阅读说明：本技术 无钉轮胎 (Studless tire ) 是由 藤本佑树 于 2019-07-11 设计创作，主要内容包括：一种无钉轮胎,在胎面部形成有多个刀槽花纹。在无钉轮胎中,在与周向垂直的剖面中,从赤道面至胎面端为止的胎面表面的轮廓由向径向外侧凸出的3个圆弧形成。在将这些圆弧中的从赤道面上朝向轴向外侧的第i个圆弧设为C<Sub>i</Sub>,并将该圆弧C<Sub>i</Sub>的半径设为R<Sub>i</Sub>时,赤道面上的圆弧C<Sub>1</Sub>的切线完全沿轴向延伸。圆弧C<Sub>i+1</Sub>与圆弧C<Sub>i</Sub>在它们的交点相切。半径R<Sub>i+1</Sub>为半径R<Sub>i</Sub>以下。半径R<Sub>2</Sub>相对于半径R<Sub>1</Sub>的比率为40％以上且70％以下。半径R<Sub>3</Sub>相对于半径R<Sub>1</Sub>的比率为15％以上且30％以下。(A studless tire has a tread portion formed with a plurality of sipes. In the studless tire, in a cross section perpendicular to the circumferential direction, the contour of the tread surface from the equatorial plane to the tread end is formed by 3 arcs protruding outward in the radial direction. C is the ith arc from the equatorial plane to the axially outer side of the arcs i And make the arc C i Is set as R i While, the arc C on the equatorial plane 1 The tangent of (a) extends completely in the axial direction. Arc C i+1 And arc C i Tangent at their intersection. Radius R i+1 Is a radius R i The following. Radius R 2 Relative to radius R 1 The ratio of (b) is 40% to 70%. Radius R 3 Relative to radius R 1 The ratio of (b) is 15% to 30%.)

1. A studless tire has a tread portion formed with a plurality of sipes,

said studless tire is characterized in that,

in a cross section perpendicular to the circumferential direction, the contour of the tread surface from the equatorial plane to the tread end is formed by 3 arcs protruding outward in the radial direction,

c represents an i-th arc of the arcs from the equatorial plane toward the axially outer side _iAnd make the arc C _iIs set as R _iWhile, the circular arc C on the equatorial plane ₁The tangent of (a) extends completely in the axial direction,

arc C _i+1And the arc C _iAt the point where they intersect each other,

radius R _i+1Is a radius R _iIn the following, the following description is given,

radius R ₂Relative to radius R ₁The ratio of (B) is 40% to 70%,

radius R ₃Relative to the radius R ₁The ratio of (b) is 15% to 30%.

2. The studless tire of claim 1, wherein,

from the equatorial plane to the circular arc C ₂And arc C ₃The ratio of the width W23 to the axial width W from the equatorial plane to the tread end is 65% to 75%, where W23 is the axial width at the intersection point.

3. The studless tire of claim 1, wherein,

from the equatorial plane to the circular arc C ₁And arc C ₂When the axial width from the intersection point to the tread end is W12, the ratio of the width W12 to the axial width W from the equatorial plane to the tread end is 35% to 45%.

4. The studless tire of claim 1, wherein,

the rubber hardness of the tread rubber arranged on the surface of the tread is 40-65 degrees.

5. The studless tire of claim 1, wherein,

the land ratio of the tread surface is 60-80%.

6. The studless tire of claim 1, wherein,

further comprises a belt layer located on the radial inner side of the tread portion,

when an axial width from the equatorial plane to an outer end of the belt layer is represented by Wb, a ratio of the width Wb to an axial width W from the equatorial plane to the tread end is 90% or more and 98% or less.

7. The studless tire of claim 1, wherein,

the tread portion includes a plurality of main grooves extending in a circumferential direction and a plurality of land portions divided between the main grooves or between the main grooves and a tread end,

the arc C ₁And arc C ₂And the arc C ₂And arc C ₃Is located at the land portion.

