Pneumatic tires

Abstract

A pneumatic tire. A pneumatic tire (1) is lightweight and has improved durability. The pneumatic tire (1) includes a carcass (6), a bead apex rubber (8), and a bead reinforcing layer (9). The height (H1) of the bead apex rubber (8) is 15% to 25% of the tire cross-sectional height (H). The bead reinforcing layer (9) includes: a first portion (9A) disposed on the tire axially outer side of a main body portion (11) of the carcass (6); and a second portion (9B) extending from the tire axially inner side of a folded portion (12) of the carcass (6) through the tire radially inner side of a bead core (5) to the tire radially outer side. The tire radially outer end (9e) of the second portion (9B) is more than 5 mm away from the tire radially outer side than the tire radially outer end (12e) of the folded portion (12).

Description

Technical Field

[0001] The present invention relates to a pneumatic tire. Background Art

[0002] If the pneumatic tires installed on various vehicles are heavy, the unsuspended mass of the vehicle will increase, which may have an adverse effect on the vehicle's handling stability and the durability of the vehicle's running system. In particular, for racing tires used under strict conditions, the above effects are significant, and lightweight tires are strongly desired.

[0003] As a method of reducing the weight of a tire, for example, the sidewall thickness is reduced or the folded portion of the carcass ply is shortened (low-folding).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-129346 Summary of the invention

[0005] However, the above-mentioned measures may reduce the rigidity of the tire, and the reduction in the rigidity of the tire leads to a deterioration in the grip during cornering and a deterioration in durability.

[0006] The present invention has been made in view of the above-mentioned actual situation, and a main object of the present invention is to provide a pneumatic tire that can achieve weight reduction and improved durability.

[0007] The present invention is an inflatable tire, which includes: a pair of bead parts, each of which is embedded with a bead core; a carcass spanning the pair of bead parts; a bead apex rubber extending from the each bead core toward the outer side in the tire radial direction; and a bead reinforcing layer composed of a cord ply arranged on the each bead part, the carcass including a first carcass ply, the first carcass ply including: a main body extending between the bead cores; and a folded-back portion folded back from the inner side of the tire axial direction to the outer side around the each bead core, the height of the bead apex rubber in the tire radial direction from the bead base line is 15% to 25% of the height of the tire cross-section, the bead reinforcing layer including: a first part, which is arranged on the outer side of the main body axial direction; and a second part, which passes through the inner side of the bead core in the tire radial direction and folds back, extends to the outer side of the tire radial direction from the inner side of the folded-back portion in the tire axial direction, and the outer end of the second part in the tire radial direction is more than 5 mm away from the outer end of the folded-back portion in the tire radial direction to the outer side of the tire radial direction.

[0008] In the pneumatic tire of the present invention, preferably, the bead reinforcing layer includes a contact portion where the first portion and the second portion are in contact.

[0009] In the pneumatic tire of the present invention, it is preferable that an outer end of the first portion in the tire radial direction is located 5 mm or more outward in the tire radial direction relative to an outer end of the second portion in the tire radial direction.

[0010] In the pneumatic tire of the present invention, preferably, the outer end of the bead reinforcing layer in the tire radial direction is located at 45% to 60% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

[0011] In the pneumatic tire of the present invention, preferably, the outer end of the folded portion in the tire radial direction is located at 30% to 45% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

[0012] In the pneumatic tire of the present invention, preferably, each of the bead portions is provided with an outer apex rubber on the outer side in the tire axial direction of the folded portion.

[0013] In the invention described in claim 7, it is preferred that the outer end of the outer apex rubber in the tire radial direction is located further outward in the tire radial direction than the outer end of the bead reinforcing layer in the tire radial direction.

[0014] In the pneumatic tire of the present invention, it is preferred that the outer end of the outer apex in the tire radial direction is spaced outward in the tire radial direction by 5 mm or more than the outer end of the bead reinforcing layer in the tire radial direction.

[0015] In the pneumatic tire of the present invention, preferably, the complex elastic modulus E*2 of the outer apex rubber is equal to or greater than the complex elastic modulus E*1 of the bead apex rubber.

[0016] In the pneumatic tire of the present invention, preferably, the complex elastic modulus E*2 of the outer apex rubber is 125% to 175% of the complex elastic modulus E*1 of the bead apex rubber.

[0017] In the pneumatic tire of the present invention, preferably, the outer end of the outer apex in the tire radial direction is located at 55% to 70% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

[0018] In the pneumatic tire of the present invention, preferably, the carcass includes a second carcass ply disposed on the outer side in the tire radial direction of the first carcass ply, and the second carcass ply is composed of a main body extending between the bead cores.

[0019] In the pneumatic tire of the present invention, preferably, the carcass includes a second carcass ply arranged on the inner side of the first carcass ply in the tire radial direction, and the second carcass ply includes: a main body portion extending between the bead cores; and a folded portion folded around each bead core from the inner side in the tire axial direction to the outer side and extending toward the outer side in the tire radial direction.

