Patent Application
20210339570
This application claims priority pursuant to 35 U.S.C. 119(a) of Japan Patent Application No. 2020-080848, filed Apr. 30, 2020, which application is incorporated herein by reference in its entirety.
The present technology relates to a tire.
Among heavy duty tires, tires marked with a severe snow mark are required to have improved snow traction performance. Tires employed in vehicles, for example, garbage collection vehicles, that have large loads and frequently start and stop are run rigorously, and thus it is difficult to provide rolling resistance performance and snow traction performance in a compatible manner.
Japan Patent No. 5250017 discloses a technology for preventing stone biting by changing a groove wall angle of a main groove.
According to the tire disclosed in Japan Patent No. 5250017, the effect of preventing stone biting can be increased. However, there is room for enhancement in improving rolling resistance performance and snow traction performance of the tires.
The present technology provides a tire with improved rolling resistance performance and snow traction performance.
A tire according to an aspect of the present technology includes a plurality of main grooves extending in a tire circumferential direction, a land portion defined by the main grooves, a plurality of lug grooves extending through the land portion, and a plurality of blocks defined by the plurality of main grooves and the plurality of lug grooves. The main grooves include, in a meridian cross-section, a bend point where an angle of a groove wall with respect to a normal line of a tread surface changes. The plurality of blocks include a first block and a second block, where among a first main groove and a second main groove having distances differing from each other in a tire width direction from a tire equatorial plane, the first block has a first edge along the first main groove where a distance in the tire width direction is closer to the tire equatorial plane and the second block has a second edge along the second main groove where a distance in the tire width direction is farther from the tire equatorial plane. Two angles between an imaginary line obtained by extending a ridge line formed by the bend point of a groove wall on the first edge side of the first main groove and imaginary lines each obtained by extending two edges that are adjacent to each other in the tire circumferential direction with the first edge interposed therebetween among edges of a road contact surface of the first block are an acute angle θa and an obtuse angle θb, and two angles between an imaginary line obtained by extending a ridge line formed by the bend point of a groove wall on the second edge side of the second main groove and imaginary lines each obtained by extending two edges that are adjacent to each other in the tire circumferential direction with the second edge interposed therebetween among edges of a road contact surface of the second block are an acute angle θc and an obtuse angle θd, a difference between the acute angle θa and the obtuse angle θb is greater than a difference between the acute angle θc and the obtuse angle θd.
A difference of angles between groove walls on both sides of the first main groove with respect to the normal line of the tread surface in a meridian cross-section of the first main groove at positions of two points where intersection points of the imaginary lines obtained by extending each of the two edges that are adjacent to each other in the tire circumferential direction with the first edge interposed therebetween and a groove center line of the first main groove are moved along the groove center line by a predetermined distance in a direction approaching each other are greater than a difference of angles between groove walls on both sides of the second main groove with respect to the normal line of the tread surface in a meridian cross-section of the second main groove at positions of two points where intersection points of the imaginary lines obtained by extending each of the two edges that are adjacent to each other in the tire circumferential direction with the second edge interposed therebetween and a groove center line of the second main groove are moved along the groove center line by a predetermined distance in a direction approaching each other.
A ratio of a maximum distance between the groove walls of the second main groove at the two points along the groove center line of the second main groove to a maximum distance between the groove walls of the first main groove at the two points along the groove center line of the first main groove is preferably 0.75 or more and 0.95 or less, and a ratio of a distance between the ridge lines at the two points along the groove center line of the second main groove to a distance between the ridge lines at the two points along the groove center line of the first main groove is preferably 0.95 or more and 1.05 or less.
A ratio of a maximum distance between the groove walls of the second main groove at the two points along the groove center line of the second main groove to a maximum distance between the groove walls of the first main groove at the two points along the groove center line of the first main groove is preferably 0.75 or more and 0.95 or less, and a ratio of a distance between the ridge lines at the two points along the groove center line of the second main groove to a distance between the ridge lines at the two points along the groove center line of the first main groove is preferably 0.95 or more and 1.05 or less.