8. The studless tire of claim 1, wherein,

in a cross section perpendicular to the circumferential direction, when a virtual line inclined at an inclination angle θ with respect to the axial direction is represented by Lt, a tangent point at which the virtual line Lt is tangent to the tread surface is represented by Pt, and an axial width from the equatorial plane to the tangent point Pt is represented by Wt, a ratio of Wt to an axial width W from the equatorial plane to the tread end at the inclination angle θ of 3 ° is 65% or less.

9. The studless tire of claim 1, wherein,

the ratio R ₂/R ₁45% or more and 65% or less.

10. The studless tire of claim 1, wherein,

the ratio R ₃/R ₁Is 18 percentAbove and below 27%.

11. The studless tire of claim 1, wherein,

the radius R ₁Is 500mm to 900mm inclusive.

12. The studless tire of claim 11,

the radius R ₁Is 600mm to 800mm inclusive.

13. The studless tire of claim 3, wherein,

the ratio W12/W is 38% or more and 42% or less.

14. The studless tire of claim 2, wherein,

the ratio W23/W is 67% or more and 73% or less.

15. The studless tire of claim 6, wherein,

the ratio Wb/W is 92% or more.

16. The studless tire of claim 7, wherein,

the tread portion 4 further includes a plurality of sub grooves extending in a direction intersecting the main grooves.

17. The studless tire of claim 6, wherein,

the tire further comprises a carcass and a belt layer.

18. The studless tire of claim 17,

the carcass includes a plurality of cords juxtaposed with a rubberizing, and each of the cords has an inclination angle of 75 DEG to 90 DEG in absolute value with respect to the equatorial plane.

19. The studless tire of claim 6, wherein,

the belt layer includes a plurality of cords arranged in parallel with a topping, and an absolute value of an inclination angle of each of the cords with respect to the equatorial plane is 10 ° or more and 35 ° or less.

20. The studless tire of claim 17,

the band layer (18) includes a rubberized tape and spirally wound cords, and the absolute value of the inclination angle of each cord with respect to the circumferential direction is 5 DEG or less.

Technical Field

The present invention relates to a studless tire, and more particularly to a studless tire capable of achieving both on-ice performance and steering stability on a dry road surface.

Background

A studless tire in which a plurality of sipes are formed in a tread portion to improve on-ice performance has been proposed. In recent years, studless tires are often used in seasons other than winter, and therefore, improvement of steering stability and uneven wear resistance on dry road surfaces is strongly demanded in addition to on-ice performance.

Japanese patent No. 6214490 (patent document 1), for example, proposes a summer tire in which the outline of the tread is formed by 3 arcs protruding outward in the radial direction, and the radius of each arc is set within a predetermined range. In the tire of patent document 1, C is an ith arc from the equatorial plane toward the axially outer side _iAnd arc C _iIs set as R _iWhile, the radius R is adjusted ₂Relative to radius R ₁The ratio of (A) is set to be 28% to 43%, and the radius R is set to be ₃Relative to radius R ₁The ratio of (b) is set to 2.5% to 8.0%. Thus, the tire of patent document 1 can form the tread into a curved shape, and can exhibit uneven wear resistance while maintaining steering stability performance.

However, in the studless tire, in order to improve steering stability performance on a dry road surface and the like, if the tread profile of patent document 1 is applied as it is, there is a problem that the on-ice performance is reduced due to a reduction in the ground contact area of the tread portion.

Further, the studless tire is set to have a smaller rigidity in the tread portion than the summer tire. Therefore, in the studless tire to which the profile of patent document 1 is applied, there is also a problem that steering stability performance on a dry road surface is lowered due to a reduction in the ground contact area of the tread portion.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and a main object thereof is to provide a studless tire capable of achieving both on-ice performance and steering stability performance on a dry road surface.

The present invention is a studless tire having a tread portion formed with a plurality of sipes, wherein, in a cross section perpendicular to a circumferential direction, a tread profile from an equatorial plane to a tread end is formed by 3 arcs protruding outward in a radial direction, and an ith arc from the equatorial plane toward an axially outer side among the arcs is defined as C _iThe arc C is formed _iIs set as R _iAt the equatorial planeArc C ₁Is completely axially extended, arc C _i+1And the above circular arc C _iTangent at the intersection of the two, radius R _i+1Less than radius R _iRadius R ₂Relative to radius R ₁Has a ratio of 40% to 70%, and a radius R ₃Relative to the radius R ₁The ratio of (b) is 15% to 30%.

