Tire

Abstract

Provided is a tire capable of improving steering stability on a snowfield surface and reducing noise outside a vehicle. In a tire in which the direction of attachment to a vehicle is specified, an inboard shoulder narrow groove (31) and a plurality of inboard shoulder lug grooves (41) are formed in an inboard shoulder land section (21), a narrow rib (61) is defined between the inboard shoulder narrow groove (31) and a first main groove (11), and a circumferential auxiliary groove (32), a plurality of first lug grooves (42), and a plurality of first sipes (52) are formed in an inboard middle land section (22). A plurality of second lug grooves (43) and a plurality of second sipes (53) are formed in the center land portion (23), a plurality of third lug grooves (44) and a plurality of third sipes (54) are formed in the outer middle land portion (24), and an outer shoulder narrow groove (35) and a plurality of outer shoulder lug grooves (45) are formed in the outer shoulder land portion (25). A thin rib (65) is defined between the outer shoulder thin groove (35) and the fourth main groove (14).

Description

Technical Field

[0001] The present invention relates to a pneumatic tire having a designated mounting direction relative to a vehicle, and more particularly to a tire capable of improving steering stability on snowy roads and reducing exterior noise. Background Art

[0002] In a tire having a designated installation direction relative to a vehicle, the following scheme is proposed: four main grooves extending in the circumferential direction of the tire are formed in the tread portion, five rows of land portions are divided by these main grooves, and a plurality of transverse grooves are formed in each land portion located between the main grooves, the plurality of transverse grooves extending in the width direction of the tire and connected to the main grooves on the inner side of the vehicle, and on the other hand, not connected to the main grooves on the outer side of the vehicle but terminating in the land portion (for example, refer to Patent Document 1).

[0003] In this tire configuration, the lug grooves formed in the land portions between the main grooves each have a structure where one end opens into the main groove and the other ends within the land portion. This ensures excellent handling stability on wet roads while maintaining sufficient rigidity in each land portion. Furthermore, since these lug grooves all open toward the vehicle's interior, pumping sounds and pattern noise during driving are radiated inward, potentially reducing exterior noise. However, in recent years, there has been a demand for further improvements in noise performance. Furthermore, in anticipation of snowfall, such tires are also required to exhibit excellent handling stability even on snowy roads.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. WO2015 / 005194 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a tire that can improve steering stability on snowy roads and reduce exterior noise.

[0009] Means for solving problems

[0010] The tire of the present invention for achieving the above-mentioned object is a tire having a designated installation direction relative to a vehicle, and is characterized in that:

[0011] The tread portion has four main grooves extending in the tire circumferential direction, and the main grooves divide the tread portion into five rows of land portions. The four main grooves include a first main groove, a second main groove, a third main groove, and a fourth main groove arranged in sequence from the vehicle inner side to the vehicle outer side. The five rows of land portions include an inner shoulder land portion, an inner middle land portion, a center land portion, an outer middle land portion, and an outer shoulder land portion arranged in sequence from the vehicle inner side to the vehicle outer side.

[0012] The inner shoulder land portion is formed with an inner shoulder narrow groove extending in the tire circumferential direction and a plurality of inner shoulder lug grooves extending in the tire width direction, and a thin rib continuous in the tire circumferential direction is defined between the inner shoulder narrow groove and the first main groove.

[0013] The inner middle land portion is formed with a circumferential auxiliary groove extending in the tire circumferential direction, a plurality of first lug grooves having one end open to the first main groove and the other end closed in the inner middle land portion, and a plurality of first sipes extending from the closed ends of the first lug grooves and communicating with the circumferential auxiliary groove, and a thin rib continuous in the tire circumferential direction is defined between the circumferential auxiliary groove and the second main groove.

[0014] The central land portion includes a plurality of second lug grooves, one end of which is open to the second main groove and the other end of which is closed in the central land portion, and a plurality of second sipes extending from the closed ends of the second lug grooves and communicating with the third main groove.

