7A and 7B extend parallel to each other, however, the sipes 7A and 7B may extend at different angles with respect to the tire width direction.

In FIG. 3, the length of the sipe 7 in the extending direction thereof is indicated by a. The length a of the sipe 7 in the extending direction thereof is, for example, between 3 and 15 mm. The length a of the sipe 7 in the extending direction thereof is preferably between 3 and 10 mm, and more preferably between 3 and 5 mm. The length a of the sipe 7 may be defined according to the depth (maximum depth) h of the sipe 7. Specifically, the length a of the sipe 7 may be determined according to the depth h within the range where the length d of the sipe 7 in the tire width direction (d=a×cos φ) and the depth h of the sipe 7 satisfy d×h≤150 mm². The length a of the sipe 7 is preferably defined within the range satisfying d×h≤100 mm², and more preferably d×h≤50 mm². The depth h of the sipe 7 may be, for example, 3 mm or more. The depth h of the sipe 7 may be 6.7 mm, for example.

Referring to FIG. 4, the cross-sectional shape of the sipe 7 in a cross section perpendicular to the extending direction thereof at the tread surface 2 is described. In this embodiment, the cross-sectional shape of the sipe 7 in a cross section perpendicular to the extending direction thereof is approximately rectangular, as illustrated in FIG. 4A. In the sipe 7 illustrated in FIG. 4A, the width w of the sipe 7 is 1 mm or less as described above, and may be 0.4 mm, for example. However, the cross-sectional shape of the sipe 7 in a cross section perpendicular to the extending direction thereof may be other than rectangular. For example, the sipe 7 may be shaped with the groove bottom portion bulging in a cross section perpendicular to the extending direction of the sipe 7, as illustrated in FIG. 4B. In addition, for example, the sipe 7 may be rounded at the bottom in a cross section perpendicular to the extending direction of the sipe 7. For example, in the cross section of the sipe 7 perpendicular to the extending direction thereof illustrated in FIG. 4A, the bottom portion of the sipe 7 may be R-chamfered at both ends in the width direction of the sipe 7, or the bottom portion of the sipe 7 may be semicircular. In the sipe 7 illustrated in FIG. 4B, the width w of the sipe 7 may be 0.4 mm, for example, in the area of 50% or more of the depth of the sipe 7.

Referring again to FIG. 3, the sipe 7B is displaced from the sipe 7A by an offset s in the tire width direction and by an offset q in the tire circumferential direction. The offset s in the tire width direction of the sipes 7A and 7B may be defined, for example, in the range satisfying s≥1.5 mm.

The pair of sipes 7A and 7B that constitute the sipe unit 8 are opposed to each other in the tire circumferential direction only in part in the tire width direction. Here, “a line segment X and a line segment Y are opposed to each other in the direction Z” means that the line segment X and the line segment Y are separated from each other in the direction Z and that each of the ends of line segment Y is located on two straight lines extended along the direction Z from each end of the line segment X. However, “the sipes 7A and 7B are opposed to each other in the tire circumferential direction only in part in the tire width direction” shall include the case where only the end points of sipes 7A and 7B respectively are located on a straight line extending along the tire circumferential direction. In this embodiment, the sipes 7A and 7B are offset by s in the tire width direction. In FIG. 3, the part 7a in the tire width direction of the sipe 7A and the part 7b in the tire width direction of the sipe 7B are opposed to each other in the tire circumferential direction. Here, the length d in the tire width direction of each of the sipes 7A and 7B (d=a×cos φ) and the offset s in the tire width direction of the sipes 7A and 7B satisfy d−s≥0. As a result, when the pair of sipes 7A and 7B in the sipe unit 8 are projected along the tire circumferential direction, at least one of the sipes 7A and 7B extends unbroken across the length of the sipe unit 8 in the tire width direction, as indicated by the shaded shading in FIG. 3. Therefore, by increasing the length of the sipe unit 8 included in the tire width direction within the range where d−s≥0 is satisfied without changing the length of each of the sipes 7A and 7B that constitute the sipe unit 8, the sipe unit 8 can provide edge effect and water removing effect in a wider range while maintaining the sipe density in the block land portion 6. This improves the on-ice gripping performance of the tire 1A.

