WO2025248829A1 - Tire - Google Patents

Abstract

The present invention provides a tire capable of exhibiting excellent braking performance on ice at an early stage of wear. In the present invention, at least one of a plurality of land parts 40 formed in a tread part 1 is a specific land part including at least one sipe s extending along the tire width direction on a tread surface and a plurality of fine grooves g extending in a direction crossing the sipe s. The fine groove g has a groove depth shallower than the sipe s and equal to or less than 1.5 mm, and an area S [unit: mm²] of the tread surface of this specific land part and the total sum V [unit: mm³] of the groove volumes of the plurality of fine grooves g satisfy the relationship: 0.25×10^-2 ≤ V/S ≤ 7.00×10^-2.

Description

tire

The present invention relates to a tire having at least one sipe and multiple fine grooves on its tread surface.

In tires for snow and ice, such as studless tires, for example, fillers and air bubbles are mixed into the tread rubber to create minute irregularities on the tread surface. These irregularities have the effect of removing water films, ensuring excellent driving performance on snow and ice. However, before the break-in period, these irregularities are not fully apparent on the tread surface, which means that the tires are unable to fully demonstrate their original driving performance in the early stages of wear.

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

Japanese Patent Application Publication No. 2004-034903

The object of the present invention is to provide a tire that can demonstrate excellent braking performance on ice in the early stages of wear.

To achieve the above object, the tire of the present invention has a tread portion extending circumferentially to form an annular shape, wherein 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, and the area S [unit: ^mm2 ] of the tread surface of the specific land portion and the sum V [unit: ^mm3 ] of the groove volumes of the plurality of narrow grooves satisfy the relationship 0.25 x ^10-2 ≦ V/S ≦ 7.00 x ^10-2 .

In this invention, to improve ice performance in the early stages of wear by using a specific land portion having at least one sipe and multiple fine grooves (fine grooves with a groove depth of 1.5 mm or less) formed on the land portion tread, the tread area S (unit: ^mm2 ) of this specific land portion and the sum of the groove volumes V (unit: ^mm3 ) of the multiple fine grooves provided in this specific land portion are made to satisfy the relationship 0.25 x ^10-2 ≦ V/S ≦ 7.00 x ^10-2 , thereby ensuring sufficient water film removal effect of the fine grooves while preventing the fine grooves from reducing the actual contact area of the specific land portion (the area of the land portion tread that actually contacts the road surface, excluding the sipes and fine grooves), thereby achieving excellent braking performance on ice. Note that the tread area S of the specific land portion is the area inside the outer contour of the specific land portion (the entire area including the sipes and fine grooves).

In the present invention, it is preferable that the pitch of the multiple fine grooves be 0.5 mm to 5.0 mm, and that the groove width of each fine groove be 0.05 mm to 1.0 mm. This ensures sufficient actual contact area of the specific land area to ensure braking performance on ice, and the water film removal effect of the fine grooves further ensures braking performance on ice, which is advantageous for improving performance on ice.

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

In the present invention, it is preferable that the inclination angle of the narrow grooves relative to the tire circumferential direction be between 30° and 70°. This allows the edge effect and drainage performance of the narrow grooves to be balanced, which is advantageous for improving performance on ice. Note that the inclination angle of the narrow grooves is the acute angle between the narrow grooves and the tire circumferential direction.

In this invention, when the center of the specific land area 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 specified to differ from the inclination direction of the narrow grooves in the central region. This improves the water film removal effect of the narrow grooves, which is advantageous for improving performance on ice.

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

Furthermore, it is preferable that the inclination angle of the narrow grooves relative to the tire circumferential direction be 30° to 60° in the central region of the specific land portion in the tire width direction, and 30° to 70° in the end regions of the specific land portion in the tire width direction. This results in a favorable inclination angle of the narrow grooves in both the central region and the end regions, which is advantageous for improving the water film removal effect of the narrow grooves and improving performance on ice. Furthermore, the inclination angle of the narrow grooves in both the central region and the end regions is the acute angle between the narrow grooves and the tire circumferential direction.

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 contact zone of the tread portion is 20% to 60%. This results in a good groove area ratio for the entire tread portion, ensuring sufficient actual contact area and 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.