A ratio of a length of the second block along the tire circumferential direction to a length of the first block along the tire circumferential direction is preferably 0.75 or more and 0.95 or less.
The groove center lines of the first main groove and the second main groove in a tread plan view have a zigzag shape with an amplitude in the tire width direction, wherein the zigzag shape of the groove center line of the first main groove is formed by repeating connections between a plurality of linear portions, a ratio of a length in the tire circumferential direction of the linear portions to a length in the tire circumferential direction of one pitch of the zigzag shape is 0.45 or more and 0.55 or less, the zigzag shape of the groove center line of the second main groove is formed by repeating connections between a long portion and a short portion having mutually different lengths in the tire circumferential direction, and a ratio of a length in the tire circumferential direction of the long portion to a length in the tire circumferential direction of one pitch of the zigzag shape by the long portion and the short portion is preferably 0.50 or more and 0.60 or less.
In a tread plan view, a ratio of an amplitude in the tire width direction of a center line of a zigzag shape of an edge portion of a tread contact surface along the first main groove to a developed tread width is preferably 0.005 or more and 0.020 or less, and in a tread plan view, a ratio of an amplitude in the tire width direction of a center line of a zigzag shape of an edge portion of a tread contact surface along the second main groove to the developed tread width is preferably 0.005 or more and 0.020 or less.
In a tread plan view, a ratio of an amplitude in the tire width direction of a center line of a zigzag shape of the ridge line along the first main groove to a developed tread width is preferably 0.005 or more and 0.030 or less, and in a tread plan view, a ratio of an amplitude in the tire width direction of a center line of a zigzag shape of the ridge line along the second main groove to the developed tread width is preferably 0.005 or more and 0.030 or less.
A ratio of an area of a road contact surface of the second block to an area of a road contact surface of the first block is preferably 0.87 or more and 0.97 or less.
A first groove width of the lug groove at a midpoint of a distance in the tire width direction between intersection points of two imaginary lines obtained by extending each of edges of the first block defined by the main grooves that are adjacent each other in the tire width direction and a groove center line of the lug groove is less than a second groove width of the lug groove at a midpoint of a distance in the tire width direction between intersection points of two imaginary lines obtained by extending each of edges of the second block defined by the main grooves that are adjacent to each other in the tire width direction and a groove center line of the lug groove, and the ratio of the second groove width to the first groove width is preferably 1.05 or more and 1.50 or less.
A raised bottom portion that is provided in a region including the midpoint of the lug grooves and raises a groove bottom of the lug grooves to make a groove depth shallower than other portions is preferably included, and a ratio of the groove depth of the lug groove in the portion where the raised bottom portion is provided to the groove depths of the first main groove and the second main groove is preferably 0.15 or more and 0.35 or less.
Chamfered portions respectively provided on both end portions in the tire circumferential direction of the first edge and chamfered portions respectively provided on both end portions in the tire circumferential direction of the second edge are preferably included.
Each of the plurality of blocks preferably includes at least one bent portion, and has a bent shape that projects to an inner side of the blocks in a plan view.
The tire according to embodiments of the present technology can improve rolling resistance performance and snow traction performance.
Embodiments of the present technology are described in detail below with reference to the drawings. In the embodiments described below, identical or substantially similar components to those of other embodiments have identical reference signs, and descriptions of those components are either simplified or omitted. The present technology is not limited by the embodiments. Constituents of the embodiments include elements that are essentially identical or that can be substituted or easily conceived by one skilled in the art. Note that it is possible to combine the configurations described below as desired. Moreover, various omissions, substitutions, and changes to the configurations can be carried out within the scope of the present technology.
