Pneumatic tire

Abstract

To provide a pneumatic tire that is configured so that reduction of rolling resistance and uneven wear in a shoulder region can be suppressed, even in a high load-type vehicle.SOLUTION: In a state where a pneumatic tire is mounted on a normal rim and is filled with normal internal pressure, a ratio A / B of a rectangular rate A at the time when a load corresponding to 120% of a maximum load is applied to the tire and a rectangular rate B at the time when a load corresponding to 100% of the maximum load is applied thereto is 108% or more and 114% or less. Respective tire standards of the normal rim, the normal internal pressure and the maximum load are based on TRA. The rectangular rate is L2 / L1, where a tread grounding length that is a length in a tire circumferential direction on a tire equator is set as L1 and a tread grounding length that is a length in the tire circumferential direction at a position shifted by 10 mm from both ends of a grounding width in the tire grounding surface shape toward inside is set as L2, in the tire grounding surface shape.SELECTED DRAWING: Figure 4B

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire suitable for use as a tire for vehicles with a relatively high load, such as a light truck. [Background technology]

[0002] Conventionally, reducing rolling resistance has been one of the issues for pneumatic tires for vehicles. For example, a design in which the contact surface of the tread is rectangular is considered to be effective in reducing rolling resistance, but on the other hand, uneven wear is likely to occur in the shoulder regions near both ends of the contact surface shape in the width direction. Patent Document 1 shows a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder regions by specifying the rectangular ratio of the tire at a load of 75% of the standard maximum load capacity (maximum load) within an appropriate range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-111357 A Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, vehicle types such as light trucks, SUVs (Sport Utility Vehicles), and EVs (Electric Vehicles), which have become increasingly popular in recent years, are heavier than conventional engine-driven passenger cars. For this reason, such heavy-load vehicles require tires that reduce rolling resistance and suppress uneven wear in the shoulder area, even when the maximum load exceeds 100%, for example.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder region even in the case of a heavy-load vehicle. [Means for solving the problem]

[0006] When the pneumatic tire of the present invention is mounted on a regular rim and inflated to the regular internal pressure, the ratio A / B of the rectangularity ratio A at a load of 120% of the maximum load to the rectangularity ratio B at a load of 100% of the maximum load is 108% or more and 114% or less, wherein the regular rim, the regular internal pressure, and the maximum load are all those conforming to the TRA tire standard, and the rectangularity ratio is L2 / L1, where L1 is the tread contact length, which is the circumferential length of the tire at the tire equator in the tire contact surface shape, and L2 is the tread contact length, which is the circumferential length of the tire at positions 10 mm inward from both ends of the contact width of the tire contact surface shape. Effect of the Invention

[0007] According to the present invention, it is possible to provide a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder region, even in the case of a heavy-load vehicle. [Brief description of the drawings]

[0008] [Figure 1] 1 is a half cross-sectional view in an axial direction of a pneumatic tire according to an embodiment. FIG. [Diagram 2] FIG. 1 is a diagram illustrating a tread pattern of a pneumatic tire according to an embodiment, and is a partial plan view of the tire. [Diagram 3] FIG. 2 is a simplified diagram showing the shape of a tire's contact patch, for explaining the rectangular ratio of the tire. [Figure 4A] FIG. 2 is a contour diagram (contour line map) showing the contact patch shape and the areas of high and low load when the tire of the embodiment is subjected to 100% load, which is the maximum load according to the TRA standard. [Figure 4B] FIG. 2 is a contour diagram (contour line diagram) showing the contact patch shape and the areas of high and low load when a tire of an embodiment is subjected to a load of 120% of the maximum load according to the TRA standard. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a diagram showing the internal structure of a tire 1, which is a pneumatic tire for vehicles according to an embodiment, and shows a half cross section in the tire axial direction. This tire 1 is a tire for light trucks.