In this invention, the "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. A "standard rim" is a rim defined for each tire by the standard system that includes the standards on which the tire is based; for example, it is called the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. "Normal internal pressure" is the air pressure set for each tire by each standard in the standard system, including the standard on which the tire is based. In the case of JATMA, it is the maximum air pressure, in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "INFLATION PRESSURE", but if the tire is for a passenger car, it is 180 kPa. "Normal load" refers to the load specified for each tire in the standard system, including the standard on which the tire is based. For JATMA, this is the maximum load capacity; for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is the "LOAD CAPACITY." However, if the tire is for a passenger car, this is a load equivalent to 88% of the above load.

FIG. 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a development view showing the tread pattern of the pneumatic tire of FIG. FIG. 3 is an explanatory diagram schematically illustrating an example of a specific land portion of the present invention. FIG. 4 is an explanatory diagram schematically showing another example of the specific land portion of the present invention. FIG. 5 is a cross-sectional view showing the shape of the narrow grooves of the present invention.

The configuration of the present invention will be described in detail below with reference to the attached drawings.

In the case of a pneumatic tire such as that shown in Figure 1, the tire of the present invention comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on either side of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In Figure 1, the symbol CL indicates the tire equator. Although not depicted in Figure 1, which is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend circumferentially in the tire direction to form an annular shape, thereby forming the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be based primarily on the meridian cross-section shown, but each tire component also extends circumferentially in the tire direction to form an annular shape.

A carcass layer 4 is mounted between a pair of left and right bead portions 3. This carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside in the tire width direction around a bead core 5 located in each bead portion 3. A bead filler 6 is positioned on the outer periphery of the bead core 5, and this bead filler 6 is enclosed by the main body and folded back portions 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.

Multiple belt layers 7 are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 contains multiple reinforcing cords (belt cords) that are inclined relative to the tire circumferential direction, and the reinforcing cords are arranged so that they cross each other between layers. In these belt layers 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°. 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 periphery of the belt layer 7 to improve high-speed durability. The belt cover layer 8 contains reinforcing cords (cover cords) that are oriented in the tire circumferential direction. In the belt cover layer 8, the reinforcing cords are set at an angle of, for example, 0° to 5° relative to the tire circumferential direction. Organic fiber cords such as nylon and aramid are preferably used as the reinforcing cords of the belt cover layer 8.

In the tread portion 1, a tread rubber layer 11 is disposed on the outer periphery 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 periphery) are laminated in the tire radial direction. A side rubber layer 12 is disposed on the outer periphery (outside 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 periphery (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. From the perspective 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 wears, fine irregularities that have a water film removal effect appear.

As described below, this invention relates to sipes and narrow grooves formed on the surface of the tire tread portion 1, so the basic structure (internal structure) of the tire is not limited to the general structure described above. Furthermore, the following explanation will be based on the pneumatic tire shown in Figure 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).

As shown in Figure 2, the surface of the tread portion 1 is formed with multiple circumferential main grooves 20 extending in the tire circumferential direction, multiple lug grooves 30 extending in the tire width direction, and multiple land portions 40 defined by these circumferential main grooves and lug grooves. The circumferential main grooves 20 are grooves that perform the primary drainage function, and generally have a groove width of 5.0 mm or more and a groove depth of 6.5 mm or more. The dimensions of the lug grooves 30 can be those typically used in tires, such as a groove width of 1.0 mm or more and a groove depth of 3.0 mm or more.

At least one of the multiple land portions 40 thus defined has at least one sipe s extending along the tire width direction on the tread surface, and multiple 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 concerned with 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.

The sipes have a groove width of, for example, 0.1 mm to 1.0 mm and a groove depth of, for example, 2.0 mm to 10.0 mm. The sipes extend primarily along the tire width direction and are arranged at intervals around the tire circumference, primarily providing edge effect and drainage. There are no particular restrictions on the shape of the individual sipes, and the zigzag shape shown in the figure can be used.