Referring again to FIG. 1, in the land portion 4, a plurality of sipe units 8 are spaced apart from each other and repeatedly arranged in the tire circumferential direction to form a sipe unit row 9. In the illustrated example, in one block land portion 6, three sipe units 8 are arranged repeatedly in the tire circumferential direction to form a sipe unit row 9. However, the number of sipe units 8 that constitute one sipe unit row 9 may be any number of two or more.

In FIG. 3, the plurality of sipe units 8 that constitute the sipe unit row 9 are arranged repeatedly at a pitch p in the tire circumferential direction. In this embodiment, the plurality of sipes 7 arranged on the block land portion 6 extend parallel to each other in the developed view of the tread surface 2. Here, when the distance in the tire circumferential direction between adjacent sipe units 8 in the tire circumferential direction in the sipe unit row 9 is denoted as the distance r between units, the distance r between units is indicated by r=p−q. In particular, when the pitch p of the sipe unit 8 that constitute the sipe unit row 9 and the offset q in the tire circumferential direction of the sipes that constitute the sipe unit 8 is q=p/2, r=q holds true, then all the sipes 7 in the sipe unit row 9 are equally spaced in the tire circumferential direction. Therefore, the sipe density in the tire circumferential direction in the block land portion 6 can be made uniform by setting q preferably in the range of (p/2)×0.8 to (p/2)×1.2, and more preferably to p/2. This allows the tread surface 2 to contact the road surface more uniformly and to equalize the distribution of the ground pressure applied to the ground contact patch of the tread surface 2, thereby increasing the footprint area of the tire 1A.

The plurality of sipe units 8 that constitute the sipe unit row 9 are preferably arranged so that both ends in the tire width direction of each sipe unit are aligned on a straight line extending along the tire circumferential direction, respectively. Specifically, in FIG. 3, both ends E1 and E2 in the tire width direction of the plurality of sipe units 8 that constitute the sipe unit row 9 are aligned on a straight line extending along the tire circumferential direction, respectively. This reduces the blank area (the area enclosed by the dashed line in the figure) where no sipes 7 are provided within the area of the block land portion 6 where the sipe unit row 9 is arranged. As a comparison, FIG. 5 illustrates an arrangement of sipe units 8, which is different from that illustrated in FIG. 3. In FIG. 5, both ends in the tire width direction of each of the plurality of sipe units 8 that constitute the sipe unit row 9 are not aligned on a straight line extending along the tire circumferential direction, respectively. Comparing FIGS. 3 and 5, the area enclosed by the dashed line in FIG. 3 is smaller than the area enclosed by the dashed line in FIG. 5. In this way, by arranging both ends in the tire width direction of the plurality of sipe units 8 that constitute the sipe unit row 9 on a straight line extending along the tire circumferential direction, the blank area where no sipes 7 are provided can be reduced within the area of the block land portion 6 where the sipe unit row 9 is arranged. However, the arrangement of the sipe units 8 may be as illustrated in FIG. 5.

Referring again to FIG. 1, the land portion 4 comprises a plurality of sipe unit rows 9 arranged side-by-side in the tire width direction. In the illustrated example, in each of the block land portions 6 of the land portions 4A and 4E respectively, two sipe unit rows 9 are arranged side by side in the tire width direction. Also, in each of the block land portions 6 of the block land portions 4B, 4C and 4D respectively, four sipe unit rows 9 are arranged side by side in the tire width direction. However, the number of sipe unit rows 9 arranged in one block land portion 6 may be any number.

The arrangement of a plurality of sipe unit rows 9 in the first embodiment is described below with reference to FIG. 6. FIG. 6 schematically illustrates the arrangement of a plurality of sipe unit rows 9 in the first embodiment. In FIG. 6, two sipe unit rows 9A and 9B are arranged side by side in the tire width direction.