[0010] The cross-sectional view of FIG. 1 is an axial cross-sectional view of a tire 1 mounted on a standard rim (not shown) and inflated to a standard internal pressure in an unloaded state.

[0011] The regular rim is the rim specified by the tire standard, and in the case of the TRA, it is the "Measuring Rim". The regular internal pressure is the air pressure specified by the tire standard, and in the case of the TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". The regular internal pressure is usually 180 kPa for passenger car tires, but is 220 kPa for tires labeled "Extra Load" or "Reinforced". In the case of the TRA, the regular load is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES".

[0012] The internal structure of the tire 1 is basically symmetrical in a cross section in the tire axial direction. Fig. 1 shows a cross section of the right half of the tire 1, and the left half (not shown) has the same structure. In Fig. 1, the symbol S1 indicates the tire equatorial plane. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis and located at the center in the tire axial direction.

[0013] Here, the tire axial direction is a direction parallel to the tire rotation axis, and is the left-right direction on the paper in Fig. 1. In Fig. 1, this is illustrated as the tire axial direction X. The tire axially inner side is a direction approaching the tire equatorial plane S1, and is the left side on the paper in Fig. 1. The tire axially outer side is a direction away from the tire equatorial plane S1, and is the right side on the paper in Fig. 1.

[0014] The tire radial direction is a direction perpendicular to the tire rotation axis, and is the up-down direction on the paper in Fig. 1. In Fig. 1, this is illustrated as tire radial direction Y. The outer side in the tire radial direction is a direction away from the tire rotation axis, and is the upper side on the paper in Fig. 1. The inner side in the tire radial direction is a direction approaching the tire rotation axis, and is the lower side on the paper in Fig. 1.

[0015] As shown in FIG. 1, the tire 1 includes a pair of beads 10, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, a shoulder 40 which is a transition portion from the sidewalls 20 to the tread 30, a carcass ply 50 disposed spanning between the pair of beads 10, and an inner liner 60 disposed on the tire cavity side of the carcass ply 50.

[0016] The pair of beads 10 are disposed on both axial ends of the tire and on the inner ends in the tire radial direction. The bead 10 includes a bead core 11, a bead filler 12 extending from the bead core 11 to the outer side in the tire radial direction, a chafer 13, a rim strip rubber 14, and a rubber sheet 15.

[0017] The bead core 11 is an annular member in which a rubber-coated metal bead wire is wound multiple times in the tire circumferential direction. The bead core 11 is a member that serves to fix the tire 1 filled with air to the rim. The bead filler 12 has a tapered shape that decreases in thickness as it extends from the tire radial inner side to the tire radial outer side. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of, for example, rubber that is harder than the surrounding rubber members.

[0018] The chafer 13 further surrounds the outside of the carcass ply 50 which is provided surrounding the bead core 11 and the bead filler 12. The rim strip rubber 14 is disposed axially outward of the chafer 13 and the carcass ply 50. The chafer 13 and the rim strip rubber 14 contact the inner surface of the rim on which the tire 1 is mounted. The rubber sheet 15 is a thin rubber layer, and is disposed axially outward of the carcass ply 50, sandwiched between the carcass ply 50, the chafer 13, and the rim strip rubber 14.

[0019] The sidewall 20 includes a sidewall rubber 21 disposed axially outward of the carcass ply 50. The sidewall rubber 21 constitutes the circumferentially outer side surface of the tire 1. The sidewall rubber 21 is the portion that bends the most when the tire 1 performs its cushioning function, and flexible rubber having fatigue resistance is usually used for the sidewall rubber 21.

[0020] A rim line 21c protruding axially outward is formed on an inner end 21a in the tire radial direction of the sidewall rubber 21. The rim line 21c is a circular line extending along the tire circumferential direction.

[0021] The tread 30 includes an endless belt 31, a cap ply 34, and a tread rubber 37. The belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction. The cap ply 34 is disposed on the outer side of the belt 31 in the tire radial direction. The tread rubber 37 is disposed on the outer side of the cap ply 34 in the tire radial direction.

