pneumatic tires

Abstract

To provide a pneumatic tire that can make both reduction in a maximum value of cornering force and increase of cornering power compatible.SOLUTION: A tire 1 includes a tread 10 which has a center land part 40 including a center in a tire width direction, mediate land parts 44 provided through first circumferential main grooves 20 at both sides in a tire width direction of the center land part, and shoulder land parts 50 provided through second circumferential main grooves 21 at outsides in the tire width direction of the mediate land parts. In the mediate land parts 44 are formed circumferential sub grooves 46 extending in a tire circumferential direction. In an area sandwiched between grounding ends T of the tread 10, a ratio of first grounding areas S1 to total areas which are a sum of the first grounding areas S1 of two shoulder land parts, second grounding areas S2 obtained by adding opening areas outside in a tire radial direction of the circumferential sub-grooves to grounding areas of the two mediate land parts and third grounding areas S3 of the center land part is 50-55%.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a tread including a plurality of land portions. [Background technology]

[0002] Conventionally, a pneumatic tire has been described in which the length (width) of a middle land portion in the tire width direction is made larger than the width of a center land portion, thereby increasing the upper limit of the slip angle during running and thereby increasing cornering power (see Patent Document 1). Patent Document 1 also describes forming a middle thin groove in the middle land portion that is narrower in width than the other circumferential grooves and extends in the circumferential direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-227007 Summary of the Invention [Problem to be solved by the invention]

[0004] In the pneumatic tire of Patent Document 1, narrow grooves are formed in the circumferential direction in the mediate land portion, which may reduce the effective contact area of ​​the mediate land portion, thereby potentially reducing CFmax, the maximum cornering force. Reducing CFmax can suppress an increase in grip force during vehicle cornering, which increases the slip angle. Therefore, even when used on tall vehicles such as minivans, minivans, and box-shaped vehicles like buses, it can suppress vehicle outward roll during cornering. However, even if CFmax can be reduced simply by reducing the effective contact area of ​​the mediate land portion, there is a possibility that cornering power (CP) will also decrease. Therefore, it is desirable to achieve both a reduction in CFmax and an improvement in CP.

[0005] An object of the present invention is to provide a pneumatic tire that can achieve both a reduction in the maximum value of cornering force and an improvement in cornering power. [Means for solving the problem]

[0006] The pneumatic tire according to the present invention has a tread including a central land portion including the center in the tire width direction, intermediate land portions provided on both sides of the central land portion in the tire width direction via first circumferential main grooves, and shoulder land portions provided on the tire width direction outer sides of each of the two intermediate land portions via second circumferential main grooves, wherein the intermediate land portions have circumferential auxiliary grooves formed therein that are smaller in width than the first circumferential main groove and the second circumferential main groove and extend in the tire circumferential direction, and in a region sandwiched between the ground contact edges on both sides in the tire width direction of the tread, the ratio of the first ground contact area to a total area that is the sum of a first ground contact area of ​​the two shoulder land portions on both sides in the tire width direction, a second ground contact area obtained by adding the ground contact area of ​​the two intermediate land portions on both sides in the tire width direction to the opening area of ​​the circumferential auxiliary grooves formed in the intermediate land portion on the tire radial outer sides, and a third ground contact area of ​​the central land portion is 50 to 55%. [Effects of the Invention]