[0020] In the pneumatic tire of the present invention, preferably, an outer end in the tire radial direction of the folded portion of the second carcass ply is located outward in the tire radial direction than an outer end in the tire radial direction of the bead reinforcing layer.

[0021] The present invention can achieve weight reduction and improve durability by adopting the above structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a tire meridian cross-sectional view of the right half of the pneumatic tire of the present invention.

[0023] Figure 2 yes Figure 1 An enlarged view of the tire bead portion.

[0024] Figure 3 yes Figure 1 An enlarged view of the tire bead portion.

[0025] Figure 4 It is an enlarged view of a bead portion according to another embodiment.

[0026] Figure 5 It is a tire meridian cross-sectional view of the right half of a pneumatic tire according to another embodiment.

[0027] Description of symbols

[0028] 1: pneumatic tire; 4: bead portion; 5: bead core; 6: carcass; 8: bead apex; 9: bead reinforcement layer; 9A: first part; 9B: second part; 9e: outer end; 11: main body; 12: folded part; H: tire cross-sectional height; H1: height of bead apex. DETAILED DESCRIPTION

[0029] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0030] Figure 1 1 is a tire meridian cross-sectional view showing the right half including the tire rotation axis (not shown) in a standard state of a pneumatic tire (hereinafter, sometimes simply referred to as a “tire”) 1 according to the present embodiment. Figure 1 2 shows a tire 1 for racing, for example. However, the present invention can also be applied to a tire 1 for passenger cars or heavy loads.

[0031] The "standard state" refers to an unloaded state in which the tire 1 is mounted on a standard rim (not shown) and filled with a standard internal pressure. In this specification, unless otherwise specified, the dimensions of various parts of the tire 1 are values ​​measured under the standard state.

[0032] “Standard rim” refers to a rim of a specification determined for each tire in a specification system including the specification to which the tire 1 is based, such as a standard rim in the case of JATMA, a “design rim” in the case of TRA, and a “measuring rim” in the case of ETRTO. “Standard internal pressure” refers to an air pressure of each specification determined for each tire in a specification system including the specification to which the tire 1 is based, such as a “maximum air pressure” in the case of JATMA, a maximum value recorded in the table “TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES” in the case of TRA, and an “INFLATION PRESSURE” in the case of ETRTO.

[0033] When there is no applicable specification as in the case of the racing tire 1 , the standard rim and the standard internal pressure are the rim and the air pressure recommended by the manufacturer.

[0034] The tire 1 of the present embodiment includes a pair of bead portions (one bead portion is omitted in the illustration) 4 in which bead cores 5 are respectively embedded, and a carcass 6 spanning between the pair of bead portions 4. In addition, in the present embodiment, the tire 1 includes a bead apex rubber 8 extending from each bead core 5 to the outside in the tire radial direction, and a bead reinforcement layer 9 composed of a cord ply 9c arranged on each bead portion 4.

[0035] The carcass 6 includes a first carcass ply 6A including a main body portion 11 extending between the bead cores 5 and a folded portion 12 folded around each bead core 5 from the inner side to the outer side in the tire axial direction.

[0036] The height H1 of the bead apex 8 in the tire radial direction from the bead base line BL is 15% to 25% of the tire cross-sectional height H. This reduces the weight of the tire 1. In this specification, the bead base line BL is a tire axial line that defines the rim diameter of the standard rim (see JATMA).

[0037] The bead reinforcing layer 9 includes: a first portion 9A, which is arranged on the outer side of the main body 11 in the tire axial direction; and a second portion 9B, which passes through the inner side of the bead core 5 in the tire radial direction and is folded back, and extends to the outer side of the tire radial direction on the inner side of the folded portion 12 in the tire axial direction. Such a bead reinforcing layer 9 cooperates with the carcass 6, the bead core 5 and the bead apex rubber 8 to further improve the bending rigidity of the bead portion 4.

[0038] The outer end 9e of the second portion 9B in the tire radial direction is 5 mm or more away from the outer end 12e of the turnback 12 in the tire radial direction. This disperses the deformation of the bead portion 4 during running, and improves the durability of the bead portion 4.

[0039] If the height H1 of the bead apex rubber 8 increases, the effect of reducing the tire quality may decrease. If the height H1 of the bead apex rubber 8 decreases, the durability of the bead portion 4 may decrease. Therefore, the height H1 of the bead apex rubber 8 is preferably not less than 18% of the tire cross-sectional height H, and more preferably not more than 22%.

[0040] The tire 1 includes a belt layer 7 disposed on the outer side in the tire radial direction of the carcass 6, and a chafer 13 disposed on the bead portion 4. The belt layer 7 and the chafer 13 are formed of a well-known structure.

[0041] The chafer 13 includes, for example, an inner portion 13a and an outer portion 13b connected to the inner portion 13a. In the present embodiment, the inner portion 13a is arranged on the inner side of the main body 11 in the tire axial direction, forming the inner end 1i in the tire radial direction of the tire 1. The outer portion 13b of the present embodiment extends from the inner end 1i toward the outer side in the tire axial direction to the outer side in the tire radial direction. The outer portion 13b extends, for example, to the outer side of the folded portion 12 in the tire axial direction.