In the description below, “tire meridian section” is defined as a cross-section of the tire taken along a plane that includes the tire rotation axis (not illustrated). The tire radial direction refers to a direction orthogonal to the rotation axis (not illustrated) of the tire 1, the inner side in the tire radial direction refers to the side toward the rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the rotation axis in the tire radial direction. Moreover, the tire circumferential direction refers to the circumferential direction with the rotation axis as the central axis. Additionally, the tire width direction refers to a direction parallel with the rotation axis, the inner side in the tire width direction refers to a side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the outer side in the tire width direction refers to a side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is orthogonal to the rotation axis of the tire 1 and passes through the center of the tire width of the tire 1, and in the tire equatorial plane CL, the center line in the tire width direction, which is the center position of the tire 1 in the tire width direction, coincides with the position in the tire width direction. “Tire width” is the width in the tire width direction between portions located on the outermost sides in the tire width direction, or in other words, the distance between the portions that are the most distant from the tire equatorial plane CL in the tire width direction. “Tire equator line” refers to a line along the tire circumferential direction of the tire 1 that lies on the tire equatorial plane CL. In the present embodiment, the tire equator line and the tire equatorial plane are denoted by the same reference sign CL.
As illustrated in
In
The end portions of the carcass layer 6 in the tire width direction are folded back around the pair of bead cores 51 from an inner side in the tire width direction to an outer side in the tire width direction, and the carcass layer 6 is stretched in a toroidal shape in the tire circumferential direction to form the framework of the tire. The carcass layer 6 is made of coating rubber-covered carcass cords (not illustrated) disposed side by side with an angle with respect to the tire circumferential direction along the tire meridian direction at an angle with respect to the tire circumferential direction. The carcass cords are made of steel or organic fibers (polyester, rayon, nylon, or the like).
The belt layer 7 has a multilayer structure in which four layers of belts 71, 72, 73, 74 are layered, for example, and in the tread portion 2, is disposed on the outer side in the tire radial direction, which is the outer circumference, of the carcass layer 6, covering the carcass layer 6 in the tire circumferential direction.
The belts 71, 72, 73, 74 are made of coating rubber-covered cords (not illustrated) disposed side by side at a predetermined angle with respect to the tire circumferential direction. The cords are made of steel or organic fibers (polyester, rayon, nylon, or the like).
The tread portion 2 is made of a rubber material (tread rubber) and is exposed on the outermost side of the tire 1 in the tire radial direction, with the surface thereof constituting the contour of the tire 1. A tread surface 21 is formed on an outer circumferential surface of the tread portion 2, in other words, on a road contact surface that comes into contact with a road surface when running. A plurality (six in the present embodiment) of circumferential main grooves 22A, 22B, and 23 extending in the tire circumferential direction are provided in the tread surface 21. A plurality (seven in the present embodiment) of land portions 20C, 20M1, 20M2, and 20S defined by the plurality of circumferential main grooves 22A, 22B, and 23 extending in the tire circumferential direction, and arranged in the tire width direction are provided in the tread surface 21.
The circumferential main groove 22A is the circumferential main groove closest to the tire equator line CL. The circumferential main groove 22B is the circumferential main groove that is second closest to the tire equator line CL. The circumferential main groove 22B is a circumferential main groove provided in the outer side in the tire width direction of the circumferential main groove 22A. The circumferential main groove 23 is a circumferential main groove provided in the outer side in the tire width direction of the circumferential main groove 22B. The circumferential main groove 23 is the circumferential main groove closest to the tire ground contact edge T. “Main groove” refers to a groove on which a wear indicator must be provided as specified by JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.). Note that the length TDW in the tire width direction between the tire ground contact edges T is the developed tread width.
The land portion 20C is provided between the circumferential main grooves 22A and 22A that are adjacent to each other with the tire equator line CL interposed therebetween. The land portion 20C is defined by the two circumferential main grooves 22A and 22A. The land portion 20M1 is provided between the circumferential main groove 22A and the circumferential main groove 22B. The land portion 20M1 is defined by the circumferential main groove 22A and the circumferential main groove 22B. The land portion 20M2 is provided between the circumferential main groove 22B and the circumferential main groove 23. The land portion 20M2 is defined by the circumferential main groove 22B and the circumferential main groove 23. The land portion 20S is provided on the outer side in the tire width direction of the circumferential main groove 23. In the following description, the circumferential main groove may simply be referred to as “main groove”.
