5 comprises a plurality of compressive elements 6. The plurality of compressive elements 6 is a plurality of holes 61 opening to the contact face 21 and extending in radially inward of the tread 1 (shown in FIG. 2). A width of one of the pair of shoulder regions 23 between an axial extremity of the tread 1 and the center of axially outermost circumferential groove 3 closest to the axial extremity of the tread 1 is from 10% to 25% of the width TW, and the compressive contact element 5 locates in at least one of the pair of shoulder regions 23. All the contact elements 4 in the pair of shoulder regions 23 are the compressive contact element 5. In the present embodiment, the width of one of the pair of shoulder regions 23 is 19% of the width TW, and a diameter of each the hole 61 as the compressive element 6 is 2.0 mm.

As shown in FIG. 2, the at least one of the compressive element 6 among the plurality of compressive elements 6 comprises an enlarged portion 63 at radially innermost portion of the compressive element 6. A radially innermost portion of the enlarged portion 63 locates at a level below radially innermost of the groove 3. As same as typical radial tire construction, a carcass 8 (or a casing), a main body of a tire which may or may not be provided with an inner liner for inhibiting loss or air pressure, and a ply 7 (or a belt), one or more rubber-coated layers of metallic or textile or other material in a form of cable or wire or strings, are provided radially inward of the tread 1. In the present embodiment, a width of each the enlarged portion 63 is 3.0 mm.

A volumetric void ratio of the at least one compressive contact element 5 in a unit region 51 surrounded by a center of the at least one circumferential groove 3 and a center of the plurality of transverse grooves 31 delimiting the compressive contact element 5 among the plurality of contact elements 4 is at least equal to 25%, and an aspect ratio defined as a ratio of a surface of the compressive contact element 5 supposed to contact with ground divided by a sum of a surface area of the compressive contact element 5 touching with air other than the surface of the compressive contact element 5 supposed to contact with ground is at most equal to 70%. In the present embodiment, the volumetric void ratio is 34%, and the aspect ratio is 30%.

An average of the volumetric void ratio of the plurality of contact elements 4 including the compressive contact element 5 at one of the pair of shoulder regions 23 is at least equal to 25%, and an average of the aspect ratio of the plurality of contact elements 4 including the compressive contact element 5 at one of the pair of shoulder regions 23 is at most equal to 70%.

Since the tread 1 is provided with at least one compressive contact element 5 comprising the plurality of compressive elements 6 among the plurality of contact elements 4, such the compressive contact element 5 can absorb deformation due to Poisson's effect and limit stiffening due to incompressibility of rubber material constituting the tread 1 thanks to the plurality of compressive elements 6. Therefore it is possible to improve noise performance.

Since the volumetric void ratio of the at least one compressive contact element 5 in a unit region 51 surrounded by a center of the at least one circumferential groove 3 and a center of the plurality of transverse grooves 31 delimiting the compressive contact element 5 among the plurality of contact elements 4 is at least equal to 25%, the compressive contact element 5 can ensure enough void to absorb deformation due to Poisson's effect. Therefore it is possible to improve effectively noise performance.

If the volumetric void ratio of the at least one compressive contact element 5 in the unit region 51 is less than 25%, there is a risk that the compressive contact element 5 cannot ensure enough void to absorb deformation due to Poisson's effect thus stiffening finally the contact element 4 leading insufficient improvement on noise performance. By setting this volumetric void ratio of the at least one compressive contact element 5 in the unit region 51 at least equal to 25%, it is possible to improve effectively noise performance.

This volumetric void ratio of the at least one compressive contact element 5 in the unit region 51 is preferably at least equal to 28%, more preferably at least equal to 30%.

Since the aspect ratio defined as the ratio of the surface of the compressive contact element 5 supposed to contact with ground divided by the sum of the surface area of the compressive contact element 5 touching with air other than the surface of the compressive contact element 5 supposed to contact with ground is at most equal to 70%, the compressive contact element 5 can limit structural stiffening of the tread. Therefore it is possible to improve effectively noise performance.

If this aspect ratio is more than 70%, there is a risk that the compressive contact element 5 cannot limit structural stiffening of the tread 1 thus stiffening finally the contact element 4 leading insufficient improvement on noise performance. By setting this aspect ratio at most equal to 70%, it is possible to improve effectively noise performance.