[0022] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 arranged on the outer side of the inner liner 60 in the tire radial direction, and an outer belt 33 arranged on the outer side of the inner belt 32 in the tire radial direction. Both the inner belt 32 and the outer belt 33 have a structure in which a plurality of belt cords such as steel cords are covered with rubber. The inner belt 32 is wider than the outer belt 33. By providing the belt 31, the rigidity of the tire 1 is ensured, and the contact of the tread 30 with the road surface is improved. Note that the belt 31 is not limited to a two-layer structure, and may have a single layer structure, or a three-layer structure or more.

[0023] The cap ply 34 is a member that reinforces the tread 30 together with the belt 31. The cap ply 34 of the embodiment has a two-layer structure including an inner cap ply 35 arranged on the tire radial outer side of the outer belt 33, and an outer cap ply 36 arranged on the tire radial outer side of the inner cap ply 35. Both the inner cap ply 35 and the outer cap ply 36 have a structure in which a plurality of insulating organic fiber cords such as polyamide fiber are covered with rubber. The cap ply 34 is wider than the belt 31 and covers the entire belt 31 from the tire outer surface side. By providing the cap ply 34, it is possible to improve the durability of the tire 1 and reduce road noise during driving. The cap ply 34 is not limited to a two-layer structure as in the embodiment, but may have a single layer structure or a three-layer structure or more.

[0024] The tread rubber 37 is disposed on the outer side in the tire radial direction of the cap ply 34. The outer surface of the tread rubber 37 constitutes a tread surface 38 that comes into contact with the road surface. A tread pattern 39 is provided on the tread surface 38.

[0025] Fig. 2 is a part of a plan view of the tire 1 shown in Fig. 1, and shows a tread surface 38 having a tread pattern 39. The tread pattern 39 is formed of a plurality of lands 70 and a plurality of grooves 80 formed between the lands 70 to partition the lands 70. The tread pattern 39 of the embodiment is a block type pattern. Note that Fig. 2 shows the tire axial direction X and the tire circumferential direction C.

[0026] The tread pattern 39 has a pattern shape in which a predetermined region in the tire circumferential direction is point-symmetrical with respect to the center of one central land 71 constituting the land 70. The tire equator S passes through the tire axial center of the central land 71. The tire equator S is an imaginary line extending along the tire circumferential direction through the tire axial center of the tread surface 38. The tire equatorial plane S1 includes the tire equator S.

[0027] The land 70 includes a plurality of central lands 71 ​​(only one is shown in FIG. 2 ) arranged at the center in the tire axial direction, a plurality of intermediate lands 72 arranged around the central land 71, and a plurality of shoulder lands 73 arranged on both sides in the tire axial direction. The groove 80 includes an annular groove 81 along the outer shape of the central land 71 between the central land 71 and the plurality of intermediate lands 72, a plurality of intermediate grooves 82 between the plurality of intermediate lands 72, a circumferential groove 83 that divides the intermediate land 72 and the shoulder land 73 and extends in a substantially zigzag shape along the tire circumferential direction, and a shoulder groove 84 that divides the plurality of shoulder lands 73 in the tire circumferential direction.

[0028] The central land 71 is elongated in the tire circumferential direction and has a roughly hexagonal shape with its length direction slightly inclined relative to the tire circumferential direction. The central land 71 has a roughly S-shaped shape with a pair of slits 71a formed on both sides of the tire equator S. Each intermediate land 72 has a different shape and has one slit 72a that communicates with either the annular groove 81 or the circumferential groove 83. The shoulder land 73 has a roughly rectangular shape.