In the studless tire of the present invention, the tire may be formed from the equatorial plane to the arc C ₂And arc C ₃The ratio of the width W23 to the axial width W from the equatorial plane to the tread end is 65% to 75% when the axial width at the intersection point of (a) is W23.

In the studless tire of the present invention, the tire may be formed from the equatorial plane to the arc C ₁And arc C ₂When the axial width at the intersection point of (a) is W12, the ratio of the width W12 to the axial width W from the equatorial plane to the tread end is 35% to 45%.

In the studless tire of the present invention, the rubber hardness of the tread rubber disposed on the tread may be 40 to 65 degrees.

In the studless tire of the present invention, the land ratio of the tread may be 60% to 80%.

In the studless tire of the present invention, a belt layer located radially inward of the tread portion may be further provided, and a ratio of the width Wb to the axial width W may be 90% to 98% where Wb is an axial width from the equatorial plane to an outer end of the belt layer.

In the studless tire of the present invention, the tread portion may include a plurality of main grooves extending in the circumferential direction, and a plurality of land portions defined between the main grooves or between the main grooves and the tread end, and the arc C may be provided ₁And arc C ₂And the arc C ₂And arc C ₃The intersection point of (a) is located at the land portion.

In the studless tire of the present invention, when a virtual line inclined at an inclination angle θ with respect to the axial direction is denoted as Lt, a tangent point at which the virtual line Lt is tangent to the tread surface is denoted as Pt, and an axial width from the equatorial plane to the tangent point Pt is denoted as Wt in a cross section perpendicular to the circumferential direction, a ratio of Wt to an axial width W from the equatorial plane to the tread end at the inclination angle θ of 3 ° may be less than 65%.

Drawings

Fig. 1 is a cross-sectional view showing an example of a studless tire according to the present embodiment.

Fig. 2 is a view showing the outline of the tread of the studless tire of fig. 1 together with the main groove.

Detailed Description

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing an example of a studless tire according to the present embodiment. Fig. 1 shows a cross section perpendicular to the circumferential direction of a studless tire (hereinafter, there is a case of being simply referred to as "tire") 3. In fig. 1, the vertical direction is the radial direction of the tire 3, the horizontal direction is the axial direction of the tire 3, and the direction perpendicular to the paper plane is the circumferential direction of the tire 3. In fig. 1, a chain line CL indicates an equatorial plane of the tire 3. The shape of the tire 3 is symmetrical with respect to the equatorial plane CL except for the tread pattern.

In the present specification, unless otherwise specified, the dimensions and the like of each part of the tire 3 are values measured in a no-load state (normal state) in which the tire 3 is assembled to a normal rim (not shown) and is filled with normal internal pressure.

The "regular Rim" is a Rim that is specified for each tire in a specification system including the specification that the tire conforms to, and means, for example, a standard Rim in case of JATMA, a "Design Rim" in case of TRA, or a "Measuring Rim" in case of ETRTO.

The "normal internal PRESSURE" is an air PRESSURE that defines the above-described specification for each TIRE, and means the maximum air PRESSURE in JATMA, the maximum value in the table "TIRE LOAD conditions AT variatus COLD INFLATION PRESSUREs" in TRA, and the maximum value in the table "INFLATION PRESSURE" in ETRTO ", but 180kPa is formed in the case of a passenger car TIRE.

The tire 3 of the present embodiment includes: a tread portion 4, a sidewall portion 6, a bead filler 8, a bead 10, a carcass 12, a belt 14, a belt layer 18, an inner liner 20, and a chafer 22. The tire 3 is exemplified by a pneumatic tire of a tubeless type, but may be a solid tire. The tire 3 of the present embodiment is exemplified for a car, but is not limited to such an embodiment, and may be a motorcycle tire, a truck tire, or the like.