In the first embodiment illustrated in FIG. 6, a plurality of sipes 7 in two adjacent sipe unit rows 9A and 9B in the tire width direction extend at an angle with respect to the tire width direction, in the same direction between the sipe unit rows 9A and 9B. Specifically, among the plurality of sipe unit rows 9A and 9B, the plurality of sipes 7 in the first sipe unit row 9A extend toward one side in the tire width direction (right in the figure) while being inclined toward one side in the tire circumferential direction (up in the figure). Furthermore, the plurality of sipes 7 in the second sipe unit row 9B which is adjacent to the first sipe unit row 9A extend, as well as the plurality of sipes 7 included in the first sipe unit row 9A, toward the one side in the tire width direction (right in the figure) while being inclined toward the one side in the tire circumferential direction (up in the figure).

Thus, the plurality of sipes 7 included in the plurality of sipe unit rows 9 adjacent to each other in the tire width direction are arranged to extend in the same direction between the sipe unit rows 9, which makes it easier to arrange the blades for forming the sipes 7 in the mold during tire manufacturing and facilitates the fabrication of molds for the tire 1A.

In FIG. 6, the tire widthwise spacing between the adjacent sipe unit rows 9A and 9B in the tire width direction is indicated by v. Also, the offset in the tire circumferential direction of the adjacent sipe unit rows 9A and 9B in the tire width direction is indicated by u. The tire widthwise spacing v and the offset in the tire circumferential direction u may each be set to any value.

The tire widthwise spacing v is preferably −s to s (s>0). Here, the s is the offset in the tire width direction between the pair of sipes 7 that constitute the sipe unit 8. As illustrated in FIG. 6, the positive value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row 9A and the area between the two ends in the tire width direction of the sipe unit row 9B adjacent to the sipe unit row 9A in the tire width direction are spaced apart in the tire width direction by the spacing v in the tire width direction. On the other hand, the negative value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row 9A and the area between the two ends in the tire width direction of the sipe unit row 9B adjacent to the sipe unit row 9A in the tire width direction overlap in the tire width direction by the absolute value of the spacing v. By defining the tire widthwise spacing v in this manner, the blank area (the area enclosed by the dashed line in the figure) where no sipes 7 are provided is reduced within the area of the block land portion 6 where the adjacent sipe unit rows 9A and 9B in the tire width direction are arranged.

More preferably, the tire widthwise spacing v is set to 0 and the offset in the tire circumferential direction u is (d+s)×tan φ. Here, φ is the angle between each of the pair of sipes 7 that constitute the sipe unit 8 and the tire width direction, d is the length of the sipe 7 in the tire width direction, and s is the offset in the tire width direction between the pair of sipes 7 that constitute the sipe unit 8. The arrangement of the sipe unit rows 9, when the tire widthwise spacing v is 0 and the offset in the tire circumferential direction u is (d+s)×tan φ, is schematically illustrated in FIG. 7.

By setting the tire widthwise spacing v to 0, the tire widthwise components of the plurality of sipes 7 are continuously arranged without gaps in the tire width direction, when the plurality of sipes 7 aligned in the tire width direction are projected along the tire circumferential direction, as illustrated by the shaded shading in FIG. 7. This allows the sipes 7 to be distributed evenly without gaps across the multiple sipe unit rows 9, thereby improving the edge effect and water removal effect in the block land portion 6. In addition, the sipe density in the block land portion 6 can be made uniform by distributing the sipes 7 evenly without gaps across the multiple sipe unit rows 9. This allows the tread surface 2 to contact the road surface more uniformly and the distribution of the ground pressure applied to the contact patch of the tread surface 2 to be equalized, thereby increasing the footprint area of the tire 1A.