The tread portion 2 will be described in detail below. Hereinafter, the groove depth is the maximum distance from the tread surface to the groove bottom and is measured when the tire is mounted on a specified rim, inflated to the specified internal pressure, and in an unloaded state. Additionally, in a configuration in which the grooves include an uneven portion or sipes on the groove bottom, the groove depth is measured excluding these portions.
As illustrated in
The land portion 20C includes lug grooves 24 that connect to the circumferential main groove 22A and the circumferential main groove 22B to join the circumferential main groove 22A and the circumferential main groove 22B. The land portion 20S is defined on the outer side in tire width direction of the circumferential main groove 23, and is disposed on the outermost side of the tread portion 2 in the tire width direction. The land portion 20S includes lug grooves 30 on the edge portion on the outer side in the tire width direction. The lug grooves 30 are provided in the land portions 20S at a predetermined pitch in the tire circumferential direction. The end portion of the lug groove 30 on the side closer to the tire equatorial plane CL terminates in the land portion 20S. The end portion of the lug groove 30 on the side farther from the tire equatorial plane CL extends beyond the tire ground contact edge T in the tire width direction and opens to the shoulder portion 3.
The tire ground contact edge T is defined as the maximum width position in the tire axial direction of the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, inflated to the specified internal pressure, placed perpendicular to the flat plate in a static state without being loaded, and loaded with a load corresponding to the specified load.
“Specified rim” refers to a “standard rim” defined by JATMA, a “Design Rim” defined by TRA (The Tire and Rim Association, Inc.), or a “Measuring Rim” defined by ETRTO (The European Tyre and Rim Technical Organisation). Additionally, “specified internal pressure” refers to a “maximum air pressure” defined by JATMA, to the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or to “INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load” refers to a “maximum load capacity” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO.
As illustrated in
In the lug groove 24, raised bottom portions 240 are provided between blocks BK that are adjacent to each other in the tire circumferential direction. The raised bottom portion 240 is a portion where the groove bottom is raised such that the groove depth is shallower than other portions.
The tread portion 2 includes the plurality of blocks BK. Each of the blocks BK is defined by the plurality of main grooves 22A, 22B, 23 and the plurality of lug grooves 24. Each of the blocks BK includes at least one bend point K. Thus, the blocks BK have a bent shape that projects to an inner side of the blocks BK in a plan view. Each of the blocks BK may include a plurality of bend points K.
In
In addition, the zigzag shape of the groove center line 230 of the main groove 22B is formed by repeating connections between a long portion and a short portion that are mutually different in the lengths in the tire circumferential direction. In other words, the zigzag shape of the groove center line 230 is formed by repeating connections between the long portion of the length Ls1 in the tire circumferential direction and the short portion of the length Ls2 in the tire circumferential direction. The ratio Ls1/PDs of the length Ls1 in the tire circumferential direction of the long portion to the length PDs in the tire circumferential direction of one pitch of the zigzag shape by the long portion and the short portion is preferably 0.50 or more and 0.60 or less.
Here, by configuring the value of the ratio Ls1/PDs with respect to the main groove 22B on the outer side in the tire width direction to be greater than the value of the ratio LC/PDc with respect to the main groove 22A on the inner side in the tire width direction, snow traction performance can be improved.
The groove wall on the first edge E1 side of the main groove 22A, which is the first main groove, has a bend point where the angle of the groove wall changes. The ridge line 222R is formed by the bend point of the groove wall. The imaginary line H11 obtained by extending the ridge line 222R and the imaginary line H12 obtained by extending the edge E3 of the road contact surface of the block BK1 defined by the lug grooves 24 intersect at the point P1. The angle between the imaginary line H11 and the imaginary line H12 is denoted by θa. The angle θa is an acute angle. Furthermore, the imaginary line H13 obtained by extending the ridge line 222R and the imaginary line H14 obtained by extending the edge E4 of the road contact surface of each of the blocks BK1 defined by the lug grooves 24 intersect at the point P2. The angle between the imaginary line H13 and the imaginary line H14 is denoted by θb. The angle θb is an obtuse angle. In other words, two angles between the imaginary lines H11 and H13 obtained by extending the ridge line 222R formed by the bend point of the groove wall on the first edge E1 side and the imaginary lines H12 and H14 obtained by extending each of the two edges E3 and E4 that are adjacent to each other in the tire circumferential direction with the first edge E1 interposed therebetween among the edges of the road contact surface of the block BK1 are the angle θa of the acute angle and the angle θb of the obtuse angle.
A groove wall on the second edge E2 side of the main groove 22B, which is the second main groove, has a bend point where the angle of the groove wall changes. The ridge line 232R is formed by the bend point of the groove wall. The imaginary line H15 obtained by extending the ridge line 232R and the imaginary line H16 obtained by extending the edge E5 of the road contact surface of the block BK2 intersect at the point P3. An angle between the imaginary line H15 and the imaginary line H16 is denoted by θc. The angle θc is an acute angle. Furthermore, the imaginary line H17 obtained by extending the ridge line 232R and the imaginary line H18 obtained by extending the edge E6 of the road contact surface of the block BK2 intersect at the point P4. An angle between the imaginary line H17 and the imaginary line H18 is denoted by θd. The angle θd is an obtuse angle. In other words, two angles between the imaginary lines H15 and H17 obtained by extending the ridge line 232R formed by the bend point of the groove wall on the second edge E2 side and the imaginary lines H16 and H18 obtained by extending each of the two edges E5 and E6 that are adjacent to each other in the tire circumferential direction with the second edge E2 interposed therebetween among the edges of the road contact surface of the block BK2, are the angle θc of the acute angle and the angle θd of the obtuse angle.
Here, the four angles θa, θb, θc, and θd have the following relationship (1).
(θd−θc)<(θb−θa) (1)
In other words, in a case where the two angles between the imaginary lines H11 and H13 obtained by extending the ridge line 222R formed by the bend point of the groove wall on the first edge E1 side of the main groove 22A and the imaginary lines H12 and H14 obtained by extending each of the two edges E3 and E4 that are adjacent to each other in the tire circumferential direction with the first edge E1 interposed therebetween are the acute angle θa and the obtuse angle θb, and the two angles between the imaginary lines H15 and H17 obtained by extending the ridge line 232R formed by the bend point of the groove wall on the second edge E2 side of the main groove 22B and the imaginary lines H16 and H18 obtained by extending each of the two edges E5 and E6 that are adjacent to each other in the tire circumferential direction with the second edge E2 interposed therebetween are the acute angle θc and the obtuse angle θd, and a difference between the acute angle θa and the obtuse angle θb is greater than a difference between the acute angle θc and the obtuse angle θd. Since the four angles θa, θb, θc, and θd have such a relationship, the rigidity of the block BK can be increased and the amount of deformation of the block BK can be reduced. In this way, rolling resistance performance can be improved.
Next, an example of the cross-sectional shape of the main groove 22A and 22B will be described.
In
In
In
In
In
In
Note that the angle difference between the angle α15 and the angle α25, described with reference to
In
Note that the angle difference between the angle α16 and the angle α26, described with reference to
In
Returning to
Additionally, in
Since, in the tread contact surface, the groove width on the inner side in the tire width direction is greater than the groove width on the outer side in the tire width direction, the snow can be compacted when grounded, and the snow traction performance can be improved. When the groove width on the inner side in the tire width direction is less than the groove width on the outer side in the tire width direction, the groove is narrow and thus snow traction performance cannot be exhibited when grounded, which is not preferable.
Additionally, as illustrated in
The ratio PHc/TDW of the amplitude PHc in the tire width direction of the zigzag-shaped groove center line 220 of the main groove 22A to the developed tread width TDW is preferably 0.005 or more and 0.020 or less. Additionally, the ratio PHs/TDW of the amplitude PHs in the tire width direction of the zigzag-shaped groove center line 230 of the main groove 22B to the developed tread width TDW is preferably 0.005 or more and 0.020 or less. When the ratio PHc/TDW or the ratio PHs/TDW is less than 0.005, snow traction performance is degraded, which is not preferable. When the ratio PHc/TDW or the ratio PHs/TDW is greater than 0.020, the amount of deformation of the block BK increases and rolling performance is degraded, which is not preferable.
Returning to
By configuring the area of the road contact surface of the block BK1 that is closer to the tire equatorial plane CL to be greater than the area of the road contact surface of the block BK2 that is farther from the tire equatorial plane CL, block rigidity can be increased and the amount of deformation is reduced so that rolling resistance performance can be improved. When the ratio SBK2/SBK1 is less than 0.87, the area on the outer side in the tire width direction is small, and block rigidity is non-uniform, and thus rolling resistance performance is degraded, which is not preferable. When the ratio SBK2/SBK1 is greater than 0.97, the ground contact surface pressure decreases and thus rolling resistance performance is degraded, which is not preferable.
In
Each of the raised bottom portions 240 is provided in a region including the midpoints P11 and P14 of each of the lug grooves 24. In the present example, the groove depth of each of the lug grooves 24 is equal to the groove depth of the main grooves 22A and 22B. However, in each of the lug grooves 24, the groove depth of the portion where each of the raised bottom portions 240 is provided is shallower than the groove depth of the main grooves 22A and 22B. Note that the maximum value of the groove depth DR of the main groove 22A is 19.1 mm, for example.
Here, the groove depth of the main grooves 22A and 22B is denoted by DR. The ratio DS/DR of the groove depth DS to the groove depth DR is preferably 0.15 or more and 0.35 or less. When the ratio DS/DR is less than 0.15, the lug groove 24 is shallower and snow traction performance is degraded, which is not preferable. When the ratio DS/DR is greater than 0.35, the lug groove 24 is deep, block rigidity is reduced and thus rolling resistance is degraded, which is not preferable.
In a case where the original groove depth of the lug grooves 24 is equal to the groove depth DR of the main grooves 22A and 22B, the ratio of the groove depth DS to the original groove depth of the lug groove 24 is preferably 0.15 or more and 0.35 or less.
As illustrated in
As described with reference to
Although the cross-sectional shapes of the main groove 22A have been described above with reference to
In the embodiments described above, pneumatic tires were described as examples of the tire. However, the configuration is not limited thereto, and the configurations described in the embodiments can be arbitrarily applied to other tires as well within the scope apparent to those skilled in the art. Examples of other tires include airless tires, solid tires, and the like.
In the examples, performance tests for rolling resistance performance and snow traction performance were performed on a plurality of types of tires of different conditions (see Tables 1 to 8). In the performance tests, tires with a size of 455/55R22.5 (heavy duty tires) were mounted on 22.5 inch×14.00 inch rims, inflated to the standard maximum air pressure (900 kPa), and mounted on the drive shaft of the test vehicle (2-D tractor head), and the actual vehicle evaluation was performed in a state where a standard maximum load was applied.
For evaluation of rolling resistance performance, the results of the rolling resistance test were expressed in the index value, according to ISO (International Organization for Standardization) 28580. Results are expressed as index values, with the result of Conventional Example being assigned as a reference (100). Larger index values indicate superior rolling resistance performance.
For evaluation of snow traction performance, the test vehicle was driven on a snowy road surface of a snowy road test site and the acceleration time until the travel speed reached 20 km/h from 5 km/h was measured. The measurement results are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). Larger index values indicate superior snow traction performance.
