JP2702495B2 - Radial tires for heavy loads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is an improvement in a metal cord applied to a carcass ply of a radial tire, and a radial tire for a truck and a bus, and a radial for a light truck, in which the durability life is greatly improved. The present invention relates to a technology for providing a heavy load radial tire such as a tire.

(Prior art) In recent years, in response to increasing social needs such as resource saving and energy saving, radial tires have been reduced in weight, rolling resistance has been reduced, and the life of products has been extended by improving the rehabilitation life.
The demand for flattening is also occurring in heavy duty radial tires. When developing a tire that meets such demands, it is important to solve the problems of corrosion fatigue resistance and fretting resistance of a metal cord as a carcass ply material.

Therefore, from the viewpoint of input to the carcass ply cord, as a method of reducing the contact pressure between the cord filaments, a steel cord having a 3 + 9 two-layer twist structure (Japanese Patent Laid-Open No.
(Japanese Patent Application No. 60-35215) and compact cord twisted structure with close-packed structure such as 1 × 12
In order to further improve the corrosion fatigue resistance and the fretting resistance described above, studies have been made on the twist properties and the like of these cords (JP-A-59-124404).

On the other hand, as a belt outermost layer cord of a large-diameter tire for rough roads, a single-layer twisted structure of 1 × 4 twist or 1 × 5 twist obtained by twisting a pre-molded filament or 1 layer
A tire using a twisted cord having a two-layer twisted structure having about two filaments as a core is disclosed in Japanese Patent Application Laid-Open No. 60-116504.

(Problems to be Solved by the Invention) The present inventors have made intensive studies to develop a heavy duty radial tire capable of greatly improving the durability life, and found that the conventional 3 + 9 two-layer twisted structure and 1 × In the compact cord twist structure of 12, the contact pressure between filaments is high,
For this reason, when this structure is applied to carcass ply cords such as radial tires for trucks and buses (TBR) and radial tires for light trucks (LSR), fretting is caused due to severe input, causing a reduction in strength and causing radial tires for heavy loads. There is a problem that the case durability is greatly reduced, and a problem that the corrosion resistance and fatigue resistance is significantly reduced.

On the other hand, the technique described in Japanese Patent Application Laid-Open No. 60-116504 relates to an improvement technique for a belt layer of a large-diameter tire for rough roads and can respond to recent social demands such as reduction in the weight of a radial tire. In addition, it is impossible to apply such a technique to a carcass ply as it is because of problems in bead durability and case strength.

Furthermore, Japanese Patent Application Laid-Open No. 57-51502 discloses that most filaments constituting a steel cord contain carbon in a range of 0.75 to 0.85.
There is disclosed a pneumatic tire in which a steel cord having a twist structure of 7 × 4 having a high tensile strength and being applied as a reinforcing material for a carcass ply is used. However, since this steel cord has a multi-twisted structure of 7 × 4, fretting between strands is very large, and could not be consistent with the solution of the technical problem aimed at by the present invention.

Accordingly, an object of the present invention is to significantly reduce the weight of the tire, improve the corrosion fatigue resistance and the fretting resistance, which are the above-mentioned problems, and at the same time, improve the performance of the radial tire in terms of the side trauma resistance (cord resistance). It is an object of the present invention to provide a technique for improving a heavy-duty radial tire that can significantly improve the tire performance.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides at least one layer arranged at an angle of substantially 90 ° on the equatorial plane of a tire and wound from inside to outside around a bead core. In a heavy-duty radial tire having a carcass ply, as a reinforcing material for the carcass ply, a filament diameter is 0.13 to 0.32 mm.
In single-twist structure of the metal filaments formed by twisting three to five is, and a metal cord elongation P ₁ is from 0.35 to 1.0% as an arithmetic mean value between the up load 0.25~5kg f / present, the The gap between the cords at the end of the carcass ply is 0.25mm or more, and the tires have a load index according to ISO 4209/1 (Lo
ad Index) is 100 or more and 121 or less, the tensile strength TS (kg f / mm ² ) of the metal filament and the filament diameter d
(Mm) is the following 1) to 3), 1) When the number of metal filaments is 5 (Where d = 0.13 to 0.25) 2) When the number of metal filaments is four (Where d = 0.14 to 0.25) 3) When the number of metal filaments is three (Where d = 0.15 to 0.25). When the tire has a load index of 122 or more according to ISO 4209/1, the tensile strength TS (kg f / mm ² ) And filament diameter d (mm) in the following 1) to 3), 1) When the number of metal filaments is 5 (Where d = 0.15 to 0.32) 2) When the number of metal filaments is four (Where d = 0.16 to 0.32) 3) When the number of metal filaments is three (Where d = 0.17 to 0.32).