[0007] In the pneumatic tire according to the present invention, the circumferential auxiliary grooves are formed in the intermediate land portions, thereby reducing the effective ground contact area of ​​the intermediate land portions, thereby reducing the maximum value of cornering force. Furthermore, the ratio of the first ground contact area to the total area, which is the sum of the first ground contact area of ​​the two shoulder land portions of the tread, the second ground contact area, which is the ground contact area of ​​the two intermediate land portions plus the opening area of ​​the circumferential auxiliary groove on the tire radial outer side, and the third ground contact area of ​​the center land portion, is set to 50 to 55%. This improves cornering power. Therefore, both a reduction in the maximum value of cornering force and an improvement in cornering power can be achieved. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a pneumatic tire as an example of an embodiment. [Figure 2] FIG. 2 is a plan view of a portion of the tread shown in FIG. 1 in the circumferential direction. [Figure 3] FIG. 2 is an enlarged view of part A in FIG. [Figure 4] FIG. 2 is a diagram clearly showing the first area, the second area, and the third area for calculating the first ground contact area, the second ground contact area, and the third ground contact area. [Figure 5] FIG. 2 is a diagram showing the relationship between cornering force (CF) and slip angle (SA) as viewed from above the tire. [Figure 6] FIG. 2 is a diagram showing an example of the relationship between cornering force (CF) and cornering power (CP) and slip angle (SA). [Figure 7] FIG. 3 is an image diagram showing the contact area when the vehicle is turning with a slip angle of 1 degree in FIG. 2. [Figure 8] FIG. 2 is an image diagram showing the contact area when the vehicle is turning at a slip angle of approximately 8 to 10 degrees. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes selective combinations of the components of the multiple embodiments and modified examples described below.

[0010] FIG. 1 is a cross-sectional view of a pneumatic tire 1 according to an embodiment. FIG. 2 is a plan view of a circumferential portion of a tread 10 shown in FIG. 1. FIG. 3 is an enlarged view of part A in FIG. 1. As shown in FIGS. 1 and 2, the pneumatic tire 1 includes a tread 10 that is a portion that comes into contact with the road surface. Hereinafter, the "pneumatic tire 1" will be referred to as the "tire 1." The tread 10 has a tread pattern that includes a plurality of land portions, and is formed in an annular shape along the circumferential direction of the tire.

[0011] The following description focuses on the portion of the tire 1 that is on the vehicle inner side (IN side) when mounted on a vehicle, centered on the tire width center CL, as the configuration of the tire 1. The outer shape of the tire 1 is symmetrical between the portion on the vehicle inner side and the portion on the vehicle outer side (OUT side) centered on the tire width center CL, except for the lug grooves and sipes described below.

[0012] The tread 10 includes land portions 40, 44, and 50 defined by, for example, four circumferential main grooves 20 and 21. The land portions 40, 44, and 50 are protrusions that protrude radially outward from the reference plane of the tread 10. The "reference plane" refers to a virtual plane along the bottom surfaces of the deepest circumferential main grooves 20 and 21, and refers to the outer peripheral surface of the tread 10 in the absence of any land portions. The tread 10 includes, by the four circumferential main grooves 20 and 21, the following land portions: a center land portion 40 including the center CL in the tire width direction; intermediate land portions 44 provided on both sides of the center land portion 40 in the tire width direction via first circumferential main grooves 20; and shoulder land portions 50 provided on the tire width direction outer sides of each of the two intermediate land portions 44 via second circumferential main grooves 21.

[0013] Each of the center land portion 40, the two intermediate land portions 44, and the two shoulder land portions 50 has a rib shape that is continuous around the entire circumference of the tire.

[0014] The tire 1 includes a sidewall 12 that is provided on the outer side of the tread 10 in the tire width direction and bulges outward most in the tire width direction, and a bead (not shown) that is fixed to the rim of a wheel. The sidewall 12 and the bead are formed in an annular shape along the tire circumferential direction and constitute a tire side surface 13. The sidewall 12 extends radially inward from both ends of the tread 10 in the tire width direction.

[0015] The tire 1 is a pneumatic tire that is filled with air at a predetermined pressure. The tread 10 and the sidewall 12 are made of, for example, different types of rubber.

[0016] The shoulder land portions 50 arranged at both widthwise ends of the tread 10 include a ground contact edge T (Figure 2), which is the outer edge of the ground contact surface in the tire width direction. The tire widthwise end of each shoulder land portion 50 extends outward in the tire width direction from the ground contact edge T, and is gently curved radially inward in the tire radial direction so that the outer peripheral surface is convex outward. The portion of each shoulder land portion 50 extending outward in the tire width direction from the ground contact edge T is called a buttress.