This aspect ratio is preferably at most equal to 60%, more preferably at most equal to 50% and still more preferably at most equal to 40%.

Since the width of one of the pair of shoulder regions 23 between an axial extremity of the tread 1 and the center of axially outermost circumferential groove 3 closest to the axial extremity of the tread 1 is from 10% to 25% of the width TW, the compressive contact element 5 locates in at least one of the pair of shoulder regions 23, it is possible to improve noise performance while maintaining reasonable level on handling performance.

If the width of one of the pair of shoulder regions 23 is less than 10% of the width TW, there is a risk that a volume of the compressive contact element 5 available on the tread 1 becomes insufficient thus insufficient improvement on noise performance. If the width of one of the pair of shoulder regions 23 is more than 25%, there is a risk that a volume of the compressive contact element 5 available on the tread 1 becomes too much thus degrading handling performance.

Since the average of the volumetric void ratio of the plurality of contact elements 4 including the compressive contact element 5 at one of the pair of shoulder regions 23 is at least equal to 25%, and an average of the aspect ratio of the plurality of contact elements 4 including the compressive contact element 5 at one of the pair of shoulder regions 23 is at most equal to 70%, it is possible to improve effectively noise performance while maintaining reasonable level on handling performance as one of the pair of shoulder regions 23 can get maximum benefit of the compressive contact element 5 available in the pair of shoulder regions 23.

Since all the contact elements 4 in the pair of shoulder regions 23 are the compressive contact element 5, it is possible to improve efficiently noise performance while maintaining reasonable level on handling performance as shoulder regions 23 can get full benefit of the compressive contact element 5 available in the shoulder regions 23.

Since the plurality of compressive elements 6 is a plurality of holes 61 opening to the contact face 21 and extending in radially inward of the tread 1, it is possible to improve efficiently noise performance while maintaining reasonable level on handling performance as the holes 61 can absorb efficiently deformation of the compressive contact element 5 due to Poisson's effect.

Since at least one of the compressive element 6 among the plurality of compressive elements 6 comprises an enlarged portion 63 at radially innermost portion of the compressive element 6, it is possible to improve efficiently noise performance while maintaining reasonable level on handling performance as the enlarged portion 63 can absorb efficiently deformation of the compressive contact element 5 due to Poisson's effect.

Since radially innermost of the enlarged portion 63 locates at a level below radially innermost of the groove 3, it is possible to improve efficiently noise performance while maintaining reasonable level on handling performance as the enlarged portion 63 can effectively support deformation of the compressive contact element 5.

The volumetric void ratio may be able to satisfy by using a foamed rubber composition. Preferably the rubber composition constituting the tread 1 is a non-foamed rubber composition.

The hole 61 as the compressive element 6 may extend in straight, curved or zig-zagged manner toward radially inward of the tread 1, with or without an angle relative to radial orientation.

The diameter or a depth of each the hole 61 may vary from one another, including with or without the enlarged portion 63. The shape of each the hole 61 on the contact face 21 may also vary from one another and may be any shape, for example circular, triangular, oblong or polygonal, or those may be the same within one compressive contact element 5.

A content of the compressive element 6 in one single compressive contact element 5 may vary from one compressive contact element 5 to another compressive contact element 5.

A tread 71 according to a second embodiment of the present disclosure will be described referring to FIGS. 3 and 4. FIG. 3 is a schematic plan view of a tread according to a second embodiment of the present disclosure. FIG. 4 is a schematic cross sectional view taken along line IV-IV in FIG. 3. The construction of this second embodiment is similar to that of the first embodiment other than the arrangement shown in FIGS. 3 and 4, thus description will be made referring to FIGS. 3 and 4.

As shown in FIG. 3, a tread 71 has a contact face 721 of a width TW (not shown), and at least one circumferential groove 73 of a depth D (shown in FIG. 4) extending in circumferential orientation and a plurality of transvers grooves 731 extending generally in axial orientation, both the at least one circumferential groove 73 and the plurality of transvers grooves 731 opening to the contact face 721. The at least one circumferential groove 73 and the plurality of transverse grooves 731 delimiting a plurality of contact elements 74. The tread 71 comprises a center region 722 and a pair of shoulder regions 723 being positioned on two axial sides of the center region 722.

