JP2024063625A - Tire for heavy load - Google Patents

Abstract

To provide a tire for heavy load which improves bead durability.SOLUTION: A first bead apex rubber 81 of a tire 1 for heavy load with a high complex modulus of elasticity includes: a first part 811; a second part 812; and a third part 813. On a first parallel line 541 which is spaced apart by 5 mm distance from a reference straight line 54 at an outer side in a tire radial direction, a length L1 of the second part is 80% - 100% of a total length L2 of the bead apex rubber. On a second parallel line 542 which is spaced apart by 20 mm distance from the reference straight line 54 at an outer side in the tire radial direction, a length L3 of the third part 813 is 0% - 50% of a total length L4 of the bead apex rubber.SELECTED DRAWING: Figure 3

Description

The present invention relates to heavy-duty tires.

Traditionally, various attempts have been made to improve the durability of beads in heavy-duty tires (see, for example, Patent Document 1).

JP 2008-037314 A

However, with recent improvements in vehicle braking performance and increases in load capacity, there is a demand for further improvements in bead durability.

The present invention was devised in light of the above circumstances, and its main objective is to provide a heavy-duty tire with improved bead durability.

The present invention is a heavy-duty tire,
A tread portion;
A pair of sidewall portions;
A pair of bead portions each having a bead core embedded therein;
a carcass extending between the pair of bead portions so as to straddle the bead core;
a pair of bead apex rubbers extending outward in a radial direction of the tire from the bead core,
the carcass includes a carcass ply having a main body portion extending between the bead cores of the pair of bead portions, and a turned-up portion connected to the main body portion and turned up around the bead cores from the inner side in the tire axial direction to the outer side, and extending outward in the tire radial direction,
the bead apex rubber includes a first bead apex rubber disposed adjacent to the main body portion, and a second bead apex rubber disposed outside the first bead apex rubber in the tire axial direction,
a complex elastic modulus of the first bead apex rubber is greater than a complex elastic modulus of the second bead apex rubber,
the first bead apex rubber includes a first portion disposed between an inner side of the bead core in the tire axial direction and the main body portion, a second portion extending from the first portion outward in the tire axial direction so as to cover an outer surface of the bead core in the tire radial direction, and a third portion extending from the second portion outward in the tire radial direction adjacent to the main body portion,
In the meridian section including the tire axis,
The outer surface of the bead core has a reference straight line extending in the tire axial direction,
On a first parallel line that is parallel to the reference line and is spaced 5 mm outwardly from the reference line in the tire radial direction, a length L1 of the second portion is 80% to 100% of a total length L2 of the bead apex rubber,
On a second parallel line that is parallel to the reference line and spaced 20 mm outward in the tire radial direction from the reference line, the length L3 of the third portion is 0% to 50% of the total length L4 of the bead apex rubber.

In the heavy-duty tire of the present invention, the first portion of the first bead apex rubber is disposed between the axially inner side of the bead core and the main body portion, so that distortion of the carcass ply near the bead core is suppressed. This improves bead durability. In addition, on the first parallel line, the length L1 of the second portion is 80 to 100% of the total length L2 of the bead apex rubber, so that distortion of the bead apex and therefore the bead portion near the bead core is suppressed. This improves bead durability. Furthermore, on the second parallel line, the length L3 of the second portion is 0% to 50% of the total length L4 of the bead apex rubber, so that flexibility is easily ensured from the bead portion to the sidewall portion. This improves bead durability.

1 is a meridian cross-sectional view of a tire including a tire rotation axis of a heavy duty tire showing one embodiment of the tire of the present invention. FIG. 2 is a cross-sectional view of the bead portion of FIG. 1 . FIG. 2 is a cross-sectional view of the bead portion of FIG. 1 . FIG. 3 is a cross-sectional view of a modified example of the bead portion of FIG. 2 . FIG. 5 is a cross-sectional view of a modified example of the bead portion of FIG. 4 .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian section including the tire rotation axis of a heavy duty tire 1 of this embodiment.

The heavy-duty tire 1 includes a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4, and a carcass layer 6.

A bead core 5 is embedded in each bead portion 4. The bead core 5 includes a main body portion 51 formed, for example, by winding a steel bead wire in multiple rows and multiple stages with a polygonal cross section, and a wrapping layer 52 surrounding the periphery of the main body portion 51. The wrapping layer 52 may be a rubber layer made only of rubber material, a cord layer with a wrapping cord embedded in rubber material, or a canvas layer made of rubberized canvas cloth, as appropriate.

The bead portion 4 includes a bead apex rubber 8. The bead apex rubber 8 extends radially outward from the bead core.

The carcass layer 6 extends between a pair of bead portions 4 so as to straddle a pair of bead cores 5. The carcass layer 6 includes a carcass ply 6A.

The carcass ply 6A is formed, for example, by covering an arrangement of carcass cords (not shown) with topping rubber. The carcass cords are made of, for example, steel.

The carcass ply 6A has a main body portion 6a and a turned-up portion 6b. The main body portion 6a extends between the bead cores 5 of a pair of bead portions 4. The turned-up portion 6b is connected to the main body portion 6a and is turned up around the bead cores 5 from the inside in the tire axial direction to the outside, extending outward in the tire radial direction.

This heavy-duty tire 1 has a belt layer 7 in the tread portion 2. The belt layer 7 is arranged on the radially outer side of the carcass layer 6. The belt layer 7 is composed of at least one belt ply, and in this embodiment, four belt plies 7A, 7B, 7C, and 7D on the inner and outer sides in the radial direction of the tire. The belt plies 7A, 7B, 7C, and 7D are formed, for example, by covering an arrangement of belt cords with topping rubber. The belt cords are arranged in the circumferential direction of the tire. In other words, it is desirable that the belt cords are arranged at an angle of, for example, 15 to 45 degrees with respect to the tire equator C. It is desirable that the belt cords are highly elastic, such as steel cords.

The bead apex rubber 8 of the carcass ply 6A includes a first bead apex rubber 81 arranged adjacent to the main body portion 6a, and a second bead apex rubber 82 arranged axially outward of the first bead apex rubber 81.

The complex elastic modulus E*1 of the first bead apex rubber 81 is greater than the complex elastic modulus E*2 of the second bead apex rubber 82.

Here, the complex modulus E* is measured by taking a viscoelasticity measurement sample of length 40 mm x width 4 mm x thickness 1 mm from the first bead apex rubber 81 and the second bead apex rubber 82 so that the long side is in the tire circumferential direction. The complex modulus E* is a value measured using a viscoelasticity spectrometer in accordance with the provisions of JIS-K6394 under the following conditions: initial strain: 10%, amplitude: ±1%, frequency: 10 Hz, deformation mode: tension, measurement temperature: 70°C. The width direction of the sample is the tire axial direction.

Figures 2 and 3 show a meridian section including the tire axis of the bead portion 4 of a heavy-duty tire 1 in a normal state, assembled on a normal rim and inflated to normal internal pressure. Hereinafter, each dimension of the heavy-duty tire 1 is measured in the normal state unless otherwise specified. However, dimensions that cannot be measured, such as those of the internal structure, are measured in a state that approximates the normal state using cut sections.

"Genuine rim" refers to the rim radius determined for each tire by the standard system that includes the standard on which the tire is based. For example, JATMA calls it the "standard rim," TRA calls it the "design rim," and ETRTO calls it the "measuring rim." In this application, unless otherwise specified, rim radius refers to the genuine rim.

"Normal internal pressure" is the air pressure set for each tire by each standard in the standard system on which the tire is based. For JATMA, it is the "maximum air pressure." For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRTO, it is the "INFLATION PRESSURE."

The first bead apex rubber 81 includes a first portion 811, a second portion 812, and a third portion 813.

The first portion 811 is disposed between the axially inner side of the bead core 5 and the main body 6a of the carcass ply 6A. The second portion 812 is connected to the first portion 811 and extends from the first portion 811 to the axially outer side so as to cover the radially outer surface 53 of the bead core 5. The third portion 813 is connected to the second portion 812 and extends from the second portion 812 to the radially outer side adjacent to the main body 6a of the carcass ply 6A.

In this heavy-duty tire 1, the first portion 811 is disposed between the axially inner side of the bead core 5 and the main body portion 6a of the carcass ply 6A, suppressing distortion of the carcass ply 6A near the bead core 5. This improves bead durability.