[0015] The outer middle land portion includes a plurality of third lug grooves, one end of which is open to the fourth main groove and the other end of which is closed in the outer middle land portion, and a plurality of third sipes extending from the closed end of the third lug groove and communicating with the third main groove.

[0016] The outer shoulder land portion is formed with an outer shoulder narrow groove extending in the tire circumferential direction and a plurality of outer shoulder lug grooves extending in the tire width direction, and a thin rib continuous in the tire circumferential direction is defined between the outer shoulder narrow groove and the fourth main groove.

[0017] Effects of the Invention

[0018] The inventors have repeatedly conducted in-depth research on the configuration of lug grooves with one end closed for a pneumatic tire with a specified installation direction relative to a vehicle. As a result, they found that when all the lug grooves are opened toward the inside of the vehicle, the pattern noise generated by the lug grooves is reflected inside the wheel arch and emitted to the outside of the vehicle, and the radiated sound is totalized, becoming a major factor in increasing the noise, thereby completing the invention of this application.

[0019] Specifically, in the present invention, the first lug grooves formed in the inner middle land portion and the second lug grooves formed in the center land portion open toward the vehicle interior, while the third lug grooves formed in the outer middle land portion open toward the vehicle exterior. Consequently, radiated sound from these first, second, and third lug grooves is dispersed toward the vehicle interior and exterior, reducing exterior vehicle noise. Furthermore, the first, second, and third lug grooves are closed within the inner middle land portion, the center land portion, and the outer middle land portion, respectively. This suppresses an increase in groove area and reduces the generation of pattern noise, a major factor in exterior vehicle noise. Furthermore, the first, second, and third sipes formed in the inner middle land portion, central land portion, and outer middle land portion, respectively, ensure sufficient edge components in the tire width direction. The inner shoulder narrow grooves formed in the inner shoulder land portion, outer shoulder narrow grooves formed in the outer shoulder land portion, and circumferential auxiliary grooves formed in the inner middle land portion ensure sufficient edge components in the tire circumferential direction, thereby improving handling stability on snowy roads. Furthermore, the thin ribs defining the inner shoulder land portion, inner middle land portion, and outer shoulder land portion are continuous and uninterrupted in the tire circumferential direction, thereby also helping to block exterior noise. This improves handling stability on snowy roads and reduces exterior noise.

[0020] In the present invention, the ratio (L3 / W3) of the third lug groove length L3 to the width (W3) of the outer middle land portion is preferably 0.1 or greater and 0.8 or less. The ratio (L2 / W2) of the second lug groove length L2 to the width (W2) of the central land portion is preferably 0.1 or greater and 0.8 or less. The ratio (L1 / W1) of the first lug groove length L1 to the width (W1) of the inner middle land portion is preferably 0.1 or greater and 0.8 or less. This improves handling stability on snowy roads while reducing exterior noise.

[0021] The inclination angle θ3 of the third lug groove relative to the tire circumferential direction is preferably 40° to 80°. The inclination angle θ2 of the second lug groove relative to the tire circumferential direction is preferably 40° to 80°. The inclination angle θ1 of the first lug groove relative to the tire circumferential direction is preferably 40° to 80°. This improves handling stability on snowy roads while reducing exterior noise.

[0022] Preferably, the inclination angle θ1 of the first lug groove, the inclination angle θ2 of the second lug groove, and the inclination angle θ3 of the third lug groove relative to the tire circumferential direction satisfy the relationship θ2 ≤ θ3 ≤ θ1. This effectively improves handling stability on snowy roads while effectively reducing exterior noise.

[0023] Preferably, the ratio (Wg / W1) of the circumferential auxiliary groove's width Wg to the width W1 of the inner middle land portion is 0.3 or less, and the circumferential auxiliary groove is positioned further outboard of the vehicle than the widthwise center of the inner middle land portion. This effectively improves handling stability on snowy roads while effectively reducing exterior noise.

[0024] Preferably, the inner shoulder grooves and the outer shoulder grooves are arranged within the central 80% of the ground contact width of the tread portion. This effectively improves steering stability on snowy roads and effectively reduces exterior noise.

[0025] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof may be filled with an inert gas such as air, nitrogen, or other gas.

[0026] In the present invention, the contact patch width of the tread portion is the contact patch width in the axial direction of the tire measured when the tire is assembled on a regular rim and filled with regular internal pressure (in the case of a pneumatic tire), placed vertically on a flat surface, and a regular load is applied. A "regular rim" refers to a rim that is determined for each tire in a standard system that includes the standard to which the tire is based, for example, in the case of JATMA, it is " "Standard Rim" refers to the pressure specified for each tire in each standard system including the standard on which the tire is based. In the case of JATMA, it is " (Maximum pressure)", if it is TRA, it is the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES (Tire load limits at various cold inflation pressures)", if it is ETRTO, it is "INFLATION PRESSURE (inflation pressure)", but when the tire is used for passenger cars, it is set to 180kPa. "Normal load" is the load determined for each tire in each standard in the standard system including the standard on which the tire is based. If it is JATMA, it is " (Maximum load capacity)". For TRA, it is the maximum value stated in the table "TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES". For ETRTO, it is "LOAD CAPACITY". However, when the tire is used for a passenger car, it is set to a load equivalent to 88% of the above load. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a meridian cross-sectional view showing a pneumatic tire according to a first embodiment of the present invention.

[0028] Figure 2 It shows Figure 1 An expanded view of the tread pattern of a pneumatic tire.

[0029] Figure 3 It will Figure 2 The tread pattern is shown in an enlarged plan view. DETAILED DESCRIPTION

[0030] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. Figures 1 to 3 1 is a diagram showing a pneumatic tire according to an embodiment of the present invention. The pneumatic tire is a tire whose front and back mounting directions when mounted on a vehicle are specified. Figures 1 to 3 In the figure, IN is the inner side of the vehicle when the vehicle is installed, and OUT is the outer side of the vehicle when the vehicle is installed.

[0031] like Figure 1 As shown, the pneumatic tire of this embodiment includes: a tread portion 1 extending in an annular shape along the tire circumferential direction; a pair of sidewall portions 2, 2 disposed on either side of the tread portion 1; and a pair of bead portions 3, 3 disposed radially inward of the sidewall portions 2. For example, an installation direction indicator 2A is formed on at least the sidewall portion 2 on the vehicle's outer side, indicating the installation direction relative to the vehicle. The installation direction indicator 2A displays, for example, "OUTSIDE" along the tire circumferential direction on the vehicle's outer side and "INSIDE" along the tire circumferential direction on the vehicle's inner side.

[0032] A carcass layer 4 is provided between a pair of bead portions 3, 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and folded back from the inside of the tire to the outside around a bead core 5 disposed in each bead portion 3. A bead filler 6 composed of a rubber composition and having a triangular cross-section is disposed on the outer periphery of the bead core 5.

[0033] On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 at the tread portion 1. These belt layers 7 include a plurality of reinforcing cords inclined relative to the tire circumferential direction, and are arranged in such a manner that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cords relative to the tire circumferential direction is set, for example, in the range of 10° to 40°. As the reinforcing cords of the belt layer 7, steel cords are preferably used. In order to improve high-speed durability, at least one belt covering layer 8 is arranged on the outer peripheral side of the belt layer 7, in which the reinforcing cords are arranged at an angle of, for example, 5° or less relative to the tire circumferential direction. As the reinforcing cords of the belt covering layer 8, organic fiber cords such as nylon and aramid are preferably used.

[0034] Furthermore, the above-described tire internal structure shows a representative example of a pneumatic tire, but is not limited thereto.

[0035] like Figure 2 As shown, the tread portion 1 is formed with four main grooves 10 extending in the tire circumferential direction. These four main grooves 10 define five rows of land portions 20. The main grooves 10 primarily function as drainage grooves, with a groove width set within a range of 6.0 mm to 12.0 mm and a groove depth set within a range of 6.0 mm to 10.0 mm. The main grooves 10 include a first main groove 11, a second main groove 12, a third main groove 13, and a fourth main groove 14, arranged sequentially from the vehicle's inner side to the vehicle's outer side. The five rows of land portions 20 include an inner shoulder land portion 21, an inner middle land portion 22, a center land portion 23, an outer middle land portion 24, and an outer shoulder land portion 25, arranged sequentially from the vehicle's inner side to the vehicle's outer side.

[0036] The inner shoulder land portion 21 is formed with a single inner shoulder narrow groove 31 extending in the tire circumferential direction, and a plurality of inner shoulder lug grooves 41 extending in the tire width direction are formed at intervals in the tire circumferential direction. Furthermore, a thin rib 61 is defined between the inner shoulder narrow groove 31 and the first main groove 11, extending continuously in the tire circumferential direction. The groove width of the inner shoulder narrow groove 31 is set within a range of 0.5 mm to 3.0 mm, and the groove depth is set within a range of 2.0 mm to 5.0 mm. The thin rib 61 is continuous in the tire circumferential direction, uninterrupted by groove components including the inner shoulder lug groove 41 and sipes.

[0037] A circumferential auxiliary groove 32 extending along the tire's circumferential direction is formed in the inner middle land portion 22. Furthermore, a plurality of first lug grooves 42, each open at one end to the first main groove 11 on the vehicle's inner side and closed at the other end within the inner middle land portion 22, and a plurality of first sipes 52, extending from the closed ends of the first lug grooves 42 and communicating with the circumferential auxiliary groove 32, are formed at intervals along the tire's circumference. Furthermore, thin ribs 62, continuous in the tire's circumferential direction, are defined between the circumferential auxiliary groove 32 and the second main groove 12. The groove width of the circumferential auxiliary groove 32 is set within a range of 0.5 mm to 3.0 mm, and the groove depth is set within a range of 2.0 mm to 5.0 mm. The thin ribs 62 are continuous in the tire's circumferential direction, uninterrupted by groove components including the lug grooves 42 and sipes 52.

[0038] In the central land portion 23, a plurality of second lug grooves 43 are formed at intervals in the tire circumferential direction, each of which has one end open to the second main groove 12 on the inner side of the vehicle and the other end closed within the central land portion 23, and a plurality of second sipes 53 extending from the closed end of the second lug groove 43 and communicating with the third main groove 13.

[0039] In the outer middle land portion 24, a plurality of third lug grooves 44 are formed at intervals in the tire circumferential direction, one end of which is open to the fourth main groove 14 on the outer side of the vehicle and the other end is closed within the outer middle land portion 24, and a plurality of third sipes 54 extending from the closed end of the third lug groove 44 and connected to the third main groove 13.

[0040] The outer shoulder land portion 25 is formed with a single outer shoulder narrow groove 35 extending in the tire circumferential direction, and a plurality of outer shoulder lug grooves 45 extending in the tire width direction are formed at intervals in the tire circumferential direction. Furthermore, a thin rib 65 that is continuous in the tire circumferential direction is defined between the outer shoulder narrow groove 35 and the fourth main groove 14. The outer shoulder narrow groove 35 has a groove width set within a range of 0.5 mm to 3.0 mm, and a groove depth set within a range of 2.0 mm to 5.0 mm. The thin rib 65 is continuous in the tire circumferential direction, uninterrupted by groove components including the outer shoulder lug groove 45 and sipes.

[0041] In the pneumatic tire described above, the first lug grooves 42 formed in the inner middle land portion 22 and the second lug grooves 43 formed in the center land portion 23 open toward the vehicle interior, while the third lug grooves 44 formed in the outer middle land portion 24 open toward the vehicle exterior. Consequently, radiated sound from these first lug grooves 42, second lug grooves 43, and third lug grooves 44 is dispersed toward the vehicle interior and exterior, thereby reducing exterior vehicle noise. Furthermore, the first lug grooves 42, second lug grooves 43, and third lug grooves 44 are closed within the interior of the inner middle land portion 22, center land portion 23, and outer middle land portion 24, respectively. This suppresses an increase in groove area and reduces the generation of pattern noise, a factor in exterior vehicle noise. Furthermore, the first sipes 52, second sipes 53, and third sipes 54 formed in the inner middle land portion 22, the center land portion 23, and the outer middle land portion 24, respectively, ensure sufficient edge components in the tire width direction. The inner shoulder narrow grooves 31 formed in the inner shoulder land portion 21, the outer shoulder narrow grooves 35 formed in the outer shoulder land portion 25, and the circumferential auxiliary grooves 32 formed in the inner middle land portion 22 ensure sufficient edge components in the tire circumferential direction. This effectively utilizes the edge effect on snow, improving handling stability on snowy roads. Furthermore, the thin ribs 61, 62, and 65 defining the inner shoulder land portion 21, the inner middle land portion 22, and the outer shoulder land portion 24 are continuous and uninterrupted in the tire circumferential direction, thereby helping to block exterior noise. This improves handling stability on snowy roads and reduces exterior noise.

[0042] In the above-mentioned pneumatic tire, if Figure 3As shown, the ratio L3 / W3 of the length L3 of the third lug groove 44 to the width W3 of the outer middle land portion 24 is preferably 0.1 or greater and 0.8 or less. If the ratio L3 / W3 is less than 0.1, the steering stability on snowy roads cannot be effectively improved. Conversely, if the ratio L3 / W3 is greater than 0.8, the generation of pumping noise cannot be effectively suppressed, and the effect of reducing exterior noise is reduced. The ratio L3 / W3 is particularly preferably 0.2 or greater and 0.5 or less.

[0043] The ratio L2 / W2 of the length L2 of the second lug groove 43 to the width W2 of the central land portion 23 is preferably 0.1 or greater and 0.8 or less. If the ratio L2 / W2 is less than 0.1, the steering stability on snowy roads cannot be effectively improved. Conversely, if the ratio L2 / W2 is greater than 0.8, the generation of pumping noise cannot be effectively suppressed, and the effect of reducing exterior noise is reduced. The ratio L2 / W2 is particularly preferably 0.2 or greater and 0.5 or less.

[0044] The ratio L1 / W1 of the length L1 of the first lug groove 42 to the width W1 of the inner middle land portion 22 is preferably 0.1 or greater and 0.8 or less. If the ratio L1 / W1 is less than 0.1, the steering stability on snowy roads cannot be effectively improved. Conversely, if the ratio L1 / W1 is greater than 0.8, the generation of pumping noise cannot be effectively suppressed, and the effect of reducing exterior noise is reduced. The ratio L1 / W1 is particularly preferably 0.2 or greater and 0.5 or less.

[0045] In the above-mentioned pneumatic tire, if Figure 3 As shown, the inclination angle θ3 of the third lug grooves 44 formed in the outer middle land portion 24 relative to the tire circumferential direction is preferably 40° or greater and 80° or less. If the inclination angle θ3 of the third lug grooves 44 is less than 40°, sufficient snow column shearing force cannot be achieved. Conversely, if the inclination angle θ3 of the third lug grooves 44 is greater than 80°, the rigidity of the outer middle land portion 24 increases, and the deformation of the outer middle land portion 24 under ground pressure decreases, which makes it difficult to effectively suppress the generation of exterior noise. The inclination angle θ3 is particularly preferably 50° or greater and 70° or less.