As shown in FIG. 3, the tread 71 is provided with at least one compressive contact element 75 among the plurality of contact elements 74. The compressive contact element 75 comprises a plurality of compressive elements 76. The plurality of compressive elements 76 is a plurality of incisions 62 opening to the contact face 721 and extending in an orientation having non-zero angle with axial orientation of the tread 71. In the present embodiment, the non-zero angle is 90 degrees, and a width of each the incision 62 is 1.5 mm.

As shown in FIG. 4, some of the incisions 62 as the compressive elements 76 are comprise an enlarged portion 763 at radially innermost portion of the compressive element 76. A radially innermost of some of the incisions 62 or the enlarged portions 763 locates at a level below radially innermost of the groove 73. In the present embodiment, a width of the enlarged portion 763 is 3.0 mm.

As shown in FIG. 4, the pair of shoulder regions 723 each comprises a shoulder rubber layer 25 of a thickness ts made of a shoulder rubber composition different from a rubber composition constituting the tread 71, and a shear storage modulus G′ of the shoulder rubber composition is less than or equal to 2.0 MPa. In the present embodiment, the shear storage modulus G′ of the shoulder rubber composition is 0.4 MPa, and a shear storage modulus G′ of the rubber composition constituting the tread 71 is 2.3 MPa.

A volumetric void ratio of the at least one compressive contact element 75 in a unit region 751 surrounded by a center of the at least one circumferential groove 73 and a center of the plurality of transverse grooves 731 delimiting the compressive contact element 75 among the plurality of contact elements 74 is at least equal to 25%, and an aspect ratio defined as a ratio of a surface of the compressive contact element 75 supposed to contact with ground divided by a sum of a surface area of the compressive contact element 75 touching with air other than the surface of the compressive contact element 75 supposed to contact with ground is at most equal to 70%. In the present embodiment, the volumetric void ratio is 34%, and the aspect ratio is 30%.

Since the plurality of compressive elements 76 is a plurality of incisions 62 opening to the contact face 721 and extending in an orientation having non-zero angle with axial orientation of the tread 71, it is possible to improve noise performance in particular exterior noise performance as the incisions 62 are not open directly to exterior of the tread 71.

The non-zero angle of the incisions 62 relative to axial orientation of the tread 71 is preferably more than 30 degrees, more preferably more than 45 degrees and still more preferably more than 60 degrees.

Since the pair of shoulder regions 723 each comprising a shoulder rubber layer 25 of a thickness ts made of a shoulder rubber composition different from a rubber composition constituting the tread 71, and a shear storage modulus G′ of the shoulder rubber composition is less than or equal to 2.0 MPa, it is possible to improve noise performance while maintaining reasonable level on handling performance since the shoulder rubber layer 25 is comprised in the pair of shoulder regions 723 and not the center region 722, degradation on handling performance is limited as the center region 722 has a dominant impact on handling performance due to longer contact length compared to shoulder regions 723, and the shoulder rubber layer 25 can effectively reduce excitation of the tread 71 during rolling thanks to the shoulder rubber composition having the shear storage modulus G′ smaller than the shear storage modulus G′ of the rubber composition constituting the tread 71.

Since the shear storage modulus G′ of the shoulder rubber composition is less than or equal to 2.0 MPa, the shoulder rubber layer 25 can effectively reduce excitation of the tread 71 during rolling.

If the shear storage modulus G′ of the shoulder rubber composition is more than 2.0 MPa, there is a risk that an improvement on noise performance would be insufficient.

The width, the depth of the incision 62 with or without enlarged portion 763 may vary from one another, or may be the same within one compressive contact element 75.

The shoulder rubber layer 25 may be invisible on the contact face 721 when the tread 71 being brand new. The shoulder rubber layer 25 may be provided radially below a level of 50% of the depth D of the at least one groove 73.

The center region may comprise a center rubber layer of a thickness tf made of a center rubber composition different from both the shoulder rubber composition and the rubber composition constituting the tread 71, and a shear storage modulus G′ of the center rubber composition may be higher than the shear storage modulus G′ of the rubber composition constituting the tread 71. The thickness tf of the center rubber layer may be thinner than the thickness ts of the shoulder rubber layer 25.