The tread portion 4 has a radially outwardly convex shape. The tread portion 4 forms a tread surface 34 that contacts the road surface. As shown in the drawing, the tread portion 4 includes a plurality of main grooves 24 extending in the circumferential direction. The main groove 24 contributes to drainage of the tire 3. Although not shown, the tread portion 4 further includes a plurality of sub grooves (not shown) extending in a direction intersecting the main grooves 24. The main groove 24 and the sub groove form a tread pattern. In the illustrated tire 3, the main grooves 24 not shown in the drawings are added together, and the number of the main grooves 24 is 4. The number of main grooves 24 is not limited to 4. The tread portion 4 may have 3 or less main grooves 24, 5 or more main grooves 24, or no main grooves 24. The tread portion 4 may not include a sub groove.

The region sandwiched (divided) by the adjacent main grooves 24 and the region divided between the main groove 24 located at the outermost position in the axial direction and the tread end 28 are referred to as land portions (ribs) 26. In the tire 3 of fig. 1, the number of land portions 26 is 5. When the tire 3 does not have the main groove 24, the region between the 2 tread ends 28 is the land portion 26. At this time, the number of land portions 26 is 1.

The land ratio of the tread 34 can be set appropriately. The land ratio in the present embodiment is set to 60% to 80%. As a result, the tire 3 can secure a large ground contact area, and therefore, responsiveness on a dry road surface and grip on ice can be improved. In the present description, the "land ratio" means a ratio (S/Sa) between the surface area S of the entire land portion 26 in the region between the tread ends 28, 28 and a virtual surface area Sa obtained by filling all the grooves (including the main groove 24 and the sub-grooves (not shown)) in the region between the tread ends 28.

A plurality of sipes (not shown) described in the literature (japanese patent application laid-open No. 2018-08354), for example, are formed on the tread surface 34 of the tread portion 4. The sipe means a cut groove having a width of less than 2 mm. Such sipes can absorb moisture on an ice road surface and increase a frictional force with the ice road surface, thereby contributing to improvement of on-ice performance.

The tread rubber 29 disposed in the tread portion 4 includes a base layer 30 and a top layer 32. The top layer 32 is located radially outward of the base layer 30 and is disposed on the tread 34. The top layer 32 is laminated to the base layer 30.

The rubber hardness of the top layer 32 can be set appropriately. The rubber hardness of the top layer 32 of the present embodiment is set to 40 to 65 degrees. This reduces the rigidity of the tread rubber 29 (top layer 32), and a large ground contact area of the tire 3 can be ensured. Therefore, the tire 3 can improve the frictional force with the road surface, and the on-ice performance can be improved. In the present specification, the "rubber hardness" is a hardness measured by a type A durometer in an environment of 23 ℃ in accordance with JIS-K6253.

The sidewall portions 6 extend substantially radially inward from the end portions of the tread portion 4. The radially outer end of each sidewall portion 6 is joined to the tread portion 4. The sidewall portion 6 is made of a crosslinked rubber excellent in cut resistance and durability. The sidewall portion 6 prevents damage to the carcass 12.

The bead opening 8 is located slightly radially inward of the sidewall portion 6. The bead 8 is located axially outward of the bead 10 and the carcass 12. The lip 8 is made of a crosslinked rubber having excellent abrasion resistance. The rim 8 abuts against a flange (not shown) of the rim.

The bead 10 is located at a position axially inward of the bezel 8. Each bead 10 includes a core portion 36 and an apex 38 extending radially outward from the core portion 36. The core 36 is annular in the circumferential direction of the tire 3. The core 36 contains a wound non-stretch thread. A typical material of the wire is steel. The apex 38 tapers radially outward at its tip. The apex 38 is composed of a crosslinked rubber of high hardness.

The carcass 12 of the present embodiment is exemplified by being constituted by one carcass ply 12a, but may be constituted by 2 or more carcass plies (not shown). The carcass ply 12a is laid between the beads 10 on both sides and along the tread portion 4 and the sidewall portion 6. The carcass ply 12a is folded back from the axially inner side toward the outer side around the core 36. By this folding back, the main portion 40 and the folded back portion 42 are formed in the carcass ply 12 a.

