Studdable tire

Abstract

To provide a studdable tire that can suppress steering stability performance from deteriorating, while maintaining detachment resistance performance.SOLUTION: In a studdable tire 1, a tread part 2 includes a crown region Cr and a pair of shoulder regions Sh. The tread part 2 includes a tread rubber 8 including a base layer 10. The total number of holes 3 formed in the shoulder regions Sh are more than the total number of holes 3 formed in the crown regions Sh. The hole 3 has a bottom part 12 for holding an inner end in a tire radial direction of a stud 50. The bottom part 12 of the hole 3 is positioned at the base layer 10. The base layer 10 includes a crown base part 10A arranged in the crown region Cr and shoulder base parts 10B arranged in the shoulder regions Sh. Rubber hardness of the shoulder base parts 10B is larger than rubber hardness of the crown base part 10A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a studdable tire. [Background technology]

[0002] Patent Document 1 below describes a studdable tire that exhibits excellent driving performance on ice. The tread of the studdable tire has a number of holes formed therein for mounting a number of studs to provide high friction with the road surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-131975 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, studdable tires are used as studded tires in which the studs are fitted into the holes, or as studless tires in which the studs are not fitted into the holes. When used as a studded tire, it is considered to provide more holes and studs in the shoulder region of the tread, where the ground pressure is relatively low, in order to prevent the studs from falling out during driving. However, when such studdable tires are used as studless tires, there is a problem in that the handling stability is significantly reduced.

[0005] The present invention was devised in consideration of the above-described circumstances, and its main object is to provide a studdable tire that can maintain stud loss resistance when used as a studless tire, while suppressing a decrease in steering stability when used as a studless tire. [Means for solving the problem]

[0006] The present invention is a studdable tire having a tread portion provided with a plurality of holes for mounting a plurality of studs, the tread portion including a crown region including the tire equator and a pair of shoulder regions including each tread edge, the total number of holes formed in each of the pair of shoulder regions is greater than the total number of holes formed in the crown region, each of the holes has a bottom for holding the inner ends of the studs in the tire radial direction, the tread portion includes tread rubber including a cap layer forming a contact surface and a base layer arranged radially inward of the cap layer, the bottoms of each of the holes are located in the base layer, the base layer includes a crown base portion arranged in the crown region and a shoulder base portion arranged in the shoulder region, the rubber hardness of the shoulder base portion is greater than the rubber hardness of the crown base portion. [Effects of the Invention]

[0007] By adopting the above-described configuration, the present invention can improve the resistance to slip-out and the steering stability. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a development view of a tread portion showing one embodiment of the present invention. [Figure 2] FIG. 2 is a tire meridian cross-sectional view of the tire of FIG. 1. [Figure 3] 1. (A) is a cross-sectional view taken along line AA in FIG. 1, and (B) is a cross-sectional view taken along line BB in FIG. [Figure 4] (A) is a perspective view of a first stud, and (B) is a perspective view of a second stud. [Figure 5] FIG. 1A is a plan view of a first stud, and FIG. 1B is a side view of the first stud. [Figure 6] (A) is a plan view of the second stud, and (B) is a side view of the second stud. [Figure 7]FIG. 1A is a vertical cross-sectional view showing a state in which a first stud is fitted into a first hole, and FIG. 1B is a vertical cross-sectional view showing a state in which a second stud is fitted into a second hole. [Figure 8] 1 shows a pair of tread half profiles in a tire meridian cross section in a normal state. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described with reference to the drawings. The drawings include exaggerated representations and representations different from the dimensional ratios of the actual structures to facilitate understanding of the present invention. Furthermore, when there are multiple embodiments, the same or common elements are designated by the same reference numerals throughout the specification, and redundant explanations will be omitted.

[0010] FIG. 1 is a development view of the tread portion 2 of a studdable tire (hereinafter sometimes simply referred to as "tire") 1 according to one embodiment of the present invention. The tire 1 may be used as a studded tire with a plurality of studs 50 (shown in FIGS. 4 to 6) attached to the tread portion 2, or as a studless tire without the plurality of studs 50. The studs 50 are made of a harder material than the tread portion 2 made of rubber, and some of them can come into contact with the ground during driving. Therefore, when used as a studded tire, the studs 50 are required to provide high friction by penetrating into icy road surfaces, thereby exhibiting excellent performance on ice.

[0011] As shown in FIG. 1 , the tread portion 2 is provided with a plurality of holes 3 for receiving a plurality of studs 50. The tread portion 2 also includes a crown region Cr including the tire equator C and a pair of shoulder regions Sh including each tread edge Te. In the case of a pneumatic tire, the tread edge Te is identified as the axially outermost contact point of the tire when the tire 1 in a normal state is placed on the ground flat with a normal load and a camber angle of 0°. The "normal state" refers to a state in which the tire 1 is mounted on a normal rim (not shown), inflated to the normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are indicated by values ​​measured in the normal state.

[0012] A "genuine rim" is a rim that is defined for each tire by a standard system that includes the standard on which tire 1 is based. Therefore, a genuine rim is, for example, a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.

[0013] The "normal internal pressure" is the air pressure determined for each tire by each standard in a standard system including the standard on which the tire 1 is based. Therefore, the normal internal pressure is, for example, the "maximum air pressure" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

[0014] The "normal load" is the load determined for each tire by each standard in the standard system including the standard on which the tire 1 is based. Therefore, the normal load is, for example, "maximum load capacity" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO.

[0015] In this embodiment, the total number As of holes 3 formed in each of the pair of shoulder regions Sh is greater than the total number Ac of holes 3 formed in the crown region Cr. Generally, the shoulder regions Sh have a relatively lower ground pressure than the crown region Cr, and therefore the external force acting on the studs 50 attached to the shoulder regions Sh is reduced. Therefore, arranging more studs 50 in the shoulder regions Sh can prevent the studs 50 from coming out of the holes 3.

[0016] Fig. 2 is a tire meridian cross-sectional view of the tire 1 in a normal state, including the tire rotation axis (not shown). As shown in Fig. 2, a tread rubber 8 is disposed in the tread portion 2. The tread rubber 8 includes a cap layer 9 that forms the contact patch 2s and a base layer 10 disposed radially inward of the cap layer 9. The base layer 10 also includes a crown base portion 10A disposed in the crown region Cr and a shoulder base portion 10B disposed in the shoulder region Sh.

[0017] Each of the holes 3 has a bottom 4 for holding an inner end 50e (shown in FIGS. 5 and 6) of a stud 50 in the tire radial direction. The bottom 4 of each of the holes 3 is located in the base layer 10. As a result, when used as a studded tire, the inner end 50e of each stud 50 is held in the base layer 10.

[0018] When used as a studless tire, the holes 3 reduce the rigidity of the tread portion 2, raising concerns about reduced rigidity in the shoulder regions Sh, where the total number As of the holes 3 is large. Therefore, in this embodiment, the rubber hardness Hs of the shoulder base portions 10B is made greater than the rubber hardness Hr of the crown base portion 10A. This prevents the reduction in rigidity of the shoulder regions Sh due to the holes 3, and ultimately prevents a reduction in steering stability. In this specification, the rubber hardness refers to a durometer A hardness measured at 23°C using a durometer type A in accordance with JIS-K6253.

[0019] The rubber hardness Hs of the shoulder base portion 10B is preferably 60 degrees or more, more preferably 62 degrees or more, and preferably 70 degrees or less, and even more preferably 68 degrees or less. Similarly, the rubber hardness Hr of the crown base portion is preferably 50 degrees or more, more preferably 52 degrees or more, and preferably less than 60 degrees, and even more preferably 58 degrees or less. This allows the tire to maintain steering stability when used as a studless tire while suppressing a decrease in resistance to slipping out when used as a studded tire. It also reduces the chance of the studs 50 being mis-driven into the tire 1, improving ease of installation (resistance to mis-driven studs).

[0020] The rubber hardness Hc of the cap layer 9 is preferably 45 degrees or more, more preferably 50 degrees or more, and preferably 65 degrees or less, and even more preferably 60 degrees or less. Because the rubber hardness Hc is 45 degrees or more, the cap layer 9 can also prevent the studs 50 from coming out and maintain high steering stability. Because the rubber hardness Hc is 65 degrees or less, the ease of attaching the studs 50 to the tire 1 can be maintained.

[0021] The thickness d2 of the base layer 10 is preferably 50% or more of the thickness d1 of the tread rubber 8, more preferably 52% or more, more preferably 60% or less, and even more preferably 58% or less. Because the thickness d2 of the base layer 10 is 50% or more of the thickness d1 of the tread rubber 8, the rigidity of the shoulder region Sh can be increased, and high steering stability can be maintained. Because the thickness d2 of the base layer 10 is 60% or less of the thickness d1 of the tread rubber 8, the depth at which the studs 50 are embedded in the tread rubber 8 is ensured, and pull-out resistance is improved. In this specification, the thickness d1 of the tread rubber 8 and the thickness d2 of the base layer 10 are calculated as the average values ​​of the maximum and minimum thicknesses between the tread ends Te on both sides.

