JP2013095336A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire 1 by which improvement of steering stability can be expected.SOLUTION: Two inner main grooves 8a and two outer main grooves 8b extended symmetrically on the right and left of a width direction center of a tread 2 as the center to a circumferential direction are formed on a tread surface 7, a center rib 15a is formed between the right and left inner main grooves 8a, an intermediate rib 15b is respectively formed between the right and left inner main grooves 8a and the outer main grooves 8b, and in the cross-section cut in a meridian direction of the tread 2, the tread surface 7 includes a first arc 21 and a second arc 22 continuing from the width direction center to the width direction end, the first arc 21 and the second arc 22 have first tread radius TR1 and a second tread radius TR2 with a different radius of curvature respectively, and the first tread radius TR1 is larger than the second tread radius TR2. The center of the first arc 21 is on an equatorial plane of the tire, and a change point P as a contact point of the first arc 21 and the second arc 22 is positioned in the width direction center of the intermediate rib 15b.

Description

  The present invention relates to a pneumatic tire.

  Conventionally, a tire having a large tread radius has been adopted as one means for improving the steering stability of a vehicle. By increasing the tread radius, the contact width of the tread portion is increased, and the contact area can be increased. The tread radius means the radius of curvature of the arc formed by the tread surface from the tread center (intersection of the tire equator plane and the tread surface) to the shoulder portion in the meridional section of the tire.

  Generally, a plurality of types of arcs having tread radii having different radii of curvature are combined from the tread center to the shoulder portion. If the tread radius of the first arc including the tread center (referred to as the first tread radius) is too large relative to the target camber amount, the adjacent second arc (the arc having the second tread radius) will not be small. I do not get. The “camber amount” means the distance in the tire radial direction between the tread center and the tread surface in the shoulder portion of the tread. The difference between the tread radii TR1 and TR2 between the adjacent arcs increases. As a result, there is a possibility that the distribution of the contact surface pressure of the tire becomes nonuniform on the left and right in the tire width direction of the contact points between adjacent arcs (change points of the tread radius). Further, the outer peripheral shape (ground contact shape) of the actual contact surface of the tire may be uneven in the vicinity of the change point. If the tire has a non-uniform distribution of the contact surface pressure or a large unevenness in the contact shape S, the steering stability may be impaired, and uneven wear of the tire may occur.

  As shown in FIGS. 4 and 5, the above problem may occur not only due to the size of the first and second tread radii TR <b> 1 and TR <b> 2 but also due to the position of the change point P on the tread surface 52. . In the tire 51 shown in FIG. 4, a contact point (change point P) between the first arc 53 and the second arc 54 is located in a main groove 55 formed along the circumferential direction of the tire 51. FIG. 4A is a cross-sectional view of the tire 51 cut in the meridian direction, and FIG. 4B is a plan view showing a ground contact shape S of the tire 51. Therefore, the change point P represented as a point in FIG. 4A is represented as a line in FIG. This line is called a change line PL.

  Since the thickness of the tread 58 is thin at the main groove 55, the bending rigidity is low. Further, when the tire 51 is pressed against the road surface, the tread surface 52 tends to become a plane (tread radius TR1, TR2 is infinite) along the road surface including the left and right side portions of the change point P. The tread surface 52 tends to become a single tread radius. In other words, the tread 58 tends to bend with the change point P as a fulcrum. Therefore, when the change point P is located in the main groove 55, the tire 51 is easily bent from the main groove 55 with the change point P as a fulcrum. Further, as shown in FIG. 4B, large unevenness is generated in the vicinity of the outer main groove 55 in the outer peripheral line of the ground contact shape S of the tire.