In addition, a single twist structure of a metal cord formed by twisting 3 to 5 metal filaments is specifically referred to as 1 × 3,
Notated as 1 × 4 and 1 × 5.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The present invention relates to the heavy load radial tire, wherein the IS
O 4209/1 Load Index
When the tensile strength TS (kg f / mm ² ) of the metal filament and the filament diameter d (mm) are 100 or more and 121 or less, the following 1) to 3) relationships: 1) When the number of metal filaments is 5 Case (A in FIG. 1) (Where d = 0.13 to 0.25) 2) When the number of metal filaments is four (A in FIG. 2) (Where d = 0.14 to 0.25) 3) When the number of metal filaments is three (A in FIG. 3) (Where d = 0.15 to 0.25).

More preferably, in the heavy load radial tire, when the load index is 100 or more and 121 or less, the tensile strength TS (kg f / mm ² ) of the metal filament is used.
And the filament diameter d (mm) in the following 1) to 3), 1) When the number of metal filaments is 5 (B in FIG. 1) (Where d = 0.18 to 0.25) 2) When the number of metal filaments is 4 (B in FIG. 2) (Where d = 0.18 to 0.25) 3) When the number of metal filaments is three (B in FIG. 3) (Where d = 0.21 to 0.25).

That is, FIGS. 1 to 3 (and FIGS. 4 to 6 described later).
Shows the conditions for obtaining the case strength necessary to improve the side trauma resistance. Trauma can be ensured. Outside of this range, it is necessary to increase the number of shots in order to obtain the required case strength, and the endurance of the carcass ply end is greatly reduced, so that the intended purpose cannot be achieved.

In the present invention, in the heavy-duty radial tire, when the load index is 122 or more, the tensile strength TS (kg f / mm ² ) and the filament diameter d (mm) of the metal filament are as follows: 1) When the number of metal filaments is 5 (A in FIG. 4) (Where d = 0.15 to 0.32) 2) When the number of metal filaments is four (A in FIG. 5) (Where d = 0.16 to 0.32) 3) When the number of metal filaments is three (A in FIG. 6) (Where d = 0.17 to 0.32).

More preferably, in the heavy-duty radial tire, when the load index is 122 or more, the tensile strength TS (kg f / mm ² ) and the filament diameter d (mm) of the metal filament are as follows: 3) 1) When the number of metal filaments is 5 (B in FIG. 4) (Where d = 0.21 to 0.32) 2) When the number of metal filaments is 4 (B in FIG. 5) (Where d = 0.23 to 0.32) 3) When the number of metal filaments is three (B in FIG. 6) (Where d = 0.27 to 0.32).

On the other hand, the twist pitch of the metal cord in the present invention is 5 to 5.
Select appropriately within the range of 20 mm.

The metal cord according to the present invention is that all or most of the filaments adjacent are in substantial contact, i.e. elongation P ₁ between up load 0.25～5Kg / book 0.25% or less as an arithmetic mean It is important that More preferably, it is 0.2% or less.

Here, Shore A is used as the rubber covering the metal cord.
It is preferable to use a rubber composition having a hardness of 60 to 80 because the durability of the end portion of the carcass ply is further improved.

(Operation) In the present invention, since the metal cord has a single twist structure, contact between filaments of the metal cord is reduced, so that fretting resistance is significantly improved and corrosion fatigue resistance is also improved.

In the present invention, elongation P ₁ in until load 0.25~5kg f / the 0.25% or less arithmetic mean value, preferably 0.
Was set to 2% or less, the elongation P ₁ is 0.25% or less, preferably when a person is not more than 0.2% for manufacturing a metal cord-rubber composite serving Treat aligned pull the metal cord, easily aligned pull Because. Further, when the metal cords are arranged in a uniform manner, the stress load of the carcass ply driven into the tire becomes uniform, and the tire carcass fly durability is improved.

In addition, when the metal filament is twisted by 1 × 2, the cord strength is small, and it is impossible to maintain the case strength that can withstand the external damage of the side portion. In this case, a 1 × 3 twist is applied to maintain the case strength to withstand the side damage.
It is necessary to increase the number of shots or to increase the filament diameter as compared with × 4 twist and 1 × 5 twist. However, the former is difficult due to the problem of tire manufacturing technology and the problem of bead portion durability reduction, and the latter is a filament. A remarkable increase in bending stiffness in proportion to the fourth power of the diameter causes a problem in that a bead floats off the cord from the bead or a decrease in corrosion fatigue resistance due to an increase in input. On the other hand, in the case of the 1 × 6 twist or more, at least one of the finments is inevitably dropped into the inside and has a substantially two-layer structure, which causes a problem in fretting resistance and corrosion fatigue resistance. Therefore, in order to satisfy the required case strength, manufacturing suitability, etc., and to ensure the corrosion fatigue resistance and the fretting resistance, it is not necessary to use a single-layer twist of 1 × 3 twist, 1 × 4 twist or 1 × 5 twist. And preferably 1 × 4 twist or 1 × 5 twist.

The lower limit of the diameter of such a filament is related to the required case strength retention and the reduction in the durability of the end portion of the carcass ply, and the upper limit is related to the bead floating and the decrease in corrosion fatigue resistance due to the increase in bending rigidity. Therefore, in the present invention, as described above, the filament has a load index of 10
In the case of a heavy load radial tire having a size of 0 or more and 121 or less, the width is limited to 0.13 to 0.25 mm in the case of 1 × 5 twist. Preferably, it is in the range of 0.18 to 0.25 mm. Also, 1 × 4
In the case of twist, it is limited to 0.14 to 0.25 mm, preferably 0.19 to 0.25 mm.
Within the range of ~ 0.25mm. Furthermore, in the case of 1 × 3 twist,
It is limited to 0.15 to 0.25 mm, preferably within a range of 0.21 to 0.25 mm.

Similarly, in a heavy duty radial tire having a load index of 122 or more, when burning 1 × 5,
It is limited to 0.15 to 0.32 mm, and preferably within the range of 0.21 to 0.32 mm. In the case of 1 × 4 twist, the width is limited to 0.16 to 0.32 mm, and preferably within the range of 0.23 to 0.32 mm. Furthermore, in the case of 1 × 3 twist, the width is limited to 0.17 to 0.32 mm, and preferably within the range of 0.27 to 0.32 mm.

In the present invention, if the relationship between the tensile strength (TS) and the filament diameter (d) described above is satisfied, the cord diameter of the metal cord can be suppressed, and the case strength can be reduced without impairing the durability of the end portion of the carcass ply. The improvement can be achieved, and the breakage of the metal cord due to the cut of the sidewall portion can be improved.

Among the metal filaments of the present invention, those having high tensile strength have, for example, a surface reduction rate of 97.5% and the number of drawing times is increased three to four times as compared with ordinary drawing by using a lubricant having a good drawing property. It can be made by performing multi-step drawing. The carbon content of the metal filament is preferably from 0.72 to 0.95%, and more preferably from 0.82 to 0.95%, since higher tensile strength can be obtained. However, if it exceeds 0.95%, the metal filament becomes brittle, which is not preferable. It is preferable that the area reduction rate is 96% or more.

In addition, the metal filament according to the present invention is preferably a steel filament, and usually uses a material coated with a single metal of Cu, Zn, Ni or Co, or an alloy such as a Cu-Zn alloy (brass).

(Examples) Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

As evaluation tires, TBR 11R24.5 having a load index of 140 (Examples 1 to 6, Comparative Examples 1 to 7) and LSR750R16 having a load index of 108 (Examples 7 to 6)
10, Comparative Examples 8 to 10) were used respectively.

In the case of 11R24.5, the carcass ply structure was 3 + 9 in the control tire of Comparative Example 1 as shown in Table 1.
× 0.23mm + 1 steel cord in the tire circumferential direction
At an angle of 90 °, it is arranged at a driving density of 26 pieces / 50 mm,
In the tires of the other comparative examples and examples, the steel cords to which each carcass ply shown in Table 1 was applied were determined at the same angle with respect to the circumferential direction and so as to conform to the case strength of the control tire of Comparative Example 1. They were arranged by the number of shots.

Further, in the case of 750R16, as shown in Table 2, in the control tire of Comparative Example 8, 3 + 9 × 0.19 mm + 1 steel cords were arranged at an angle of 90 ° with respect to the tire circumferential direction at a driving density of 30 wires / 50 mm. In the tires of Comparative Example and Example, the driving angle was determined at the same angle with respect to the circumferential direction of the steel cord to which each carcass ply is applied as shown in Table 2 and adapted to the case strength of the control tire of Comparative Example 8. Sequenced by number.

As the coating rubber, a rubber composition containing 100 parts by weight of natural rubber having a shear A hardness of 68 and 50 parts by weight of carbon black HAF was used.

The following performance evaluations were performed on the prototype tire.

Fretting resistance From the prototype tire (the same method for running tires and new tires), the cord of the carcass cord layer with rubber from one bead to the other bead is pulled out and cut in half at the crown center. Next, the rubber is dissolved with a solvent and loosened one by one. Place the crown center end and bead side end of each unraveled filament between chucks and set them on a microscope so that the fracture surface of the filament obtained by measuring the strength with a tensile tester can be seen from directly above, and then enlarged. Take a photograph, cover the enlarged photograph with graph paper and draw a circle along the rim of the portion where no fretting occurs. FIG. 7 shows the portion 2 where the fretting occurred against the non-abraded portion 1 where no fretting occurred. The value obtained by measuring the area S and dividing by the cross-sectional area of the new steel filament was obtained for 10 steel cords and the average was the fretting amount.

In the case of TBR 11R24.5 tires, this value is
In the case of LSR 750R16, Comparative Example 8 was set as 100 as a control tire, and the index was shown so that the smaller the fretting amount, the larger the index.
This is the fretting resistance of the table.

Corrosion fatigue resistance (degree of decrease) As shown in FIG. 8, the test method is as follows. A rubber cord 3 taken out of a tire is hung on three pulleys 4 having a diameter of 40 mm as shown in FIG. Tensile load is applied to the weight 6 corresponding to 10% of the cord breaking load, and the three pulleys are repeatedly moved 20 cm left and right to repeatedly apply bending strain to the cord to cause the cord to fatigue-rupture. The value of the degree of decrease in corrosion fatigue resistance is the value obtained as the average number of times of breakage, and the degree of decrease in corrosion resistance compared to that of a new tire is set to 100 for the code of a new tire.
The corrosion fatigue resistance shown in Tables 1 and 2 is based on the above values.
In the case of TBR 11R24.5 tires, use Comparative Example 1 and LSR 750
In the case of R16, control example 8 was used as the control tire,
The index value is set to 00, which is indicated by an index value. The larger the value, the better the corrosion fatigue resistance.

Side trauma resistance A steel cord used for a prototype tire is embedded vertically in rubber in a 3 mm thick, 50 mm wide, 300 mm long sample. Apply a certain tension, drop a 20kg blade with a blade that falls naturally at right angles to the cord direction, and compare the side trauma resistance with the cutting height. In Tables 1 and 2, this property is shown with the control tires of Comparative Examples 1 and 8 as 100, and the larger the numerical value, the better the side trauma resistance.

Carcass ply end fracture resistance The tread rubber of the prototype tire is buffed, and the carcass ply end fracture resistance is evaluated in a state where the belt layer does not fail due to the heat generated by the belt layer. Specifically, load each prototype tire
JIS 200%, speed 60km / hr, internal pressure 8.25kg / 11R24.5
In the case of cm ² and 750R16, turn on the drum under the condition of internal pressure 8.0 kg / cm ² , separation occurs at the tip of the carcass ply cord, and the drum travel distance when vibration increases becomes the respective travel distance as a comparative example It was indicated by an index in comparison with the control tires of Comparative Example 1 and Comparative Example 8. The larger the value, the better the carcass ply end resistance.

Weight reduction effect The steel cord used for the prototype tire is filled with carcass coating rubber to make a ply treat composite,
In order to obtain the same strength as the ply treat of the control tire of Comparative Example 1 as a composite, the steel cord used to reduce the weight by reducing the number of shots when changing the number of shots of each trial treatment is used per tire. Comparative Examples 1 and 8 are shown in terms of the weight used as a control tire comparison index. The smaller the value, the better the weight reduction effect.

Measurement method of elongation P ₁ After removing the rubber of the steel cord sample removed from the tire, 200 mm length between chucks, tensile speed 5 mm
/ min, full-scale 10 kg, using an Instron-type tensile tester to calculate the elongation between a load of 0.25 and 5 kgf / line by a load-elongation test, and calculate the arithmetic average of the results of the 50-line test to obtain an elongation P ₁ And

The performance evaluation results of the prototype tire described above were compared with the TBR11R2
See Table 1 below for the 4.5 tires and LSR 750R1
The tires No. 6 are shown in Table 2 below.

From the test results shown in Tables 1 and 2, the following was confirmed.

First, the case of the TRB11R24.5 tire shown in Table 1 will be described.

Although the twisted structures of Examples 1, 4, and 5 are all 1 × 5,
In the fourth embodiment, since the tensile strength is slightly deviated from the optimum range in relation to the filament diameter, the case strength is slightly lower than in the first embodiment due to the limitation of the driving limit. For this reason, the side trauma resistance is slightly lower than that of Example 1, and the carcass ply edge end fracture resistance is slightly inferior due to the increased number of shots. However, all the performances were significantly improved as compared with the control of Comparative Example 1.

In Example 5, the case strength is lower than the driving limit because the filament diameter is at the lower limit of the optimum range of the filament diameter in relation to the tensile strength. Therefore, the side trauma resistance in Example 1
The carcass ply ends are somewhat inferior in breaking resistance due to the large number of shots. However, in comparison with the control of Comparative Example 1, the results are sufficiently good, and the weight reduction effect is also good.

Examples 2 and 3 are examples of a 1 × 3 and 1 × 4 twisted structure, respectively, in which the number of filaments is smaller than in Example 1. For this reason, it is necessary to maintain the case strength at a certain level or more in order to maintain the side trauma resistance. Therefore, in these embodiments, the filament diameter is increased and the number of shots is increased. For this reason, the corrosion fatigue resistance and the carcass ply end fracture resistance are slightly deteriorated as compared with Example 1, but are equal to or higher than the control.

Example 6 is an example of a structure in which a spiral of 1 × 5 + 1 is wound. By winding the spiral, the contact pressure is increased, and the fretting resistance and corrosion fatigue resistance are slightly improved in comparison with the control of Comparative Example 1. To the extent, the side trauma resistance and the carcass ply edge fracture resistance are comparable to the control. The effect of reducing the weight is good.

Comparative Example 2 is an example in which the tensile strength is too low, and the case strength is significantly reduced, and the side trauma resistance is significantly reduced. It is necessary to increase the number of driving in order to secure the fracture resistance of the end portion of the carcass ply.

Comparative Example 3 is an example in which the number of shots was increased in order to increase the side trauma resistance of Comparative Example 2, but on the contrary, the carcass ply end fracture resistance was significantly reduced.

Comparative Example 4 is an example in which the filament diameter is too small. In this example, even if the filament is driven to the driving limit, the case strength is insufficient, the side trauma resistance is not increased, and the carcass ply end fracture resistance is significantly reduced. . Further, when the tire side is hit by a curb, the cord is bent due to buckling.

Comparative Example 5 is an example in which the filament diameter is too large. In this example, the corrosion fatigue resistance is lower than in Comparative Example 1 because the filament diameter is too large.

Comparative Examples 6 and 7 are examples of 1 × 2 and 1 × 6 twisted structures, respectively. In the case of 1 × 2, the number of filaments is too small, and the filament diameter is large enough not to reduce the corrosion fatigue resistance. Even when the number of shots was increased to near the driving limit because the side trauma resistance was reduced, the side trauma resistance was equivalent to that of the control, but the carcass ply end fracture resistance was reduced.

On the other hand, in the case of 1 × 6, since the twist structure is unstable, one filament is dropped and the filaments are entangled, and a large contact pressure is generated in some parts, and the corrosion fatigue resistance compared with the control is greatly reduced. doing.

Next, the case of the LSR750R16 tire shown in Table 2 will be described.

Example 7 has a 1 × 5 twist structure and a filament diameter of 0.21 m.
m and tensile strength of 380 kg / mm ^{2. In} this example, the performance such as corrosion resistance and fretting resistance is much better than the control of Comparative Example 8.

Embodiments 8 and 9 are examples of the 1 × 3 and 1 × 4 twisted structures, respectively, in which the filament diameter is increased or the number of shots is increased due to the necessity of maintaining the case strength at a certain value or more. In these examples, various performances were slightly deteriorated as compared with the example 7, but compared with the control of the comparative example 8, the same or more durability was shown.

Example 10 is a case where there is a spiral. The presence of the spiral increases the contact pressure and the durability is at the same level as Comparative Example 8, but has a weight reducing effect.

Comparative Example 9 is an example of a 1 × 2 twist structure. in this case,
After increasing the number of shots to maintain case strength,
The carcass ply end portion has deteriorated in fracture resistance. Furthermore, even if such measures are taken, the side trauma resistance is inferior to the control because the case strength is still low.

Comparative Example 10 is an example of a 1 × 6 twisted structure. In this example, since one filament is easily dropped, the filament is entangled in a portion where the filament is present, the contact pressure is significantly increased, and the corrosion fatigue resistance is controlled. (Comparative Example 8) The comparison is poor.

(Effects of the Invention) As is clear from the tire performance evaluation results shown in Tables 1 and 2, all of the performances of the prototype tire of the present invention are greatly improved.
The durability life of heavy duty radial tires such as a radial tire for a bus and a radial tire for a light truck can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the metal filament diameter d of a 1 × 5 open twisted structure and the tensile strength TS of the filament at a load index of 100 to 121, and FIG. 2 is a load index of 100 to 121. Is a graph showing the relationship between the metal filament diameter d of the 1 × 4 open-twisted structure and the tensile strength TS of the filament. FIG. 3 is a diagram showing the diameter of the metal filament of the 1 × 3 open-twisted structure at a load index of 100 to 121. 4 is a graph showing the relationship between d and the tensile strength TS of the filament.
5 is a graph showing the relationship between the metal filament diameter d of the open twist structure and the tensile strength TS of the filament, FIG.
4 is a graph showing the relationship between the metal filament diameter d of the open twisted structure and the tensile strength TS of the filament. FIG. 6 shows 1 × at a load index of 122 or more.
3 is a graph showing the relationship between the metal filament diameter d of the open twisted structure and the tensile strength TS of the filament, FIG. 7 is an explanatory diagram of a fretting resistance test, and FIG. 8 is an explanatory diagram of a corrosion fatigue test. . 1 ... non-wearing part 2 ... part where fretting occurred 3 ... cord with rubber, 4 ... pulley 5 ... fixed pulley, 6 ... weight

Claims (4)

(57) [Claims] 1. A carcass ply comprising at least one carcass ply arranged at an angle of substantially 90 ° in the tire equatorial plane and wound inward and outward around a bead core, and having a load index of 100 according to ISO 4209/1. In the heavy duty radial tire having a diameter of not less than 121 or less, as a reinforcing material of the carcass ply, a filament diameter is
A metal cord having a single-twisted structure in which three to five metal filaments of 0.13 to 0.32 mm are twisted together, and an elongation P ₁ of 0.25% or less as an arithmetic mean value between 0.25 and 5 kgf / wire Are arranged so that the cord gap at the end of the carcass ply is 0.25 mm or more, and the tensile strength TS (kg f / mm ² ) of the metal filament and the filament diameter d (mm) are the following 1) to 3). Relationship: 1) When the number of metal filaments is 5 (Where d = 0.13 to 0.25) 2) When the number of metal filaments is four (Where d = 0.14 to 0.25) 3) When the number of metal filaments is three (Where d = 0.15 to 0.25). A radial tire for heavy loads, characterized in that: 2. Tensile strength TS of metal filament (kg f / mm ² )
And the filament diameter d (mm) are the following 1) to
3) Relationship 1) When the number of metal filaments is 5 (Where d = 0.18 to 0.25) 2) When the number of metal filaments is four (Where d = 0.19 to 0.25) 3) When the number of metal filaments is three 2. The heavy-duty radial tire according to claim 1, wherein d = 0.21 to 0.25. 3. A carcass ply comprising at least one layer of carcass plies arranged substantially at an angle of 90 ° in the tire equatorial plane and wound inwardly and outwardly around a bead core, and having a load index of 122 according to ISO 4209/1. In the heavy load radial tire described above, the filament diameter is as a reinforcing material of the carcass ply.
A metal cord having a single-twisted structure in which three to five metal filaments of 0.13 to 0.32 mm are twisted together, and an elongation P ₁ of 0.25% or less as an arithmetic mean value between 0.25 and 5 kgf / wire Are arranged so that the cord gap at the end of the carcass ply is 0.25 mm or more, and the tensile strength TS (kg f / mm ² ) and the filament diameter d (mm) of the metal filament are 1) to 3) below. Relationship: 1) When the number of metal filaments is 5 (Where d = 0.15 to 0.32) 2) When the number of metal filaments is four (Where d = 0.16 to 0.32) 3) When the number of metal filaments is three (Where d = 0.17 to 0.32). A radial tire for heavy loads, characterized in that: 4. The tensile strength TS of a metal filament (kg f / mm ² )
And the filament diameter d (mm) are the following 1) to
3) Relationship 1) When the number of metal filaments is 5 (Where d = 0.21 to 0.32) 2) When the number of metal filaments is four (Where d = 0.23 to 0.32) 3) When the number of metal filaments is three 4. The heavy duty radial tire according to claim 3, wherein d = 0.27 to 0.32.