JP7364873B2 - Pneumatic tires for heavy loads - Google Patents

Description

The present invention relates to a pneumatic tire for heavy loads, and more particularly, to a pneumatic tire for heavy loads that can maintain wet traction, steering stability, and rolling resistance at practically sufficient levels.

A pneumatic tire is mainly composed of a pair of left and right bead portions and sidewall portions, and a tread portion that is continuous with both sidewall portions and includes a cap tread and an undertread. A carcass is provided inside the tire, and both ends of the carcass are folded back so as to wrap around the bead core from the inside to the outside of the tire.
The bead portion includes a bead core and a bead filler made of a rubber composition having a triangular cross section on the outer periphery of the bead core.

On the other hand, safe and comfortable operation is important for pneumatic tires for heavy loads such as truck or bus tires. Therefore, for heavy-duty pneumatic tires, emphasis is placed on slope start performance (wet traction performance) and handling stability on wet roads such as during rainy weather. To improve wet traction, there is a method of softening the cap tread rubber to increase the ground contact area and increasing the tan δ, but it is said that handling stability deteriorates and rolling resistance deteriorates due to the high tan δ. There is a problem.
As described above, it is difficult to maintain the wet traction properties, steering stability, and rolling resistance of heavy-duty pneumatic tires at practically sufficient levels.

Note that techniques for improving the wet traction properties of heavy-duty pneumatic tires are disclosed, for example, in Patent Documents 1 and 2.

Japanese Patent Application Publication No. 6-48122 Japanese Patent Application Publication No. 1-306304

Therefore, an object of the present invention is to provide a heavy-duty pneumatic tire that can maintain wet traction, steering stability, and rolling resistance at practically sufficient levels.

As a result of extensive research, the present inventor has determined the composition of undertread rubber, tan δ at 60°C (tan δ @ 60°C (UT)), and storage modulus at 20°C (E' @ 20°C (UT)) of undertread rubber. ), the relationship between the upper bead filler's tan δ at 60°C (tan δ @ 60°C (UBF)) and the above (tan δ @ 60°C (UT)), the storage modulus of the lower bead filler at 20°C (E' @ 20°C ( By specifying the relationship between LBF)) and the above (E'@20°C (UT)), as well as the relationship between the mass of the undertread rubber (WU) and the total mass (WT) of the cap tread rubber and the undertread rubber. , have discovered that the above problems can be solved, and have completed the present invention.
That is, the present invention is as follows.

1. A heavy-duty pneumatic tire comprising a bead filler provided in a tire bead portion, a cap tread rubber constituting a tire contact surface, and an undertread rubber provided inside the cap tread rubber in the tire radial direction,
The undertread rubber contains diene rubber including natural rubber,
The proportion of butadiene rubber in 100 parts by mass of the diene rubber is 15 parts by mass or less,
The undertread rubber contains 25 parts by mass or more of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 130 m ² /g based on 100 parts by mass of the diene rubber, and has a nitrogen adsorption specific surface area (N 2 SA) of 70 to 130 m 2 /g. ₂ SA) contains 10 parts by mass or more of silica of 140 to 180 m ² /g,
The undertread rubber has a tan δ (tan δ @ 60 °C (UT)) of 0.03 to 0.10 at 60 °C, and a storage modulus (E' @ 20 °C (UT)) of 3. 0 to 5.5,
The bead filler includes an upper bead filler located on the outer side in the tire radial direction, and a lower bead filler located on the inner side in the tire radial direction with respect to the upper bead filler,
The tan δ of the upper bead filler at 60° C. (tan δ @ 60° C. (UBF)) and the (tan δ @ 60° C. (UT)) satisfy the following relational expression (1),
The storage elastic modulus of the lower bead filler at 20°C (E'@20°C (LBF)) and the above (E'@20°C (UT)) satisfy the following relational expression (2), and the cap tread rubber and the above A pneumatic tire for heavy loads, characterized in that the mass (WU) of the undertread rubber with respect to the total mass (WT) of the undertread rubber satisfies the following relational expression (3).
0.3≦(tanδ@60℃(UBF))/(tanδ@60℃(UT))≦1.3 (1)
3.0≦(E'@20℃(LBF))/(E'@20℃(UT))≦6.0 (2)
0.10≦(WU)/(WT)≦0.60 (3)
2. Item 1 above, wherein the carbon black is blended in an amount of 25 to 45 parts by mass, and the silica is blended in an amount of 10 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. pneumatic tires for heavy loads.

The heavy-duty pneumatic tire of the present invention (hereinafter sometimes simply referred to as a pneumatic tire) includes a bead filler provided in a tire bead portion, a cap tread rubber constituting a tire contact surface, and a cap tread rubber. an undertread rubber provided on the inner side in the tire radial direction, the undertread rubber containing diene rubber containing natural rubber, and the proportion of butadiene rubber in 100 parts by mass of the diene rubber is 15 parts by mass. The undertread rubber contains 25 parts by mass or more of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 130 m ² /g based on 100 parts by mass of the diene rubber, and The undertread rubber contains 10 parts by mass or more of silica with a specific surface area (N ₂ SA) of 140 to 180 m ² /g, and has a tan δ at 60°C (tan δ @ 60°C (UT)) of 0.03 to 0.10. and has a storage elastic modulus at 20°C (E'@20°C (UT)) of 3.0 to 5.5, and the bead filler includes an upper bead filler located on the outside in the tire radial direction, and a storage modulus at 20°C (E'@20°C (UT)) of and a lower bead filler located on the inner side in the tire radial direction with respect to the bead filler, and the tan δ of the upper bead filler at 60°C (tan δ @ 60° C. (UBF)) and the above (tan δ @ 60° C. (UT)) have the following relationship. Formula (1) is satisfied, and the storage modulus of the lower bead filler at 20 °C (E'@20 °C (LBF)) and the above (E'@20 °C (UT)) satisfy the following relational formula (2), In addition, since the mass (WU) of the undertread rubber with respect to the total mass (WT) of the cap tread rubber and the undertread rubber satisfies the following relational expression (3), wet traction performance, handling stability and Rolling resistance can be maintained at a practically sufficient level.
0.3≦(tanδ@60℃(UBF))/(tanδ@60℃(UT))≦1.3 (1)
3.0≦(E'@20℃(LBF))/(E'@20℃(UT))≦6.0 (2)
0.10≦(WU)/(WT)≦0.60 (3)

As mentioned above, in order to improve wet traction, there is a method of softening the cap tread rubber to increase the ground contact area and increasing the tan δ, but this deteriorates handling stability and increases the rolling resistance due to the high tan δ. There was a problem that sex deteriorated. In the present invention, the composition of the undertread rubber, the tan δ at 60°C (tan δ @ 60°C (UT)) and the storage modulus at 20°C (E' @ 20°C (UT)) of the undertread rubber, and the 60 The relationship between tan δ (tan δ @ 60 °C (UBF)) and the above (tan δ @ 60 °C (UT)) at °C, and the storage modulus of the lower bead filler at 20 °C (E' @ 20 °C (LBF)) and the above (E '@20℃ (UT)) and the relationship between the mass of the undertread rubber (WU) and the total mass (WT) of the cap tread rubber and undertread rubber. Even when handling stability and rolling resistance are reduced, the undertread rubber, upper bead filler, and lower bead filler play a role in supplementing handling stability and rolling resistance, resulting in improved wet traction and handling stability. It is possible to provide a pneumatic tire that maintains both rolling resistance and rolling resistance at practically sufficient levels.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire.

The present invention will be explained in more detail below.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire.
In FIG. 1, a pneumatic tire consists of a pair of left and right bead portions 1 and sidewalls 2, and a tread 3 continuous to both sidewalls 2, and a carcass layer 4 forming the tire frame is mounted between the bead portions 1 and 1. The end portion of the carcass layer 4 is folded back and rolled up from the inside of the tire to the outside around the bead core 5 and bead filler 6.
The tread 3 includes a cap tread rubber 30 that constitutes a tire contact surface, and an undertread rubber 31 provided inside the cap tread rubber 30 in the tire radial direction.
The bead filler 6 is composed of two members, and includes an upper bead filler 62 located on the outer side in the tire radial direction, and a lower bead filler 64 located on the inner side in the tire radial direction with respect to the upper bead filler 62.
Further, a belt layer 7 is arranged on the outside of the carcass layer 4 over one circumference of the tire. Belt cushions 8 are arranged at both ends of the belt layer 7. An inner liner 9 is provided on the inner surface of the pneumatic tire in order to prevent the air filled inside the tire from leaking to the outside of the tire, and a tie rubber 10 for bonding the inner liner 9 is attached to the carcass layer 4. It is laminated between the inner liner 9 and the inner liner 9.
The tire radial direction is a direction perpendicular to the tire rotation axis, the tire radial inner side refers to the direction approaching the tire rotation axis, and the tire radial outer side refers to the direction away from the tire rotation axis.

In the present invention, the composition of the undertread rubber is specified. That is, the undertread rubber contains diene rubber including natural rubber, and the proportion of butadiene rubber in 100 parts by mass of the diene rubber is 15 parts by mass or less, and the undertread rubber contains diene rubber including natural rubber. Contains 25 parts by mass or more of carbon black with a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 130 m ² /g per 100 parts by mass of rubber, and has a nitrogen adsorption specific surface area (N ₂ SA) of 140 to 180 m ^{2 /} g. 10 parts by mass or more of silica.

In the undertread rubber, when the proportion of the butadiene rubber (BR) exceeds 15 parts by mass and the amount of the carbon black is less than 25 parts by mass, the nitrogen adsorption specific surface area (N ₂ SA) of the carbon black If the content is outside the range of 70 to 130 m ² /g, the amount of the silica is less than 10 parts by mass, and/or the nitrogen adsorption specific surface area (N ₂ SA) of the silica is 140 to 180 m ² /g. If it is outside the range, the effect of the present invention of maintaining wet traction, steering stability, and rolling resistance at practically sufficient levels cannot be achieved.

Here, from the viewpoint of improving the effects of the present invention, the following embodiments are preferable.
(1) In the undertread rubber, the proportion of NR is preferably 80 to 100 parts by mass based on 100 parts by mass of the diene rubber.
(2) In the undertread rubber, the blending amount of the carbon black is preferably 25 to 45 parts by mass based on 100 parts by mass of the diene rubber.
(3) In the undertread rubber, the amount of silica blended is preferably 10 to 30 parts by mass per 100 parts by mass of the diene rubber.
(4) In the undertread rubber, the carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 130 m ² /g. Note that two or more types of carbon black may be used as a blend.
(5) In the undertread rubber, the silica preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 145 to 190 m ² /g. Note that two or more types of silica may be used as a blend.
Note that NR as used in the present invention includes synthetic isoprene rubber (IR). Further, the nitrogen adsorption specific surface area (N ₂ SA) is a value measured according to JIS K 6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

In addition to natural rubber (NR) and butadiene rubber (BR), the rubber constituting the undertread rubber used in the present invention is styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and styrene-butadiene copolymer rubber (SBR). ) etc. can also be used together. The rubber used in the present invention is not particularly limited in its molecular weight or microstructure, and may be terminally modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or may be epoxidized.

In addition to the above-mentioned components, the undertread rubber also contains various fillers, various oils, anti-aging agents, plasticizers, zinc oxide, and other additives that are commonly included in undertread rubber. can do. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

The undertread rubber in the present invention has a tan δ at 60°C (tan δ @ 60°C (UT)) of 0.03 to 0.10, and a storage modulus (E' @ 20°C (UT)) at 20°C. is required to be between 3.0 and 5.5. If these physical property ranges are not satisfied, the above-mentioned effects of the present invention cannot be achieved.
(tan δ@60°C (UT)) is more preferably 0.03 to 0.08.
(E'@20°C (UT)) is more preferably 3.5 to 5.0.
Note that tan δ at 60° C. in this specification is measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under conditions of initial strain 10%, amplitude ±2%, frequency 20 Hz, and temperature 60° C.
In addition, the storage modulus at 20°C in this specification is a value measured using a viscoelastic spectrometer under the conditions of initial strain 10%, amplitude ±2%, frequency 20Hz, and 20°C in accordance with JIS K6394 ( MPa).

The bead filler in the present invention includes an upper bead filler located on the outer side in the tire radial direction as described above, and a lower bead filler located on the inner side in the tire radial direction with respect to the upper bead filler.
In the present invention, the compositions of the upper bead filler and the lower bead filler are as described below: As long as the relationship (E'@20°C (UT)) can be satisfied, there is no particular restriction and it can be selected as appropriate.
For example, various ingredients commonly included in bead fillers such as diene rubber, various fillers such as silica and carbon black, coupling agents, various oils, anti-aging agents, plasticizers, and zinc oxide may be blended. I can do it. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

Further, the cap tread rubber in the pneumatic tire of the present invention is a rubber that constitutes the contact surface of the pneumatic tire, and from the viewpoint of improving the effect of the present invention, tan δ at 60 ° C. is preferably 0.03 to 0.18. , 0.04 to 0.15 are more preferable. Further, the hardness at 20° C. is preferably 50 to 80, more preferably 60 to 75.
Note that hardness is measured at 20°C in accordance with JIS K6253.

In the present invention, the composition of the cap tread rubber is not particularly limited and can be appropriately selected.
For example, various ingredients commonly included in cap tread rubber such as diene rubber, various fillers such as silica and carbon black, coupling agents, various oils, anti-aging agents, plasticizers, and zinc oxide are blended. be able to. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

Furthermore, with respect to the members constituting the other members in the pneumatic tire of the present invention, the blending ratio of each component is not particularly limited and can be appropriately selected.
For example, various commonly used components such as diene rubber, various fillers, various oils, anti-aging agents, plasticizers, zinc oxide, etc. can be blended as rubber compositions for other members. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

In the pneumatic tire of the present invention, it is necessary that the tan δ of the upper bead filler at 60° C. (tan δ @ 60° C. (UBF)) and the above (tan δ @ 60° C. (UT)) satisfy the following relational expression (1). be.
0.3≦(tanδ@60℃(UBF))/(tanδ@60℃(UT))≦1.3 (1)

Further, in the pneumatic tire of the present invention, the storage elastic modulus of the lower bead filler at 20°C (E'@20°C (LBF)) and the above (E'@20°C (UT)) are expressed by the following relational expression (2). It is necessary to satisfy the following.
3.0≦(E'@20℃(LBF))/(E'@20℃(UT))≦6.0 (2)

That is, the value of (tanδ@60℃(UBF))/(tanδ@60℃(UT)) is within the range of 0.3 to 1.3, and (E'@20℃(LBF))/ (E'@20℃(UT)) is within the range of 3.3 to 6.0, as mentioned above, the cap tread rubber is responsible for improving wet traction, improving steering stability and rolling resistance. Even when reduced, the undertread rubber, upper bead filler, and lower bead filler play a role in supplementing handling stability and rolling resistance, and as a result, wet traction, handling stability, and rolling resistance are each sufficiently improved for practical use. We can provide pneumatic tires that maintain the level.

Note that from the viewpoint of further improving the effects of the present invention, (tan δ @ 60 ° C. (UBF)) / (tan δ @ 60 ° C. (UT)) in the above formula (1) is more preferably from 0.4 to 1.2. .
(E'@20°C (LBF))/(E'@20°C (UT)) in the above formula (2) is more preferably from 3.5 to 5.5.
Further, (tan δ@60°C (UBF)) is preferably 0.03 to 0.10, more preferably 0.03 to 0.08.
(E'@20°C (LBF)) is preferably 15 to 30 (MPa), more preferably 20 to 30 (MPa).

The above (tan δ @ 60 ° C (UT)), the above (E' @ 20 ° C (UT)), the above (tan δ @ 60 ° C (UBF)) and the above (E' @ 20 ° C (LBF)) can be adjusted, for example. This is possible by increasing or decreasing the filler, vulcanizing agent or crosslinking agent.

Further, in the pneumatic tire of the present invention, it is necessary that the mass (WU) of the undertread rubber with respect to the total mass (WT) of the cap tread rubber and the undertread rubber satisfies the following relational expression (3).
0.10≦(WU)/(WT)≦0.60 (3)
If (WU)/(WT) is outside the range of 0.10 to 0.60, provide a pneumatic tire that maintains wet traction, handling stability, and rolling resistance at practically sufficient levels. The effect of the present invention cannot be achieved.

Note that from the viewpoint of further improving the effects of the present invention, the above (WU)/(WT) is preferably 0.15 to 0.60, more preferably 0.20 to 0.60.

Furthermore, the pneumatic tire of the present invention can be manufactured according to conventional pneumatic tire manufacturing methods.

EXAMPLES The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Standard example, Examples 1 to 5 and Comparative examples 1 to 4
In the formulation (parts by mass) shown in Table 1, the components excluding the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 16 liter closed Banbury mixer, and the rubber was discharged outside the mixer and cooled at room temperature. Next, the rubber was put into the same mixer again, a vulcanization accelerator and sulfur were added, and further kneaded to obtain various underdread rubber compositions.

On the other hand, an upper bead filler and a lower bead filler were prepared according to a conventional method, and bead fillers having various physical properties shown in Table 1 were obtained by increasing or decreasing the amounts of a vulcanizing agent, a crosslinking agent, and a filler.

(tanδ@60°C (UT)), (E'@20°C (UT)), (tanδ@60°C (UBF)) and (E'@20°C (LBF)) were measured as described above. In addition, (WU)/(WT) was measured. The results are shown in Table 1.

Various test tires with tire sizes of 275/80R22.5 and 151/148J were manufactured by incorporating the bead filler and the cap tread rubber. In addition, the conditions for each member other than the undertread rubber and bead filler were the same among the various test tires. The hardness of the cap tread rubber at 20°C was 63, and the tan δ (60°C) was 0.25.

The various test tires obtained were evaluated as follows. The results are shown in Table 1.

Wet traction performance: The test tires were mounted on a test vehicle (tractor head) with a displacement of 12,770cc, the air pressure was adjusted to 900kPa at the front and 900kPa at the rear, and the tires were run on a paved road surface with a water depth of 1mm, at speeds of 6 to 21km/h. The slip rate of the rear wheels during acceleration was measured. The results were expressed as an index with the value of the standard example set as 100. The larger the index, the better the wet traction properties.

Rolling resistance: A pneumatic tire with a tire size of 275/80R22.5 is vulcanized and molded, the resulting tire is assembled on a standard rim (a wheel with a size of 22.5 x 7.5), and an indoor tire that conforms to JIS D4230 is assembled. It was attached to a drum testing machine (drum diameter 1707 mm), and the resistance force was measured when running at an air pressure of 900 kPa, a load of 33.8 kN, and a speed of 80 km/hour, which was defined as rolling resistance. The results were expressed as an index with the value of the standard example set as 100. The larger the index, the lower the rolling resistance.

Steering stability: Using the test vehicle, a sensory evaluation was conducted by a test driver. The evaluation was performed on a five-level scale, with a score of "3" as the standard, and a relative evaluation was made.
5: Compared to point "3", there is a remarkable improvement in steering stability.
4: Compared to score "3", there is an improvement in maneuvering stability.
3: Criterion 2: Compared to the "3" score, the steering stability was inferior.
1: Compared to the score "3", the steering stability was significantly inferior.

*1:NR (RSS#3)
*2: BR (Nipol BR1220 manufactured by Zeon Corporation)
*3: Carbon black ISAF (Show Black N234 manufactured by Cabot Japan, N ₂ SA = 123 m ² /g)
*4: Carbon black HAF (Show Black N339 manufactured by Cabot Japan, N ₂ SA = 88 m ² /g)
*5: Silica (ULTRASIL VN3GR manufactured by Evonik, N ₂ SA = 170 m ² /g)
*6: Anti-aging agent (Ozonone 6C manufactured by Seiko Kagaku Co., Ltd.)
*7: Wax (paraffin wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
*8: Stearic acid (industrial stearic acid N manufactured by Chiba Fatty Acid Co., Ltd.)
*9: Zinc oxide (3 types of zinc oxide manufactured by Seido Kagaku Kogyo Co., Ltd.)
*10: Sulfur (fine powder sulfur with Kinka seal oil manufactured by Tsurumi Chemical Industry Co., Ltd.)
*11: Vulcanization accelerator (Noxeler NS-P manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)

As is clear from Table 1 above, in each example, the composition of the undertread rubber, the tan δ at 60°C (tan δ @ 60°C (UT)), and the storage modulus at 20°C (E' @ 20°C) of the undertread rubber. ℃ (UT)), the relationship between the upper bead filler's tan δ at 60 ℃ (tan δ @ 60 ℃ (UBF)) and the above (tan δ @ 60 ℃ (UT)), the lower bead filler's storage modulus at 20 ℃ (E' Determine the relationship between (@20℃ (LBF)) and the above (E'@20℃ (UT)), as well as the relationship between the mass of the undertread rubber (WU) and the total mass (WT) of the cap tread rubber and undertread rubber. It can be seen that wet traction, steering stability, and rolling resistance are each maintained at a practically sufficient level.
On the other hand, in Comparative Example 1, the tan δ at 60° C. (tan δ @ 60° C. (UT)) of the undertread rubber exceeded the upper limit defined by the present invention, so the rolling resistance deteriorated.
In Comparative Example 2, since silica was not blended, the steering stability deteriorated.
Comparative Example 3 shows that (tanδ@60℃(UBF))/(tanδ@60℃(UT)) and (E'@20℃(LBF))/(E'@20℃(UT)) according to the present invention. Since it was outside the specified range, rolling resistance and steering stability deteriorated.
In Comparative Example 4, (WU)/(WT) was less than the lower limit defined by the present invention, so wet traction performance and steering stability deteriorated.

1 Bead portion 2 Sidewall 3 Tread 30 Cap tread rubber 31 Undertread rubber 4 Carcass layer 5 Bead core 6 Bead filler 62 Upper bead filler 64 Lower bead filler 7 Belt layer 8 Belt cushion 9 Inner liner

Claims (2)

A heavy-duty pneumatic tire comprising a bead filler provided in a tire bead portion, a cap tread rubber constituting a tire contact surface, and an undertread rubber provided inside the cap tread rubber in the tire radial direction,
The undertread rubber contains diene rubber including natural rubber,
The proportion of butadiene rubber in 100 parts by mass of the diene rubber is 15 parts by mass or less,
The undertread rubber contains 25 parts by mass or more of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 130 m ² /g based on 100 parts by mass of the diene rubber, and has a nitrogen adsorption specific surface area (N 2 SA) of 70 to 130 m 2 /g. ₂ SA) contains 10 parts by mass or more of silica of 140 to 180 m ² /g,
The undertread rubber has a tan δ (tan δ @ 60 °C (UT)) of 0.03 to 0.10 at 60 °C, and a storage modulus (E' @ 20 °C (UT)) of 3. 0 to 5.5,
The bead filler includes an upper bead filler located on the outer side in the tire radial direction, and a lower bead filler located on the inner side in the tire radial direction with respect to the upper bead filler,
The tan δ of the upper bead filler at 60° C. (tan δ @ 60° C. (UBF)) and the (tan δ @ 60° C. (UT)) satisfy the following relational expression (1),
The storage elastic modulus of the lower bead filler at 20°C (E'@20°C (LBF)) and the above (E'@20°C (UT)) satisfy the following relational expression (2), and the cap tread rubber and the above The mass (WU) of the undertread rubber relative to the total mass (WT) of the undertread rubber satisfies the following relational expression (3),
The cap tread rubber has a tan δ of 0.03 to 0.25 at 60°C, and a hardness of the cap tread rubber at 20°C of 50 to 80.
A pneumatic tire for heavy loads.
0.3≦(tanδ@60℃(UBF))/(tanδ@60℃(UT))≦1.3 (1)
3.0≦(E'@20℃(LBF))/(E'@20℃(UT))≦6.0 (2)
0.10≦(WU)/(WT)≦0.60 (3)
(However, the unit of storage elastic modulus at 20°C is MPa.) 2. The method according to claim 1, wherein the carbon black is blended in an amount of 25 to 45 parts by mass, and the silica is blended in an amount of 10 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. Heavy-duty pneumatic tires listed.

Images