[0046] The second lug grooves 43 formed in the central land portion 23 preferably have an inclination angle θ2 with respect to the tire circumferential direction of 40° or greater and 80° or less. If the inclination angle θ2 of the second lug grooves 43 is less than 40°, sufficient snow column shearing force cannot be achieved. Conversely, if the inclination angle θ2 of the second lug grooves 43 is greater than 80°, the rigidity of the central land portion 23 increases, and the deformation of the central land portion 23 under ground pressure decreases, thus failing to effectively suppress the generation of exterior noise. The inclination angle θ2 is particularly preferably 50° or greater and 70° or less.

[0047] The first lug grooves 42 formed in the inner middle land portion 22 preferably have an inclination angle θ1 with respect to the tire circumferential direction of 40° or greater and 80° or less. If the inclination angle θ1 of the first lug grooves 42 is less than 40°, sufficient snow column shearing force cannot be achieved. Conversely, if the inclination angle θ1 of the first lug grooves 42 is greater than 80°, the rigidity of the inner middle land portion 22 increases, and deformation of the inner middle land portion 22 under ground pressure decreases, thus failing to effectively suppress exterior noise. The inclination angle θ1 is particularly preferably 50° or greater and 70° or less.

[0048] The inclination angles θ1 to θ3 of the lug grooves 42 to 44 are angles formed by a straight line passing through the groove width center position at the open end and the groove width center position at the closed end of each of the lug grooves 42 to 44 with respect to the tire circumferential direction.

[0049] In the above-described pneumatic tire, the inclination angle θ1 of the first lug groove 42, the inclination angle θ2 of the second lug groove 43, and the inclination angle θ3 of the third lug groove 44 relative to the tire circumferential direction preferably satisfy the relationship θ2 ≤ θ3 ≤ θ1. By satisfying this relationship, the inclination angles θ1, θ2, and θ3 of the first lug groove 42, the second lug groove 43, and the third lug groove 44 are optimized, effectively improving handling stability on snowy roads while effectively reducing exterior noise. It is particularly preferable that the relationship θ2 < θ3 < θ1 be satisfied.

[0050] In the above-described pneumatic tire, the ratio (Wg / W1) of the groove width Wg of the circumferential auxiliary groove 32 to the width W1 of the inner middle land portion 22 is preferably 0.3 or less. The circumferential auxiliary groove 32 is preferably located further outboard of the vehicle than the widthwise center of the inner middle land portion 22. This effectively improves handling stability on snowy roads while effectively reducing exterior vehicle noise. If the ratio (Wg / W1) exceeds 0.3, the rigidity of the inner middle land portion 22 is excessively reduced, reducing the effect of improving handling stability on snowy roads. Furthermore, if the circumferential auxiliary groove 32 is located further inboard of the vehicle than the widthwise center of the inner middle land portion 22, the area where the first lug grooves 42 and the first sipes 52 are located is reduced, reducing the effect of improving handling stability on snowy roads.

[0051] In the pneumatic tire described above, the inner shoulder narrow grooves 31 and the outer shoulder narrow grooves 35 are preferably located within a region that is 80% of the center of the contact patch width TCW of the tread portion 1. This effectively improves handling stability on snowy roads while also effectively reducing exterior noise. If the inner shoulder narrow grooves 31 and the outer shoulder narrow grooves 35 are located outside of this region, the effect of improving handling stability on snowy roads and reducing exterior noise are reduced.

[0052] Example

[0053] The tires of Examples 1 to 17 were manufactured in a pneumatic tire having a tire size of 265 / 45R21 and a specified installation direction relative to a vehicle. The tires had the following structure: four main grooves extending in the tire circumferential direction were formed in the tread portion, and the main grooves divided the tire into five rows of land portions. The four main grooves included a first main groove, a second main groove, a third main groove, and a fourth main groove arranged in order from the vehicle inner side to the vehicle outer side. The five rows of land portions included an inner shoulder land portion, an inner middle land portion, a center land portion, an outer middle land portion, and an outer shoulder land portion arranged in order from the vehicle inner side to the vehicle outer side. The inner shoulder land portion formed a There is one inner shoulder fine groove and multiple inner shoulder transverse grooves, and fine ribs are divided between the inner shoulder fine groove and the first main groove. A circumferential auxiliary groove, multiple first transverse grooves and multiple first knife groove patterns are formed in the inner middle land portion, and fine ribs are divided between the circumferential auxiliary groove and the second main groove. Multiple second transverse grooves and multiple second knife groove patterns are formed in the central land portion, and multiple third transverse grooves and multiple third knife groove patterns are formed in the outer middle land portion. One shoulder fine groove and multiple outer shoulder transverse grooves are formed in the outer shoulder land portion, and fine ribs are divided between the outer shoulder fine groove and the above-mentioned fourth main groove.

[0054] For comparison, a conventional tire having the same structure as Example 1 was prepared, except that the lug grooves formed in the inner middle land portion, the central land portion, and the outer middle land portion were all arranged to open toward the vehicle inner side and no circumferential auxiliary grooves were provided in the inner middle land portion.

[0055] In the tires of the conventional example and Examples 1 to 17, the opening direction of the lug grooves, the ratios of the lug groove length to the land portion width (L3 / W3, L2 / W2, and L1 / W1), the inclination angles θ3, θ2, and θ1 of the lug grooves relative to the tire circumferential direction, the ratio Wg / W1 of the circumferential auxiliary groove width (Wg) to the width W1 of the inner middle land portion, and the position of the shoulder grooves are shown in Tables 1 to 3. Regarding the opening direction of the lug grooves, "IN" indicates that they open toward the vehicle's inner side, and "OUT" indicates that they open toward the vehicle's outer side. Regarding the position of the shoulder grooves, "within the 80% region" indicates that the inner and outer shoulder grooves are located inside the central 80% region of the tread portion's contact width, while "outside the 80% region" indicates that they are located outside the central 80% region of the tread portion's contact width. Furthermore, in the tires of Examples 1 to 6, the circumferential auxiliary groove is arranged on the vehicle outer side relative to the widthwise center position of the inner middle land portion.

[0056] These test tires were evaluated for steering stability on snowy roads and exterior noise using the following test methods. The results are collectively shown in Tables 1 to 3.

[0057] Handling stability on snowy roads:

[0058] Each test tire was assembled onto a 21×9J wheel rim and installed in a 2400cc front-wheel drive SUV. After preheating, the tire was set to a pressure of 230 kPa and subjected to sensory evaluation by a test driver while driving on snowy roads. The evaluation results were expressed as an index, with the conventional value set to 100. A higher index value indicates better handling stability on snowy roads.

[0059] Noise outside the vehicle:

[0060] Each test tire was assembled onto a 21×9J wheel rim and installed in a 2400cc front-wheel drive SUV. After preheating, the tire was set to a pressure of 230 kPa and subjected to a test in accordance with UN.R117 to measure exterior noise. The evaluation results were expressed as an index, using the reciprocal of the measured value, with the conventional value set to 100. A higher index value indicates less exterior noise.

[0061] [Table 1]

[0062]

[0063] [Table 2]

[0064]

[0065] [Table 3]

[0066]

[0067] As can be seen from Tables 1 to 3, the tires of Examples 1 to 17 have good steering stability on snowy roads and reduced exterior noise when compared with the conventional tires.

[0068] Description of Reference Numerals

[0069] 1. Tread

[0070] 2 Sidewall

[0071] 3 Bead

[0072] 10, 11, 12, 13, 14 main slots

[0073] 20, 21, 22, 23, 24, 25 Land Department

[0074] 31, 35 fine grooves

[0075] 32 Circumferential auxiliary groove

[0076] 41, 42, 43, 44, 45 transverse grooves

[0077] 52, 53, 54 sipes

[0078] 61, 62, 65 thin ribs

Claims

1. A tire having a designated installation direction relative to a vehicle, characterized in that: The tread portion has four main grooves extending in the tire circumferential direction, and the main grooves divide the tread portion into five rows of land portions. The four main grooves include a first main groove, a second main groove, a third main groove, and a fourth main groove arranged in sequence from the vehicle inner side to the vehicle outer side. The five rows of land portions include an inner shoulder land portion, an inner middle land portion, a center land portion, an outer middle land portion, and an outer shoulder land portion arranged in sequence from the vehicle inner side to the vehicle outer side. The inner shoulder land portion is formed with an inner shoulder narrow groove extending in the tire circumferential direction and a plurality of inner shoulder lug grooves extending in the tire width direction, and a thin rib continuous in the tire circumferential direction is defined between the inner shoulder narrow groove and the first main groove. The inner middle land portion is formed with a circumferential auxiliary groove extending in the tire circumferential direction, a plurality of first lug grooves having one end open to the first main groove and the other end closed in the inner middle land portion, and a plurality of first sipes extending from the closed ends of the first lug grooves and communicating with the circumferential auxiliary groove, and a thin rib continuous in the tire circumferential direction is defined between the circumferential auxiliary groove and the second main groove. The central land portion includes a plurality of second lug grooves, one end of which is open to the second main groove and the other end of which is closed in the central land portion, and a plurality of second sipes extending from the closed ends of the second lug grooves and communicating with the third main groove. The outer middle land portion includes a plurality of third lug grooves, one end of which is open to the fourth main groove and the other end of which is closed in the outer middle land portion, and a plurality of third sipes extending from the closed end of the third lug groove and communicating with the third main groove. The outer shoulder land portion is formed with an outer shoulder narrow groove extending in the tire circumferential direction and a plurality of outer shoulder lug grooves extending in the tire width direction, and a thin rib continuous in the tire circumferential direction is defined between the outer shoulder narrow groove and the fourth main groove.

2. The tire according to claim 1, wherein A ratio L3 / W3 of the length L3 of the third lug groove to the width W3 of the outer middle land portion is greater than or equal to 0.1 and less than or equal to 0.

8.

3. The tire according to claim 1 or 2, characterized in that A ratio L2 / W2 of the length L2 of the second lug groove to the width W2 of the central land portion is greater than or equal to 0.1 and less than or equal to 0.

8.

4. The tire according to any one of claims 1 to 3, characterized in that A ratio L1 / W1 of the length L1 of the first lug groove to the width W1 of the inner middle land portion is greater than or equal to 0.1 and less than or equal to 0.

8.

5. The tire according to any one of claims 1 to 4, characterized in that An inclination angle θ3 of the third lug groove with respect to the tire circumferential direction is greater than or equal to 40° and less than or equal to 80°.

6. The tire according to any one of claims 1 to 5, characterized in that An inclination angle θ2 of the second lug groove with respect to the tire circumferential direction is greater than or equal to 40° and less than or equal to 80°.

7. The tire according to any one of claims 1 to 6, characterized in that An inclination angle θ1 of the first lug groove with respect to the tire circumferential direction is greater than or equal to 40° and less than or equal to 80°.

8. The tire according to any one of claims 1 to 7, characterized in that The inclination angle θ1 of the first lug groove relative to the tire circumferential direction, the inclination angle θ2 of the second lug groove relative to the tire circumferential direction, and the inclination angle θ3 of the third lug groove relative to the tire circumferential direction satisfy the relationship θ2≤θ3≤θ1.

9. The tire according to any one of claims 1 to 8, characterized in that A ratio Wg / W1 of a groove width Wg of the circumferential auxiliary groove to a width W1 of the inner middle land portion is 0.3 or less, and the circumferential auxiliary groove is arranged on the vehicle outer side relative to a widthwise center position of the inner middle land portion.

10. The tire according to any one of claims 1 to 9, characterized in that The inner shoulder narrow groove and the outer shoulder narrow groove are arranged in a region of 80% of the center side of the ground contact width of the tread portion.

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