Each of the tires of Examples 1 to 61 in Tables 1 to 8 has a bend point on the groove wall of the main groove, and the relationship of the angle differences between both end portions of the edges E1 and E2 of the first block BK1 on the inner side and the second block BK2 on the outer side is (θd−θc)<(θb−θa), in other words, the angle difference of the first block BK1 on the inner side is larger than the angle difference of the second block BK2 on the outer side.
In the tires of Examples 1 to 61, both groove wall angles of the main groove 22A at the point P56, in other words, both groove wall angles at the midpoint of the edge E1 of the block BK1 on the inner side are equal to each other and different from each other, both groove wall angles of the main groove 22B at the point P78, in other words, both groove wall angles at the midpoint of the edge E2 of the block BK2 on the outer side are equal to each other and different from each other, the ratio of the maximum distance between the wall surfaces of the main groove 22B at the two points P7 and P8 with respect to the maximum distance between the wall surfaces of the main groove 22A at the two points P5 and P6 is 0.75 or more and 0.95 or less and otherwise, the ratio of the distance between the ridge lines 232R at the two points P7 and P8 with respect to the distance between the ridge lines 222R at the two points P5 and P6 is 0.95 or more and 1.05 or less and otherwise, the ratio of the length of the block BK2 on the outer side along the tire circumferential direction with respect to the length of each of the blocks BK1 on the inner side along the tire circumferential direction is 0.75 or more and 0.95 or less and otherwise, the ratio of the length of the linear portion LC of the zigzag with respect to the one pitch length of the zigzag of the center line of the main groove 22A is 0.45 or more and 0.55 or less and otherwise, the ratio of a length Ls1 of the long portion with respect to the one pitch length of the zigzag of the center line of the main groove 22B is 0.50 or more and 0.60 or less and otherwise, the ratio of the amplitude of the center line of the zigzag shape of the edge portion of the tread contact surface along the main groove 22A with respect to the developed tread width TDW is 0.005 or more and 0.020 or less and otherwise, the ratio of the amplitude of the center line of the zigzag shape of the edge portion of the tread contact surface along the main groove 22B with respect to the developed tread width TDW is 0.005 or more and 0.020 or less and otherwise, the ratio of the amplitude of the center line of the zigzag shape of the ridge line of the main groove 22A with respect to the developed tread width TDW is 0.005 or more and 0.030 or less and otherwise, the ratio of the amplitude of the center line of the zigzag shape of the ridge line of the main groove 22B with respect to the developed tread width TDW is 0.005 or more and 0.030 or less and otherwise, the ratio of the area of the road contact surface of the block BK2 with respect to the area of the road contact surface of the block BK1 is 0.87 or more and 0.97 or less and otherwise, the ratio of the lug groove widths at both ends of the edge E2 of the block BK2 with respect to the lug groove widths at both ends of the edge E1 of the block BK1 is 1.05 or more and 1.50 or less and otherwise, the ratio of the groove depth of the lug groove 24 at the portion where the raised bottom portion 240 is provided with respect to the groove depth of the main grooves 22A and 22B is 0.15 or more and 0.35 or less and otherwise, both ends of the edge E1 of the block BK1 include the chamfer and otherwise, and both ends of the edge E2 of the block BK2 include the chamfer and otherwise.
The tire of the Conventional Example in Table 1 has a bend point on the groove wall of the main groove, and the relationship of the angle differences between both end portions of each of the edges of the first block on the inner side and the second block on the outer side is (θd−θc)=(θb−θa), in other words, the angle difference between the second block BK2 on the outer side and the angle difference between the first block BK1 on the inner side are equal, and both groove wall angles at the midpoint of the edge of the block on the inner side are equal, and both groove wall angles at the midpoint of the edge of the block on the outer side are equal.
As described in the test results in Tables 1 to 8, it can be understood that the tires of each of Examples have better rolling resistance performance and snow traction performance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-080848 | Apr 2020 | JP | national |