In the meridian section of FIG. 2, the outer surface 53 of the bead core 5 has a reference line 54 extending in the tire axial direction. The reference line 54 is an imaginary line connecting both ends of the outer surface of the bead core 5 in the tire radial direction.

Two parallel lines, a first parallel line 541 and a second parallel line 542, are defined by the reference line 54. The first parallel line 541 is a straight line parallel to the reference line 54 and spaced 5 mm outward from the reference line 54 in the tire radial direction. The second parallel line 542 is a straight line parallel to the reference line 54 and spaced 20 mm outward from the reference line 54 in the tire radial direction.

As shown in FIG. 3, in this heavy-duty tire 1, on the first parallel line 541, the length L1 of the second portion 812 is 80% to 100% of the total length L2 of the bead apex rubber 8. By having the length L1 of the second portion 812 be 80% to 100% of the total length L2 of the bead apex rubber 8, distortion of the bead apex rubber 8 and therefore the bead portion 4 in the vicinity of the bead core 5 is suppressed. This improves bead durability.

Furthermore, in this heavy-duty tire 1, the length L3 of the third portion 813 on the second parallel line 542 is 0% to 50% of the total length L4 of the bead apex rubber 8. This makes it easy to ensure flexibility while maintaining a gentle gradient of stiffness from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

The more desirable range for the length L1 is 90% or less of the length L2. By making the length L1 90% or less of the length L2, distortion of the bead apex rubber 8 and therefore the bead portion 4 in the vicinity of the main body portion 6a of the carcass ply 6A is further suppressed. This improves bead durability.

Moreover, a more desirable range for the length L3 is 30% or more of the length L4. By making the length L3 30% or more of the length L4, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This further distributes stress under load, improving bead durability.

The thickness T perpendicular to the outer edge of the bead core 5 between the axially outer side of the bead core 5 of the first portion 811 and the turned-up portion 6a of the carcass ply 6A is preferably 1.0 to 2.0 mm. By making the thickness T 1.0 mm or more, distortion of the turned-up portion 6a is reduced and bead durability is improved. By making the thickness T 2.0 mm or less, the weight increase of the heavy-duty tire 1 can be suppressed.

Moreover, a more desirable range for the thickness T is 1.5 mm or less. By making the thickness T 1.5 mm or less, distortion of the carcass ply 6A under load is suppressed, and the weight increase of the heavy-duty tire 1 can be suppressed.

The complex elastic modulus E*1 of the first bead apex rubber 81 is preferably 60 to 90 MPa. When the complex elastic modulus E*1 of the first bead apex rubber 81 is 60 MPa or more, distortion of the bead apex rubber 8 and thus the bead portion 4 in the vicinity of the bead core 5 and the main body portion 6a of the carcass ply 6A is suppressed. This improves bead durability. When the complex elastic modulus E*1 of the first bead apex rubber 81 is 90 MPa or less, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

The complex modulus E*1 of the first bead apex rubber 81 is preferably 15 to 30 times the complex modulus E*2 of the second bead apex rubber. By making the complex modulus E*1 of the first bead apex rubber 81 15 times or more the complex modulus E*2 of the second bead apex rubber, distortion of the bead apex rubber 8 and thus the bead portion 4 in the vicinity of the bead core 5 and the main body portion 6a of the carcass ply 6A is suppressed. This improves bead durability. By making the complex modulus E*1 of the first bead apex rubber 81 30 times or less the complex modulus E*2 of the second bead apex rubber, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

Figure 4 is a cross-sectional view of a bead portion 4A of a heavy duty tire 1A, which is a modified version of the heavy duty tire 1 of Figure 1. The configuration of the heavy duty tire 1 described above can be adopted for parts of the heavy duty tire 1A that are not described below.

The bead portion 4A further includes a first reinforcing ply 9 arranged on the outside of the carcass ply 6A from the main body portion 6a of the carcass ply 6A along the turned-up portion 6b.

The first reinforcing ply 9 is formed, for example, by covering a steel reinforcing cord with a topping rubber. The reinforcing cord is arranged in multiple pieces at an angle of 10 to 60 degrees with respect to the tire circumferential direction.