In FIG. 7, each of the plurality of sipes 7 in the second sipe unit row 9B extends over an extension line of any of the sipes 7 in the first sipe unit row 9A. As a result, in the block land portion 6, the plurality of sipes 7 are arranged in a straight line in the tire width direction. Because of this, by setting u preferably in the range of ((d+s)×tan φ)×0.8 to ((d+s)×tan φ)×1.2, and more preferably to (d+s)×tan φ, water captured in the voids of the sipes 7 is drained along the plurality of sipes 7 which are arranged in a straight line, toward the tire width direction, thereby improving the on-ice gripping performance on the land portion 4. Furthermore, the plurality of sipes 7 in the adjacent sipe unit rows 9A and 9B are aligned in the same straight line, which facilitates the fabrication of molds with blades for forming the sipes 7.

Referring again to FIG. 1, twelve sipes 7 are arranged in each of the block land portions 6 of the land portions 4A and 4E respectively, and twenty-four sipes 7 are arranged in each of the block land portions 6 of the land portions 4B, 4C, and 4D respectively. However, the number of sipes 7 arranged in one block land portion 6 may be any number.

For example, the number of sipes 7 arranged in the block land portion 6 may be determined based on the sipe density in the tire circumferential direction SD. The sipe density in the tire circumferential direction SD is a measure of the density in the tire circumferential direction of transverse sipes that completely cross the block land portion 6. If the equivalent length in the tire circumferential direction of the block land portion 6 which is obtained by dividing the outer contour area of the block land portion 6 (mm²) by the maximum width BW is BL (mm), and the number of transverse sipes which are provided to completely cross the block land portion 6 is N′, the average sipe spacing in the tire circumferential direction is expressed as BL/(N′+1). The sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing by the following formula (1).

SD
=

(

N
′

+
1

)

/
BL

(
1
)

The “outer contour area” of the block land portion 6 is the area enclosed by the outer contour of the block land portion 6 in the expanded view of the tread surface 2. Therefore, even if non-grounded areas such as sipes, small holes, narrow grooves, etc. are arranged within the block land portion 6, the area that does not exclude the area of the sipes, small holes, narrow grooves, etc. are considered.

The following is a description of the method used to calculate the sipe density SD in this embodiment. For example, assume a diamond-shaped block land portion 6 provided with multiple sipes 7, as illustrated in the table providing sipe shapes in FIG. 14. First, if the number of sipes 7 in the block land portion 6 is n, the length of sipes 7 in the tire width direction is d (mm), and the maximum width of the block land portion 6 in the tire width direction is BW (mm), the number of equivalent sipes N is expressed as d×n/BW. Here, the number of equivalent sipes N is the number of sipes when the sipes 7 in this embodiment are converted to transverse sipes (equivalent sipes) that are provided to completely cross the block land portion 6. Furthermore, if the equivalent length in the tire circumferential direction of the block land portion 6 is BL (mm), the average sipe spacing in the tire circumferential direction is expressed as BL/(N+1). Here, the average sipe spacing in the tire circumferential direction is the spacing in the tire circumferential direction of the equivalent sipes in the block land portion 6, when the sipes 7 in this embodiment are converted to the equivalent sipes. The sipe density SD in the tire circumferential direction is expressed as the reciprocal of the average sipe spacing by the following formula (2).

SD
=

(

N
+
1

)

/
BL

=

(

(

d
×
n
/
BW

)

+
1

)

/
BL

(
2
)

Note, that the number n of sipes 7 in the block land portion 6, the length d in the tire width direction of the sipes 7, the maximum width BW of the block land portion 6 in the tire width direction, and the outer contour area of the block land portion 6 are the values measured in the developed view of the tread surface 2.

For example, a plurality of sipes 7 may be arranged in the block land portion 6 so that the sipe density SD is 0.15 (l/mm) or more. This improves the on-ice gripping performance of the tire 1A.

