JP2024031211A - tire - Google Patents

Abstract

[Problem] To provide a tire 2 that can achieve improved appearance. [Solution] The tire 2 has an outer diameter smaller than the maximum outer diameter of new dimensions minus 4 mm as specified in the JATMA standard or ETRTO standard, and 5 mm subtracted from the maximum total width of the new dimensions. has a total width less than the value. The outer surface 2G of the tire 2 includes a tread surface 24 and a pair of side surfaces 28. The tread surface 24 has an equatorial PC that is an intersection with the equatorial plane. Each side surface 28 has a maximum width position PW. The tire 2 is assembled on the regular rim R, the internal pressure of the tire 2 is adjusted to the regular internal pressure, and no load is applied to the tire 2. In the normal state, the shoulder line segment length LSh is relative to the reference line segment length LBS. The ratio is 85.9% or more and 89.3% or less, and the ratio of the radius of the center arc to the radius of the middle arc is 1.85 or more and 2.00 or less. [Selection diagram] Figure 2

Description

The present invention relates to tires. In particular, the present invention relates to tires mounted on passenger cars.

As shown in FIG. 6, the tire T is housed in a wheel house H. The shape of the tire T is set so that the tire T does not interfere with the wheel house H.
The shape of the tire T affects performance such as steering stability, ride comfort, rolling resistance, and uneven wear resistance. In order to improve uneven wear resistance, for example, the contour line of the tread surface in a meridian cross section is adjusted (see Patent Document 1 below).

Japanese Patent Application Publication No. 2013-060129

In recent years, in passenger cars, not only performance but also appearance has become important. In particular, with regard to the appearance, there is a need to improve the appearance of the vehicle and tires as one unit.
As described above, the tires T are housed in the wheel house H of the vehicle B. A gap (represented by symbol G in FIG. 7) is provided between the wheel house H and the tire T so that the tire T does not interfere with the wheel house H. The gap G is the distance from the outer surface of the tire T to the wheel house, measured along a straight line passing through a first reference point PB1 and a second reference point PB2, which will be described later.
As the gap G becomes smaller, the sense of unity between the vehicle B and the tires T increases. A heightened sense of unity contributes to improved appearance.
As shown by the dotted line in FIG. 7, if the shoulder portion S is modified to have an angular shape, the gap G becomes smaller and the sense of unity between the vehicle B and the tire T increases.
However, this modification involves changing the contour of the tread surface. As a result of the shoulder portion S protruding, there is a concern that the ground pressure of the shoulder portion S increases and uneven wear occurs.
In order to improve the appearance, it is necessary to enhance the sense of unity between the vehicle B and the tires T, taking into consideration the effect on uneven wear resistance.

The present invention has been made in view of these circumstances. An object of the present invention is to provide a tire that can achieve improved appearance.

The tire according to the present invention has an outer diameter smaller than a value obtained by subtracting 4 mm from the maximum outer diameter of new dimensions, and a value obtained by subtracting 5 mm from the maximum total width of the new dimensions, as specified in the JATMA standard or ETRTO standard. has a total width less than . The outer surface of the tire includes a tread surface that comes into contact with a road surface, and a pair of side surfaces that are continuous with the tread surface. The tread surface has an equator that is an intersection with an equatorial plane. Each said side surface has a maximum width position where said tire exhibits its maximum width. In the meridian cross section of the tire, the intersection of the bead baseline and the equatorial plane is the first reference point, and the intersection of a straight line passing through the equator and extending in the axial direction and a straight line passing through the maximum width position and extending in the radial direction. is a second reference point, a line segment connecting the first reference point and the second reference point is a reference line segment, and the intersection of the reference line segment and the outer surface of the tire is a shoulder reference point, A line segment connecting the first reference point and the shoulder reference point is a shoulder line segment. The contour line of the tread surface is composed of a plurality of arcs arranged in the axial direction. The plurality of arcs include a center arc that passes through the equator, a pair of shoulder arcs that are located at the outermost side in the axial direction and have the smallest radius, and a shoulder arc that is located next to the center arc and has a radius smaller than the radius of the center arc. A pair of middle circular arcs having a small radius, and a pair of side circular arcs located between the middle circular arc and the shoulder circular arc and having a radius smaller than the radius of the middle circular arc. The ratio of the length of the shoulder line segment to the length of the reference line segment in a normal state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire. is 85.9% or more and 89.3% or less, and the ratio of the radius of the center arc to the radius of the middle arc is 1.85 or more and 2.00 or less.

According to the present invention, a tire that can achieve improved appearance can be obtained.

1 is a sectional view showing a part of a tire according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a reference line segment and a shoulder line segment. It is a sectional view explaining the outline of a tread surface. FIG. 2 is a schematic diagram showing the shape of the contact surface of a tire. It is a sectional view showing a part of the mold used for manufacturing a tire. FIG. 2 is a side view showing the front part of the vehicle on which tires are mounted. 7 is a cross-sectional view taken along line VII-VII in FIG. 6. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

The tire is mounted on the rim. The inside of the tire is filled with air, and the internal pressure of the tire is adjusted. In the present invention, a tire assembled on a rim is a tire-rim assembly. A tire-rim assembly includes a rim and a tire mounted on the rim.

In the present invention, a state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire is referred to as a regular state.

In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions.
The dimensions and angles of each part in the meridian cross section of the tire, which cannot be measured with the tire mounted on the regular rim, can be measured using the cross section of the tire (hereinafter referred to as the reference cutting plane), which is obtained by cutting the tire along the plane that includes the rotation axis. ) is measured. In this measurement, the distance between the left and right beads is set to match the distance between the beads in a tire assembled on a regular rim.

Regular rim means a rim defined in the standard on which the tire is based. A "standard rim" in the JATMA standard, a "Design Rim" in the TRA standard, and a "Measuring Rim" in the ETRTO standard are regular rims.

Regular internal pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

Regular load means the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are regular loads.

In the present invention, the "tire name" is the "tire name" specified in JIS D4202 "Automotive Tires - Nomenclature and Specifications."

In the present invention, the rubber composition is a composition containing an uncrosslinked base rubber obtained by mixing the base rubber and a chemical in a kneading machine such as a Banbury mixer. Crosslinked rubber is a crosslinked product of a rubber composition obtained by pressurizing and heating the rubber composition. Crosslinked rubber includes a crosslinked product of base rubber. Crosslinked rubber is also referred to as vulcanized rubber, and the rubber composition is also referred to as unvulcanized rubber.

Base rubbers include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). and butyl rubber (IIR). Chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, sulfur and Examples include vulcanization accelerators. The selection of the base rubber and chemicals, the content of the selected chemicals, etc. are determined as appropriate depending on the specifications of each element, such as the tread and sidewalls, to which the rubber composition is applied.

In the present invention, the tread portion of a tire is a portion of the tire that comes into contact with the road surface. The bead is a part of the tire that fits onto the rim. The side part is a part of the tire that bridges between the tread part and the bead part. The tire includes a tread portion, a pair of bead portions, and a pair of side portions. The central portion of the tread portion is also referred to as the crown portion. The end portion of the tread portion is also called a shoulder portion.

[Overview of embodiments of the present invention]
[Configuration 1]
The tire according to one aspect of the present invention has an outer diameter smaller than the maximum outer diameter of the new dimensions by 4 mm, and 5 mm from the maximum total width of the new dimensions, as specified in the JATMA standard or the ETRTO standard. A tire having a total width smaller than the subtracted value, wherein the outer surface of the tire includes a tread surface that contacts the road surface, and a pair of side surfaces that are connected to the tread surface, and the tread surface is connected to an equatorial surface. each of the side surfaces has a maximum width position at which the tire exhibits its maximum width, and in the meridian section of the tire, the intersection of the bead baseline and the equatorial plane is the first The reference point is a second reference point, and the intersection of the straight line passing through the equator and extending in the axial direction and the straight line passing through the maximum width position and extending in the radial direction is the second reference point, and the first reference point and the second reference point A line segment connecting the reference line segment is a reference line segment, an intersection point between the reference line segment and the outer surface of the tire is a shoulder reference point, and a line segment connecting the first reference point and the shoulder reference point is a shoulder line segment. The outline of the tread surface is composed of a plurality of circular arcs arranged in the axial direction, and the plurality of circular arcs are located at the outermost side in the axial direction and have the smallest radius. a pair of middle arcs located next to the center arc and having a radius smaller than the radius of the center arc, and a pair of middle arcs located between the middle arc and the shoulder arc, the middle arc being located between the middle arc and the shoulder arc; and a pair of side circular arcs having a radius smaller than the radius of the tire, when the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire. The ratio of the length of the line segment to the length of the reference line segment is 85.9% or more and 89.3% or less, and the ratio of the radius of the center arc to the radius of the middle arc is 1.85 or more. It is 2.00 or less.

By arranging the tire in this way, the gap between the tire and the wheel house can be brought closer to the interference limit gap amount. Since the gap becomes smaller, the sense of unity between the vehicle and the tires is enhanced. A heightened sense of unity can contribute to improved appearance. With this tire, the difference between the radius of the center arc and the radius of the side arc located next to the middle arc can be kept small. Slippage of the shoulder portion is effectively suppressed, so occurrence of uneven wear is suppressed. This tire can achieve improved appearance while suppressing a decrease in uneven wear resistance.

[Configuration 2]
Preferably, in the tire of "Configuration 1" described above, a ratio of the radius of the middle arc to the radius of the side arc is 2.08 or more and 2.74 or less.
By arranging the tire in this way, a tread surface is constructed that can effectively contribute to forming a gap close to the interference limit gap amount while taking into account interference with the wheel house. This tire can effectively enhance the sense of unity with the vehicle. Slippage of the shoulder portion is effectively suppressed, so occurrence of uneven wear is suppressed. This tire can achieve improved appearance while suppressing a decrease in uneven wear resistance.

[Configuration 3]
Preferably, in the tire of the above-mentioned "Configuration 1" or [Configuration 2], the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and a load of 70% of the regular load is applied to the tire. The ratio of the contact width of the contact surface of the tire to the cross-sectional width of the tire, which is obtained by bringing the tire into contact with a flat surface, is 74% or more and 84% or less.
By arranging the tire in this way, a contact patch having an appropriate size is formed, and local increases in ground contact pressure are suppressed. Slippage on the shoulder area is also effectively suppressed. This tire can suppress the occurrence of uneven wear.

[Details of embodiments of the present invention]
FIG. 1 shows a part of a tire 2 according to a first embodiment of the present invention. This tire 2 is a pneumatic tire for a passenger car.
FIG. 1 shows a part of a cross section (hereinafter referred to as a meridian cross section) of the tire 2 along a plane including the rotation axis of the tire 2. As shown in FIG. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2. A dashed line CL represents the equatorial plane of the tire 2.
In FIG. 1, the tire 2 is mounted on a rim R (regular rim). The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted.

In FIG. 1, a solid line BBL extending in the axial direction is a bead baseline. This bead baseline is a line that defines the rim diameter of the rim R (see JATMA, etc.).

The position indicated by the symbol PC in FIG. 1 is the intersection of the outer surface of the tire 2 (specifically, the tread surface to be described later) and the equatorial plane. The intersection PC is the equator of the tire 2. When a groove is located on the equatorial plane, the equatorial PC is specified based on a virtual outer surface obtained assuming that there is no groove. The equator PC is the outer end of the tire 2 in the radial direction.

The position indicated by the symbol PW in FIG. 1 is the axially outer end of the tire 2 (hereinafter referred to as outer end PW). If there is decoration such as a pattern or letters on the outer surface, the outer end PW is specified based on a virtual outer surface obtained assuming that there is no decoration.
The axial distance from the first outer end PW to the second outer end PW obtained in the normal state is the cross-sectional width of the tire 2 (see JATMA, etc.). The outer end PW is also called the maximum width position. The maximum width position is a position where the tire 2 exhibits its maximum width. The maximum width obtained in the normal state corresponds to the cross-sectional width.

The position indicated by the symbol PT in FIG. 1 is the toe of the tire 2. Toe PT is the boundary between the outer surface 2G and inner surface 2N of the tire 2.

This tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, a pair of chafers 18, an inner liner 20, and a pair of fixing layers 22. .

The tread 4 makes contact with the road surface at the tread surface 24. The tread 4 has a tread surface 24 that comes into contact with the road surface. Grooves 26 are cut into the tread 4.
The tread surface 24 is a part of the outer surface 2G of the tire 2. A side surface 28 is continuous with the tread surface 24. The tire outer surface 2G includes a tread surface 24 and a pair of side surfaces 28. Tread surface 24 has an equatorial PC. Each side surface 28 has a maximum width position PW.

The tread 4 includes a cap portion 30 and a base portion 32. Cap portion 30 includes tread surface 24 . The cap portion 30 is made of crosslinked rubber with consideration given to wear resistance and grip performance. The base portion 32 is located inside the cap portion 30 in the radial direction. The entire base portion 32 is covered by the cap portion 30. The base portion 32 is made of crosslinked rubber with low heat build-up.

Each sidewall 6 is continuous with the tread 4. The sidewall 6 is located on the radially inner side of the tread 4. The sidewall 6 is made of crosslinked rubber with cut resistance taken into consideration. The sidewall 6 constitutes a part of the side surface 28.

Each clinch 8 is located inside the sidewall 6 in the radial direction. Clinch 8 makes contact with rim R. The clinch 8 is made of crosslinked rubber with consideration given to wear resistance. The clinch 8 constitutes a part of the side part.

Each bead 10 is located inside the clinch 8 in the axial direction. The bead 10 is located inside the sidewall 6 in the radial direction.
The bead 10 includes a core 34 and an apex 36. The core 34 extends in the circumferential direction. Although not shown, core 34 includes steel wire. Apex 36 is located radially outward of core 34 . Apex 36 tapers radially outwardly. The apex 36 is made of crosslinked rubber with high rigidity.

The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between the first bead 10 and the second bead 10 of the pair of beads 10. Carcass 12 includes at least one carcass ply 36.

The carcass 12 of this tire 2 is composed of two carcass plies 38. Although not shown, each carcass ply 38 includes a number of parallel carcass cords. These carcass cords intersect the equatorial plane. The carcass 12 of this tire 2 has a radial structure. In this tire 2, a cord made of organic fiber is used as a carcass cord. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

Of the two carcass plies 38, the carcass ply 38 located radially inward inside the tread 4 is the first carcass ply 40. The carcass ply 38 located on the radially outer side of the first carcass ply 40 inside the tread 4 is the second carcass ply 42 .

The first carcass ply 40 includes a first ply main body 40a and a pair of first folded parts 40b. The first ply main body 40a bridges the beads on both sides. Each of the first folded portions 40b extends from the first ply body 40a and is folded back from the inner side to the outer side in the axial direction at each bead 10.

The second carcass ply 42 includes a second ply main body 42a and a pair of second folded parts 42b. The second ply main body 42a bridges the beads 10 on both sides. Each of the second folded portions 42b is continuous with the second ply main body 42a and folded back from the inner side to the outer side in the axial direction at each bead 10.

In this tire 2, the end of the first folded portion 40b is located on the radially outer side of the maximum width position PW. The end of the second folded portion 42b is located on the radially inner side of the maximum width position PW. The end of the second folded portion 42b is located between the outer end of the apex 36 and the core 34 in the radial direction.
The second folded portion 42b is located inside the first folded portion 40b in the axial direction. The end of the second folded portion 42b is located between the apex 36 and the first folded portion 40b.

The belt 14 is located inside the tread 4 in the radial direction. The belt 14 is laminated to the carcass 12. The aforementioned equatorial plane intersects the belt 14 at the center of its axial width.
In this tire 2, the axial width of the belt 14 is 70% or more and 90% or less of the cross-sectional width of the tire 2.

Belt 14 includes a first layer 44 and a second layer 46. The first layer 44 is located on the radially outer side of the second ply body 42a and is laminated on the second ply body 42a. The second layer 46 is located radially outward of the first layer 44 and is laminated thereon.

As shown in FIG. 1, the ends of the second layer 46 are located radially inward of the ends of the first layer 44. Second layer 46 is narrower than first layer 44 . The length from the end of the second layer 46 to the end of the first layer 44 is 3 mm or more and 10 mm or less. The axial width of the belt 14 described above is represented by the axial width of the wide first layer 44.

Although not shown, the first layer 44 and the second layer 46 each include a number of parallel belt cords. These belt cords are covered with topping rubber. Each belt cord is inclined with respect to the equatorial plane. The material of the belt cord is steel.

Band 16 is located between tread 4 and belt 14 in the radial direction. Band 16 is laminated to belt 14.
The ends of band 16 are located axially outward of the ends of belt 14. The length from the end of the belt 14 to the end of the band 16 is 3 mm or more and 7 mm or less.
Although not shown, band 16 includes a helically wound band cord. The band cord is covered with a topping rubber. The band cord extends substantially circumferentially. Specifically, the angle that the band cord makes with respect to the circumferential direction is 5° or less. The band 16 has a jointless structure.
The band cord is an organic fiber cord. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

Band 16 includes a full band 48 and a pair of edge bands 50.
Full band 48 is laminated to belt 14. Full band 48 covers the entire belt 14. Each end of full band 48 is located axially outwardly of the end of belt 14.
The pair of edge bands 50 are arranged apart from each other in the axial direction across the equatorial plane. Each edge band 50 is laminated to the full band 48. The edge band 50 covers the end 52e of the full band 48.
This band 16 may be composed of only the full band 48. This band 16 may be composed of only a pair of edge bands 50.

Each chafer 18 is located inside the bead 10 in the radial direction. The chafer 18 contacts the rim R. The chafer 18 of this tire 2 is made of cloth and rubber impregnated into the cloth.

Inner liner 20 is located inside carcass 12. The inner liner 20 constitutes the inner surface 2N of the tire 2. The inner liner 20 is made of crosslinked rubber with excellent air shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

The respective fixing layers 22 are arranged apart from each other in the axial direction. The fixing layer 24 is located on the outer side of the belt 14 in the axial direction. The inner end of the fixing layer 22 is located between the cap part 30 and the base part 32. The outer end of the fixing layer 22 is located between the sidewall 6 and the carcass 12. The fixing layer 24 is made of crosslinked rubber with adhesive strength taken into consideration.

FIG. 2 schematically shows a meridian cross section of the tire 2. FIG. 2 shows the contour of the outer surface 2G. The contour line is represented by a virtual outer surface obtained assuming that there are no decorations such as grooves, patterns, or letters. The dotted line in FIG. 2 is a rim guard as an example of decoration.
Although not described in detail, in the present invention, the contour line of the outer surface 2G is obtained by measuring the outer surface shape of the tire 2 in a normal state using, for example, a displacement sensor.

In FIG. 2, the length indicated by the symbol ODX is the maximum outer diameter value of new dimensions specified in the JATMA standard. A solid line DL extending in the axial direction is a dimension line indicating the maximum outer diameter ODX. When the tire name is "235/55R19", the maximum outer diameter ODX of new dimensions is 749 mm.
In FIG. 2, a straight line DBL extending in the axial direction is an outer diameter reference line that indicates an outer diameter that is 4 mm smaller than the maximum outer diameter ODX of new dimensions. The double arrow d is the radial distance from the dimension line DL to the outer diameter reference line DBL. In the present invention, the radial distance d is 2.0 mm. When the tire designation is "235/55R19", the radial distance from the first outer diameter reference line DBL to the second outer diameter reference line DBL (not shown) is 745 mm.
As the maximum outer diameter value ODX, the maximum outer diameter value of new dimensions specified in the ETRTO standard may be used.

In FIG. 2, the length indicated by the symbol AWX is the maximum total width of new dimensions specified in the JATMA standard. A solid line WL extending in the radial direction is a dimension line indicating the maximum total width AWX. If the tire name is "235/55R19", the maximum total width of the new tire is 255 mm.
In FIG. 2, a straight line WBL extending in the radial direction is a total width reference line that indicates a total width that is 5 mm smaller than the maximum total width AWX of new dimensions. The double-headed arrow w is the axial distance from the dimension line WL to the total width reference line WBL. In the present invention, the axial distance w is 2.5 mm. When the tire designation is "235/55R19", the axial distance from the first total width reference line WBL to the second total width reference line WBL (not shown) is 250 mm.
As the maximum total width AWX, the maximum total width of new dimensions specified in the ETRTO standard may be used.

This tire 2 is entirely within an area surrounded by a first outer diameter reference line DBL, a second outer diameter reference line DBL, and a first total width reference line WBL and a second total width reference line WBL. It fits in. In other words, this tire 2 has an outer diameter that is smaller than the maximum outer diameter of new dimensions minus 4 mm as specified in the JATMA standard or ETRTO standard, and a value that is smaller than the maximum total width of new dimensions minus 5 mm. has a total width less than .

The position indicated by the symbol PB1 in FIG. 2 is the intersection of the bead baseline and the equatorial plane. In the present invention, this intersection PB1 is the first reference point.
In FIG. 2, a solid line PCL is a straight line that passes through the equator PC and extends in the axial direction. The solid line PWL is a straight line passing through the maximum width position PW and extending in the radial direction. The position indicated by the symbol PB2 is the intersection of the straight line PCL and the straight line PWL. In the present invention, this intersection PB2 is the second reference point. A line segment connecting the first reference point PB1 and the second reference point PB2 is a reference line segment, and the length indicated by the symbol LBS in FIG. 2 is the length of the reference line segment.
In FIG. 2, the symbol PBG is the intersection of the reference line segment and the outer surface 2G. In the present invention, this intersection PBG is the shoulder reference point. The line segment connecting the first reference point PB1 and the shoulder reference point PBG is the shoulder line segment, and the length indicated by the symbol LSh in FIG. 2 is the length of the shoulder line segment.

In the present invention, the distance from the outer surface 2G of the tire 2 to the wheel house (not shown), measured along a straight line passing through the first reference point PB1 and the second reference point PB2, is shown in FIG. Additionally, there is a gap G formed between the tire T and the wheel house H of the vehicle B. When this gap G becomes less than 22 mm, the tire 2 interferes with the wheel house. In other words, the interference limit clearance amount in the vehicle is 22 mm.

In this tire 2, in the normal state, the ratio (LSh/LBS) of the length LSh of the shoulder line segment to the length LBS of the reference line segment is 85.9% or more and 89.3% or less.
Since the ratio (LSh/LBS) is 89.3% or less, this tire 2 is placed at an appropriate distance from the wheel house. This tire 2 is prevented from interfering with the wheel house. Since the protrusion of the shoulder portion is maintained appropriately, uneven wear can be effectively suppressed.

In conventional tires, the ratio (LSh/LBS) is less than 85.9%. On the other hand, the ratio (LSh/LBS) of this tire 2 is 85.9% or more. This tire 2 has a larger ratio (LSh/LBS) than the conventional tire. Since the shoulder line segment occupies a large proportion of the reference line segment, a gap G close to the interference limit gap amount is formed in this tire 2. In other words, this tire 2 can reduce the gap G.
Since the gap G becomes smaller, the sense of unity between the vehicle and the tire 2 is enhanced. A heightened sense of unity can contribute to improved appearance.

Increasing the ratio (LSh/LBS) in a tire involves modifying the tread surface contour. There is a concern that the ground pressure of the shoulder portion S will increase and uneven wear will occur. It is necessary to adjust the contour of the tread surface in consideration of the effect on uneven wear resistance.

FIG. 3 shows a portion of the contour shown in FIG.
In the meridian cross section, the contour line of the tread surface 24 is composed of a plurality of circular arcs arranged in the axial direction.
Among the plurality of circular arcs, the circular arc located at the center in the axial direction is the center circular arc. The arrow indicated by the symbol Rc in FIG. 3 is the radius of the center arc. The center arc passes through the equator PC. The center of the center arc is located on the equatorial plane.
Among the plurality of circular arcs, the circular arc located on the outside in the axial direction is the shoulder circular arc. The arrow indicated by the symbol Rsh in FIG. 3 is the radius of the shoulder arc. The shoulder arc has the smallest radius Rsh among the plurality of arcs forming the contour of the tread surface 24.
The contour line of the tread surface 24 of this tire 2 includes two circular arcs between the center circular arc and the shoulder circular arc. Of these two arcs, the arc located on the center arc side is the middle arc, and the arc located on the shoulder arc side is the side arc. In FIG. 3, the arrow indicated by the symbol Rm is the radius of the middle arc, and the arrow indicated by the symbol Rs is the radius of the side arc. The radius Rm of the middle arc is smaller than the radius Rc of the center arc. The radius Rs of the side arc is smaller than the radius Rm of the middle arc.
In this tire 2, the plurality of circular arcs constituting the contour line of the tread surface 24 include a center circular arc passing through the equator PC, a pair of shoulder circular arcs located at the outermost side in the axial direction and having the smallest radius Rsh, and a center circular arc. A pair of middle arcs located next to the center arc and having a radius Rm smaller than the radius Rc of the center arc, and a pair of middle arcs located between the middle arc and the shoulder arc and having a radius Rs smaller than the radius Rm of the middle arc. Including side arcs. Specifically, the plurality of arcs includes a center arc, a pair of middle arcs, a pair of side arcs, and a pair of shoulder arcs.

The position indicated by the symbol CM in FIG. 3 is the boundary between the center arc and the middle arc. The middle arc contacts the center arc at the boundary CM. The position indicated by the symbol MS is the boundary between the middle arc and the side arc. The side arc contacts the middle arc at the boundary MS. The position indicated by the symbol SH is the boundary between the side arc and the shoulder arc. The shoulder arc contacts the side arc at the boundary SH. The position indicated by the symbol HU is the boundary between the shoulder arc and the contour line of the side surface 28. The contour line of the side surface 28 touches the shoulder arc at the boundary HU.

The length indicated by the symbol WCM in FIG. 3 is the axial distance from the first boundary CM to the second boundary CM. The center of the axial distance WCM coincides with the position of the equatorial plane. The length indicated by the symbol WMS is the axial distance from the first boundary MS to the second boundary MS. The center of the axial distance WSM coincides with the position of the equatorial plane. The length indicated by the symbol WX is the cross-sectional width of this tire 2.
In this tire 2, the ratio (WCM/WX) of the axial distance WCM to the cross-sectional width WX is 25% or more and 40% or less. The ratio (WMS/WX) of the axial distance WMS to the cross-sectional width WX is 45% or more and 60% or less.

In FIG. 3, straight line LSH is a tangent that touches the shoulder arc at boundary SH. The straight line LHU is a tangent that touches the shoulder arc at the boundary HU. The symbol PE is the intersection of the tangent LSH and the tangent LHU. In the present invention, this intersection PE is the reference end of the tread 4. The length indicated by the symbol WT is the axial distance from the first reference end PE to the second reference end PE. In the present invention, the axial distance WT is the width of the tread 4.

In this tire 2, the ratio (Rc/Rm) of the radius Rc of the center arc to the radius Rm of the middle arc is 1.85 or more and 2.00 or less.
Since the ratio (Rc/Rm) is 1.85 or more, the difference between the radius Rc of the center arc and the radius Rs of the side arc located next to the middle arc can be kept small. Since slippage of the shoulder portion S is effectively suppressed, occurrence of uneven wear is suppressed. This tire 2 provides good resistance to uneven wear.
Since the ratio (Rc/Rm) is 2.00 or less, the shoulder arc can be configured with an arc having a larger radius Rs. The tread surface 24 can be made closer to a flat surface. The tread surface 24 of the tire 2 can effectively contribute to forming a gap G close to the interference limit gap amount. This tire 2 can reduce the gap G.

In this tire 2, when mounted on a vehicle, the gap G formed between the tire 2 and the wheel house H is small. This tire 2 can enhance the sense of unity with the vehicle. This tire 2 can contribute to improving the appearance. As described above, in this tire 2, the contour line of the tread surface 24 is arranged in consideration of the influence on uneven wear resistance. This tire 2 can enhance the sense of unity with the vehicle while maintaining good uneven wear resistance.

As mentioned above, the ratio (Rc/Rm) is 1.85 or more and 2.00 or less. In this tire 2, the ratio (Rc/Rm) is preferably 1.90 or more from the viewpoint of obtaining good uneven wear resistance. From the viewpoint of enhancing the sense of unity between the tire 2 and the vehicle, the ratio (Rc/Rm) is preferably 1.95 or less.

In this tire 2, the ratio (Rm/Rs) of the radius Rm of the middle arc to the radius Rs of the side arc is preferably 2.08 or more and 2.74 or less.
By setting the ratio (Rm/Rs) to 2.08 or more, the tread surface 24 can effectively contribute to forming a gap G close to the interference limit clearance amount while taking into account interference with the wheel house. is configured. This tire 2 can effectively enhance the sense of unity with the vehicle. From this point of view, the ratio (Rm/Rs) is more preferably 2.30 or more.
By grounding the ratio (Rm/Rs) to 2.74 or less, the difference between the radius Rc of the center arc located next to the middle arc and the radius Rm of the side arcs can be kept small. Since slippage of the shoulder portion S is effectively suppressed, occurrence of uneven wear is suppressed. This tire 2 provides good resistance to uneven wear. From this viewpoint, the ratio (Rm/Rs) is more preferably 2.50 or less.

In this tire 2, the ratio (WT/WX) of the width WT of the tread 4 to the cross-sectional width WX is preferably 87% or more and 92% or less.
By setting the ratio (WT/WX) to 87% or more, a ground plane having an appropriate size is formed. Since local ground pressure increases are suppressed, occurrence of uneven wear is suppressed. From this viewpoint, the ratio (WT/WX) is more preferably 88% or more.
By setting the ratio (WT/WX) to 92% or less, slippage of the shoulder portion S can be effectively suppressed. Also in this case, occurrence of uneven wear is suppressed. From this viewpoint, the ratio (WT/WX) is more preferably 91% or less.

In this tire 2, the ratio (Rc/WT) of the radius Rc of the center arc to the width WT of the tread 4 is preferably 3.90 or more and 4.30 or less.
By setting the ratio (Rc/WT) to 3.90 or more, the tread surface 24 can be made closer to a flat surface. The tread surface 24 of the tire 2 can effectively contribute to forming a gap G close to the interference limit gap amount. This tire 2 can reduce the gap G. From this viewpoint, the ratio (Rc/WT) is more preferably 3.95 or more, and even more preferably 4.00 or more.
By setting the ratio (Rc/WT) to 4.30 or less, interference between the tire 2 and the wheel house is suppressed. Since slippage of the shoulder portion S is effectively suppressed, occurrence of uneven wear is suppressed. From this viewpoint, the ratio (Rc/WT) is more preferably 4.25 or less, and more preferably 4.20 or less.

In this tire 2, a portion of the outline of the side surface 28 between the boundary HU and the maximum width position PW is represented by a circular arc. The contour line of the side surface 28 includes an upper arc that is continuous with the shoulder arc and passes through the maximum width position PW. The arrow indicated by the symbol Ru in FIG. 3 is the radius of the upper arc. The center of the upper arc is located on a straight line LW passing through the maximum width position PW and extending in the axial direction.

In this tire 2, the ratio (Ru/WT) of the radius Ru of the upper arc to the width WT of the tread 4 is preferably 0.22 or more and 0.28 or less.
By setting the ratio (Ru/WT) to 0.22 or more, the tread surface 24 can be made closer to a flat surface. The tread surface 24 of the tire 2 can effectively contribute to forming a gap G close to the interference limit gap amount. This tire 2 can reduce the gap G. From this viewpoint, the ratio (Ru/WT) is more preferably 0.23 or more, and even more preferably 0.24 or more.
By setting the ratio (Ru/WT) to 0.28 or less, interference between the tire 2 and the wheel house can be suppressed. Since slippage of the shoulder portion S is effectively suppressed, occurrence of uneven wear is suppressed. From this viewpoint, the ratio (Rc/WT) is more preferably 0.27 or less, and more preferably 0.26 or less.

FIG. 4 shows the shape of the contact patch of this tire 2. In FIG. 4, the left-right direction corresponds to the axial direction of the tire 2. The vertical direction corresponds to the circumferential direction of the tire 2.

As mentioned above, the grooves 26 are cut into the tread 4. The groove 26 includes a groove extending in the circumferential direction (hereinafter referred to as a circumferential groove 52). In this tire 2, four circumferential grooves 52 are cut into the tread 4, and five land portions 54 are formed. The contact surface shape shown in FIG. 4 includes the contours of five land portions 54.

The contact patch is obtained by applying a load of 70% of the normal load to the tire 2 in a normal state using a tire contact patch shape measuring device (not shown) and bringing the tire 2 into contact with a flat surface. By tracing the outline of each land portion 54 included in the ground plane, the ground plane shape shown in FIG. 4 is obtained. To obtain a ground contact surface, the tire 2 is arranged so that its axial direction is parallel to the road surface, and the above-mentioned load is applied to the tire 2 in a direction perpendicular to the road surface.

The position indicated by the symbol GE in FIG. 4 is the axially outer end of the ground plane. The length indicated by the symbol WC is the axial distance from the first axial outer end GE to the second axial outer end GE of the ground plane. In the present invention, this axial distance WC is the ground contact width of the contact surface of the tire 2 obtained by applying a load of 70% of the normal load to the tire 2 in a normal state and bringing the tire 2 into contact with a flat surface. be.

In this tire 2, the ratio (WC/WX) of the ground contact width WC to the cross-sectional width WX of this tire 2 is preferably 74% or more and 84% or less.
By setting the ratio (WC/WX) to 74% or more, a ground plane having an appropriate size is formed. Since local ground pressure increases are suppressed, occurrence of uneven wear is suppressed. From this viewpoint, the ratio (WC/WX) is more preferably 79% or more.
By setting the ratio (WC/WX) to 84% or less, slippage of the shoulder portion S can be effectively suppressed. Also in this case, occurrence of uneven wear is suppressed. From this point of view, the ratio (WC/WX) is more preferably 81% or less.

In FIG. 4, a dashed-dotted line LP is a straight line corresponding to the equator PC of the tire 2 on the ground contact surface. If it is difficult to identify the equator PC on the ground contact surface, the axial center line of the ground contact width WC is used as the straight line corresponding to the equator PC. The double-headed arrow P100 is the length of the line of intersection between the plane containing the straight line LP and the ground plane. In this tire 2, the length P100 of this intersection line is the equatorial ground contact length measured along the equator PC on the ground contact surface.

In FIG. 4, a solid line LE is a straight line that passes through the axially outer end PE of the ground plane and is parallel to the straight line LP. The solid line L80 is located between the straight line LE and the straight line LP, and is a straight line parallel to the straight line LE and the straight line LP. Double-headed arrow A100 represents the axial distance from straight line LP to straight line LE. This distance A100 corresponds to half of the ground contact width WC. Double-headed arrow A80 represents the axial distance from straight line LP to straight line L80. In FIG. 4, the ratio of distance A80 to distance A100 is set to 80%. That is, the straight line L80 represents a position corresponding to 80% of the ground contact width WC of the ground plane. Double-headed arrow P80 is the length of the line of intersection between the plane containing straight line L80 and the ground plane. In this tire 2, the length P80 of this intersection line is the reference ground contact length at a position corresponding to 80% of the ground contact width on the ground contact surface.

In this tire 2, an equatorial ground contact length P100 and a reference ground contact length P80 are specified on the ground contact surface shown in FIG. An index F is obtained.

In this tire 2, the shape index F is preferably 1.05 or more and 1.35 or less.
By setting the shape index F to 1.05 or more, slippage of the shoulder portion is effectively suppressed, and occurrence of uneven wear is suppressed.
By setting the shape index F to 1.35 or less, a ground plane having an appropriate size is formed. Since a local increase in ground pressure is suppressed, occurrence of uneven wear is also suppressed in this case.

The tire 2 described above is manufactured as follows. Although not described in detail, in manufacturing this tire 2, unvulcanized rubber is prepared for the elements constituting the tire 2, such as the tread 4, sidewalls 6, and beads 10.

In manufacturing this tire 2, unvulcanized rubber is shaped in a rubber molding machine (not shown) such as an extruder to prepare a preformed body of a tire component. In a tire molding machine (not shown), an unvulcanized tire 2 (hereinafter also referred to as a green tire) is prepared by combining preformed bodies such as a tread 4, sidewalls 6, and beads 10. .

In manufacturing this tire 2, a green tire is put into a mold of a vulcanizer (not shown). The green tire is pressurized and heated in a mold to obtain a tire 2. The tire 2 is a vulcanized product of a green tire.

The method for manufacturing the tire 2 includes a step of preparing a green tire, and a step of pressurizing and heating the green tire using a mold. Although not described in detail, in manufacturing this tire 2, there are no particular restrictions on vulcanization conditions such as temperature, pressure, time, etc., and general vulcanization conditions are employed.

FIG. 5 shows a part of a cross section of the tire mold 62 along a plane including the rotation axis of the tire 2. As shown in FIG. In FIG. 5, the left-right direction is the radial direction of the tire 2, and the up-down direction is the axial direction of the tire 2. The direction perpendicular to the paper surface is the circumferential direction of the tire 2. The dashed line CL is the equatorial plane of the tire 2. For convenience of explanation, the dimensions of the mold 62 will hereinafter be expressed by the dimensions of the tire 2.

This mold 62 includes a tread ring 64, a pair of side plates 66, and a pair of bead rings 68. In FIG. 5, the mold 62 is in a state in which the tread ring 64, a pair of side plates 66, and a pair of bead rings 68 are combined, that is, in a closed state. This mold 62 is a split mold.

Tread ring 64 constitutes a radially outer portion of mold 62. The tread ring 64 includes a tread forming surface 70 on its inner surface. The tread forming surface 70 shapes the tread surface 24 of the tire 2. The tread ring 64 of this mold 62 is composed of a large number of segments 72. These segments 72 are arranged in a ring shape.

Each side plate 66 is located on the radially inner side of the tread ring 64. The side plate 66 continues to the end of the tread ring 64. The side plate 66 includes a sidewall forming surface 74 on its inner surface. The sidewall forming surface 74 shapes the side surface 28 of the tire 2.

Each bead ring 68 is located inside the side plate 66 in the radial direction. The bead ring 68 continues to the end of the side plate 66. The bead ring 68 includes a bead forming surface 76 on its inner surface. The bead forming surface 76 shapes a portion of the bead 10 of the tire 2, specifically, a portion fitted to the rim R.

In this mold 62, a cavity surface 78 that shapes the outer surface of the tire 2 is configured by combining a large number of segments 72, a pair of side plates 66, and a pair of bead rings 68. The cavity surface 78 includes a tread forming surface 70, a pair of sidewall forming surfaces 60, and a pair of bead forming surfaces 62.

Although not shown, in the pressurization and heating process (hereinafter referred to as the vulcanization process), the green tire 2r is pressed against the cavity surface 78 of the mold 62 by the expanded bladder. This shapes the outer surface of the tire 2.

As described above, in this tire 2, the ratio (LSh/LBS) of the length LSh of the shoulder line segment to the length LBS of the reference line segment is 85.9% or more and 89.3% or less.
In the vulcanization process, the bladder presses the green tire 2r against the cavity surface 78, but since the part of the green tire 2r that the shoulder part contacts is located further back than the part that the crown part contacts, this shoulder part is located at the equator. It is pressed against the cavity surface 78 by the bladder with a force that is slightly weaker than the other parts. In order to sufficiently vulcanize the shoulder portion, it is necessary to set the vulcanization time longer than that for the equator portion or bead portion. If the segments 72, side plates 66, and bead rings 68 are made of the same material, there is a concern that vulcanization will proceed excessively at the equator and bead portions, resulting in a decrease in performance such as rolling resistance.

In this mold 62, the side plates 66 have a higher thermal conductivity than the thermal conductivity of the segments 72. Heat is effectively supplied to the shoulder portion through the side plate 66. Since vulcanization is promoted in the shoulder region, over-vulcanization in the equatorial region is prevented. According to this mold 62, a tire 2 having low rolling resistance can be obtained. From this point of view, it is preferable that the side plate 66 has a higher thermal conductivity than the thermal conductivity of the segments 72. Specifically, the ratio of the thermal conductivity of the side plate 66 to the thermal conductivity of the segment 72 is preferably 2.0 or more, and more preferably 2.5 or more. This ratio is preferably 4.0 or less, more preferably 3.5 or less.

In this mold 62, the side plate 66 has a higher thermal conductivity than the bead ring 68. Heat is effectively supplied to the shoulder portion through the side plate 66. Since vulcanization is promoted in the shoulder region, over-vulcanization in the bead region is prevented. According to this mold 62, a tire 2 having low rolling resistance can be obtained. From this point of view, it is preferable that the side plate 66 has a higher thermal conductivity than that of the bead ring 68. Specifically, the ratio of the thermal conductivity of the bead ring 68 to the thermal conductivity of the bead ring 68 is preferably 2.0 or more, and more preferably 2.5 or more. This ratio is preferably 4.0 or less, more preferably 3.5 or less.

In FIG. 5, the symbol CLm is the equatorial plane of the mold 62. The equatorial line CLm corresponds to the equatorial plane CL shown in FIG. The symbol BBLm is the baseline of the mold 62. This baseline BBLm corresponds to the bead baseline BBL shown in FIG. The symbol PCm is the equator of the cavity surface 78. This equatorial PCm corresponds to the equatorial PC shown in FIG. The symbol PWm is the maximum width position of the cavity surface 78. This maximum width position PWm corresponds to the maximum width position PW shown in FIG. The symbol PB1m is the intersection of the equatorial plane CLm and the baseline BBLm. This intersection point PB1m corresponds to the above-mentioned first reference point PB1, and is also referred to as the first mold reference point. The symbol PB2m is the intersection of a straight line PCLm passing through the equator PCm and extending in the axial direction, and a straight line PWLm passing through the maximum width position PWm and extending in the radial direction. This intersection PB2m corresponds to the second reference point PB2 described above, and is also referred to as a second mold reference point.

In FIG. 5, the position indicated by the symbol PV represents the boundary between the segment 72 and the side plate 66 on the cavity surface 78. This boundary PV is the position where the mold 62 is divided. The angle indicated by the symbol α represents the angle formed by a straight line passing through the first mold reference point PB1m and the second mold reference point PB2m and a straight line passing through the first mold reference point PB1m and the boundary PV. When the boundary PV is located closer to the equator PC than the straight line passing through the first mold reference point PB1m and the second mold reference point PB2m, this angle α is expressed as positive. When the boundary PV is located closer to the maximum width position PW than the straight line passing through the first mold reference point PB1m and the second mold reference point PB2m, this angle α is expressed as a negative value.

As described above, in this mold 62, the shoulder portion of the green tire 2r is pressed against the cavity surface 78 by the bladder with a rather weak force. In the vulcanization process, there is a concern that air may remain in the area between the cavity surface 78 and the shoulder portion.

In this mold 62, a boundary PV between the segment 72 and the side plate 66 is provided at a portion where the shoulder portion abuts. The boundary PV, ie, the split position, functions as an air exhaust route. In this mold, air is effectively discharged even in the portion where the shoulder portion contacts the cavity surface 78 with a weak force. According to this mold 62, a tire 2 with excellent appearance quality can be obtained. From this point of view, it is preferable that the segment 72 and the side plate 66 be separated at a portion where the shoulder portion abuts. Specifically, the angle α is preferably -5 degrees or more and 5 degrees or less, and more preferably -3 degrees or more and 3 degrees or less.

As explained above, according to the present invention, a tire that can achieve improved appearance can be obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
A pneumatic tire for a passenger car (tire size = 235/55R19) having the basic configuration shown in FIG. 1 was obtained.
The ratio (LSh/LBS), ratio (Rc/Rm) and ratio (Rm/Rs) are as shown in Table 1 below.
Set the radius Rc of the center arc, the radius Rm of the middle arc, and the radius Rs of the side arcs as shown in Table 1, adjust the positions of the boundary CM and boundary MS, and set the length LSh of the shoulder segment and the reference line. Minute length LBS was controlled as shown in Table 1.
The ratio (WC/WX) of the ground contact width WC of the ground contact surface to the cross-sectional width WX was 80%.

[Example 2 and Comparative Example 1-2]
Example 2 By adjusting the positions of the boundary CM between the center arc and the middle arc and the boundary MS between the middle arc and the side arcs, the length LSh and the length LBS are controlled as shown in Table 1 below. A tire of Comparative Example 1-2 was obtained.

[Example 3-4 and Comparative Example 3-4]
The radius Rm of the middle arc was set as shown in Table 2 below, the positions of the boundary CM and the boundary MS were adjusted, and the length LSh was controlled as shown in Table 2. A tire of Comparative Example 3-4 was obtained.
When the ratio (WC/WX) of Comparative Example 4 of Example 3-4 and Comparative Example 3-4 was measured, it was 73%.

[Example 5-8]
The radius Rs of the side arc was set as shown in Table 3 below, the positions of the boundary CM and the boundary MS were adjusted, and the length LSh was controlled as shown in Table 3 to obtain the results of Example 5-8. I got a tire.
When the ratio (WC/WX) of Example 5 out of Examples 5-8 was measured, it was 86%.

[Appearance]
The prototype tire was assembled on a rim (size = 19 x 7.5 J) and filled with air to give an internal pressure of 250 kPa. This tire was installed on a test vehicle. With one driver on board and the vehicle stationary, the gap amount G (see FIG. 7) was measured, and the ratio to the interference limit gap amount was calculated. The results are shown in Table 1 below as an index. The closer it is to 100, the better the appearance. When the index is smaller than 100, it means that the gap is small and it is easy to interfere with the wheel house, and when it is larger than 100, it means that the gap is large and the appearance is disadvantageous.

[Uneven wear resistance]
A prototype tire was assembled on a rim (size = 19 x 7.5 J), and the internal pressure was adjusted to 250 kPa by filling it with air. This tire was attached to a wear energy measuring device. The tire wear energy was measured by setting the camber angle to 0° and the slip angle to 0°. A ratio (Ec/Es) as an index of uneven wear resistance was determined from the abrasion energy Ec at the equatorial plane and the abrasion energy Es at the ground contact edge. The results are shown in Table 1 below as an index with Comparative Example 1 as 100. The larger the value, the better the uneven wear resistance.

[comprehensive evaluation]
Comprehensive evaluation was performed based on appearance and uneven wear resistance index. Since appearance is better as it approaches 100, an index for comprehensive evaluation was obtained by subtracting the absolute value of the difference between the appearance index and 100 from the uneven wear resistance index. The results are shown in Table 1-3 below. The larger the value, the better the balance between appearance and uneven wear resistance.

As shown in Table 1-3, in the examples, an improvement in appearance was achieved while suppressing a decrease in uneven wear resistance. From this evaluation result, the superiority of the present invention is clear.

The techniques for improving appearance described above can be applied to various tires.

2... Tire 4... Tread 6... Sidewall 10... Bead 14... Belt 24... Tread surface 28... Side surface

Claims (3)

It has an outer diameter smaller than the value obtained by subtracting 4 mm from the maximum outer diameter of the new dimensions specified in the JATMA standard or ETRTO standard, and has a total width smaller than the value obtained by subtracting 5 mm from the maximum total width of the new dimensions. A tire,
The outer surface of the tire includes a tread surface that contacts the road surface, and a pair of side surfaces that are connected to the tread surface,
The tread surface has an equator that is an intersection with an equatorial plane,
each side surface has a maximum width position at which the tire exhibits a maximum width;
In the meridian cross section of the tire,
The intersection of the bead baseline and the equatorial plane is a first reference point,
The intersection of the straight line passing through the equator and extending in the axial direction and the straight line passing through the maximum width position and extending in the radial direction is a second reference point,
A line segment connecting the first reference point and the second reference point is a reference line segment,
The intersection of the reference line segment and the outer surface of the tire is a shoulder reference point,
A line segment connecting the first reference point and the shoulder reference point is a shoulder line segment,
The contour line of the tread surface is composed of a plurality of circular arcs arranged in the axial direction,
The plurality of circular arcs include a center arc that is an arc passing through the equator, a pair of shoulder arcs that are located on the outermost side in the axial direction and have the smallest radius, and a pair of shoulder arcs that are located next to the center arc and are located next to the center arc, and a pair of middle circular arcs having a radius smaller than the radius, and a pair of side circular arcs located between the middle circular arc and the shoulder circular arc and having a radius smaller than the radius of the middle circular arc,
In a normal state where the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to the tire,
The ratio of the length of the shoulder line segment to the length of the reference line segment is 85.9% or more and 89.3% or less,
The ratio of the radius of the center arc to the radius of the middle arc is 1.85 or more and 2.00 or less,
tire. The ratio of the radius of the middle arc to the radius of the side arc is 2.08 or more and 2.74 or less,
The tire according to claim 1. The contact surface of the tire is obtained by assembling the tire on a regular rim, adjusting the internal pressure of the tire to the regular internal pressure, applying a load of 70% of the regular load to the tire, and bringing the tire into contact with a flat surface. The ratio of the ground contact width to the cross-sectional width of the tire is 74% or more and 84% or less,
The tire according to claim 1 or 2.

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