In case the center region comprises the center rubber layer, the shear storage modulus G′ of the center rubber composition is preferably from 2 to 10 times of the rubber composition constituting the tread 71 for handling performance improvement, as if the shear storage modulus G′ of the center rubber composition is less than 2 times of the shear storage modulus G′ of the rubber composition constituting the tread 71, there is a risk that improvement on handling performance becomes insufficient due to relatively insufficient modulus of the center rubber composition, and if the shear storage modulus G′ of the center rubber composition is more than 10 times of the shear storage modulus G′ of the rubber composition constituting the tread 71, there is a risk that improvement on handling performance becomes insufficient either as too hard center rubber composition may make flattening of the tire difficult which leads contact patch length shorter resulting generating less lateral force.

The shear storage modulus G′ of the rubber composition constituting the tread 71 other than the center rubber layer or the shoulder rubber layer 25 may be less than or equal to 6.0 MPa for noise performance improvement while improving or at least maintaining reasonable level on handling performance, as if the shear storage modulus G′ of the rubber composition constituting the tread 71 other than the center rubber layer or the shoulder rubber layer 25 is more than 6.0 MPa, there is a risk that improvement on noise performance becomes insufficient, as the tread 71 itself becomes too hard even provided with the shoulder rubber layer 25. The shear storage modulus G′ of the rubber composition constituting the tread 71 other than the center rubber layer or the shoulder rubber layer 25 is preferably less than or equal to 4.0 MPa, more preferably less than or equal to 3.0 MPa.

The disclosure is not limited to the examples described and represented and various modifications can be made there without leaving its framework.

FIG. 5 is a schematic plan view of a tread according to prior art. A tread 101 has a contact face 1021, at least one circumferential groove 103 and a plurality of transverse grooves 1031 both opening to the contact face 1021. The at least one circumferential groove 103 and the plurality of transverse grooves 1031 delimiting a plurality of contact elements 104. A unit region 1051 is defined as a region surrounded by a center of the at least one circumferential groove 103 and a center of the plurality of transverse groove 1031 delimiting the contact element 104. In this prior art, a volumetric void ratio of the contact element 104 in the unit region 1051 is 17%, an aspect ratio defined as a ratio of a surface of the contact element 104 supposed to contact with ground divided by a sum of a surface area of the contact element 104 touching with air other than the surface of the contact element 104 supposed to contact with ground is 130%.

FIG. 6 is a schematic plan view of a tread according to another prior art. A tread 201 has a contact face 2021, at least one circumferential groove 203 and a plurality of transverse grooves 2031 both opening to the contact face 2021. The at least one circumferential groove 203 and the plurality of transverse grooves 2031 delimiting a plurality of contact elements 204. In an axially outermost region of the tread 201, a plurality of incisions 2062 is provided without the plurality of transverse grooves 2031. In this prior art, a volumetric void ratio of the contact element 204 at the axially outermost region of the tread 201 is 17%, an aspect ratio defined as a ratio of a surface of the axially outermost region of the tread 201 supposed to contact with ground divided by a sum of a surface area of the axially outermost region of the tread 201 touching with air other than the surface of the axially outermost region of the tread 201 supposed to contact with ground is 50%.

EXAMPLES

In order to confirm the effect of the present disclosure, one type of tire of Example to which the present disclosure is applied and other types of tire of Reference and Comparative Example were prepared.

The Example was a tire provided with a tread as described in the above first embodiment: a width of one shoulder region was 25% of a width of the tread TW, a shear storage modulus G′ of a rubber composition constituting the tread was 2.3 MPa. The volumetric void ratio of the compressive contact element was 34%, the aspect ratio of the compressive contact element was 30%. The Reference was a tire provided with a tread as shown in FIG. 5. The Comparative Example was a tire provided with a tread as shown in FIG. 6.

Noise Performance Test:

Unused test tires were mounted onto all four wheels of a 2,500 cc rear-wheel drive vehicle. On a straight path weathered asphalt, the vehicle was driven at a constant speed of 80 kph. An interior noise was measured using a microphone positioned at a passenger's ear close to window. An A-weighted sound pressure level between 0 and 500 Hz was calculated.

The results are shown in table 1. In this table 1, results are represented by difference in dB (A) against Reference, lower the value indicates better the performance. Improvement of more than 0.3 dB (A) could be considered as “improvement”. Handling test: