Tire

Abstract

To provide a tire capable of exhibiting on-ice brake performance that is superior at an early stage of abrasion.SOLUTION: At least one out of a plurality of land parts 40 formed on a tread part 1 is a specific land part comprising at least one sipe s extending along a tire width direction on a tread, and a plurality of thin grooves g extending in a direction crossing the sipes s. The thin grooves g are shallower than the sipes s and have a groove depth of 1.5 mm or less. An area S [unit: mm2] of the tread of the specific land part and a total sum V [unit: mm3] of a groove capacity of the plurality of thin grooves g satisfy the relationship of 0.25*10-2≤V / S≤7.00*10-2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a tire having at least one sipe and a plurality of narrow grooves on its tread surface. [Background technology]

[0002] In snow and ice tires, such as studless tires, minute irregularities are formed on the tread surface by mixing fillers or air bubbles into the tread rubber, and these irregularities have the effect of removing water films, ensuring excellent driving performance on snow and ice. However, before the break-in period, the irregularities are not fully apparent on the tread surface, which is a problem in that the tires are unable to fully demonstrate their inherent driving performance in the early stages of wear.

[0003] To solve these problems, for example, Patent Document 1 proposes forming multiple sipes and numerous fine grooves (minor grooves with a smaller groove depth than sipes) on the tread surface of the land portions defined in the tread. In such tires, even when the above-mentioned unevenness is not fully expressed, the sipes and fine grooves on the land portion surface provide an edge effect and a water film removal effect, so driving performance on icy roads can be ensured even in the early stages of wear. However, in recent years, the performance required of tires has become more sophisticated, and further improvement in braking performance on ice in the early stages of wear is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-034903 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a tire that can exhibit excellent braking performance on ice in the early stages of wear. [Means for solving the problem]

[0006] The tire of the present invention for achieving the above object has a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion being formed with a plurality of circumferential main grooves extending along the tire circumferential direction, a plurality of lug grooves extending in a direction intersecting the circumferential main grooves, and a plurality of land portions defined by the circumferential main grooves and / or the lug grooves, at least one of the plurality of land portions being a specific land portion having at least one sipe extending along the tire width direction on the tread surface and a plurality of narrow grooves extending in a direction intersecting the sipe, the narrow groove being shallower than the sipe and having a groove depth of 1.5 mm or less, and the tread area S (unit: mm 2 ] and the total groove volume of the plurality of narrow grooves V [unit: mm 3 ] and 0.25 x 10 -2 ≦V / S≦7.00×10 -2 The above relationship is satisfied. [Effects of the Invention]

[0007] In the present invention, in order to improve the performance on ice in the early stage of wear by using a specific land portion in which at least one sipe and a plurality of fine grooves (fine grooves with a groove depth of 1.5 mm or less) are formed on the tread surface of the land portion, the area S of the tread surface of this specific land portion [unit: mm 2 ] and the total groove volume V of the multiple narrow grooves provided in this specific land portion [unit: mm 3 ] and 0.25 x 10 -2 ≦V / S≦7.00×10 -2 Since the relationship is satisfied, the water film removal effect of the fine grooves is sufficiently ensured, while the reduction in the actual contact area of ​​the specific land portion (the area of ​​the land surface that actually contacts the road surface, excluding sipes and fine grooves) due to the fine grooves is suppressed, thereby achieving excellent braking performance on ice. Note that the area S of the contact area of ​​the specific land portion is the area inside the outer contour of the specific land portion (the entire area including sipes and fine grooves).

[0008] In the present invention, it is preferable that the pitch of the plurality of fine grooves is 0.5 mm to 5.0 mm and the width of each fine groove is 0.05 mm to 1.0 mm, which is advantageous for improving performance on ice because it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice and also ensures braking performance on ice due to the water film removal effect of the fine grooves.

[0009] In the present invention, it is preferable that the ratio of the total area of ​​the plurality of fine grooves to the tread area S of the specific land portion is 5% to 19%. This is advantageous for improving performance on ice, as it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice, and further ensures braking performance on ice due to the water film removal effect of the fine grooves.

[0010] In the present invention, the inclination angle of the fine grooves relative to the tire circumferential direction is preferably 30° to 70°. This allows the edge effect and drainage performance of the fine grooves to be exhibited in a balanced manner, which is advantageous for improving performance on ice. Note that the inclination angle of the fine grooves is the acute angle between the fine grooves and the tire circumferential direction.

[0011] In the present invention, when the center of the specific land portion in the tire width direction is defined as the central region and both sides of the central region in the tire width direction are defined as edge regions, the inclination direction of the narrow grooves in at least one edge region can be made different from the inclination direction of the narrow grooves in the central region, which improves the water film removal effect of the narrow grooves and is advantageous for improving performance on ice.

[0012] In this case, it is preferable that the area of ​​the edge regions, where the narrow grooves have a different inclination direction from the narrow grooves in the central region, is smaller than the area of ​​the central region, which results in a good balance between the areas of the central region and the edge regions, where the narrow grooves have different inclination directions, and is advantageous for improving the water film removal effect of the narrow grooves and improving performance on ice.

[0013] In this case, it is further preferable that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the central region in the tire width direction of the specific land portion, and 30° to 70° in the end regions in the tire width direction of the specific land portion. This results in a good inclination angle of the narrow groove in each of the central region and the end regions, which is advantageous for improving the water film removal effect of the narrow groove and improving performance on ice. Note that the inclination angle of the narrow groove is an acute angle between the narrow groove and the tire circumferential direction in both the central region and the end regions.

[0014] In the present invention, it is preferable that the ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and fine grooves, to the area of ​​the ground contact region of the tread portion is 20% to 60%. This improves the groove area ratio of the entire tread portion, ensuring a sufficient actual ground contact area to ensure braking performance on ice, and further ensuring braking performance on ice through the water film removal effect of the fine grooves, which is advantageous for improving performance on ice.

[0015] In the present invention, the "ground contact area" of the tread is the area that comes into contact with a flat surface when the tire is mounted on a standard rim, inflated to the standard internal pressure (in the case of a pneumatic tire), placed vertically on a flat surface, and subjected to a standard load. The "standard rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based. For example, this refers to the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. The "standard internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based. This refers to the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" table for TRA, and the "INFLATION PRESSURE" for ETRTO, but is 180 kPa when the tire is for a passenger car. "Normal load" is the load specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the maximum load capacity, for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "LOAD CAPACITY." However, if the tire is for a passenger car, it is a load equivalent to 88% of the above load. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is a development view showing the tread pattern of the pneumatic tire of FIG. [Figure 3] FIG. 2 is an explanatory diagram schematically illustrating an example of a specific land portion of the present invention. [Figure 4] FIG. 10 is an explanatory diagram schematically illustrating another example of the specific land portion of the present invention. [Figure 5] FIG. 2 is a cross-sectional view showing the shape of a narrow groove according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] In the case of a pneumatic tire as shown in FIG. 1, the tire of the present invention includes a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby forming the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 will be based basically on the meridian cross-section shape shown, but each tire component also extends in the tire circumferential direction and forms an annular shape.

[0019] A carcass layer 4 is mounted between a pair of left and right bead portions 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inner side to the outer side in the tire width direction around a bead core 5 disposed in each bead portion 3. A bead filler 6 is disposed on the outer periphery of the bead core 5, and this bead filler 6 is enclosed by the main body portion and folded back portion of the carcass layer 4. The bead filler 6 has a triangular cross section, for example, as shown in the figure, and is made of a rubber composition.

[0020] A plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords (belt cords) inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes reinforcing cords (cover cords) oriented in the tire circumferential direction. In the belt cover layer 8, the angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, to 0° to 5°. Organic fiber cords such as nylon and aramid cords are preferably used as the reinforcing cords of the belt cover layer 8.

[0021] In the tread portion 1, a tread rubber layer 11 is disposed on the outer peripheral side of the carcass layer 4, belt layer 7, and belt reinforcing layer 8. The tread rubber layer 11 may have a structure in which two types of rubber layers with different physical properties (a cap tread layer that forms the tread surface of the tread portion 1 and an undertread layer disposed on its inner peripheral side) are laminated in the tire radial direction. A side rubber layer 12 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the bead portion 3. From the viewpoint of improving performance on ice, it is preferable that the rubber composition that constitutes the tread rubber layer 11 (particularly the cap tread layer) contains fillers and air bubbles so that when the tread surface is worn, fine irregularities that have a water film removal effect appear.

[0022] As described below, the present invention relates to sipes and narrow grooves formed on the surface of the tire tread portion 1, and therefore the basic structure (internal structure) of the tire is not limited to the general structure described above. Also, the following description will be based on the pneumatic tire shown in Fig. 1 etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as they have a surface that comes into contact with the road surface (a region corresponding to the surface of the tread portion 1 in a pneumatic tire).

[0023] 2, a plurality of circumferential main grooves 20 extending in the tire circumferential direction, a plurality of lug grooves 30 extending in the tire width direction, and a plurality of land portions 40 defined by the circumferential main grooves and lug grooves are formed on the surface of the tread portion 1. The circumferential main grooves 20 are grooves that perform the main drainage function, and generally have a groove width of 5.0 mm or more and a groove depth of 6.5 mm or more.

[0024] At least one of the plurality of land portions 40 thus defined and partitioned has at least one sipe s extending along the tire width direction on the tread surface and a plurality of narrow grooves g whose groove depth is smaller than that of the sipe s, as shown in Figures 3 and 4. In the following description, the land portion 40 having these sipes s and narrow grooves g may be referred to as a specific land portion. Since the present invention is primarily related to this specific land portion, the details of the tread pattern are not particularly limited as long as it includes at least one specific land portion.

[0025] The sipes s have a groove width set within a range of, for example, 0.1 mm to 1.0 mm and a groove depth set within a range of, for example, 2.0 mm to 10.0 mm. The sipes s extend mainly along the tire width direction, are arranged at intervals around the tire circumference, and mainly exert an edge effect and drainage performance. The shape of each sipe s is not particularly limited, and a zigzag shape as shown in the figure, for example, can be adopted.

[0026] As described above, the narrow grooves g are shallower than the sipes s. As shown in FIG. 5, the narrow grooves g have a groove depth d of 1.5 mm or less, preferably 0.1 mm to 1.0 mm. The groove width w of the narrow grooves g is preferably 0.05 mm to 1.0 mm, more preferably 0.1 mm to 0.8 mm. The narrow grooves g are thus minute grooves that extend in a direction intersecting the sipes s as shown in the figure, and are arranged in a plurality in the circumferential direction of the tire. In particular, as shown in FIGS. 3 and 4, it is preferable that a plurality of narrow grooves g are periodically and repeatedly arranged evenly over the entire surface of the land portion 40 (specific land portion). By providing a plurality of narrow grooves g, the narrow grooves g can remove water film even in the early stages of wear (before the tread rubber's inherent performance is fully exerted), thereby achieving excellent braking performance on ice. If the groove depth d of the narrow grooves g exceeds 1.5 mm, it becomes difficult to ensure the rigidity of the land portion 40. If the groove width w of the narrow groove g is less than 0.05 mm, the narrow groove g is too small to achieve sufficient water removal, making it difficult to improve braking performance on ice.If the groove width w of the narrow groove g is more than 1.0 mm, the actual contact area decreases, making it difficult to improve braking performance on ice.

[0027] The cross-sectional shape of the narrow grooves g is not particularly limited. For example, a shape with a flat groove bottom (rectangular) as shown in FIG. 5 can be used, as well as a U-shaped or V-shaped cross section. When multiple narrow grooves g are periodically arranged as shown in FIGS. 3 and 4, the pitch p of the multiple narrow grooves g (the distance between the periodically arranged narrow grooves g) shown in FIG. 5 is preferably 0.5 mm to 5.0 mm, more preferably 0.7 mm to 4.0 mm. This is advantageous for improving ice performance, as it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice and further ensures braking performance on ice through the water film removal effect of the narrow grooves g. If the pitch p of the narrow grooves g is less than 0.5 mm, it becomes difficult to improve braking performance on ice due to the reduced actual contact area. If the pitch p of the narrow grooves g is greater than 5.0 mm, it becomes difficult to arrange a sufficient number of narrow grooves g within the specific land portion, which results in insufficient water removal effect, making it difficult to improve braking performance on ice.

[0028] As described above, the present invention is not particularly limited in detail to the tread pattern as long as it includes at least one specific land portion. However, the tread pattern of the example in Fig. 2 includes, as circumferential main grooves 20, a pair of inner main grooves 21 arranged on both sides of the tire equator CL and a pair of outer main grooves 22 arranged outward in the tire width direction from the inner main grooves 21. One of the pair of inner main grooves 21 (the inner main groove 21a on the right in the figure) extends in a zigzag pattern along the tire circumferential direction, while the other of the pair of inner main grooves 21 (the inner main groove 21b on the left in the figure) extends so that the groove width varies along the tire circumferential direction due to the groove wall on the outer side in the tire width direction being zigzag. Both outer main grooves 22 extend linearly along the tire circumferential direction.

[0029] In the illustrated example, a plurality of block-shaped land portions (center land portions 41) are arranged in the tire circumferential direction between a pair of inner main grooves 21, each defined by the pair of inner main grooves 21 and a lug groove 30 (center lug groove 31). On one side of the tire equator (the right side in the drawing), a plurality of block-shaped land portions (intermediate land portions 42a) are arranged in the tire circumferential direction between the zigzag inner main groove 21a and outer main groove 22, each defined by the grooves and the lug groove 30 (intermediate lug groove 32a). Each intermediate land portion 42 is provided with a circumferential auxiliary groove 51 that extends in a zigzag pattern along the tire circumferential direction and connects adjacent lug grooves in the tire circumferential direction. On the other side of the tire equator (the left side in the drawing), a rib-shaped land portion (intermediate land portion 42b) is formed between the inner main groove 21b and outer main groove 22, whose groove widths vary, defined by these grooves and continuing around the entire tire circumference. The intermediate land portion 42b is provided with lug grooves 30 (intermediate lug grooves 32b) that are connected to the inner main groove 21b and the outer main groove 22 and terminate within the land portion. On the outer side of the pair of outer main grooves 22 in the tire width direction, a plurality of block-shaped land portions (shoulder land portions 43) that are partitioned by the outer main grooves 22 and the lug grooves 30 (shoulder lug grooves 33) are arranged in the tire circumferential direction. Each shoulder land portion 43 is provided with a circumferential narrow groove 52 that is connected to the shoulder lug groove 33, extends along the tire circumferential direction, and terminates within the land portion.

[0030] Among the land portions 40 of various shapes included in the tread pattern as described above, if they are provided with sipes s and narrow grooves g, they are considered to be specific land portions in the present invention. In particular, in the example of Figure 2, all land portions 40 are specific land portions, and the area relationships described below are applied to all land portions 40.

[0031] As described above, by providing at least one sipe s and multiple fine grooves g, it is possible to ensure ice performance in the initial stage of wear in the specific land portion. In this case, the tread area S of the specific land portion (unit: mm 2 ] and the total groove volume of multiple narrow grooves V [unit: mm 3 ] and ratio V / S [unit: mm 3 / mm 2 ] is 0.25 × 10 -2 ≦V / S≦7.00×10 -2 relationship, preferably 0.50 x 10 -2 ≦V / S≦5.00×10 -2 By satisfying this relationship, the water film removal effect of the fine grooves g is ensured sufficiently, while the reduction in the actual contact area of ​​the specific land area due to the fine grooves g can be suppressed, resulting in excellent braking performance on ice. In this case, the ratio V / S is 0.25 x 10 -2 If the ratio V / S is less than 7.00×10, the groove volume of the narrow grooves g is small and sufficient water removal performance cannot be obtained, making it difficult to improve braking performance on ice. -2 If the value exceeds this, the actual contact area decreases, making it difficult to improve braking performance on ice.