[0017] "Ground contact edge T" means both ends in the tire width direction of the area that comes into contact with a flat road surface when an unused tire 1 is mounted on a standard rim and inflated to the standard internal pressure, and a load of 70% of the standard load at the standard internal pressure is applied.

[0018] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0019] Although not shown, the tire 1 includes a carcass, a belt, and an inner liner. The carcass is a cord layer coated with rubber and forms the framework of the tire 1, which can withstand loads, impacts, air pressure, etc. The belt is a reinforcing band placed between the carcass and the rubber that makes up the tread 10. The belt tightly tightens the carcass, increasing the rigidity of the tire 1. The inner liner is a rubber layer provided on the inner surface of the carcass and maintains the air pressure of the tire 1. The bead includes a bead core and a bead filler.

[0020] A plurality of lug grooves 60 are formed extending substantially in the tire width direction at a plurality of positions in the tire circumferential direction of each shoulder land portion 50. The inner end of each lug groove 60 in the tire width direction terminates within the shoulder land portion 50 and does not open to the wall surface of the shoulder land portion 50. Forming such lug grooves 60 improves drainage toward the outside in the tire width direction.

[0021] A plurality of thin sipes 91, 80, 81 extending substantially in the tire width direction or in a direction inclined relative to the tire width direction are formed on the contact surface of each land portion 40, 44, 50. In Fig. 2, the position of each sipe 91, 80, 81 is schematically indicated by a dashed line. Each sipe 91, 80, 81 is a thin groove that is narrower than each circumferential main groove 20, 21, the circumferential sub-groove 46 (described later), and the lug groove 60. The sipes 91, 80, 81 enhance the edge effect that grips snow and ice, thereby achieving good braking / driving performance and handling stability on snowy and icy roads.

[0022] 2, sipes 80, 81 formed in each shoulder land portion 50 have first straight portions 82, 84 located on the outer side in the tire width direction and extending substantially in the tire width direction, and second straight portions 83, 85 connected to the inner ends of the first straight portions 82, 84 in the tire width direction and extending in a direction inclined relative to the tire width direction. One end of the second straight portions 83, 85 opens into the second circumferential main groove 21. Each intermediate land portion 44 and center land portion 40 has a substantially straight sipe 91 formed therein, extending in a direction inclined toward one side in the tire width direction and substantially toward the same side in the tire circumferential direction.

[0023] Furthermore, each intermediate land portion 44 is formed with a circumferential sub-groove 46 that is smaller in width than each of the first circumferential main grooves 20 and each of the second circumferential main grooves 21 and extends in the tire circumferential direction. The circumferential sub-groove 46 is formed, for example, in the ground contact surface of each intermediate land portion 44 so as to be recessed in the tire radial direction at approximately the center in the tire width direction. The tire radial depth d1 (FIG. 3) of each circumferential sub-groove 46 at the tire width center is smaller than the tire radial depths d2, d3 (FIG. 3) of each of the first circumferential main grooves 20 and each of the second circumferential main grooves 21 at the tire width center. By forming the circumferential sub-groove 46 in this way in the intermediate land portion 44, the ground contact area of ​​the intermediate land portion 44 can be reduced by the amount of the circumferential sub-groove 46. This allows the maximum value CFmax of cornering force CF to be reduced, as described below.

[0024] Furthermore, in each intermediate land portion 44, a tapered chamfer 47 is formed at the open end on the tire radial outer side of the wall surface 45 on the second circumferential main groove 21 side. The chamfer 47 is formed over the entire tire circumferential length on the outer side of the wall surface 45 of each intermediate land portion 44. The angle of inclination of the chamfer 47 with respect to the tire radial direction is greater than the angle of inclination of the portion of the wall surface 45 on which the chamfer 47 is formed, which is closer to the groove bottom than the chamfer 47, with respect to the tire radial direction. Note that, although the configuration of this example shows the chamfer 47 formed at the open end of one wall surface of the intermediate land portion 44, the chamfer may be omitted.