[0022] 1, the tread portion 2 of this embodiment is designated with a tire rotation direction R. The tire rotation direction R is indicated, for example, on a sidewall portion (not shown) of the tire 1. Note that the tire rotation direction R does not necessarily have to be designated for the tread portion 2.

[0023] The tread portion 2 includes, for example, a first tread portion 2A between the tire equator C and one tread edge Te (left side in the figure), and a second tread portion 2B between the tire equator C and the other tread edge Te (right side in the figure). The first tread portion 2A and the second tread portion 2B are configured to be substantially line-symmetrical, except that they are misaligned in the tire circumferential direction. The tread portion 2 is not limited to the tread pattern shown in the figure, and various tread patterns can be adopted.

[0024] In this embodiment, the tread portion 2 includes a plurality of inclined grooves 40 inclined with respect to the tire axial direction and a plurality of blocks 41 separated by the inclined grooves 40. Each block 41 is provided with a plurality of sipes 42. When used as a studless tire, the tire 1 is required to exhibit high performance on snow and ice and excellent steering stability on dry and wet roads. The blocks 41 include a plurality of first blocks 41A each having a hole 3 and a plurality of second blocks 41B each having no hole 3. In this embodiment, each first block 41A has one hole 3. In this specification, a sipe means a cut having a width of less than 1.5 mm and is clearly distinguished from a groove including an inclined groove 40 having a groove width of 1.5 mm or more.

[0025] In this embodiment, the tread portion 2 includes a middle region Mi disposed between the crown region Cr and the shoulder regions Sh. The middle regions Mi are disposed on both sides of the tire equator C. The middle regions Mi have a relatively lower ground contact pressure than the crown region Cr and a relatively higher ground contact pressure than the shoulder regions Sh. Therefore, by setting the total number Am of holes 3 formed in the middle regions Mi to be equal to or greater than the total number Ac of holes 3 formed in the crown region Cr and equal to or less than the total number As of holes 3 formed in the shoulder regions Sh, it is possible to further prevent the studs 50 from falling out of the holes 3. To improve the resistance to falling out, it is desirable that the total number Am of holes 3 formed in the middle regions Mi be greater than the total number Ac of holes 3 formed in the crown region Cr and less than the total number As of holes 3 formed in the shoulder regions Sh.

[0026] As shown in Figure 2, the bottoms 4 of the holes 3 formed in the middle region Mi are preferably located in the crown base portion 10A. The crown base portion 10A has a relatively low rubber hardness Hr, which makes it easier to insert studs 50 into the holes 3 formed in the middle region Mi, and maintains high resistance to impact damage.

[0027] Between the tire equator C and the tread edge Te, the axial length Lc of the crown region Cr, the axial length Lm of the middle region Mi, and the axial length Ls of the shoulder region Sh are 30%, 30%, and 40% of the tread half width Wt, respectively. The tread half width Wt is the axial length between the tire equator C and the tread edge Te. In this embodiment, the length Lc of the crown region Cr, the length Lm of the middle region Mi, and the length Ls of the shoulder region Sh are the same in the first tread portion 2A and the second tread portion 2B.

[0028] Between the tire equator C and the tread edge Te, the total number Ac of holes 3 formed in the crown region Cr is preferably 15% or more of the total number A of all holes 3, more preferably 17% or more, more preferably 25% or less, and even more preferably 23% or less. The total number Am of holes 3 formed in the middle region Mi is preferably 30% or more of the total number A, more preferably 32% or more, more preferably 40% or less, and even more preferably 38% or less. The total number As of holes 3 formed in the shoulder region Sh is preferably 40% or more of the total number A, more preferably 42% or more, more preferably 50% or less, and even more preferably 48% or less. By limiting the total number of holes 3 formed in the crown region Cr, middle region Mi, and shoulder region Sh in this manner, high levels of slippage resistance, steering stability, and impact resistance can be maintained. The total number of holes 3 throughout the tire 1 is preferably 150 to 250. When used as a studded tire, for example, a stud 50 is attached to each of the holes 3. In this embodiment, the total number A is the sum of the total number Ac, the total number Am, and the total number As.

[0029] As shown in Fig. 1, the holes 3 are, for example, circular openings in a plan view of the tread portion 2. In this embodiment, the holes 3 extend parallel to the normal direction of the contact patch 2s (as shown in Fig. 2). Note that the holes 3 may also extend parallel to the tire radial direction.