By arranging the first reinforcing ply 9 on the outside of the carcass ply 6A, distortion of the carcass ply 6A and therefore the bead portion 4 near the bead core 5 is suppressed. This improves bead durability.

The radial height H1 from the bead baseline BL of the radial outer end 91 of the first reinforcing ply 9 along the turned-up portion 6b of the carcass ply 6A is preferably 270% to 320% of the radial height H0 from the bead baseline BL of the radial outer end R1 of the flange of the normal rim R. The height H1 is measured from a CT image taken by irradiating an X-ray on a normal pneumatic tire 1 (the same applies to the height H2 below).

By making the height H1 270% or more of the height H0, distortion of the carcass ply 6A and therefore the bead portion 4 in the vicinity of the turned-up portion 6b of the carcass ply 6A is suppressed. This improves bead durability. By making the height H1 320% or less of the height H0, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

The height H1 is preferably 34 to 42 mm. By making the height H1 34 mm or more, distortion of the carcass ply 6A and therefore the bead portion 4 in the vicinity of the turned-up portion 6b of the carcass ply 6A is suppressed. This improves bead durability. By making the height H1 42 mm or less, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

From this perspective, a more desirable range for the height H1 is 38 to 40 mm.

Figure 5 is a cross-sectional view of the bead portion 4B of a heavy duty tire 1B, which is a modified version of the heavy duty tire 1A in Figure 4. For parts of the heavy duty tire 1B that are not described below, the configurations of the heavy duty tires 1 and 1A described above can be adopted.

The bead portion 4B further includes a second reinforcing ply 10 arranged from the radially inner side of the first reinforcing ply 9 to the axially outer side of the tire.

In this embodiment, the second reinforcing ply 10 is formed by covering reinforcing cords made of organic fibers such as nylon with topping rubber. The reinforcing cords are arranged in multiple rows at an angle of 10 to 60 degrees with respect to the circumferential direction of the tire.

By arranging the second reinforcing ply 10 along the first reinforcing ply 9, distortion of the carcass ply 6A and thus the bead portion 4 near the bead core 5 is suppressed. This improves bead durability.

The tire radial height H2 from the bead baseline BL of the tire radial outer end 11 of the second reinforcing ply 10 along the turned-up portion 6b of the carcass ply 6A is preferably 440% to 540% of the tire radial height H0 from the bead baseline of the outer end R1 of the flange of the regular rim R.

By making the height H2 440% or more of the height H0, distortion of the carcass ply 6A and therefore the bead portion 4 in the vicinity of the turned-up portion 6b of the carcass ply 6A is suppressed. This improves bead durability. By making the height H1 540% or less of the height H0, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

The height H2 is preferably 50 to 74 mm. By making the height H2 50 mm or more, distortion of the carcass ply 6A and therefore the bead portion 4 in the vicinity of the turned-up portion 6b of the carcass ply 6A is suppressed. This improves bead durability. By making the height H2 74 mm or less, flexibility is easily ensured while maintaining a gentle gradient of rigidity from the bead portion 4 to the sidewall portion 3. This distributes stress under load and improves bead durability.

From this perspective, a more desirable range for the height H1 is 56 to 68 mm.

As shown in Figures 2 and 3, it is desirable that the radially inner end 821 (see Figure 3) of the second bead apex rubber 82 is disposed radially outward of the reference line 54 (see Figure 2). This suppresses distortion of the carcass ply 6A and thus the bead portion 4 in the vicinity of the bead core 5, improving bead durability.

Heavy-duty tires 1 to 1B of the present invention have been described in detail above, but the present invention is not limited to the specific embodiments described above and may be modified and implemented in various ways.

[Additional Notes]
The present invention includes the following aspects.

[Invention 1]
A heavy-duty tire,
A tread portion;
A pair of sidewall portions;
A pair of bead portions each having a bead core embedded therein;
a carcass extending between the pair of bead portions so as to straddle the bead core;
a pair of bead apex rubbers extending outward in a radial direction of the tire from the bead core,
the carcass includes a carcass ply having a main body portion extending between the bead cores of the pair of bead portions, and a turned-up portion connected to the main body portion and turned up around the bead cores from the inner side in the tire axial direction to the outer side, and extending outward in the tire radial direction,
the bead apex rubber includes a first bead apex rubber disposed adjacent to the main body portion, and a second bead apex rubber disposed outside the first bead apex rubber in the tire axial direction,
a complex elastic modulus of the first bead apex rubber is greater than a complex elastic modulus of the second bead apex rubber,
the first bead apex rubber includes a first portion disposed between an inner side of the bead core in the tire axial direction and the main body portion, a second portion extending from the first portion outward in the tire axial direction so as to cover an outer surface of the bead core in the tire radial direction, and a third portion extending from the second portion outward in the tire radial direction adjacent to the main body portion,
In the meridian section including the tire axis,
The outer surface of the bead core has a reference straight line extending in the tire axial direction,
On a first parallel line that is parallel to the reference line and is spaced 5 mm outward from the reference line in the tire radial direction, a length L1 of the second portion is 80% to 100% of a total length L2 of the bead apex rubber,
On a second parallel line that is parallel to the reference line and is spaced 20 mm outward from the reference line in the tire radial direction, the length L3 of the third portion is 0% to 50% of the total length L4 of the bead apex rubber.
Heavy duty tires.
[Invention 2]
The heavy duty tire according to the first aspect of the present invention, wherein the length L1 is 90% or less of the length L2, and the length L3 is 30% or more of the length L4.
[The present invention 3]
The heavy load tire according to the first or second aspect of the present invention, wherein a thickness T of the first portion between an axially outer side of the bead core and the turned-up portion perpendicular to an outer edge of the bead core is 1.0 to 2.0 mm.
[Invention 4]
A heavy duty tire according to claim 3, wherein the thickness T of the first portion is 1.5 mm or less.
[Invention 5]
The heavy duty tire according to any one of claims 1 to 4, wherein the complex elastic modulus of the first bead apex rubber is 60 to 90 MPa.
[Invention 6]
The heavy load tire according to any one of claims 1 to 5, wherein the complex elastic modulus of the first bead apex rubber is 15 to 30 times the complex elastic modulus of the second bead apex rubber.
[Invention 7]
The heavy duty tire according to any one of claims 1 to 6, further comprising a first reinforcing ply arranged outside the carcass ply along the turn-up portion from the main body portion.
[The present invention 8]
A heavy-duty tire according to Invention 7, wherein a height H1 in the radial direction of the tire from a bead baseline of an outer end in the radial direction of the first reinforcing ply along the turned-up portion is 270% to 320% of a height H0 in the radial direction of the tire from a bead baseline of an outer end in the radial direction of the tire of a flange of a regular rim.
[The present invention 9]
9. The heavy duty tire according to claim 8, wherein the height H1 is 34 to 42 mm.
[Invention 10]
The heavy duty tire according to the 9th aspect of the present invention, wherein the height H1 is 38 to 40 mm.
[Invention 11]
11. The heavy-duty tire according to any one of claims 7 to 10, further comprising a second reinforcing ply arranged from the inner side in the tire radial direction of the first reinforcing ply to the outer side in the tire axial direction.
[Invention 12]
A heavy-duty tire according to the present invention 11, wherein a height H2 in the radial direction of the tire from a bead baseline of an outer end in the radial direction of the second reinforcing ply along the turned-up portion is 440% to 540% of a height H0 in the radial direction of the tire from a bead baseline of an outer end in the radial direction of the flange of a regular rim.
[The present invention 13]
13. The heavy duty tire according to claim 12, wherein the height H2 is 50 to 74 mm.
[The present invention 14]
14. The heavy duty tire according to claim 13, wherein the height H2 is 56 to 68 mm.
[The present invention 15]
15. The heavy duty tire according to any one of claims 1 to 14, wherein an inner end of the second bead apex rubber in the tire radial direction is disposed outward in the tire radial direction from the reference straight line.

1: Heavy load tire 1A: Heavy load tire 1B: Heavy load tire 1mm: Thickness 2: Tread portion 3: Sidewall portion 4: Bead portion 4A: Bead portion 4B: Bead portion 5: Bead core 6A: Carcass ply 6a: Main body portion 6b: Turn-up portion 8: Bead apex rubber 9: First reinforcing ply 10: Second reinforcing ply 11: Outer end 51: Main body portion 53: Outer surface 54: Reference straight line 81: First bead apex rubber 82: Second bead apex rubber 91: Outer end 541: First parallel line 542: Second parallel line 811: First portion 812: Second portion 813: Third portion 821: Inner end BL: Bead baseline H0: Height H1: Height H2: Height R: Regular rim R: Rim R1 : Outer end T : Thickness

Claims (15)

A heavy-duty tire,
A tread portion;
A pair of sidewall portions;
A pair of bead portions each having a bead core embedded therein;
a carcass extending between the pair of bead portions so as to straddle the bead core;
a pair of bead apex rubbers extending outward in a radial direction of the tire from the bead core,
the carcass includes a carcass ply having a main body portion extending between the bead cores of the pair of bead portions, and a turned-up portion connected to the main body portion and turned up around the bead cores from the inner side in the tire axial direction to the outer side, and extending outward in the tire radial direction,
the bead apex rubber includes a first bead apex rubber disposed adjacent to the main body portion, and a second bead apex rubber disposed outside the first bead apex rubber in the tire axial direction,
a complex elastic modulus of the first bead apex rubber is greater than a complex elastic modulus of the second bead apex rubber,
the first bead apex rubber includes a first portion disposed between an inner side of the bead core in the tire axial direction and the main body portion, a second portion extending from the first portion outward in the tire axial direction so as to cover an outer surface of the bead core in the tire radial direction, and a third portion extending from the second portion outward in the tire radial direction adjacent to the main body portion,
In the meridian section including the tire axis,
The outer surface of the bead core has a reference straight line extending in the tire axial direction,
On a first parallel line that is parallel to the reference line and is spaced 5 mm outward from the reference line in the tire radial direction, a length L1 of the second portion is 80% to 100% of a total length L2 of the bead apex rubber,
On a second parallel line that is parallel to the reference line and is spaced 20 mm outward from the reference line in the tire radial direction, the length L3 of the third portion is 0% to 50% of the total length L4 of the bead apex rubber.
Heavy duty tires. The heavy-duty tire according to claim 1, wherein the length L1 is 90% or less of the length L2, and the length L3 is 30% or more of the length L4. The heavy-duty tire according to claim 1, wherein the thickness T of the first portion perpendicular to the outer edge of the bead core between the axially outer side of the bead core and the rolled-up portion is 1.0 to 2.0 mm. The heavy-duty tire according to claim 3, wherein the thickness T of the first portion is 1.5 mm or less. The heavy-duty tire according to claim 1, wherein the complex elastic modulus of the first bead apex rubber is 60 to 90 MPa. The heavy-duty tire according to claim 1, wherein the complex elastic modulus of the first bead apex rubber is 15 to 30 times the complex elastic modulus of the second bead apex rubber. The heavy-duty tire according to claim 1, further comprising a first reinforcing ply arranged on the outside of the carcass ply along the turnup portion from the main body portion. a height H1 in the radial direction of the tire from a bead baseline of an outer end of the first reinforcing ply in the radial direction of the tire along the turned-up portion is 270% to 320% of a height H0 in the radial direction of the tire from a bead baseline of an outer end of a flange of a regular rim in the radial direction of the tire;
8. A heavy duty tire according to claim 7. The heavy-duty tire according to claim 8, wherein the height H1 is 34 to 42 mm. The heavy-duty tire according to claim 9, wherein the height H1 is 38 to 40 mm. The heavy-duty tire according to claim 7, further comprising a second reinforcing ply arranged from the inner side in the tire radial direction to the outer side in the tire axial direction of the first reinforcing ply. The heavy-duty tire according to claim 11, wherein the tire radial height H2 from the bead baseline of the tire radial outer end of the second reinforcing ply along the turned-up portion is 440% to 540% of the tire radial height H0 from the bead baseline of the tire radial outer end of the flange of a regular rim. The heavy-duty tire according to claim 12, wherein the height H2 is 50 to 74 mm. The heavy-duty tire according to claim 13, wherein the height H2 is 56 to 68 mm. The heavy-duty tire according to claim 1, wherein the inner end of the second bead apex rubber in the tire radial direction is disposed outside the reference straight line in the tire radial direction.

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