[0029] The shoulder 40 is a portion where the sidewall 20 transitions to the tread 30. The shoulder 40 includes a shoulder pad 41 and an axially outer end 37a of the tread rubber 37. An axially inner portion of the shoulder pad 41 is sandwiched between an axially outer end 31a of the belt 31 and the carcass ply 50. The axially outer portion of the shoulder pad 41 covers an axially outer end 21b of the sidewall rubber 21 from the tire outer surface side. A part of the axially outer end 31a of the belt 31 and a part of the axially outer end 34a of the cap ply 34 cover an axially outer portion of the shoulder pad 41 from the tire outer surface side.

[0030] A side block 22 is formed in a portion of the sidewall 20 extending from near the tire radial center to the shoulder 40. The side block 22 is a block that protrudes axially outward from a profile line (not shown) of the sidewall 20. The side block 22 extends from near the tire radial center of the sidewall 20 to the axially outer end of the tread rubber 37. The side block 22 is formed from the sidewall rubber 21 on the inner side from near the tire radial center, and from near the tire radial center to the outer side by the tread rubber 37. A buttress 42a protruding axially outward is formed on the outer surface of the axially outer end 37a of the tread rubber 37 that forms the side block 22.

[0031] The carcass ply 50 is laid between a pair of beads 10. The carcass ply 50 is embedded inside the tire 1 in a manner that the carcass ply 50 passes between the pair of beads 10, through a pair of sidewalls 20, a pair of shoulders 40, and the tire cavity side of the tread 30. In the tread 30, a belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction.

[0032] The carcass ply 50 includes a plurality of ply cords (not shown) that form the framework of the tire 1. The plurality of ply cords extend, for example, along a plane along the tire axial direction, and are arranged side by side in the tire circumferential direction. The ply cords are made of insulating organic fiber cords such as polyester or polyamide. The carcass ply 50 is formed by covering the plurality of ply cords with rubber.

[0033] The carcass ply 50 includes a ply main body 50A and a pair of turned-up portions 50B. The ply main body 50A is a portion that extends from the tread 30 through a pair of shoulders 40 and a pair of sidewalls 20 toward the axially inner side of each of the pair of beads 10. The pair of turned-up portions 50B are portions that are folded back toward the radially outer side of the tire by being wound from the ply main body 50A around each of the pair of bead cores 11, and extend along the sidewalls 20.

[0034] The ply main body 50A is disposed in the tread 30 radially inward of the belt 31 and the shoulder pad 41, and in the sidewall 20, is disposed axially inward of the sidewall rubber 21.

[0035] The carcass ply 50 of the embodiment has a two-layer structure in which a first carcass ply 51 and a second carcass ply 52 are overlapped. In the ply body portion 50A, the first carcass ply 51 is disposed on the tire inner cavity side of the second carcass ply 52. ​​In the turned-up portion 50B, the first carcass ply 51 is disposed on the tire axially outer side of the second carcass ply 52. ​​The first carcass ply 51 of the turned-up portion 50B extends to the tire radial direction inner side of the side block 22. The second carcass ply 52 of the turned-up portion 50B does not reach the side block 22, but extends to the tire radial direction center of the sidewall 20. The part of the turned-up portion 50B that is radially outer than the bead filler 12 is overlapped on the tire axially outer side of the ply body portion 50A.

[0036] The chafer 13 of the bead 10 described above surrounds the end of the carcass ply 50 on the inner side in the tire radial direction, the end winding around the bead core 11 .

[0037] Although the carcass ply 50 in the embodiment has a two-layer structure, the carcass ply 50 may have one layer or three or more layers. When the carcass ply 50 has a two-layer or more layer structure, it is preferable because the tire 1 is sufficiently prevented from locally deforming near the mounting portion of the rim.

[0038] The inner liner 60 forms the tire cavity surface by covering the inner surface of the ply body portion 50A of the carcass ply 50 and the axially inner portion of the chafer 13 between the pair of beads 10. The inner liner 60 is made of air-resistant rubber and prevents air in the tire cavity from leaking to the outside.