[0030] The holes 3 include a plurality of first holes 3A formed in the crown region Cr and a plurality of second holes 3B formed in each of the pair of shoulder regions Sh. The first holes 3A are also formed in, for example, the middle region Mi.

[0031] FIG. 3(A) is a cross-sectional view taken along line AA in FIG. 1, showing a longitudinal section of the first hole 3A. FIG. 3(B) is a cross-sectional view taken along line BB in FIG. 1, showing a longitudinal section of the second hole 3B. FIGS. 3(A) and 3(B) are cross-sections parallel to the tire circumferential direction, with the studs 50 attached to each hole 3 shown in phantom lines. As shown in FIGS. 3(A) and 3(B), the inner diameter of each hole 3A, 3B is smaller than the outer diameter of the stud 50 over almost the entirety. Each hole 3A, 3B also includes a bottom portion 4 and a raised portion 5 extending radially outward from the bottom portion 4. In this embodiment, the raised portion 5 includes an inner portion 5a connected to the bottom portion 4 and having a smaller inner diameter than the bottom portion 4, and an outer portion 5b connected to the ground contact patch 2s and having a larger inner diameter than the inner portion 5a.

[0032] The circumferential length Lb of the bottom 4b of the second hole 3B is greater than the circumferential length La of the bottom 4a of the first hole 3A. In this way, the first hole 3A and the second hole 3B are formed, for example, so that the circumferential lengths (shapes) of the bottoms 4a, 4b are different. Note that the circumferential length (shape) of the raised portion 5B of the second hole 3B is the same as that of the raised portion 5A of the first hole 3A.

[0033] Furthermore, the first holes 3A are arranged, for example, in the same position as the tire circumferential center line 5c1 of the raised portion 5A and the tire circumferential center line 4c1 of the bottom portion 4a so that they form a single straight line. Furthermore, the second holes 3B are arranged, for example, in a position where the tire circumferential center line 5c2 of the raised portion 5B and the tire circumferential center line 4c2 of the bottom portion 4b are different. In this embodiment, the second holes 3B have the center line 4c2 of the bottom portion 4b positioned further rearward in the tire rotation direction R than the center line 5c2 of the raised portion 5B. Although not particularly limited, the tire circumferential distance Ld between the center line 5c2 of the raised portion 5B and the center line 4c2 of the bottom portion 4b in the second holes 3B is set to 2.0 to 3.0 mm.

[0034] Next, the stud 50 will be described. Figure 4(A) is a perspective view of the stud 50 to be attached to the first hole 3A, and Figure 4(B) is a perspective view of the stud 50 to be attached to the second hole 3B. Thus, the stud 50 includes a first stud 50A to be attached to the first hole 3A and a second stud 50B to be attached to the second hole 3B.

[0035] 4(A) and 4(B), each stud 50A, 50B includes an embedded portion 51 and a pin portion 52. When the stud 50 is attached to the hole 3, the embedded portion 51 is embedded in the block 41, and the pin portion 52 is exposed from the block 41.

[0036] The embedded portion 51 includes an inner flange 53 that is held by the bottom portion 4, and a body 54 that connects to the inner flange 53. In this embodiment, the body 54 is held by the raised portion 5 of the hole 3. The body 54 includes, for example, an outer flange 55 that has a mounting surface 55a on which the pin portion 52 is placed, and a neck 56 that connects the outer flange 55 and the inner flange 53 and has an outer diameter smaller than that of the outer flange 55 and the inner flange 53. The pin portion 52A and body 54A of the first stud 50A have the same shape as, for example, the pin portion 52B and body 54B of the second stud 50B. The mounting surface 55a may be exposed to the ground surface 2s (shown in FIG. 3).

[0037] FIG. 5(A) is a plan view of the first stud 50A, and FIG. 5(B) is a side view of the first stud 50A. FIG. 6(A) is a plan view of the second stud 50B, and FIG. 6(B) is a side view of the second stud 50B. As shown in FIGS. 4 to 6, the outer flange 55 and neck 56 of this embodiment are each formed in a cylindrical (axial) shape. In this embodiment, the outer flange 55 and neck 56 are circular in plan view. Here, the circular shape includes not only a perfect circle or ellipse for the outer edge 55e of the outer flange 55 and the outer edge 56e of the neck 56, but also a shape in which the outer edges 55e, 56e are cut out by multiple arcs. The outer flange 55 and neck 56 are not limited to being circular, but may also be polygonal, such as a triangular, pentagonal, or hexagonal shape.

[0038] In this embodiment, in a plan view, the centroids of the outer flange 55 and the neck 56 of each of the bodies 54 of the studs 50A, 50B are located at the same position. As a result, the centroid of the outer flange 55 is defined as the centroid c1 of the body 54. In this specification, the linear axis that passes through the centroid c1 and extends in the longitudinal direction of the body 54 is defined as the longitudinal axis Z. Note that the shape of the body 54 is not limited to this cylindrical shape.

[0039] The inner flange 53A of the first stud 50A has a different shape from the inner flange 53B of the second stud 50B, for example. The inner flange 53A of the first stud 50A is formed as, for example, a circular base 58 centered on the longitudinal axis Z in plan view. The inner flange 53B of the second stud 50B includes, for example, a circular base 58 centered on the longitudinal axis Z in plan view, and a protrusion 59 connected to the base 58 and protruding away from the longitudinal axis Z. Both the base 58 of the first stud 50A and the base 58 of the second stud 50B include recesses 60 recessed toward the longitudinal axis Z. For example, three recesses 60 are provided for each base 58.

[0040] The protruding portion 59 of the second stud 50B has, for example, recessed portions 60 adjacent to both sides thereof, and includes a pair of long edges 59a extending parallel to and away from the longitudinal axis Z, and an arc-shaped edge 59b connecting the outer ends of the long edges 59a and convex in a direction away from the longitudinal axis Z. The linear axis connecting the midpoint 59c of the arc-shaped edge 59b to the longitudinal axis Z is defined as the lateral axis Y. In this embodiment, each long edge 59a is parallel to the lateral axis Y.

[0041] The inner flange 53 and the outer flange 55 have chamfered surfaces 62. The chamfered surfaces 62 form sharp knife edges that bite into the tread rubber 8 around the studs 50, improving the holding power of the studs 50. The chamfered surfaces 62 are formed, for example, by cutting out the inner flange 53 and the outer flange 55 so as to be inclined relative to the longitudinal axis Z.

[0042] The pins 52 are relatively small protrusions that protrude in the direction of the longitudinal axis Z from the mounting surface 55a of the body 54. The pins 52 mainly come into contact with the road surface, thereby providing high friction with the road surface. Various shapes can be adopted for the pins 52.

[0043] The pin portion 52 of this embodiment is formed in a substantially E-shape in plan view. The pin portion 52 is formed by a first portion 63 forming a convex arc 65 on one side and a second portion 64 connecting both ends of the first portion 63 and extending in a wave-like manner. In the second stud 50B, the convex direction (projection direction) of the first portion 63 extends in the same direction as the horizontal axis Y. The second portion 64 is formed, for example, in a three-wavelength shape with substantially the same amplitude. In the second stud 50B, the amplitude direction of the second portion 64 is, for example, the same direction as the horizontal axis Y. Note that in the first stud 50A, a linear axis passing through the center of the first portion 63 and the longitudinal axis Z is defined as the horizontal axis Y. The shape of the pin portion 52 is not limited to this example.

[0044] In this embodiment, each of the first stud 50A and the second stud 50B has a line-symmetric shape with respect to the transverse axis Y. However, each of the first stud 50A and the second stud 50B may have a non-line-symmetric shape with respect to the transverse axis Y.

[0045] The studs 50 are not particularly limited as long as they are made of a material harder than rubber, but are preferably made of a metal material. In another embodiment, the studs 50 may be made of a resin or rubber material that is harder than the tread rubber 8, particularly the base layer 10. Furthermore, the embedded portion 51 and the pin portion 52 of the studs 50 may be made of different materials, for example.

[0046] Next, the state in which the studs 50 are installed in the holes 3 (shown in FIG. 1) will be described. FIG. 7(A) is a longitudinal cross-sectional view showing the first stud 50A installed in the first hole 3A, and FIG. 7(B) is a longitudinal cross-sectional view showing the second stud 50B installed in the second hole 3B. FIG. 7 is a cross-section parallel to the tire circumferential direction. As shown in FIG. 7, in this embodiment, the entire inner flange 53 is held in the base layer 10. This improves the pull-out resistance of each stud 50A, 50B.

[0047] When each stud 50 is installed in each hole 3, each inner flange 53 includes a leading portion 68 arranged on the leading side of the centroid c1 (longitudinal axis Z) of the body 54 in the tire rotation direction R, and a trailing portion 69 arranged on the trailing side of the centroid c1 in the tire rotation direction R.

[0048] It is desirable that the tire circumferential length L4 of the trailing portion 69B of each second stud 50B be greater than the tire circumferential length L3 of the leading portion 68B. In other words, it is desirable that the protruding portion 59 be located rearward in the tire rotational direction R from the longitudinal axis Z. This prevents the protruding portion 59 from deforming or moving overall of the second stud 50B when driving on ice, improving its resistance to slip-out. In this embodiment, the second studs 50B are arranged such that the lateral axis Y is parallel to the tire circumferential direction. Furthermore, the midpoint 59c of the arcuate edge 59b of each second stud 50B is located rearward-most in the tire rotational direction R. It is also desirable that the tire circumferential length L1 of the leading portion 68A of each first stud 50A is substantially the same as the tire circumferential length L2 of the trailing portion 69A.

[0049] Although not particularly limited, the tire circumferential length L4 of the trailing portion 69B is preferably at least 1.5 times the tire circumferential length L3 of the leading portion 68B, more preferably at least 1.7 times, and more preferably at most 2.1 times, and even more preferably at most 1.9 times.

[0050] The first studs 50A and second studs 50B are installed so that the first portion 63 of the pin portion 52 is located further back in the tire rotation direction R than the second portion 64. This improves the studs' performance on ice. The studs 50 are installed in the holes 3 by well-known methods, and the studs 50 are fixed in place by the elastic deformation of the tread rubber 8.

[0051] Fig. 8 shows each of a pair of tread half profiles Tp. The pair of tread half profiles Tp is the shape of the contact patch 2s (excluding grooves and holes 3) of the tread portion 2 extending from the tire equator C toward each tread edge Te in a tire meridian cross section in a normal state. As shown in Fig. 8, in this embodiment, each tread half profile Tp has an axisymmetric shape with the tire equator C as the axis of axis symmetry.

[0052] The tread half profile Tp includes a first arc T1 extending axially outward from the tire equator C, a second arc T2 connected to the first arc T1 and extending axially outward, and a third arc T3 connecting the second arc T2 and the tread edge Te. The tread half profile Tp also includes a first connection point P1 connecting the first arc T1 and the second arc T2, and a second connection point P2 connecting the second arc T2 and the third arc T3. The curvature radius R1 of the first arc T1 is, for example, preferably 500 mm or more, more preferably 600 mm or more, and more preferably 1400 mm or less, and even more preferably 1300 mm or less.

[0053] The radius of curvature R2 of the second circular arc T2 is preferably 50% to 54% of the radius of curvature R1 of the first circular arc T1. The radius of curvature R3 of the third circular arc T3 is preferably 20% to 24% of the radius of curvature R1 of the first circular arc T1. Furthermore, the axial length Le from the tire equator C to the first connection point P1 is preferably 37% to 47% of the tread half width Wt. The axial length Lf from the tire equator C to the second connection point P2 is preferably 65% ​​to 75% of the tread half width Wt. Such a tread half profile Tp uniforms the ground contact pressure from the tire equator C to the tread edge Te, thereby improving the impact resistance of a studless tire while suppressing a decrease in steering stability.

[0054] In such a tire 1, the land ratio Lr of the tread portion 2 is preferably, for example, 55% to 70%. This improves steering stability on dry roads and snow performance in a well-balanced manner. In this specification, the "land ratio" refers to the ratio Sb / Sa of the actual total contact area Sb to the total area Sa of the virtual contact area in which all grooves, sipes, and holes 3 are filled.

[0055] Although a tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and practiced in various aspects. [Example]

[0056] Using tires with the basic pattern shown in Figure 1 and the basic structure shown in Figure 2, the tires were tested for handling stability on dry and wet roads as studless tires, as well as for performance on ice and resistance to breakage as studless tires. Furthermore, the tires were tested for resistance to breakage when studs are attached to them. The test method and common specifications are shown below. Tire size: 205 / 55R16 Rim size: 16 x 6.6 Internal pressure: 240kPa (front wheels), 220kPa (rear wheels) Land ratio: 64% Tread half width Wt: 86mm Cap layer rubber hardness: 55 degrees R1: 774mm Number of holes: 200 per tire

[0057] <Ice performance, slippage resistance, handling stability on dry and wet roads> For ice performance, the traction and braking performance when the test vehicle was driven on ice were evaluated by the driver's sense of touch. For slip-out resistance, the driver evaluated the degree to which the studs had slipped out after driving on ice. For handling stability on dry and wet roads (handling stability), the driver evaluated the operability and stability when the test vehicle was driven on asphalt roads in both dry and wet conditions. All results were expressed on a scale of 10, with higher scores indicating better performance.

[0058] <Hit resistance> The number of missed studs was measured when the studs shown in Figures 4 to 6 were fitted to studless tires. The results are shown as a percentage of the number of missed studs when studs were driven into 20 tires. The smaller the number, the better.

[0059] [Table 1]

[0060] The test results are shown in Table 1. As shown in Table 1, the tires of the examples have improved steering stability and slippage resistance compared to the tires of the comparative examples.

[0061] [Note] The present invention includes the following aspects.

[0062] [Invention 1] A studdable tire having a plurality of holes in the tread portion for mounting a plurality of studs, The tread portion includes a crown region including a tire equator and a pair of shoulder regions including respective tread edges, a total number of the holes formed in each of the pair of shoulder regions is greater than a total number of the holes formed in the crown region; each of the holes having a bottom for holding a radially inner end of the stud; the tread portion includes a tread rubber including a cap layer that forms a contact surface and a base layer disposed radially inward of the cap layer, the bottom of each of the holes is located in the base layer; the base layer includes a crown base portion disposed in the crown region and a shoulder base portion disposed in the shoulder region, The rubber hardness of the shoulder base portion is greater than the rubber hardness of the crown base portion. Studdable tires. [Invention 2] The rubber hardness of the crown base portion is equal to or greater than 50 degrees and less than 60 degrees, The studdable tire according to invention 1, wherein the shoulder base portion has a rubber hardness of 60 to 70 degrees. [Invention 3] 3. The studable tire according to claim 1 or 2, wherein the rubber hardness of the cap layer is 45 to 65 degrees. [Invention 4] 4. The studdable tire according to any one of inventions 1 to 3, wherein the thickness of the base layer is 50% to 60% of the thickness of the tread rubber. [Invention 5] A studdable tire according to any one of the first to fourth aspects of the present invention, wherein the length in the tire circumferential direction of the bottom of the hole formed in each of the pair of shoulder regions is greater than the length in the tire circumferential direction of the bottom of the hole formed in the crown region. [Invention 6] the tread portion includes a middle region disposed between the crown region and the shoulder region, A studdable tire according to any one of the first to fifth aspects of the present invention, wherein the total number of holes formed in the middle region is greater than the total number of holes formed in the crown region and less than the total number of holes formed in the shoulder region. [Invention 7] A studdable tire according to invention 6, wherein the bottom of the hole formed in the middle region is located in the crown base portion. [Invention 8] Between the tire equator and the tread edge, The tire axial length of the crown region is 30% of the tread half width, The axial length of the middle region is 30% of the tread half width, The axial length of the shoulder region is 40% of the tread half width, the total number of the holes formed in the crown region is 15% to 25% of the total number A of all holes, the total number of the holes formed in the middle region is 30% to 40% of the total number A; 8. The studdable tire according to invention 6 or 7, wherein the total number of the holes formed in the shoulder region is 40% to 50% of the total number A. [Invention 9] In a tire meridian cross section in a normal state, the tread portion includes a tread half profile extending from the tire equator toward each of the tread ends, The tread half profile includes a first arc extending axially outward from the tire equator, a second arc connected to the first arc and extending axially outward, and a third arc connected to the second arc and the tread edge, The radius of curvature of the second arc is 50% to 54% of the radius of curvature of the first arc, 9. The studdable tire according to any one of inventions 1 to 8, wherein the radius of curvature of the third arc is 20% to 24% of the radius of curvature of the first arc. [Invention 10] a length in the tire axial direction from the tire equator to a first connection point where the first arc and the second arc are connected is 37% to 47% of a half tread width; 10. The studdable tire according to invention 9, wherein the length in the tire axial direction from the tire equator to a second connection point where the second arc and the third arc are connected is 65% to 75% of the tread half width. [Invention 11] The tread portion has a designated tire rotation direction, the plurality of studs include a plurality of first studs fitted in the holes formed in the crown region and a plurality of second studs fitted in the holes formed in the shoulder region, With the studs attached to the holes, Each of the plurality of studs includes an inner flange held at the bottom portion and a body extending radially outward from the inner flange, In a plan view of the tread portion, each of the inner flanges of the plurality of studs includes a leading portion disposed on a leading side of the centroid of the body in the tire rotation direction, and a trailing portion disposed on a trailing side of the centroid of the body in the tire rotation direction, The length of the leading portion of each first stud in the tire circumferential direction is the same as the length of the trailing portion of each first stud in the tire circumferential direction, 11. A studdable tire according to any one of inventions 1 to 10, wherein the length of the trailing portion of each second stud in the tire circumferential direction is greater than the length of the leading portion in the tire circumferential direction. [Explanation of symbols]

[0063] 1 Studdable tire 2 Tread section 8 Tread rubber 10 Base Layer 10A Crown base 10B Shoulder base 3 holes 4 Bottom 50 studs Cr Crown region Sh Shoulder region

Claims

1. A studdable tire having a plurality of holes in the tread portion for mounting a plurality of studs, The tread portion includes a crown region including a tire equator and a pair of shoulder regions including respective tread edges, a total number of the holes formed in each of the pair of shoulder regions is greater than a total number of the holes formed in the crown region; each of the holes having a bottom for holding a radially inner end of the stud; the tread portion includes a tread rubber including a cap layer that forms a contact surface and a base layer disposed radially inward of the cap layer, the bottom of each of the holes is located in the base layer; the base layer includes a crown base portion disposed in the crown region and a shoulder base portion disposed in the shoulder region, The rubber hardness of the shoulder base portion is greater than the rubber hardness of the crown base portion. Studdable tires.

2. the rubber hardness of the crown base portion is equal to or greater than 50 degrees and less than 60 degrees; 2. The studdable tire according to claim 1, wherein the shoulder base portion has a rubber hardness of 60 to 70 degrees.

3. 3. The studdable tire according to claim 2, wherein the rubber hardness of the cap layer is 45 to 65 degrees.

4. 2. The studdable tire according to claim 1, wherein the thickness of the base layer is 50% to 60% of the thickness of the tread rubber.

5. 5. The studdable tire according to claim 1, wherein a length in the tire circumferential direction of the bottom of the hole formed in each of the pair of shoulder regions is greater than a length in the tire circumferential direction of the bottom of the hole formed in the crown region.

6. the tread portion includes a middle region disposed between the crown region and the shoulder region, 5. The studdable tire according to claim 1, wherein the total number of holes formed in the middle region is greater than the total number of holes formed in the crown region and less than the total number of holes formed in the shoulder regions.

7. 7. The studdable tire according to claim 6, wherein the bottom of the hole formed in the middle region is located in the crown base portion.

8. Between the tire equator and the tread edge, The axial length of the crown region is 30% of the tread half width, The axial length of the middle region is 30% of the half width of the tread, The axial length of the shoulder region is 40% of the tread half width, the total number of the holes formed in the crown region is 15% to 25% of the total number A of all holes; the total number of the holes formed in the middle region is 30% to 40% of the total number A; 7. The studdable tire according to claim 6, wherein the total number of the holes formed in the shoulder region is 40% to 50% of the total number A.

9. In a tire meridian cross section in a normal state, the tread portion includes a tread half profile extending from the tire equator toward each of the tread ends, the tread half profile includes a first arc extending axially outward from the tire equator, a second arc connected to the first arc and extending axially outward, and a third arc connected to the second arc and the tread edge, the radius of curvature of the second arc is 50% to 54% of the radius of curvature of the first arc; 5. The studdable tire according to claim 1, wherein the radius of curvature of the third arc is 20% to 24% of the radius of curvature of the first arc.

10. a length in the tire axial direction from the tire equator to a first connection point where the first arc and the second arc are connected is 37% to 47% of a tread half width, 10. The studdable tire according to claim 9, wherein a length in the tire axial direction from the tire equator to a second connection point where the second arc and the third arc are connected is 65% to 75% of a half tread width.

11. The tread portion has a designated tire rotation direction, the plurality of studs include a plurality of first studs fitted in the holes formed in the crown region and a plurality of second studs fitted in the holes formed in the shoulder region, With the studs attached to the holes, Each of the plurality of studs includes an inner flange held at the bottom portion and a body extending radially outward from the inner flange, each of the inner flanges of the plurality of studs includes a leading portion disposed on a leading side of the centroid of the body in the tire rotation direction, and a trailing portion disposed on a trailing side of the centroid of the body in the tire rotation direction, The length of the leading portion of each first stud in the circumferential direction of the tire is the same as the length of the trailing portion of each first stud in the circumferential direction of the tire, 5. A studdable tire according to claim 1, wherein the length of the trailing portion of each second stud in the tire circumferential direction is greater than the length of the leading portion in the tire circumferential direction.

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