  In the tire 56 shown in FIG. 5, the change point P between the first arc 53 and the second arc 54 is located in a lateral groove (also referred to as lug groove) 57 formed along the width direction of the tire 56. Yes. FIG. 5A is a cross-sectional view of the tire 56 cut in the meridian direction, and FIG. 5B is a plan view showing a ground contact shape S of the tire 56. Accordingly, the change point P represented as a point in FIG. 5A is represented as a line in FIG. 5B. The portion where the lug groove 57 is formed has low bending rigidity. When the change point P is located in the lateral groove 57, when the tire 56 is pressed against the road surface, the tire 56 is easily bent from the lateral groove 57 portion with the change point P as a fulcrum. Further, as shown in FIG. 5B, large unevenness is generated in the vicinity of the outer main groove 55 in the outer peripheral line of the ground contact shape S of the tire.

  Japanese Patent Laid-Open No. 5-229308 discloses a pneumatic radial tire that eliminates tire buckling and stabilizes maneuverability by considering the arrangement of different tread radius arcs. Japanese Patent Application Laid-Open No. 2002-316510 discloses a pneumatic radial tire in which high-speed durability performance, uneven wear resistance performance, groove crack resistance performance, and the like are improved by considering the arrangement of different tread radius arcs. . However, in any of the tires described above, the groove formed in the tread is not taken into consideration for the arrangement of the arcs.

JP-A-5-229308 JP 2002-316510 A

  This invention is made | formed in view of this present condition, and it aims at providing the pneumatic tire which can anticipate improvement, such as a steering stability and the suppression effect of the partial wear of a tire.

The pneumatic tire according to the present invention is
It has a tread whose outer surface forms a tread surface,
Two main inner grooves and two outer main grooves extending in the circumferential direction are formed on the tread surface so as to be bilaterally symmetrical about the center in the width direction of the tread.
A central rib is formed between the left and right inner main grooves, and intermediate ribs are formed between the left and right inner main grooves and the outer main grooves, respectively.
In the cross section cut in the meridian direction of the tread,
The tread surface includes a continuous first arc and a second arc from the center in the width direction toward the end in the width direction.
The first arc and the second arc have a first tread radius TR1 and a second tread radius TR2 that have different radii of curvature.
The size of these tread radius is TR1> TR2,
The center of the first arc is on the equator of the tire,
A change point that is a contact point between the first arc and the second arc is located on the intermediate rib.

  According to the pneumatic tire of the present invention, it is possible to make the distribution of the contact surface pressure uniform and prevent local unevenness of the contact shape.

  Preferably, the change point is located in the center of the intermediate rib in the width direction.

Preferably, a sidewall extending radially inward from both ends of the tread, a bead extending radially inward from the sidewall, a carcass spanned between both beads along the inside of the tread and the sidewall, It further includes an outer layer belt and an inner layer belt laminated on the carcass,
The axial distance from the center of the tread in the width direction to the change point is L1, the axial distance from the center of the tread to the outer edge of the outer main groove is L2, and the axial width of the outer layer belt is BW. When
0.17 x BW ≤ L1 ≤ 0.22 x BW
0.31 x BW ≤ L2 ≤ 0.34 x BW
It is.

Preferably, the relationship between the first tread radius TR1 and the second tread radius TR2 is
0.27 ≦ TR2 / TR1 ≦ 0.30
It is.

  According to the present invention, it is possible to improve the steering stability of a vehicle equipped with a tire and to suppress the uneven wear of the tire by uniformizing the distribution of the contact surface pressure of the tire and preventing local unevenness of the contact shape. Improvements can be expected.

Drawing 1 is a sectional view cut in the meridian direction which shows a part of pneumatic tire concerning one embodiment of the present invention. FIG. 2 is a cross-sectional view taken in the meridian direction showing the arrangement of the tread radius of the tire of FIG. 1. Fig.3 (a) is sectional drawing of the meridian direction which shows the shape of the tread part of the pneumatic tire which concerns on one Embodiment of this invention, FIG.3 (b) is a top view which shows the contact shape of this tire is there. Fig.4 (a) is sectional drawing of the meridian direction which shows the shape of the tread part in an example of the conventional tire, FIG.4 (b) is a top view which shows the grounding shape of this tire. Fig.5 (a) is sectional drawing of the meridian direction which shows the shape of the tread part in the other example of the conventional tire, FIG.5 (b) is a top view which shows the contact shape of this tire.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  Drawing 1 is a sectional view cut in the meridian direction which shows a part of pneumatic tire 1 concerning one embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction, the horizontal direction is the axial direction (width direction), and the direction perpendicular to the paper surface is the circumferential direction. The tire 1 has a substantially symmetrical shape with respect to the center line CL in FIG. This center line CL is also called a tread center line and represents the equator plane of the tire 1. The tire 1 includes a tread 2, a sidewall 3, a bead 4, a carcass 5, and a belt 6. The tire 1 is a tubeless type. The tire 1 is mounted on a passenger car. The tire 1 has a nominal width of 195 mm or more and a flatness ratio of 55% or less. The flatness ratio is a percentage of the tire height H with respect to the tire width W.

  The tread 2 is made of a crosslinked rubber having excellent wear resistance. The tread 2 has a tread surface 7. The tread surface 7 has a radially outwardly convex shape in a cross section cut in the meridian direction of the tire 1. The tread surface 7 is in contact with the road surface. The tread surface 7 has a plurality of main grooves 8 extending in the circumferential direction and a large number of lateral grooves 9 extending outward in the vicinity of the shoulder portion 16. These grooves 8 and 9 form a tread pattern. The sidewall 3 extends substantially inward in the radial direction from the end of the tread 2. The sidewall 3 is made of a crosslinked rubber.

  In the present embodiment, four main grooves 8 are formed. The intersection of the tread surface 7 and the tread center line CL, that is, the center in the width direction of the tread surface 7 is referred to as a tread center TC. As shown in FIGS. 1 and 2, two main grooves 8 are formed on the left and right sides of the center groove 8 around the tread center TC. The arrangement of the main grooves 8 is symmetrical with respect to the tread center TC. The two left and right main grooves near the tread center TC are called inner main grooves 8a, and the two main grooves on the outer side in the width direction are called outer main grooves 8b. In the present invention, as long as the two inner main grooves 8a and the two outer main grooves 8b are included, another main groove may be added to the outside.

  Ribs 15 extending in the circumferential direction are formed between the main grooves 8 and between the main grooves 8 and the lateral grooves 9. A rib sandwiched between the two inner main grooves 8a with the tread center TC as the center in the width direction is referred to as a central rib 15a, and a rib sandwiched between the inner main groove 8a and the outer main groove 8b is referred to as an intermediate rib 15b. . Although not shown, in the present invention, a circumferential rib (outer rib) may be provided outside the outer main groove 8b. The shapes of the ribs 15a and 15b are symmetrical with respect to the tread center TC. The lateral groove 9 is formed on the outer side of the outer main groove 8b in an axial direction or a direction inclined from the axial direction. A portion of the tread 2 that is outside (shoulder portion 16 side) from the outer main groove 8 b and is partitioned by the lateral groove 9 is a shoulder block 23. In FIG. 2, an outer edge of the outer main groove 8 b that intersects with the tread surface 7 (hereinafter referred to as an outer groove end) is indicated by a symbol Q. The outer groove end Q will be described later.

  As shown in FIG. 1, the bead 4 is positioned substantially radially inward of the sidewall 3. The bead 4 includes a core 10 and an apex 11 that extends radially outward from the core 10. The core 10 has a ring shape along the circumferential direction of the tire. The core 10 is formed by winding a non-stretchable wire. Typically, a steel wire is used for the core 10. The apex 11 is tapered outward in the radial direction. The apex 11 is made of a highly hard crosslinked rubber.

  The carcass 5 includes a carcass ply 12. The carcass ply 12 is bridged between the beads 4 on both sides, and extends along the inside of the tread 2 and the sidewall 3. The carcass ply 12 is folded around the core 10 from the inner side to the outer side in the axial direction. Although not shown, the carcass ply 12 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane CL is usually 70 ° to 90 °. In other words, the carcass 5 has a radial structure.

  The belt 6 is located outside the carcass 5 in the radial direction. The belt 6 is laminated on the carcass 5. The belt 6 reinforces the carcass 5. The belt 6 includes an inner layer belt 13 and an outer layer belt 14. Although not shown, each of the inner layer belt 13 and the outer layer belt 14 includes a large number of cords and topping rubbers arranged in parallel. Each cord is inclined with respect to the equatorial plane CL. The absolute value of the tilt angle is not less than 10 ° and not more than 35 °. The cord inclination direction of the inner layer belt 13 is opposite to the cord inclination direction of the outer layer belt.

  FIG. 2 is a cross-sectional view of the tire 1 cut in the meridian direction. FIG. 2 shows the arrangement of the tread radius TR1 and TR2. The shape of the tread surface 7 of the tire 1 of FIG. 1 will be described with reference to FIG. The tread surface 7 includes a portion formed by a combination of two arcs 21 and 22 having different radii of curvature (tread radius). The tread surface 7 has a shape protruding outward in the radial direction. Such a combination of the arcs 21 and 22 is defined in the design of the molding die of the tire 1. The center O1 of the first arc 21 is on the tread center line (equatorial plane) CL.

  If there is only one arc constituting the tread surface, the degree of freedom in tire design is greatly limited. If the arcs constituting the tread surface increase, there is a high possibility that a change point P, which will be described later, is located in the lateral groove in order to ensure the drainage performance, soil removal performance, snow performance, and the like of the tire. For this reason, there is a possibility that the tread pattern design may be restricted.

  The curvature radius of the first arc 21 is the first tread radius TR1, and the curvature radius of the second arc 22 is the second tread radius TR2. The first tread radius TR1 is larger than the second tread radius TR2. The second arc 22 is inscribed in the first arc 21.

  In FIG. 2, the contact point between the first arc 21 and the second arc 22 is referred to as a change point P. In the cross section cut in the meridian direction of the tire 1 as shown in FIG. 2, the change point P is represented as a point. However, in the plan view showing the ground contact surface of the tire 1 as shown in FIG. 3B, the portion corresponding to the change point P appears in a linear shape. These are called change lines PL. The outer groove end Q described above is represented by the symbol Q in both the sectional view (FIGS. 2 and 3A) and the plan view (FIG. 3B).

  The change point P (change line PL) is located on the intermediate rib 15. In the present embodiment, the change point P is particularly located at the center of the intermediate rib 15 in the width direction. Since the change point P is located on the intermediate rib 15, the deformation of the tread 2 when the tire 1 is pressed against the road surface does not concentrate on one place. When the tire 1 is pressed against the road surface, the tread 2 tends to bend with the change point P as a fulcrum. Since the rib 15 portion is thicker than the grooves 8 and 9, the rib 15 has high bending rigidity and is not easily bent. Therefore, the deformation of the tread 2 does not vary greatly along the tire width direction. From this point of view, the change point P is best located on the intermediate rib 15 particularly in the center in the width direction.

  FIG. 3 shows a cross section of the tread 2 of the tire 1 (FIG. 3A) and a ground contact shape S of the tire 1 (FIG. 3B). The ground contact shape diagram shows a result calculated by the finite element method, and corresponds to a plan view. The horizontal direction in FIG. 3B is the axial direction of the tire, and the vertical direction is the circumferential direction of the tire. The contact shape S indicates the outer peripheral shape of the contact surface of the tire.

  In the tire 1 shown in FIG. 3, the change point P is located at the center in the width direction of the intermediate rib 15b (FIG. 3A). In the embodiment of FIG. 3, there is almost no protrusion in the circumferential direction of the ground contact area (ground contact shape S) in the shoulder portion 16 (FIG. 3B). Accordingly, nonuniform distribution of the contact surface pressure from the tread center TC to the shoulder portion 16 is prevented.

  On the other hand, in the tire 51 (FIG. 4) according to the conventional technique described above, the change point P is located in the outer main groove 55. Further, in the tire 56 (FIG. 5) according to the other prior art described above, the change point P is located in the range of the lateral groove 57 and the shoulder block. In the tires 51 and 56 according to any of the conventional techniques, the ground contact range protrudes in the circumferential direction on both the tread center TC side and the shoulder portion side of the outer main groove 55. As a result, the contact surface pressure distribution is non-uniform from the tread center TC to the shoulder portion 60.

  As described above, when the change point P is located on the intermediate rib 15b, particularly at the center in the width direction, bending with the change point P as a fulcrum may occur in the grooves 8 and 9 having low bending rigidity. Is prevented. As a result, the deformation of the tire at the time of contact is reduced, and the amount of slip is also reduced. As a result, it is possible to make the contact surface pressure uniform and to prevent the occurrence of local unevenness in the contact shape and to improve the handling stability of a vehicle equipped with the tire. In addition, an improvement in the effect of suppressing uneven wear of the tire can be expected.

As shown in FIG. 2, the axial distance from the tread center line CL to the change point P is the change point distance L1. The axial distance from the tread center line CL to the outer groove end Q of the outer main groove 8b described above is the outer groove end distance L2. The axial width of the outer layer belt 14 is BW. At this time, the relationship between L1 and L2 and BW is
0.17 x BW ≤ L1 ≤ 0.22 x BW
0.31 x BW ≤ L2 ≤ 0.34 x BW
It is preferable that The range of the change point distance L1 and the outer groove end distance L2 is determined based on the axial width BW of the outer layer belt 14 for the following reason. That is, because the outer layer belt 14 is designed with a ratio to the size nominal width, the range of the change point distance L1 and the outer groove end distance L2 can be easily determined even if the nominal width is changed.

  When the change point distance L1 is set to be smaller than 0.17 × BW, the change point P approaches the tread center TC side. For this reason, the tread radius TR2 on the shoulder portion 16 side must be increased. As a result, the contact surface pressure at the contact end (on the shoulder 16 side of the tread surface 7) may increase. Further, the change point P may be located in the inner main groove 8a. On the other hand, when the change point distance L1 is set larger than 0.22 × BW, the change point P approaches the shoulder portion 16 side. For this reason, the tread radius TR2 on the shoulder portion 16 side has to be small. As a result, the ground contact area on the shoulder 16 side may be excessively reduced. As described above, when the contact surface pressure on the contact end portion side of the tire is too high or too low, the distribution of the contact surface pressure becomes non-uniform. If the change point is located in the main groove, the ground contact shape S may be greatly uneven. If the tire has a non-uniform distribution of the contact surface pressure or a large unevenness in the contact shape S, the steering stability may be impaired, and uneven wear of the tire may occur.

  The purpose of determining the range of the outer groove end distance L2 is to determine a preferable range of the position in the tire width direction of the outer main groove 8b. If the outer main groove 8b is close to the tread center TC, the hydro performance is improved. Conversely, if the outer main groove 8b is close to the shoulder portion side, the noise performance (performance for reducing noise) is improved. When this outer groove end distance L2 is set to be smaller than 0.31 × BW, there is a concern that the noise performance is degraded. On the other hand, if the outer groove end distance L2 is set to be larger than 0.34 × BW, there is a concern that the hydro performance is deteriorated.