Although not shown, the carcass ply 12a is composed of a plurality of cords and a topping arranged in parallel. The absolute value of the angle formed by each cord with respect to the equatorial plane CL is, for example, 75 ° to 90 °. In other words, the carcass 12 has a radial configuration. The cord of the present embodiment is made of an organic fiber. Preferred organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

The belt layer 14 is located at a position radially inward of the tread portion 4. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt layer 14 of the present embodiment is exemplified by a case where it is composed of a first layer 14a and a second layer 14 b. Although not shown, each of the first layer 14a and the second layer 14b is composed of a plurality of cords and a coating adhesive arranged in parallel. Each cord is inclined with respect to the equatorial plane CL. The absolute value of the inclination angle is, for example, 10 ° or more and 35 ° or less. The cords of the first layer 14a are inclined in the opposite direction with respect to the equatorial plane CL than the cords of the second layer 14 b. The preferred material for the cord is steel. The cord may also use organic fibers.

The belt layer 18 is constituted by at least 1, in the present embodiment, 1 full belt ply covering the entire width of the belt layer 14. The belt layer 18 terminates axially outboard of the outer end of the first layer 14a of the tire. Although not shown, the band layer 18 is composed of a cord and a topping. The cord is spirally wound. The belt layer 18 has a so-called jointless construction. The cords extend substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and more preferably 2 ° or less. The cord is composed of organic fibers. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. Such a band layer 18 can equalize the ground contact pressure over the tire axial direction of the tread portion 4, and therefore, the responsiveness on a dry road surface and the grip on ice can be improved.

The inner liner 20 is positioned inside the carcass 12. The inner liner 20 engages the inner surface of the carcass 12. The inner liner 20 is composed of a crosslinked rubber. The inner liner 20 is made of rubber having excellent air-shielding properties. Typical base rubber for the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 maintains the internal pressure of the tire 3.

The wiper 22 is located in a position near the bead 10. When the tire 3 is assembled to a rim (not shown), the respective wiper pieces 22 abut against the rim. By this contact, the vicinity of the bead 10 is protected. The wiper 22 is composed of a cloth and rubber impregnated in the cloth. The wiping cloth 22 may be formed integrally with the lip 8.

Fig. 2 is a diagram showing the contour 35 of the main groove 24 and the tread surface 34 of the tire 3 of fig. 1. The contour 35 of the tread surface 34 is a contour as an imaginary tread surface obtained in a case where the tread portion 4 has no groove. In the present invention, the dimensions and angles associated with the profile 35 are premised on the cavity surface of the mold. Fig. 2 is the same as fig. 1, and shows a cross section perpendicular to the circumferential direction of the tire 3. In fig. 2, the vertical direction is the radial direction of the tire 3, the horizontal direction is the axial direction of the tire 3, and the direction perpendicular to the paper plane is the circumferential direction of the tire 3. In fig. 2, a chain line CL indicates an equatorial plane of the tire 3.

The contour 35 of the tread surface 34 from the equatorial plane CL to the tread end 28 is formed by a plurality of arcs protruding radially outward. The contour 35 of the present embodiment is formed by 3 circular arcs.

Here, when i is a natural number, the i-th arc from the equatorial plane CL toward the tread end 28 is denoted as C _iArc of a circle C _iIs denoted as R _i. Arc C ₁Is located on the equatorial plane CL. Arc C on equatorial plane CL ₁The tangent of (a) extends completely in the axial direction. Two circular arcs C adjacent to each other _iAnd C _i+1Tangent at their intersection. Radius R _i+1Is a radius R _iThe following.

In the tire 3, when determining the contour 35 of the tread surface 34, the ground contact width of the tire 3 is first determined. The ground contact width is determined, for example, in consideration of the on-ice performance of the tire 3, steering stability performance on a dry road surface, wear resistance performance, and the like. When the ground contact width of the tire 3 is determined, the width, number, and interval of the main grooves 24 are determined. In other words, the number, position, and width of the land portions 26 are determined. This is mainly determined in consideration of drainage, on-snow performance, and the like.

Further, in the tire 3 of the present embodiment, the arc C ₂Radius R of ₂Relative to the circular arc C ₁Radius R of ₁Ratio (R) of ₂/R ₁) Is 40% to 70%, and has a circular arc C ₃Radius R of ₃Relative to the circular arc C ₁Radius R of ₁Ratio (R) of ₃/R ₁) Is set to 15% or more and 30% or less. In the present specification, "ratio" is entirely expressed by "percentage (%)".