[0025] As described above, the circumferential sub-grooves 46 formed in the intermediate land portion 44 can reduce CFmax, but simply forming the circumferential sub-grooves 46 also tends to reduce cornering power (CP). A reduction in CP reduces the vehicle's turning speed, leading to a deterioration in cornering performance, so improvement is desirable. In this embodiment, to resolve this problem, the ratio of the first contact area S1 to the total area, which is the sum of the first contact area S1 of the two shoulder land portions 50, the second contact area S2 of the two intermediate land portions 44, and the third contact area S3 of the center land portion 40, is restricted to a predetermined range higher than that of the conventional configuration.

[0026] FIG. 4 clearly shows the first region G1, the second region G2, and the third region G3 used to calculate the first contact area S1, the second contact area S2, and the third contact area S3 in FIG. 2. The hatched area in FIG. 4 indicates the first region G1. As shown in FIG. 4, the first region G1 is the combined region of the contact areas G1a and G1b of the two shoulder land portions 50 on both sides in the tire width direction, sandwiched between the two contact edges T of the tread 10 on both sides in the tire width direction. The first contact area S1 is the area of ​​the first region G1. Therefore, the first contact area S1 is the contact area of ​​the two shoulder land portions 50 on both sides in the tire width direction, sandwiched between the contact edges T of the tread 10 on both sides in the tire width direction. As can be seen from FIG. 4, the first contact area S1 does not include the lug grooves 60 of the shoulder land portions 50. In calculating the contact areas S1, S2, and S3, sipes that are much narrower than the lug grooves can be ignored.

[0027] The diagonal grid portion in FIG. 4 indicates the second region G2. The second region G2 is a region sandwiched between two ground contact edges T on both sides of the tread 10 in the tire width direction, and is a sum of regions G2a and G2b, which are the ground contact regions of the two intermediate land portions 44 on both sides in the tire width direction plus the tire radially outer opening areas of the circumferential sub-grooves 46 formed in the intermediate land portions 44. The second ground contact area S2 is the area of ​​the second region G2. Therefore, the second ground contact area S2 is the area obtained by adding the ground contact areas of the two intermediate land portions 44 to the tire radially outer opening areas of the circumferential sub-grooves 46 formed in the intermediate land portion 44. In this example, one circumferential sub-groove 46 is formed in each intermediate land portion 44. However, if each intermediate land portion 44 has multiple circumferential sub-grooves aligned in the tire width direction, the second ground contact area is the sum of the opening areas of all the circumferential sub-grooves formed in the intermediate land portions.

[0028] The sandy area in Fig. 4 indicates the third region G3. The third region G3 is the ground contact area of ​​the central land portion 40 in the region sandwiched between the two ground contact edges T on both sides of the tread 10 in the tire width direction. The third ground contact area S3 is the area of ​​the third region G3. Therefore, the third ground contact area S3 is the ground contact area of ​​the central land portion 40.

[0029] The ratio of the first contact area S1 to the total area, which is the sum of the first contact area S1, the second contact area S2, and the third contact area S3 (=S1×100 / (S1+S2+S3)) is 50 to 55%. Furthermore, the first contact area S1 is larger than the second contact area S2 (S1>S2), and the second contact area S2 is larger than the third contact area S3 (S2>S3).

[0030] According to the tire 1 described above, the circumferential sub-grooves 46 are formed in the intermediate land portions 44, thereby reducing the effective contact area of ​​the intermediate land portions 44, thereby reducing CFmax, which is the maximum cornering force. Furthermore, the ratio of the first contact area S1 to the total area, which is the sum of the first contact area S1 of the two shoulder land portions 50 of the tread 10, the second contact area S2, which is the contact area of ​​the two intermediate land portions 44 plus the opening area of ​​the circumferential sub-grooves 46 on the tire radial outer side, and the third contact area S3 of the center land portion, is set to 50 to 55%. This improves cornering power, or CP. Therefore, both a reduction in CFmax and an improvement in CP can be achieved.

[0031] To explain this in more detail, we will first explain CFmax and CP in detail. As shown in Figure 5, when the steering wheel is operated to turn a vehicle, the tire forward direction (arrow P), which coincides with the vehicle's forward direction, differs from the tire longitudinal direction (dotted-dash line Q), which passes through the tire's widthwise center, i.e., the tire's orientation. At this time, the angle between the tire forward direction (arrow P) and the tire longitudinal direction (dotted-dash line Q) is the slip angle SA. At this time, when viewing tire 1 from above, the point of application of cornering force (CF) is located at a position shifted rearward by pneumatic trail dN from the center C of tire 1's contact point. A drag force (DF) acts on tire 1 in the rearward direction, perpendicular to CF. The resultant force F of CF and DF can be separated into two orthogonal components: a side force SF, which is a lateral force, and rolling resistance R between tire 1 and the ground. A vehicle can turn when the lateral force, which approximates CF, balances with centrifugal force.

[0032] FIG. 6 shows an example of the relationship between CF and SA. As shown in FIG. 6, CF increases as SA increases. Normally, CF reaches its maximum value, CFmax, when SA is around 8 to 10 degrees, as shown in FIG. 8, which will be described later. Also, CP represents the gradient of CF with respect to SA when SA is around 0, that is, the increase in CF with respect to the increase in SA.

[0033] In the embodiment, the formation of the circumferential sub-groove 46 as described above reduces the effective ground contact area of ​​the intermediate land portion 44, thereby increasing the effective average ground contact pressure on the ground contact surface. Meanwhile, CFmax is calculated by the following formula, where μ is the lateral friction coefficient acting between the tire 1 and the ground, and N is the vertical load acting on the ground contact portion of the tire 1. CFmax=μ×N (1)

[0034] In addition, the friction coefficient μ of rubber is pressure-dependent, and the friction coefficient μ decreases as the ground contact pressure increases. Therefore, when the effective ground contact pressure of the tire 1 increases as in the embodiment, CFmax decreases when the normal load N acting on the tire 1 remains the same.

[0035] Furthermore, in this example, the ratio of the first contact area S1 to the total area, which is the sum of the first contact area S1, the second contact area S2, and the third contact area S3, is set to 50 to 55%. This allows for an increase in CP while reducing CFmax compared to a configuration in which the ratio of the first contact area S1 is less than 50%. The reduction in CFmax prevents excessive grip even when the tire of this embodiment is used on vehicles with a large vehicle height, such as minivans or box-type vehicles, thereby suppressing vehicle roll to the outside during cornering. Generally, vehicles with an aspect ratio, i.e., the ratio (H / W) of the vehicle height (catalog value) H to the vehicle width (catalog value) W, of 1 or greater are more likely to roll to the outside during cornering than vehicles with an aspect ratio of less than 1. Therefore, the effect of suppressing vehicle roll by reducing CFmax, achieved by a configuration in which a circumferential auxiliary groove is formed in the intermediate land portion as in this embodiment, is more pronounced when the aspect ratio is 1 or greater.

[0036] The first contact area S1 is larger than the second contact area S2 (S1>S2), and the second contact area S2 is larger than the third contact area S3 (S2>S3). Furthermore, the ratio of the second contact area S2 to the total area is 30-35%. This allows a higher level of compatibility between a lower CFmax and an increased CP.