A plurality of sipes 7 may be connected in the block land portion 6 by a shallow groove 10. FIG. 8 schematically illustrates the arrangement of sipe units 8 in which the sipes 7 in the first embodiment are connected by the shallow grooves 10. The block land portion 6 illustrated in FIG. 8 corresponds, for example, to the block land portion 6B of the tire 1A illustrated in FIG. 1. In FIG. 8, four of sipe unit rows 9, aligned in the tire width direction, are arranged in the block land portion 6. In each of the sipe unit rows 9, three sipe units 8 are arranged repeatedly in the tire circumferential direction. In FIG. 8, the sipes 7, which are aligned in the tire width direction, are connected by the shallow groove 10 that completely crosses the block land portion 6. A cross-section (B-B′ section) of the tire 1A that is cut along the extending direction of the shallow groove 10 illustrated in FIG. 8 is illustrated in FIG. 9. In FIG. 9, the depth (maximum depth) H of the shallow groove 10 may be defined according to the depth h of the sipe 7. For example, the depth H of the shallow groove 10 may be defined in the range of 5 to 60%, and preferably 5 to 20%, of the depth h of the sipe 7. For example, the depth h of the sipe 7 may be 6.7 mm and the depth H of the shallow groove 10 may be 0.7 mm. With this configuration, water captured in the voids of the sipes 7 is drained through the shallow grooves 10 toward the tire width direction, thereby improving the on-ice gripping performance in the block land portion 6.

Referring again to FIG. 1, the block land portion 6 of the tire 1A may be provided with sipes other than the sipe unit 8 described above. For example, in the illustrated example, the land portions 4A and 4E are provided with a plurality of zigzag-shaped sipes 11 extending in the tire width direction toward the tread edge TE. This improves drainage performance at the tread surface 2, and thus the on-ice gripping performance of the tire 1A.

Second Embodiment

Hereinafter, a tire 1 (1B) according to the second embodiment of the present disclosure will be described with reference to FIG. 10. FIG. 10 is a schematic developed view of the tread pattern of the tire 1B according to the second embodiment of this disclosure. Hereafter, tires 1A and 1B will be referred to collectively as simply tire 1 when no particular distinction is made between them.

As illustrated in FIG. 10, the second embodiment differs from the first embodiment in that the plurality of sipes 7 in the two adjacent sipe unit rows 9 in the tire width direction are arranged to extend in different directions between the sipe unit rows 9. The following is a description of the second embodiment, focusing on the points where it differs from the first embodiment. Note, that parts having the same configuration as those in the first embodiment are given the same reference numerals.

As in the first embodiment, the tire 1B has, on the tread surface 2, one or more (four in the illustrated example) circumferential main grooves 3 (3A, 3B, 3C, 3D) extending in the tire circumferential direction; and a plurality (five in the illustrated example) of land portions 4 (4A, 4B, 4C, 4D, 4E) which are defined by the circumferential main grooves 3 adjacent to each other in the tire width direction of the one or more circumferential main grooves 3, or by the circumferential main groove 3 (3A or 3D) and the tread edge TE.

As in the first embodiment, in the tire 1B, each land portion 4 is divided into a plurality of block land portions 6 by one or more width direction grooves 5 that completely cross the land portion 4 and extend in the tire width direction. For example, within the illustration, the land portion 4C is divided into three block land portions 6A, 6B and 6C adjacent to each other in the tire circumferential direction by two width direction grooves 5A and 5B adjacent to each other in the tire circumferential direction.

The land portion 4 comprises a sipe unit 8 consisting of a pair of sipes 7, as in the first embodiment. More specifically, a sipe unit 8, consisting of a pair of sipes 7A and 7B, is arranged in the block land portion 6 included in the land portion 4.

As in the first embodiment, each of the pair of sipes 7A and 7B that constitutes the sipe unit 8 extends such that both ends in the extending direction of the sipe 7 terminate within the land portion 4. More specifically, each of the pair of sipes 7A and 7B extends such that both ends in the extending direction of the sipe 7 terminate within the block land portion 6.

As in the first embodiment, each of the pair of sipes 7A and 7B that constitutes the sipe unit 8 extends in a straight line at an angle with respect to the tire width direction in the developed view of the tread surface 2. Each of the pair of sipes 7A and 7B that constitute the sipe unit 8 extends in a straight line such that the angle φ with respect to the tire width direction satisfies 0°<φ<45°.

