Thus, the drainage performance to the side of the tire can be sufficiently obtained.

The first gentle slope grooves 9a and 9b mainly drain the water to the side of the tire, so that the first gentle slope grooves 9a and 9b
It is preferable that the opening widths of a and 9b are wider than the opening widths of the second gentle inclined grooves 11a and 11b.

In addition, making the opening width of the first gentle slope grooves 9a, 9b larger than the opening width of the second gentle slope grooves 11a, 11b can be achieved by setting one of the tread half areas 4a or 4b and the other tread half area. The gently inclined grooves 9a, 9b, 11 located at 4b or 4a, respectively.
Since there is also an effect of dispersing the impacts of a and 11b, it also effectively acts to reduce pattern noise.

In addition, the tread portion 1 of the tire wears as it is used, and the groove volume decreases accordingly, so that the pattern noise is reduced as compared with a new tire, but the drainage performance is also deteriorated. Tend.

Therefore, even if the tire 1 has worn tread, if sufficient drainage performance is to be ensured, as shown in FIG. 2, the second gentle slope groove 11a or 11b is located at the bottom of the groove. It is preferable that the groove width W1 is set to be wider than the groove width W2 at the tread opening side position, for example, the cross-sectional shape of the second gentle inclined grooves 11a and 11b is a flask shape. Note that, due to restrictions on the strength of the mold, in practice, the second gentle inclined grooves 11a, 11b
Preferably, the groove width W1 on the groove bottom side is about twice the groove width W2 at the tread opening position.

The above is merely an example of the embodiment of the present invention, and various changes can be made within the scope of the claims. For example, in order to improve the drainage performance while securing the block rigidity, the corner of the land formed by arranging two compound inclined grooves 10a, 10a or 10b, 10b adjacent in the tire circumferential direction 6 is chamfered. May be applied.

[0043]

Next, a pneumatic tire according to the present invention was prototyped and its performance was evaluated, and will be described below. -Example The tire of the example has a tread pattern shown in Fig. 1 and has a tire size of PSR205 / 55R16 (tread width: 170 m).
m), and the dimensions and the like of the circumferential main groove, the compound inclined groove, and the like are collectively shown in Table 1. Incidentally, the second gentle inclined groove portion is shown in FIG.
Table 1 has the cross-sectional shape of the flask shown in Table 1.
Is shown in In addition, the tire structure other than the tread portion was substantially the same as that of a normal pneumatic tire for a passenger car.

[0044]

[Table 1]

Conventional Example The conventional tire has a tread pattern shown in FIG. 3, has a tire size of PSR205 / 55R16, and has a circumferential groove 101.
Table 2 summarizes the dimensions and the like of 〜103 and the inclined grooves 104 傾斜 106.

[0046]

[Table 2]

(Evaluation of Performance) Drainage performance, steering stability performance and pattern noise were evaluated for each of the test tires when they were new and when they were worn by 50%, and will be described below. Each of the test tires was mounted on a standard rim (61 / 2JJ), and the following tests were performed under the conditions of a tire internal pressure: 230 kPa and a tire load: equivalent to two actual vehicles.

The drainage performance was evaluated both during straight running and during cornering. The drainage performance during straight running was evaluated by measuring a critical speed at which a hydroplaning phenomenon occurs when the vehicle travels straight and passes on a wet road surface having a depth of 5 mm.

The drainage performance during cornering was 5
limit when hydroplaning occurs when passing on a wet road with a radius of 80m
G was measured and evaluated accordingly.

The steering stability performance was evaluated by running a sports course on a dry circuit course in various running modes and feeling by a test driver at that time. The pattern noise was evaluated by the test driver's feeling of the cabin noise when coasting from 100 km / h on a straight and smooth road surface.

Table 3 shows the results of these evaluations. Table 3
Numerical values in each of the figures indicate an index ratio with respect to the conventional example as 100, and the larger the value, the better the performance.

[0052]

[Table 3]

From the evaluation results in Table 3, it can be seen that the embodiment has excellent drainage performance and steering stability and reduces pattern noise in both the case of a new product and the case of 50% wear as compared with the conventional example. ing.

[0054]

According to the present invention, a pneumatic tire realizing low pattern noise without sacrificing other performances such as drainage performance and steering stability performance, particularly a so-called high performance having a low flatness and a wide tread width. It is now possible to provide tires.

[Brief description of the drawings]

FIG. 1 is a developed view of a part of a tread portion of a pneumatic tire according to the present invention.

FIG. 2 is a view showing a cross-sectional shape of a second inclined groove portion.

FIG. 3 is a development view of a part of a tread portion of a conventional tire.

[Explanation of symbols]

 1 Tread part 2 Pattern center 3a, 3b Tread edge 4a, 4b Tread half area 5a, 5b Center position of width of tread half area 6 Tire circumferential direction 7a, 7b Circumferential main groove 8a, 8b Steep groove part of compound inclined groove 9a, 9b First gently sloping groove of compound sloping groove 10a, 10b Compound sloping groove 11a, 11b Second gently sloping groove of compound sloping groove 12 End position of steeply sloping groove 13 Opening position of first gently sloping groove to tread end 14 Steep Groove wall position on the tread end side of the inclined groove portion 15 Opening position of the second gentle inclined groove portion on the tread end 16 Tire rotation direction m First virtual line n Second virtual line W1 Groove on the groove bottom side of the second gentle inclined groove portion Width W2 Groove width at the tread opening position of the second gentle slope groove

Claims (9)

[Claims] At least one tread half area divided by a pattern center and a tread edge is located at or near the center of the width of the tread half area and has one circumferential main groove extending along the tire circumferential direction. The steeply grooved portion located between the pattern center and the circumferential main groove and extending at a relatively small angle with respect to the tire circumferential direction, and the end position and the steeply grooved portion located on the tread end side of the steeply grooved portion. First and second gentle slopes extending from the middle of the extending direction and from the groove wall position side on the tread end side while being curved and inclining until opening at the tread end at a relatively large angle with respect to the tire circumferential direction. A plurality of compound inclined grooves having a groove portion, a pair of compound inclined grooves adjacent to each other across the pattern center are disposed at a predetermined phase difference in the tire circumferential direction, and the end position of the steeply inclined groove portion and the first Slowly inclined groove The relationship between the position of the first gentle slope groove relative to the first imaginary line (m) connecting the opening position to the tread end with a straight line is the groove wall position on the tread end side of the steep slope groove and the tread end of the second gentle slope groove. The pneumatic tire is characterized in that the position is opposite to the positional relationship of the second gentle slope groove portion with respect to a second imaginary line (n) connecting the opening positions to the second virtual line (n). 2. The pneumatic tire according to claim 1, wherein the pair of compound inclined grooves adjacent to each other across the pattern center form steeply inclined groove portions with a phase difference of a half pitch in the tire circumferential direction. 3. The pneumatic tire according to claim 1, wherein the first gentle inclination groove portion gradually increases the inclination angle with respect to the tire circumferential direction, and the second gentle inclination groove portion gradually decreases the inclination angle. 4. When the tire is rotated and grounded on a road surface, the first gentle slope groove is formed by a first gentle inclination groove when viewed on the same tire circumference.
It is arranged in an extended shape that is grounded later than the virtual line,
4. The pneumatic tire according to claim 1, wherein the second gentle slope groove portion is provided in an extended shape such that the second gentle slope groove comes in contact with the ground ahead of the second virtual line. 5. 5. The pneumatic tire according to claim 1, wherein the steeply inclined groove portion of the compound inclined groove extends at an inclination angle of 30 ° or less with respect to the tire circumferential direction. 6. The first and second gently inclined grooves have inclination angles with respect to the tire circumferential direction of 60 to 85 ° and 80 to 60 °, respectively.
The pneumatic tire according to any one of claims 1 to 5, wherein 7. The pneumatic tire according to claim 1, wherein the opening width of the first gentle slope groove is wider than the opening width of the second gentle slope groove. 8. The pneumatic tire according to claim 1, wherein a groove width of the second gentle slope groove portion is wider on a groove bottom side than on a tread opening side. 9. The pneumatic tire according to claim 1, wherein the second gentle slope groove has a flask-like cross-sectional shape.