[0032] The ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion is preferably 5% to 19%, and more preferably 7% to 17%. This is advantageous for improving performance on ice, as it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice, and further ensures braking performance on ice through the water film removal effect of the narrow grooves. If the ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion is less than 5%, the water removal performance of the narrow grooves g will not be sufficient, making it difficult to improve braking performance on ice. If the ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion exceeds 19%, the actual contact area will be reduced, making it difficult to improve braking performance on ice.

[0033] The inclination angle θ of the narrow grooves g relative to the tire circumferential direction is preferably 30° to 70°, more preferably 35° to 55°. This allows the narrow grooves g to achieve a good balance between the edge effect and drainage performance, which is advantageous for improving performance on ice. If the inclination angle θ of the narrow grooves g is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect cannot be sufficiently secured. If the inclination angle θ of the narrow grooves g exceeds 70°, it becomes difficult to improve braking performance on ice because the narrow grooves g cannot sufficiently remove water.

[0034] As shown in Figure 4, when the center side of the specific land portion in the tire width direction is designated as a central region C and both sides of the central region in the tire width direction are designated as edge regions E, the inclination direction of the narrow grooves g in at least one edge region E can be made different from the inclination direction of the narrow grooves g in the central region C. This design is advantageous for improving performance on ice because it can enhance the water film removal effect of the narrow grooves g compared to when the narrow grooves g extend in a single direction. In this case, it is preferable that the area of ​​the edge region E, in which narrow grooves g having an inclination direction different from the inclination direction of the narrow grooves g in the central region C are provided, is smaller than the area of ​​the central region C. In particular ... specific land portion is smaller than the area of ​​the central region C. L Width W of the end region E (the part where the inclination direction of the narrow groove is different) E As shown in the figure, when the inclination direction of the narrow groove g is different in the end regions E on both sides in the tire width direction, the width WE is the sum of the widths of the two end regions E. This results in a good balance of the areas of the central region C and the end regions E, where the inclination directions of the narrow grooves g are different, which is advantageous for improving the water film removal effect of the narrow grooves g and improving performance on ice.

[0035] As mentioned above, when the inclination direction of the narrow grooves g differs between the central region C and the edge regions E, the inclination angle θc in the central region C is preferably 30° to 60°, more preferably 35° to 55°, and the inclination angle θe in the edge regions E is preferably 30° to 70°, more preferably 35° to 60°. This ensures a good inclination angle of the narrow grooves g in both the central region C and the edge regions E, which is advantageous for improving the water film removal effect of the narrow grooves g and improving performance on ice. If the inclination angle θc in the central region C is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect is insufficient. If the inclination angle θc in the central region C is more than 60°, it becomes difficult to improve braking performance on ice because the water removal performance of the narrow grooves g is insufficient. If the inclination angle θe in the edge regions E is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect is insufficient. If the inclination angle θe in the end region E exceeds 70°, the fine grooves g will not be able to provide sufficient water removal performance, making it difficult to improve braking performance on ice.

[0036] As described above, the present invention relates to the specific land portion (particularly the narrow groove g), and therefore the overall structure (tread pattern) of the tread portion 1 is not particularly limited. However, from the viewpoint of improving performance on ice, the ratio of the total groove area of ​​all grooves formed in the tread portion 1, including the sipes s and narrow grooves g, to the area of ​​the ground contact patch of the tread portion 1 (i.e., the groove area ratio of the tread portion 1) is preferably 20% to 60%, and more preferably 25% to 55%. Note that, in the case of FIG. 2, for example, all grooves formed in the tread portion 1, including the sipes s and narrow grooves g, are the circumferential main grooves 20 (inner main groove 21 and outer main groove 22), lug grooves 30 (center lug groove 31, intermediate lug grooves 32a and 32b, and shoulder lug grooves 33), circumferential auxiliary groove 51, circumferential narrow groove 53, sipes s, and narrow grooves g. Optimizing the overall groove area ratio of the tread 1 in this way ensures sufficient actual contact area to ensure braking performance on ice, and furthermore, the water film removal effect of the fine grooves ensures braking performance on ice, which is advantageous for improving performance on ice. If the groove area ratio of the tread 1 is less than 20%, the drainage performance of the tread 1 as a whole cannot be ensured sufficiently, so even if the specific land portion of the present invention is adopted, the effect of improving performance on ice will be limited. If the groove area ratio of the tread 1 is more than 60%, the actual contact area of ​​the tread 1 as a whole cannot be ensured sufficiently, so even if the specific land portion of the present invention is adopted, the effect of improving performance on ice will be limited.