As mentioned above, the fine grooves g are shallower than the sipes s. As shown in Figure 5, the groove depth d is set to 1.5 mm or less, preferably 0.1 mm to 1.0 mm. The groove width w of the fine grooves g is preferably 0.05 mm to 1.0 mm, more preferably 0.1 mm to 0.8 mm. Thus, the fine grooves g are minute grooves that extend in a direction intersecting the sipes s as shown, and are arranged in multiple rows around the tire circumferential direction. In particular, as shown in Figures 3 and 4, it is preferable for multiple fine grooves g to be periodically and repeatedly arranged evenly across the entire surface of the land portion 40 (specific land portion). By providing multiple fine grooves g, the fine grooves g can remove water film even in the early stages of wear (before the tread rubber's inherent performance is fully realized), thereby achieving excellent braking performance on ice. If the groove depth d of the fine 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 grooves g is less than 0.05 mm, the narrow grooves g will be too small to provide sufficient water removal, making it difficult to improve braking performance on ice. If the groove width w of the narrow grooves g exceeds 1.0 mm, the actual contact area will decrease, making it difficult to improve braking performance on ice.

The cross-sectional shape of the narrow grooves g is not particularly limited. For example, in addition to a shape (rectangular) with a flat groove bottom in cross section as shown in Figure 5, a U-shaped or V-shaped cross section can be used. When multiple narrow grooves g are periodically arranged as shown in Figures 3 and 4, the pitch p of the multiple narrow grooves g (the distance between the periodically arranged narrow grooves g) shown in Figure 5 is preferably 0.5 mm to 5.0 mm, and more preferably 0.7 mm to 4.0 mm. 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 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 exceeds 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.

As mentioned above, the present invention is not particularly limited in terms of the details of the tread pattern as long as it includes at least one specific land portion. However, the tread pattern in the example of Figure 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 (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 (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.

In the illustrated example, a plurality of block-shaped land portions (center land portions 41) are arranged circumferentially between a pair of inner main grooves 21, each separated by the pair of inner main grooves 21 and the lug grooves 30 (center lug grooves 31). On one side of the tire equator (the right side in the figure), a plurality of block-shaped land portions (intermediate land portions 42a) are arranged circumferentially between the zigzag inner main groove 21a and outer main groove 22, each separated by the grooves and the lug grooves 30 (intermediate lug grooves 32a). Each intermediate land portion 42 is provided with a circumferential auxiliary groove 51 that extends zigzag 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 figure), 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, separated 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 communicate with the inner main groove 21b and the outer main groove 22 and terminate within the land portion. On the tire widthwise outer side of the pair of outer main grooves 22, multiple block-shaped land portions (shoulder land portions 43) defined by the outer main grooves 22 and 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 communicates with the shoulder lug groove 33, extends circumferentially, and terminates within the land portion.

Among the land portions 40 of various shapes included in the tread pattern described above, if they are equipped 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 apply to all land portions 40.

As described above, by providing at least one sipe (s) and multiple narrow grooves (g), it is possible to ensure good ice performance in the initial stage of wear in the specific land portion. In this case, the ratio V/S (unit: mm3/ ^mm2 ) of the tread area (S) (unit: ^mm2 ) of the specific land portion to the sum of the groove volumes (V) of the multiple narrow grooves (unit: ^{mm3 )} satisfies the relationship 0.25× ^10-2 ≦V/S≦7.00× ^10-2 , preferably 0.50× ^10-2 ≦V/S≦5.00× ^10-2 . By satisfying this relationship, the water film removal effect of the narrow grooves (g) is sufficiently ensured, while the reduction in the actual contact area of the specific land portion due to the narrow grooves (g) is suppressed, resulting in excellent braking performance on ice. If the ratio V/S is less than 0.25× ^10-2 , the groove volume of the narrow grooves (g) is too small to achieve sufficient water removal performance, making it difficult to improve braking performance on ice. If the ratio V/S exceeds 7.00×10 ⁻² , the actual contact area decreases, making it difficult to improve braking performance on ice.

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 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 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.

The inclination angle θ of the narrow grooves g relative to the tire circumferential direction is preferably 30° to 70°, and 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 will be difficult to improve braking performance on ice because the edge effect will not be sufficient. If the inclination angle θ of the narrow grooves g exceeds 70°, it will be difficult to improve braking performance on ice because the narrow grooves g will not be able to provide sufficient water removal performance.