[0039] Here, the rubber used for the bead filler 12 has a hardness higher than at least the sidewall rubber 21 and the inner liner 60. The hardness of the rubber is a hardness measured by "JIS K6253-3:2012 durometer hardness type A".

[0040] For example, when the hardness of the sidewall rubber 21 is used as a standard, the hardness of the bead filler 12 is preferably about 1.2 to 2.3 times the hardness of the sidewall rubber 21. The hardness of the rim strip rubber 14 is more preferably about 1 to 1.6 times the hardness of the sidewall rubber 21. By setting the hardness in this range, a balance between the flexibility of the tire and the rigidity in the vicinity of the bead 10 can be ensured.

[0041] The above is the internal structure and tread pattern 39 of the tire 1 according to the embodiment. This tire 1 has the following characteristics regarding the rectangular ratio when in contact with the road surface. Note that the regular rim, regular internal pressure, and maximum load described below are in accordance with the TRA tire standards.

[0042] The rectangularity of a tire indicates the degree of rectangularity of the tire's contact patch when the tire is mounted on a standard rim, inflated to the standard internal pressure, and in contact with the road surface. It is the ratio of the circumferential length of the tire contact patch at a position 10 mm inward from both axial ends of the tire to the circumferential length of the tire at the axial center of the tire's contact patch, i.e., at the tire equator.

[0043] Fig. 3 is a simplified diagram showing the tire contact patch shape and is a diagram for explaining the rectangular ratio of the tire. In Fig. 3, in the contact patch shape F of the tread surface 38 of the tire 1 of the embodiment, the tread contact length in the tire circumferential direction on the tire equator S is indicated by L1, the tread contact length in the tire circumferential direction at a position 10 mm inward from both ends of the contact width W is indicated by L2, and the rectangular ratio is L2 / L1. Note that the actual L2 may differ between the left and right, so the average of both is taken.

[0044] In the embodiment, when the tire 1 is mounted on a standard rim and inflated to the standard internal pressure, the rectangularity ratio L2 / L1 at a load of 120% of the maximum load is defined as A, and the rectangularity ratio L2 / L1 at a load of 100% of the maximum load is defined as B, and the ratio A / B is specified as being 108% or more and 114% or less.

[0045] When the A / B is 108% or more and 114% or less, uneven wear of the shoulder 40 including the shoulder land 73 is suppressed under high load, thereby improving steering stability. Furthermore, by suppressing uneven wear of the shoulder 40, distortion is less likely to occur in the shoulder 40, and as a result, rolling resistance is reduced. Note that when the A / B is below 108%, the shoulder 40 is less likely to contact the ground, resulting in reduced steering stability. On the other hand, when the A / B is above 114%, the shoulder 40 is more susceptible to wear and uneven wear is more likely to occur.

[0046] The tire 1 of the embodiment is for light trucks as described above. In general, the rectangular ratio of a tire for light trucks at 100% load of the maximum load of the tire standard TRA is about 0.7% to 0.8 (70% to 80%). In a tire for light trucks or a tire for a vehicle of a heavy load type equivalent to a light truck, the load applied to the shoulder increases as the load increases (for example, about 120% of the maximum load), and the contact surface shape is likely to become square or drum-shaped. If the contact surface shape becomes square rather than elliptical, an excessive load is applied to the shoulder, and uneven wear of the shoulder is likely to occur. However, as in the tire 1 of the embodiment, when the ratio A / B of the rectangular ratio A at 120% load of the maximum load and the rectangular ratio B at 100% load of the maximum load is 108% to 114%, the squareness of the contact surface shape is suppressed. As a result, uneven wear of the shoulder 40 is suppressed, improving the steering stability and reducing the rolling resistance.

[0047] In the tire 1 of the embodiment, the tread length L1 under 120% load is preferably 108% to 112% of the tread length L1 under 100% load. Furthermore, the tread length L2 under 120% load is preferably 115% to 125% of the tread length L2 under 100% load. With these characteristics, the A / B ratio is likely to be 108% to 114%.

[0048] The tire 1 according to the embodiment described above provides the following advantages.

[0049] (1) When a tire 1 according to the embodiment is mounted on a regular rim and inflated to the regular internal pressure, the ratio A / B of the rectangularity ratio A at a load of 120% of the maximum load to the rectangularity ratio B at a load of 100% of the maximum load is 108% or more and 114% or less. However, the regular rim, regular internal pressure, and maximum load are all those in accordance with the TRA tire standard, and the rectangularity ratio is L2 / L1, where L1 is the tread length, which is the circumferential length of the tire on the tire equator S in the tire contact surface shape F, and L2 is the tread length, which is the circumferential length of the tire at positions 10 mm inward from both ends of the contact width of the tire contact surface shape.

[0050] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0051] (2) In the tire 1 according to the above embodiment (1), the tread contact length L1 under a 120% load is preferably 108% to 112% of the tread contact length L1 under a 100% load.

[0052] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0053] (3) In the tire 1 according to the above embodiments (1) and (2), the tread contact length L2 under 120% load is preferably 115% to 125% of the tread contact length L2 under 100% load.

[0054] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0055] (4) The tire 1 according to the above embodiments (1) to (3) is suitable for use on light trucks.

[0056] In other words, the tire 1 according to the embodiment is suitable as a tire for light trucks subjected to heavy loads, or as a tire for heavy loads equivalent to those for light trucks, and even under heavy loads, the squaring of the contact patch shape F is suppressed, uneven wear of the shoulder 40 is suppressed, improving handling stability and reducing rolling resistance.

[0057] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and even if modifications and improvements are made within the scope of the present invention, they will still be included in the scope of the present invention.

[0058] The tire 1 in the above embodiment is for light trucks, but the configuration of this tire 1 can be adopted as a tire for heavy-duty passenger vehicles such as SUVs and EVs, or for various vehicles such as trucks and buses in addition to passenger cars.

[0059] The tire 1 of the above embodiment is applicable to square shoulder tires for use in AT (all terrain), HT (highway terrain), MT (mud terrain), and the like. EXAMPLES

[0060] Examples will be described below. Seven tires of a simulation model were prepared, which have the same internal configuration as the above embodiment, but have different rectangular ratios A / B. For each tire, the tread length L1, which is the tire circumferential length on the tire equator in the tire ground contact surface shape, and the tread length L2, which is the tire circumferential length at a position 10 mm inward from both ends of the ground contact width of the tire ground contact surface shape, were measured at 100% load and 120% load, which are the maximum loads in the TRA standard. Each tire was mounted on a regular rim in the TRA standard, and inflated to a regular internal pressure. The rectangular ratio L2 / L1 at 100% load is B, and the rectangular ratio L2 / L1 at 120% load is A. Table 1 shows the rectangular ratios B and A, and also lists the ratio A / B of the rectangular ratios B and A in %. Note that TW100 and TW120 in Table 1 mean 100% load and 120% load, respectively, of the maximum loads in the TRA standard.

[0061] [Table 1]

[0062] The tires with the ratios of rectangularity A and B: A / B of 108%, 110%, and 114% are respectively Examples 1 to 3 which satisfy the provisions of the present invention. The tires with the ratios of rectangularity A and B: A / B of 100%, 105%, 117%, and 120% are respectively Comparative Examples 1 to 4 which are outside the provisions of the present invention.

[0063] Next, the steering stability, RRC (rolling resistance coefficient), and wear were evaluated for each tire of Examples 1 to 3 and Comparative Examples 1 to 4. Each evaluation was performed by applying a 100% load (1380 kgf) according to the TRA standard to the tire. The results are shown in Table 2.

[0064] The evaluation methods for the steering stability, RRC, and wear are as follows. The steering stability was evaluated by evaluating the wobble when steering the steering wheel while the vehicle equipped with the tire was running. The RRC was evaluated by mounting one tire on a drum-type tire testing machine and measuring the rolling resistance coefficient. The steering stability and RRC were both evaluated when the tire was first mounted (when the tire was in a new state). The wear was measured by measuring the friction energy when the tire was running after running a specified distance of 12,000 km. In Table 2, the evaluations of the steering stability, RRC (rolling resistance coefficient), and wear are each given an index of 100 for each value of Example 1, and the other values ​​are compared with Example 1 to give an index evaluation. That is, an index of 100 is used as the standard, and an index below 100 indicates a worse evaluation, and an index above 100 indicates a better evaluation.

[0065] [Table 2]

[0066] According to Table 2, when the ratio of the rectangularity ratio A / B is below 108%, the steering stability is deteriorated as in Comparative Examples 1 and 2, and when it is 108% or more, it is good as in Examples 1 to 3 and Comparative Examples 3 and 4. On the other hand, when the ratio of the rectangularity ratio A / B is above 114%, it is deteriorated as in Comparative Examples 3 and 4, and when it is 114% or less, it is good as in Examples 1 to 3 and Comparative Examples 1 and 2. That is, the steering stability is not satisfied in Comparative Examples 1 and 2, and the RRC and abrasion are not satisfied in Comparative Examples 3 and 4. In contrast, Examples 1 to 3 are satisfactory in all evaluations. Therefore, it was confirmed that even when a high load of about 120% of the maximum load is applied according to the TRA standard, if the ratio of the rectangularity ratio at a load of 120% of the maximum load to the rectangularity ratio at a load of 100% of the maximum load: A / B is 108% or more and 114% or less, the steering stability, RRC, and abrasion properties are all good.

[0067] Figures 4A and 4B are both of tires of Example 2, and Figure 4A is a contour diagram (contour map) showing the contact patch shape and the high and low load areas at a load of 100% of the maximum load according to the TRA standard, and Figure 4B is a contour diagram showing the contact patch shape and the high and low load areas at a load of 120% of the maximum load according to the TRA standard. The high and low loads indicate higher loads as the color becomes darker and lower loads as the color becomes lighter. The high and low loads indicate the high and low contact pressure against the road surface.

[0068] As shown in these figures, in the tire of Example 2, there is no significant change in contact pressure, including at the shoulder, and no significant bias in contact pressure is observed, even under a maximum load of 100% or 120%. Therefore, even under a high load, uneven wear in the shoulder is suppressed and rolling resistance is reduced. [Explanation of symbols]

[0069] 1...Tire (pneumatic tire) 10...Bead 20…Sidewall 30…Tread 38…Tread surface 39…Tread pattern 40…Shoulder F…Contact surface shape S…Tire equator W…Ground width

Claims

1. A pneumatic tire, A pneumatic tire in which, when mounted on a standard rim and inflated to a standard internal pressure, the ratio A / B of a rectangularity ratio A at a load of 120% of a maximum load to a rectangularity ratio B at a load of 100% of a maximum load is 108% or more and 114% or less. However, the regular rim, the regular internal pressure, and the maximum load are those based on TRA tire standards, and the rectangular ratio is L2 / L1, where L1 is the tread contact length, which is the circumferential length of the tire at the tire equator in the tire contact surface shape, and L2 is the tread contact length, which is the circumferential length of the tire at a position 10 mm inward from both ends of the contact width of the tire contact surface shape.

2. The pneumatic tire according to claim 1, wherein the tread contact length L1 under a 120% load is equal to or greater than 108% and equal to or less than 112% of the tread contact length L1 under a 100% load.

3. 3. The pneumatic tire according to claim 1, wherein the tread contact length L2 under a 120% load is equal to or greater than 115% and equal to or less than 125% of the tread contact length L2 under a 100% load.

4. The pneumatic tire according to claim 1 or 2, which is for a light truck.

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