Ratio (R) ₂/R ₁) Set to 70% or less, therefore, even in the state of camber angle during turning, the grounding pressure can be prevented from concentrating on the arc C ₂The tread surface 34. In addition, the ratio (R) ₃/R ₁) Is set to 30% or less, and is thus from the arc C ₂To arc C ₃Can be used with a smaller radius R ₃And (4) connecting. Thus, even when the tire 3 is in a state of having a larger camber angle at the time of cornering, the ground contact pressure can be prevented from concentrating on the circular arc C ₃The tread surface 34. Therefore, the tire 3 can make a stable turn on a dry road surface, and steering stability performance on a dry road surface can be improved.

Ratio (R) ₂/R ₁) Is set to 40% or more, and is thus from the arc C ₁To arc C ₂Can be provided with a larger radius R ₂Are gently connected. Thus, the tire 3 of the present embodiment can form the arc C ₁And arc C ₂Uniformly ground. In addition, the ratio (R) ₃/R ₁) Is set to 15% or more, and thus can form the arc C ₂And arc C ₃Uniformly ground. Thus, the tire 3 can prevent a reduction in the ground contact area of the tread portion 4, and therefore can improve responsiveness on a dry road surface and grip on ice.

In this way, the tire 3 of the present embodiment is configured such that the ratio (R) is set ₂/R ₁) And the ratio (R) ₃/R ₁) By satisfying the above range, both the on-ice performance and the steering stability performance on a dry road surface can be achieved.

In addition, if the ratio (R) ₂/R ₁) If the contact angle exceeds 70%, the contact pressure is concentrated on the arc C in the state where the camber angle is attached during turning ₂Leading to a reduction in handling stability performance on dry roads, resulting in uneven wear. On the contrary, if the ratio (R) ₂/R ₁) Less than 40%, the arc C cannot be formed ₁And arc C ₂The tread surface 34 of (a) is uniformly grounded, so that there is a concern that the responsiveness on a dry road surface and the grip on ice are reduced. From such a viewpoint, the ratio (R) ₂/R ₁) Preferably 65% or less, and preferably 45% or more.

In addition, if the ratio (R) ₃/R ₁) If the contact angle exceeds 30%, the contact pressure is concentrated on the arc C in the state where the camber angle is large during turning ₃Leading to a reduction in handling stability performance on dry roads, resulting in uneven wear. On the contrary, if the ratio (R) ₃/R ₁) Less than 15%, the arc C cannot be formed ₂And arc C ₃The tread 34 of (a) is uniformly grounded, so that there is a concern that the responsiveness on a dry road surface and the grip on ice are reduced. From such a viewpoint, the ratio (R) ₃/R ₁) Preferably 27% or less, and more preferably 18% or more.

Arc C ₁Radius R of ₁The radius R of the present embodiment can be set appropriately according to the size of the tire 3 ₁Preferably, the thickness is set to 500mm to 900 mm. Radius R ₁By setting the thickness to 900mm or less, the tread surface 34 can be formed into a shape having an appropriate arc. Thereby the device is provided withThe tire 3 can make a stable turn on a dry road surface, and thus can improve steering stability performance on a dry road surface. On the other hand, the radius R ₁By setting the thickness to 500mm or more, the ground contact area of the tread portion 4 can be prevented from decreasing. Thereby, the tire 3 can improve the responsiveness on a dry road surface and the grip on ice. From such a viewpoint, the radius R ₁Preferably 800mm or less, and preferably 600mm or more.

In fig. 2, a double-headed arrow W indicates an axial width from the equatorial plane CL to the tread end 28. Further, the double-headed arrow W12 is from the equatorial plane CL to the arc C ₁And arc C ₂Axial width up to the intersection point 46. The ratio (W12/W) of the width W12 to the axial width W is preferably set to 35% or more and 45% or less.