[0037] For example, if the tire 1 has a tire section width of 225 mm, a ratio of the tire section height to the tire section width of 60%, and a wheel rim outer diameter of 18 inches, the dimension (width) of the circumferential sub-groove 46 in the tire width direction is preferably 1 to 3 mm, and more preferably approximately 1.5 mm. In this case, the distance between the two ground contact edges T on both sides in the tire width direction is, for example, 164 mm. If the width of the circumferential sub-groove 46 is less than 1 mm, the effect of reducing the CFmax by reducing the ground contact area of ​​the intermediate land portion 44 is reduced. On the other hand, if the width of the circumferential sub-groove 46 exceeds 3 mm, tire noise such as pneumatic pipe resonance noise becomes large.

[0038] Under the above tire conditions, the depth d1 of the circumferential sub groove 46 in the tire radial direction is preferably about 3 mm.

[0039] 7 and 8 are conceptual diagrams showing an example of the contact areas 86 to 90 when the vehicle is turning in Fig. 2. In Fig. 7, the slip angle (SA) is 1 degree, close to 0. In Fig. 8, the SA is about 8 to 10 degrees.

[0040] As shown in Figure 7, when SA is 1 degree, the area of ​​the contact patches 86, 90 of each shoulder land portion 50 increases. Therefore, it can be seen that increasing the contact area of ​​each shoulder land portion 50 increases CF and therefore CP. In this example, the ratio of the first contact area S1 corresponding to the ratio of the contact area of ​​the shoulder land portion 50 is 50 to 55%, so CP can be increased compared to a configuration in which the ratio of the first contact area S1 is less than 50%.

[0041] As shown in Figure 8, when SA is around 8 to 10 degrees, CFmax is maximized as explained above. In this case, the area of ​​the ground contact patch 86 in the shoulder land portion 50 on the inside of the turn (left side of Figure 8) is significantly smaller. For this reason, it can be seen that forming the circumferential sub-groove 46 in the intermediate land portion 44 as in the embodiment is more likely to achieve the desired effect regardless of the turning direction of the tire than forming a circumferential sub-groove in the shoulder land portion 50. Furthermore, of the two intermediate land portions 44 on both sides of the turn, the intermediate land portion 44 on the outside of the turn (right side of Figure 8) is more effective in reducing CFmax due to the reduced contact area achieved by forming the circumferential sub-groove 46.

[0042] Next, the results of a simulation conducted by the inventor to confirm the effects of the present invention will be described. In the simulation, CP and CFmax at an SA of 1 degree were calculated using the tire of the example and the tires of comparative examples 1 to 4.

[0043] The example has the same configuration as the embodiment shown in Figures 1 to 4. The ratio of the first ground contact area S1, the second ground contact area S2, and the third ground contact area S3 to the total area is 52:32:16.

[0044] In Comparative Example 1, no circumferential sub-grooves are formed in the land portions 40, 44, and 50. The ratio of the first contact area S1, the second contact area S2, and the third contact area S3 to the total area is 37:43:20. The rest of the configuration is the same as in the Examples.

[0045] In the comparative example 2, unlike the comparative example 1, the circumferential sub-groove 46 is formed in each intermediate land portion 44 in the same manner as in the example.

[0046] In Comparative Example 3, the ratio of the first ground contact area S1, the second ground contact area S2, and the third ground contact area S3 to the total area is 45:32:23. The other configurations are the same as those of the Examples.

[0047] In Comparative Example 4, the ratio of the first ground contact area S1, the second ground contact area S2, and the third ground contact area S3 to the total area is 60:32:8. The other configurations are the same as those of the Examples.

[0048] Table 1 shows the simulation results for CP and CFmax in the examples and comparative examples 1 to 4. In the simulation results in Table 1, the values ​​for comparative examples 2 to 4 and the examples are shown as relative values ​​when the CP and CFmax for comparative example 1 are each set to a reference value of 100.