As shown in FIG. 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 specified to be different from the inclination direction of the narrow grooves g in the central region C. This specification 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, where the narrow grooves g have an inclination direction different from the inclination direction of the narrow grooves g in the central region C, is smaller than the area of the central region C. In particular, it is preferable that the width W _E of the edge region E (the portion where the inclination direction of the narrow grooves is different) is 5% to 49% of the maximum width W _L of the specific land portion. When the inclination directions of the narrow grooves g are different in the edge regions E on both sides in the tire width direction as shown in the figure, the width W _E is the sum of the widths of the two edge regions E. This results in a good balance of areas between the central region C and the end region E, where the inclination directions of the narrow grooves g are different from each other, which is advantageous for improving the water film removal effect of the narrow grooves g and improving performance on ice.

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 results in a favorable 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 cannot be sufficiently secured. If the inclination angle θc in the central region C exceeds 60°, it becomes difficult to improve braking performance on ice because the water removal performance of the narrow grooves g cannot be sufficiently secured. 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 cannot be sufficiently secured. If the inclination angle θe in the end region E exceeds 70°, the fine grooves g will not be able to adequately remove water, making it difficult to improve braking performance on ice.

As described above, the present invention relates to specific land portions (particularly narrow grooves g), and therefore the overall structure (tread pattern) of the tread portion 1 is not particularly limited. However, from the perspective of improving performance on ice, the ratio of the total groove area of all grooves formed in the tread portion 1, including sipes s and narrow grooves g, to the area of the 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 Figure 2, all grooves formed in the tread portion 1, including sipes s and narrow grooves g, refer to, for example, 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 the water film removal effect of the fine grooves further 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 area 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 exceeds 60%, the actual contact area of the tread 1 as a whole cannot be ensured sufficiently, so even if the specific land area of the present invention is adopted, the effect of improving performance on ice will be limited.

The present invention will be further explained below using examples, but the scope of the present invention is not limited to these examples.

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

In Tables 1 to 3, the "groove volume ratio of fine grooves" is the ratio V/S of the tread area S (unit: mm ² ) of a specific land portion where sipes and fine grooves are provided to the sum V (unit: mm ³ ) of the groove volumes of the fine grooves formed in that specific land portion. The "groove area ratio of fine grooves" is the ratio of the total area of the fine grooves to the tread area S of the specific land portion. In the "inclination direction of fine grooves" column, cases where the inclination direction of the fine grooves is the same in the central region and the end region of the 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 the end region of the specific land portion are indicated as "different directions." The "inclination angle of fine grooves" has two columns, one for the "central region" and one for the "end region," and when the "inclination direction of fine grooves" 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 end region are indicated. Note that when the "inclination direction of fine grooves" 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.

These test tires were evaluated for braking performance on ice using the test method below, and the results are shown in Tables 1 to 3.

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 250/240 kPa. A braking test (20 km/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 set at 100. The higher the index value, the shorter the braking distance and the better the braking performance on ice.

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 its effect in 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 its effect in improving braking performance on ice was limited.

REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 20 circumferential main groove 30 lug groove 40 land portion s sipe g fine groove CL tire equator

Claims (8)

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,
A tire characterized in that the area S (unit: mm ² ) of the tread surface of the specific land portion and the sum V (unit: mm ³ ) of the groove volumes of the plurality of narrow grooves satisfy the relationship 0.25×10 ⁻² ≦V/S≦7.00×10 ⁻² . The tire described in claim 1, characterized in that the pitch of the multiple narrow grooves is 0.5 mm to 5.0 mm, and the groove width of each narrow groove is 0.05 mm to 1.0 mm. The tire described in claim 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%. A tire according to any one of claims 1 to 3, characterized in that the inclination angle of the narrow grooves relative to the tire circumferential direction is between 30° and 70°. A tire as described in any one of claims 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 differs from the inclination direction of the narrow grooves in the central region. The tire described in claim 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. The tire described in claim 5 or 6, characterized in that the inclination angle of the narrow groove relative to the tire circumferential direction is 30° to 60° in the central region of the specific land portion in the tire width direction, and 30° to 70° in the end regions of the specific land portion in the tire width direction. A tire described in any one of claims 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 narrow grooves, to the area of the contact patch of the tread portion is 20% to 60%.