As in the first embodiment, the pair of sipes 7A and 7B that constitute the sipe unit 8 are opposed to each other in the tire circumferential direction only in part in the tire width direction.

As in the first embodiment, in the land portion 4, a plurality of sipe units 8 are repeatedly arranged in the tire circumferential direction to form a sipe unit row 9. In the illustrated example, in one block land portion 6, three sipe units 8 are arranged repeatedly in the tire circumferential direction to form a sipe unit row 9. The plurality of sipe units 8 that constitute the sipe unit row 9 are preferably arranged so that both ends in the tire width direction of each sipe unit are aligned on a straight line extending along the tire circumferential direction, respectively.

In the land portion 4, a plurality of sipe unit rows 9 are arranged side by side in the tire width direction. In the illustrated example, two sipe unit rows 9 are arranged side by side in the tire width direction in the block land portions 6 of the land portions 4A and 4E, respectively. Also, in the block land portions 4B, 4C and 4D, four sipe unit rows 9 are arranged side by side in the tire width direction in the block land portions 6 of the land portions 4B, 4C and 4D, respectively.

Hereinafter, referring to FIG. 11, the arrangement of the plurality of sipe unit rows 9 in the second embodiment is described. FIG. 11 schematically illustrates the arrangement of the plurality of sipe unit rows in the second embodiment. In FIG. 11, two sipe unit rows 9A and 9B are arranged side by side in the tire width direction.

In the second embodiment illustrated in FIG. 11, unlike the first embodiment, a plurality of sipes 7 in two adjacent sipe unit rows 9A and 9B in the tire width direction extend at an angle with respect to the tire width direction, in a different direction between the sipe unit rows 9A and 9B. Specifically, among the plurality of the sipe unit rows 9A and 9B, the plurality of sipes 7 in the first sipe unit row 9A extend toward one side in the tire width direction (right in the figure) while being inclined toward one side in the tire circumferential direction (up in the figure). On the other hand, the plurality of sipes 7 in the second sipe unit row 9B which is adjacent to the first sipe unit row 9A extend toward the one side in the tire width direction (right in the figure) while being inclined toward the other side in the tire circumferential direction (down in the figure).

This arrangement of the sipe unit rows 9 prevents the block land portion 6 from collapsing when external force is input to the tire 1B, because the block land portion 6 is supported within the area where the adjacent sipe unit rows 9A and 9B are arranged. For example, when an external force is input in the direction indicated by the arrow in FIG. 11, the block land portion 6 around the sipes 7 in the sipe unit row 9A collapses toward the lower right in the drawing. On the other hand, the block land portion 6 around the sipes 7 in the sipe unit row 9B collapses toward the lower left in the drawing. In this way, when an external force is input to the tire 1B, the block land portion leans and collapses in different directions within the area where the adjacent sipe unit rows 9A and 9B in the tire width direction are arranged, so that the block land portion be supported within that area, and this makes the block land portion less likely to collapse. This increases the rigidity of the block land portion 6. In addition, when an external force in the tire circumferential direction is applied to the tread surface 2, the tire widthwise components of the external force applied to around the sipe unit rows 9A and 9B in the block land portion 6 cancel each other out, thereby preventing unexpected forces in the tire width direction from being applied to the tire 1B and reducing the impact on the steering stability of a vehicle equipped with the tire 1B.

In FIG. 11, the length of sipe 7 in the extending direction thereof is indicated by a, and the angle between the sipe 7 and the tire width direction is indicated by φ. In this embodiment, the plurality of sipes 7 in one sipe unit row 9 extend parallel to each other in the developed view of the tread surface 2. In the sipe unit 8, a pair of sipes 7A and 7B is displaced each other by an offset s in the tire width direction and by an offset q in the tire circumferential direction. In addition, the plurality of sipe units 8 that constitute the sipe unit row 9 are arranged repeatedly at a pitch p in the tire circumferential direction. Here, when the distance in the tire circumferential direction between adjacent sipe units 8 in the sipe unit row 9 is denoted as the distance r between units, the distance r between units is indicated by r=p−q.