[0049] [Table 1]

[0050] In the simulation results in Table 1, in the columns for CP and CFmax, ◯ indicates good performance, and × indicates insufficient performance. As can be seen from the simulation results in Table 1, in the case of Comparative Example 1, there was no circumferential sub-groove and the ratio of the first contact area S1 of the shoulder land portion was low at 37%, so both CP and CFmax were insufficient in performance.

[0051] In the case of Comparative Example 2, the circumferential sub-groove was formed compared to Comparative Example 1, and as a result, CFmax could be reduced, but CP also decreased, and both performances were insufficient.

[0052] In the case of Comparative Example 3, the ratio of the second contact area S2 of the intermediate land portion was reduced compared to Comparative Example 2, which, combined with the formation of the circumferential sub-groove, reduced CFmax and resulted in good performance. On the other hand, in Comparative Example 3, the ratio of the first contact area S1 of the shoulder land portion was increased to 45%, which increased CP, but was still insufficient.

[0053] In the case of Comparative Example 4, the ratio of the first contact area S1 of the shoulder land portion was increased to 60%, which increased CP and provided good performance compared to Comparative Example 2. On the other hand, in Comparative Example 4, the ratio of the second contact area S2 of the intermediate land portion was reduced and circumferential sub-grooves were formed, but the ratio of the first contact area S1 was too high at 60%, so the reduction in CFmax was insufficient.

[0054] In the case of the example, the ratio of the first contact area S1 of the shoulder land portion 50 was 52%, and the circumferential sub-groove 46 was formed in the intermediate land portion 44, so both the CP and CFmax were good. This confirmed the effect of the present invention.

[0055] In the above embodiment, the center land portion 40, the intermediate land portion 44, and the shoulder land portion 50 are each described as having a rib shape that is continuous around the entire circumference of the tire and is not divided in the tire circumferential direction by lug grooves. However, each land portion may be configured as a plurality of blocks that are divided in the tire circumferential direction by a plurality of lug grooves extending from a first side to a second side in the tire width direction. [Explanation of symbols]

[0056] 1 tire, 10 tread, 12 sidewall, 13 tire side surface, 20 first circumferential main groove, 21 second circumferential main groove, 40 center land portion, 44 intermediate land portion, 45 wall surface, 46 circumferential secondary groove, 47 chamfer, 50 shoulder land portion, 60 lug groove, 80, 81 sipe, 82 first straight portion, 83 second straight portion, 84 first straight portion, 85 second straight portion, 86-90 ground contact portion, 91 sipe.

Claims

1. The tread includes a center land portion including a center in the tire width direction, intermediate land portions provided on both sides of the center land portion in the tire width direction via first circumferential main grooves, and shoulder land portions provided on the outer sides of each of the two intermediate land portions in the tire width direction via second circumferential main grooves, The intermediate land portion has a circumferential sub-groove formed therein, the circumferential sub-groove having a smaller dimension in the tire width direction than the first circumferential main groove and the second circumferential main groove and extending in the tire circumferential direction, In a region sandwiched between the ground contact edges on both sides in the tire width direction of the tread, a ratio of the first ground contact area to a total area which is the sum of a first ground contact area of ​​the two shoulder land portions on both sides in the tire width direction, a second ground contact area which is obtained by adding the ground contact area of ​​the two intermediate land portions on both sides in the tire width direction to the opening area of ​​the circumferential sub-groove formed in the intermediate land portion on the tire radial outer side, and a third ground contact area of ​​the center land portion is 50 to 55%. Pneumatic tires.

2. the first contact area is larger than the second contact area, and the second contact area is larger than the third contact area; The pneumatic tire according to claim 1 .

3. The ratio of the second ground contact area to the total area is 30 to 35%. The pneumatic tire according to claim 2.

4. The center land portion, the two intermediate land portions, and the two shoulder land portions each have a rib shape that is continuous over the entire circumference in the tire circumferential direction. The pneumatic tire according to claim 1 or 2.

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