[0037] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0038] Seventeen types of pneumatic tires (test tires) were manufactured: Conventional Example 1, Comparative Examples 1 and 2, and Examples 1 to 14. The tire size was 195 / 65R15 91Q, and the basic structure (internal structure) was shown in FIG. 1. The tread pattern was based on the tread pattern shown in FIG. 2. The groove volume ratio of the narrow grooves, the depth of the narrow grooves, the width of the narrow grooves, the pitch of the narrow grooves, the groove area ratio of the narrow grooves, the inclination direction of the narrow grooves, the inclination angle of the narrow grooves, and the groove area ratio of the entire tread portion were set as shown in Tables 1 to 3.

[0039] In Tables 1 to 3, the "groove volume ratio of fine grooves" refers to the tread area S of the specific land portion where sipes and fine grooves are provided [unit: mm 2 ] and the total volume of the fine grooves formed in that specific land area V [unit: mm 3 ] is the ratio V / S. The "groove area ratio of fine grooves" is the ratio of the total area of ​​fine grooves to the tread area S of a specific land portion. In the "narrow groove inclination direction" column, cases where the inclination direction of the fine grooves is the same in the central region and edge region of a specific land portion are indicated as "same direction," and cases where the inclination direction of the fine grooves is different in the central region and edge region of a specific land portion are indicated as "different directions." The "narrow groove inclination angle" has two columns, one for the "central region" and one for the "edge region," and when the "narrow groove inclination direction" is "different directions," both the inclination angle of the fine groove in the central region of the specific land portion and the inclination angle of the fine groove in the edge region are indicated. Note that when the "narrow groove inclination direction" is "same direction," the inclination angle value is indicated only in the "central region" column. The "groove area ratio of the entire tread portion" is the ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and fine grooves, to the area of ​​the contact patch of the tread portion.

[0040] The braking performance on ice of these test tires was evaluated by the following test method, and the results are shown in Tables 1 to 3.

[0041] Braking performance on ice Each test tire was mounted on a 15x6.5J rim wheel and fitted to all wheels of a front-wheel drive vehicle with an 1800cc engine displacement, and the tires were inflated to an air pressure of 250 / 240kPa. A braking test (20km / h) was conducted by a test driver on an ice rink. The evaluation results were expressed as an index using the reciprocal of the measured value, with Conventional Example 1 being 100. The higher the index value, the shorter the braking distance and the better the braking performance on ice.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] As can be seen from Tables 1 to 3, the tires of Examples 1 to 14 had improved braking performance on ice compared to Conventional Example 1. On the other hand, the tire of Comparative Example 1 had a large groove volume ratio (ratio V / S) of the fine grooves, so the effect of improving braking performance on ice was limited. The tire of Comparative Example 2 had a small groove volume ratio (ratio V / S) of the fine grooves, so the effect of improving braking performance on ice was limited.

[0046] The present disclosure includes the following inventions. Invention [1] A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion is formed with a plurality of circumferential main grooves extending along the tire circumferential direction, a plurality of lug grooves extending in a direction intersecting the circumferential main grooves, and a plurality of land portions defined by the circumferential main grooves and / or the lug grooves, At least one of the plurality of land portions is a specific land portion having at least one sipe extending along the tire width direction on the tread surface and a plurality of narrow grooves extending in a direction intersecting the sipe, the narrow grooves being shallower than the sipes and having a groove depth of 1.5 mm or less, The area S of the tread surface of the specific land portion [unit: mm 2 ] and the total groove volume of the plurality of narrow grooves V [unit: mm 3 ] and 0.25 x 10 -2 ≦V / S≦7.00×10 -2 A tire characterized by satisfying the relationship: Invention [2] The tire according to invention [1], wherein the pitch of the plurality of narrow grooves is 0.5 mm to 5.0 mm, and the groove width of each of the narrow grooves is 0.05 mm to 1.0 mm. Invention [3] The tire according to invention [1] or [2], characterized in that the ratio of the total area of ​​the plurality of narrow grooves to the tread area S of the specific land portion is 5% to 19%. Invention [4] The tire according to any one of inventions [1] to [3], characterized in that the narrow grooves have an inclination angle of 30° to 70° with respect to the tire circumferential direction. Invention [5] A tire according to any one of inventions [1] to [4], characterized in that when the center side of the specific land portion in the tire width direction is defined as a central region and both sides of the central region in the tire width direction are defined as end regions, the inclination direction of the narrow grooves in at least one of the end regions is different from the inclination direction of the narrow grooves in the central region. Invention [6] A tire according to invention [5], characterized in that the area of ​​the end regions, in which the narrow grooves having an inclination direction different from the inclination direction of the narrow grooves in the central region are provided, is smaller than the area of ​​the central region. Invention [7] A tire according to invention [5] or [6], characterized in that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the central region in the tire width direction of the specific land portion, and 30° to 70° in the end region in the tire width direction of the specific land portion. Invention [8] A tire according to any one of inventions [1] to [7], characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and the narrow grooves, to the area of ​​the contact area of ​​the tread portion is 20% to 60%. [Explanation of symbols]

[0047] 1 Tread section 2 Sidewall 3 Bead section 20 Circumferential main groove 30 lug grooves 40 Land s sipe g narrow groove CL Tire Equator

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion is formed with a plurality of circumferential main grooves extending along the tire circumferential direction, a plurality of lug grooves extending in a direction intersecting the circumferential main grooves, and a plurality of land portions partitioned by the circumferential main grooves and / or the lug grooves, At least one of the plurality of land portions is a specific land portion having at least one sipe extending along the tire width direction on the tread surface and a plurality of narrow grooves extending in a direction intersecting the sipe, the narrow grooves being shallower than the sipes and having a groove depth of 1.5 mm or less, The area S of the tread surface of the specific land portion [unit: mm 2 ] and the total groove volume V of the plurality of narrow grooves [unit: mm 3 ] and 0.25 × 10 -2 ≦V / S≦7.00×10 -2 A tire characterized by satisfying the relationship:

2. 2. The tire according to claim 1, wherein the pitch of the plurality of narrow grooves is 0.5 mm to 5.0 mm, and the groove width of each of the narrow grooves is 0.05 mm to 1.0 mm.

3. 3. The tire according to claim 1, wherein the ratio of the total area of ​​the plurality of narrow grooves to the tread area S of the specific land portion is 5% to 19%.

4. The tire according to claim 1 or 2, characterized in that the narrow groove has an inclination angle of 30° to 70° with respect to the tire circumferential direction.

5. 3. The tire according to claim 1, wherein the central side of the specific land portion in the tire width direction is defined as a central region, and both sides of the central region in the tire width direction are defined as end regions, and the inclination direction of the narrow grooves in at least one of the end regions is different from the inclination direction of the narrow grooves in the central region.

6. 6. The tire according to claim 5, wherein the area of ​​the end regions, in which the narrow grooves having an inclination direction different from the inclination direction of the narrow grooves in the central region are provided, is smaller than the area of ​​the central region.

7. The tire according to claim 5, characterized in that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in a central region in the tire width direction of the specific land portion, and is 30° to 70° in an end region in the tire width direction of the specific land portion.

8. The tire according to claim 1 or 2, characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and the narrow grooves, to the area of ​​the ground contact region of the tread portion is 20% to 60%.

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