In particular, when the pitch p of the sipe unit 8 that constitute the sipe unit row 9 and the offset q in the tire circumferential direction of the sipes that constitute the sipe unit 8 is q=p/2, r=q holds true, then all the sipes 7 in the sipe unit row 9 are equally spaced in the tire circumferential direction. Therefore, the sipe density in the tire circumferential direction in the block land portion 6 can be made uniform by setting q preferably in the range of (p/2)×0.8 to (p/2)×1.2, and more preferably to p/2. This allows the tread surface 2 to contact the road surface more uniformly and to equalize the distribution of the ground pressure applied to the ground contact patch of the tread surface 2, thereby increasing the footprint area of the tire 1B.

In FIG. 11, the tire widthwise spacing between the adjacent sipe unit rows 9A and 9B in the tire width direction is indicated by v. Also, the offset in the tire circumferential direction of the adjacent sipe unit rows 9A and 9B in the tire width direction is indicated by u.

The tire widthwise spacing v is preferably −s to s (s>0). Here, the s is the offset in the tire width direction between the pair of sipes 7 of the sipe unit 8 that constitute the sipe unit row 9. As illustrated in FIG. 11, the positive value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row 9A and the area between the two ends in the tire width direction of the sipe unit row 9B adjacent to the sipe unit row 9A in the tire width direction are spaced apart in the tire width direction by the spacing v in the tire width direction. On the other hand, the negative value of the tire widthwise spacing v means that the area between the two ends in the tire width direction of the sipe unit row 9A and the area between the two ends in the tire width direction of the sipe unit row 9B adjacent to the sipe unit row 9A in the tire width direction overlap in the tire width direction by the absolute value of the spacing v. By defining the tire widthwise spacing v in this manner, the blank area (the area enclosed by the dashed line in the figure) where no sipes 7 are provided is reduced within the area of the block land portion 6 where the adjacent sipe unit rows 9A and 9B in the tire width direction are arranged.

More preferably, the tire widthwise spacing v is set to 0 and the offset in the tire circumferential direction u is (d+s)×tan φ. Here, φ is the angle between each of the pair of sipes 7 that constitute the sipe unit 8 and the tire width direction, d is the length of the sipe 7 in the tire width direction, and s is the offset in the tire width direction between the pair of sipes 7 that constitute the sipe unit 8. The arrangement of the sipe unit rows 9 when the tire widthwise spacing v is 0 and the offset in the tire circumferential direction u is (d+s)×tan φ is schematically illustrated in FIG. 12.

By setting the tire widthwise spacing v to 0, the tire widthwise components of the plurality of sipes 7 are continuously arranged without gaps in the tire width direction, when the plurality of sipes 7 aligned in the tire width direction are projected along the tire circumferential direction, as illustrated by the shaded shading in FIG. 12. This allows the sipes 7 to be distributed evenly without gaps across the multiple sipe unit rows 9, thereby improving the edge effect and water removal effect in the block land portion 6. In addition, the sipe density in the block land portion 6 can be made uniform by distributing the sipes 7 evenly without gaps across the multiple sipe unit rows 9. This allows the tread surface 2 to contact the road surface more uniformly and the distribution of the ground pressure applied to the contact patch of the tread surface 2 to be equalized, thereby increasing the footprint area of the tire 1B.

In FIG. 12, each of the plurality of sipes 7 included in the second sipe unit row 9B extends to intersect with an extension line of any of the sipes 7 included in the first sipe unit row 9A. Therefore, when water captured in the void of one sipe 7 is drained from the sipe 7 along the extending direction of the sipe 7, the water is captured again in another sipe 7 extending to intersect with the extension line of the sipe 7, so that the on-ice gripping performance on the land portion 4 is less likely to be degraded.

In the tire 1B, the number of sipes 7 arranged in the block land portion 6 may also be determined based on the sipe density SD, as described above in the first embodiment. For example, a plurality of sipes 7 may be arranged in the block land portion