By setting the ratio (W12/W) to 45% or less, the tread surface 34 can be formed into a shape with an appropriate arc. As a result, the tire 3 can make a stable turn on a dry road surface, and steering stability performance on a dry road surface can be improved. On the other hand, by setting the ratio (W12/W) to 35% or more, the arc C can be formed ₁And arc C ₂Uniformly ground. Thus, the tire 3 can prevent a reduction in the ground contact area of the tread portion 4, and therefore can improve responsiveness on a dry road surface and grip on ice. From such a viewpoint, the ratio (W12/W) is more preferably 42% or less, and still more preferably 38% or more.

In FIG. 2, the double-headed arrow W23 is from the equatorial plane CL to the arc C ₂And arc C ₃Axial width up to the intersection point 48. The ratio (W23/W) of the width W23 to the axial width W is preferably set to 65% to 75%.

The ratio (W23/W) is set to 75% or less, thereby preventing the ground contact pressure from concentrating on the arc C even in a state where a large camber angle is imparted during cornering ₃The tread surface 34. Therefore, the tire 3 can make a stable turn on a dry road surface, and steering stability performance on a dry road surface can be improved. On the other hand, the ratio (W23/W) is set to 65% or more, whereby the ratio can be set toMake into a circular arc C ₂And arc C ₃Uniformly ground. Thus, the tire 3 can prevent a reduction in the ground contact area of the tread portion 4, and therefore can improve responsiveness on a dry road surface and grip on ice. From such a viewpoint, the ratio (W23/W) is more preferably 73% or less, and still more preferably 67% or more.

Arc C ₁And arc C ₂Intersection point 46 and arc C ₂And arc C ₃Preferably at the land portion 26. This is because, when the intersections 46, 48 are arranged at the positions of the main groove 24, arcs (i.e., arcs C) on both sides of the intersections 46, 48 are formed ₁、C ₂、C ₃) The difference in curvature of (3) tends to cause a curvature of the tread surface 34 (a warp of the tread portion 4). In the present embodiment, by locating the intersections 46, 48 at the land portions 26, it is possible to prevent the tread surface 34 from being curved, and thus to prevent the ground contact pressure from becoming uneven. Thereby, the tire 3 can improve the responsiveness on a dry road surface and the grip on ice.

In fig. 2, a straight line Lt is an imaginary line having an inclination angle θ with respect to the axial direction. The imaginary line Lt is inclined from the axially inner side toward the outwardly side to the radially inner side. The point Pt is a tangent point when the imaginary line Lt is tangent to the contour 35 of the tread surface 34. The double-headed arrow Wt indicates the axial width from the equatorial plane CL to the tangent point Pt. The width Wt varies depending on the value of the inclination angle θ. Under the same profile 35, the greater the inclination angle θ, the greater the width Wt.

The ratio (Wt/W) of the width Wt to the axial width W at the inclination angle θ of 3 ° is preferably set to 65% or less. By setting the ratio (Wt/W) at the inclination angle θ of 3 ° to 65% or less, it is possible to prevent the ground contact pressure from concentrating on the arc C even in a state where a large camber angle is attached during cornering ₃The tread surface 34. Therefore, the tire 3 can make a stable turn on a dry road surface, and steering stability performance on a dry road surface and grip on ice can be improved.

In fig. 1, a double-headed arrow W indicates an axial width from the equatorial plane CL to the tread end 28. This is the same as the axial width W of fig. 2. The double-headed arrow Wb indicates an axial width from the equatorial plane CL to the outer end of the belt layer 14 (first layer 14 a). The ratio (Wb/W) of the width Wb to the axial width W is preferably set to 90% or more and 98% or less.

By setting the ratio (Wb/W) to 98% or less, it is possible to suppress the rigidity on the tread end 28 side from becoming excessively large. This suppresses the ground contact pressure on the tread end 28 side of the tire 3 to an appropriate level, and thus improves uneven wear resistance. On the other hand, by setting the ratio (Wb/W) to 90% or more, the rigidity of the tread end 28 side is maintained to be appropriate. Thereby, the tire 3 can make a stable turn on a dry road surface. From such a viewpoint, the ratio (Wb/W) is preferably 92% or more.

While the above description has been made of the particularly preferred embodiment of the present invention, the present invention is not limited to the illustrated embodiment, and can be modified into various embodiments.