The ratio (TR2 / TR1) between the first tread radius TR1 and the second tread radius TR2 is:
0.27 ≦ TR2 / TR1 ≦ 0.30
It is preferable that

  When the ratio (TR2 / TR1) is set to be smaller than 0.27, the difference between the first and second tread radius TR1 and TR2 increases. For this reason, there is a concern that the distribution of the contact surface pressure varies greatly (becomes uneven). On the other hand, when the ratio (TR2 / TR1) is set to be larger than 0.30, the second tread radius TR2 is increased. For this reason, the contact surface pressure at the middle portion (intermediate portion between the center portion 17 and the shoulder portion 16) 18 may be higher than the center portion 17 of the tread surface 7. As a result, the distribution of the contact surface pressure greatly fluctuates (becomes uneven).

  The above-mentioned provisions regarding the relationship between the change point distance L1 and the outer groove end distance L2 and the belt width BW and the ratio of the tread radius TR1 and TR2 apply to tires having a nominal width of 195 mm or more and a flatness of 55% or less. It is preferable to apply. This is because, in a tire having a nominal width of less than 195 mm, there is a concern about a decrease in wear resistance due to a decrease in rigidity, and in a tire having a flatness ratio of 60% or more, there is a concern about wear in the shoulder due to a decrease in belt rigidity. .

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
As Example 1, the first tread radius TR1, the second tread radius TR2, the ratio of the first tread radius TR1 to the second tread radius TR2 (TR2 / TR1), the ratio of the change point distance L1 to the outer layer belt width BW (L1) / BW) and the ratio of the outer groove end distance L2 to the outer layer belt width BW (L2 / BW) were prepared, and tires having the values shown in Table 1 were prepared. This tire has the basic structure shown in FIGS. The change point P is located at the center in the width direction of the intermediate rib 15b. The size of this tire is 235 / 40R19. The dimensions of each part of the tire are defined in the mold drawing. 235 indicates a tire width (mm), 40 indicates a flatness ratio (%), R indicates a radial tire, and 19 indicates a rim diameter (inch).

[Example 2]
As Example 2, a tire having the same specifications as the tire of Example 1 was prepared except for the specifications shown in Table 1 below. That is, the camber amount of the tread profile at the contact end, the rubber thickness from the tread portion to the sidewall, and the internal structure are the same as those of the tire of the first embodiment. The change point P is located on the intermediate rib 15b, but is not the center in the width direction.

[Example 3]
As Example 3, a tire having the same specifications as the tire of Example 1 was prepared except for the specifications shown in Table 1 below. That is, the camber amount of the tread profile at the contact end, the rubber thickness from the tread portion to the sidewall, and the internal structure are the same as those of the tire of the first embodiment. The change point P is located on the intermediate rib 15b, but is not the center in the width direction.

[Example 4]
As Example 4, a tire having the same specifications as the tire of Example 1 was prepared except for the specifications shown in Table 1 below. That is, the camber amount of the tread profile at the contact end, the rubber thickness from the tread portion to the sidewall, and the internal structure are the same as those of the tire of the first embodiment. The change point P is located on the intermediate rib 15b, but is not the center in the width direction.

[Comparative Example 1]
As Comparative Example 1, a tire having the same specifications as the tire of Example 1 was prepared except for the specifications shown in Table 1 below. That is, the change point P is located in the inner main groove 8a. The amount of camber of the tread profile at the contact end, the rubber thickness from the tread to the sidewall, and the internal structure are the same as those of the tire of the first embodiment.

[Comparative Example 2]
As Comparative Example 2, a tire having the same specifications as the tire of Example 1 was prepared except for the specifications shown in Table 1 below. That is, the change point P is located in the inner main groove 8a. The amount of camber of the tread profile at the contact end, the rubber thickness from the tread to the sidewall, and the internal structure are the same as those of the tire of the first embodiment.

[Desktop evaluation of tire performance]
In order to evaluate the performance of each tire of Examples 1 to 4 and Comparative Examples 1 and 2, the contact shape and contact surface pressure of the road surface of each tire were evaluated by the finite element method under the conditions of an internal pressure of 230 kpa and a vertical load of 4.60 kN. Distribution, contact length, contact width, and contact area were calculated. The uniformity of the contact surface pressure distribution was evaluated on a five-point scale. A higher numerical value indicates higher uniformity. For the ground contact shape, the degree of local unevenness was evaluated on a five-point scale. The higher the value, the less local unevenness and the better. The contact length, the contact width, and the contact area are indicated by index values with the result of Comparative Example 1 being 100. The larger this value, the better. The evaluation results are shown in Table 1.

[Sensory test of steering stability]
The tires of Examples 1 to 4 and Comparative Examples 1 and 2 were sequentially mounted on a Japanese four-wheeled passenger car, and these tires were improved in steering stability during cornering, hydro performance during straight travel, and noise performance. A test was conducted. The engine displacement is 3500 cc. A passenger car is a rear-wheel drive vehicle in which the engine is mounted on the front. The internal pressure of each tire was 230 kpa. The steering stability performance, hydro performance, and noise performance were evaluated in 5 stages as sensory evaluation of the driver. It shows that it is so favorable that a numerical value is high. The evaluation results are shown in Table 1.

  As shown in Table 1, in Examples 1, 2, 3, and 4, good results were obtained for all evaluation items with respect to Comparative Examples 1 and 2. From this evaluation result, the superiority of the present invention is clear.

  The pneumatic tire according to the present invention is suitable for various vehicles.

DESCRIPTION OF SYMBOLS 1 ... Tire 2 ... Tread 3 ... Side wall 4 ... Bead 5 ... Carcass 6 ... Belt 7 ... Tread surface 8 ... Main groove 9 ... Lateral groove 10. .. Core 11 ... Apex 12 ... Carcass ply 13 ... Inner layer belt 14 ... Outer layer belt 15 ... Rib 16 ... Shoulder part 17 ... Center part 18 ... Middle part 21 ... First arc 22 ... Second arc 23 ... Shoulder block BW ... Axial width of belt outer layer CL ... Center line (tread center line)
H ... Tire height L1 ... Change point distance L2 ... Outer groove end distance O1 ... Center of first arc P ... Change point PL ... Change line Q ... Outer groove end S・ ・ Contact shape TC ・ ・ ・ Tread center TR1 ・ ・ ・ First tread radius TR2 ・ ・ ・ Second tread radius W ・ ・ ・ Tire width

Claims (4)

It has a tread whose outer surface forms a tread surface,
Two main inner grooves and two outer main grooves extending in the circumferential direction are formed on the tread surface so as to be bilaterally symmetrical about the center in the width direction of the tread.
A central rib is formed between the left and right inner main grooves, and intermediate ribs are formed between the left and right inner main grooves and the outer main grooves, respectively.
In the cross section cut in the meridian direction of the tread,
The tread surface includes a continuous first arc and a second arc from the center in the width direction toward the end in the width direction.
The first arc and the second arc have a first tread radius TR1 and a second tread radius TR2 that have different radii of curvature.
The size of these tread radius is TR1> TR2,
The center of the first arc is on the equator of the tire,
A pneumatic tire in which a change point that is a contact point between the first arc and the second arc is located on the intermediate rib.   The pneumatic tire according to claim 1, wherein the change point is located at a center in the width direction of the intermediate rib. Laminated on the carcass, a sidewall extending radially inward from both ends of the tread, a bead extending radially inward from the sidewall, a carcass spanned between both beads along the inside of the tread and the sidewall An outer layer belt and an inner layer belt,
The axial distance from the center of the tread in the width direction to the change point is L1, the axial distance from the center of the tread to the outer edge of the outer main groove is L2, and the axial width of the outer layer belt is BW. When
0.17 x BW ≤ L1 ≤ 0.22 x BW
0.31 x BW ≤ L2 ≤ 0.34 x BW
The pneumatic tire according to claim 1 or 2. The relationship between the first tread radius TR1 and the second tread radius TR2 is as follows:
0.27 ≦ TR2 / TR1 ≦ 0.30
The pneumatic tire according to any one of claims 1 to 3.

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