[0042] The outer end 13e of the outer side portion 13b of the chafer 13 in the tire radial direction is formed to be substantially the same height as the outer end 8e of the bead apex 8 in the tire radial direction. As a result, the rigidity of the bead apex 8 near which a greater lateral force acts is increased during cornering, thereby improving durability. The “substantially the same height” refers to the distance La (0.030 m) in the tire radial direction between the outer end 13e of the chafer 13 and the outer end 8e of the bead apex 8. Figure 2 The thickness of the fiberglass is less than 3 mm.

[0043] The outer end 12e of the folded portion 12 is preferably located at 30% to 45% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction. Since the outer end 12e of the folded portion 12 is more than 30% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, the durability of the bead portion 4 can be improved. Since the outer end 12e of the folded portion 12 is less than 45% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, the mass reduction effect of the tire 1 can be exerted.

[0044] In the present embodiment, the carcass 6 includes a first carcass ply 6A and a second carcass ply 6B disposed on the outer side of the first carcass ply 6A in the tire radial direction.

[0045] In the present embodiment, the second carcass ply 6B is formed by a main body 14 extending between the bead cores 5. The inner end 14i of the main body 14 in the tire radial direction is arranged, for example, at the bead portion 4. In the present embodiment, the inner end 14i of the main body 14 is located inwardly in the tire radial direction than the outer end 5e of the bead core 5 in the tire radial direction. Such a second carcass ply 6B improves the rigidity of the bead portion 4. The inner end 14i of the main body 14 is located inwardly in the tire radial direction than the middle position 5c of the bead core 5 in the tire radial direction, for example.

[0046] In this embodiment, the inner end 14i of the main body 14 is located radially inward of the outer end 13e of the outer portion 13b of the chafer 13. The second carcass ply 6B is arranged, for example, to be in contact with the outer portion 13b of the chafer 13. Thus, the durability of the bead portion 4 is further improved.

[0047] The first carcass ply 6A and the second carcass ply 6B are formed by, for example, covering carcass cords arranged at an angle of 70 to 90 degrees relative to the tire circumferential direction with a topping rubber (not shown). The carcass cords are preferably organic fiber cords such as nylon, polyester or rayon, or steel cords. The topping rubber has a known structure.

[0048] In the present embodiment, the cross section of the bead core 5 is formed into a circular shape. The bead core 5 is formed into a ring shape by, for example, spirally winding a bead wire (not shown) pre-coated with rubber. In addition, the cross section of the bead core 5 is not limited to a circular shape, and may be, for example, a rectangular or hexagonal shape.

[0049] Figure 2 4 is an enlarged view of the tire bead portion 4. Figure 2 As shown, the bead apex rubber 8 has: an outward end 8a, which is located on the outermost side of the tire axial direction on the bead core 5; and an outer side surface 8b, which connects the outward end 8a and the outer end 8e. In this embodiment, the outer side surface 8b is formed as a concave surface that is recessed toward the inner side of the tire axial direction. The outer side surface 8b is formed as a smooth arc-shaped surface, for example. Such a bead apex rubber 8 imparts traction to the bead reinforcing layer 9 and the folded portion 12 of the carcass 6 relative to the larger lateral force acting during cornering, thereby further improving durability. In addition, the outer side surface 8b is not limited to such a method.

[0050] The outer side surface 8b is inclined toward the outer side in the tire radial direction toward the inner side in the tire axial direction. In the present embodiment, the angle θ1 of the outer side surface 8b relative to the tire radial direction is 5 degrees to 25 degrees. Such an outer side surface 8b effectively exerts the above-mentioned function. The angle θ1 is the angle of the imaginary line 8c formed by connecting the outward end 8a and the outer end 8e with a straight line.

[0051] The bead apex rubber 8 preferably has a complex elastic modulus E*1 greater than the complex elastic modulus E*a of the rubber of the carcass 6. In the present embodiment, the complex elastic modulus E*1 of the bead apex rubber 8 is preferably 40 MPa or more, more preferably 60 MPa or more, and preferably 120 MPa or less, more preferably 100 MPa or less. Such a bead apex rubber 8 improves the bending rigidity of the bead portion 4. In addition, such a bead apex rubber 8 is suitable for use in a racing tire 1.

[0052] The complex elastic modulus E* was measured using a viscoelasticity spectrometer (testing machine manufactured by GABO Corporation) under the following measurement conditions in accordance with the provisions of "JIS K6394".

[0053] Initial deformation: 5%

[0054] Amplitude: ±1.0%

[0055] Frequency: 10Hz

[0056] Deformation mode: traction

[0057] Measurement temperature: 30℃

[0058] The first portion 9A of the bead reinforcing layer 9 is in contact with, for example, the main body portion 11 and the bead apex 8. The second portion 9B is in contact with, for example, the folded portion 12 and the bead apex 8.

[0059] The bead reinforcement layer 9 is formed by, for example, covering a plurality of reinforcing cords with reinforcing rubber (not shown). The reinforcing cords of the bead reinforcement layer 9 are inclined at an angle smaller than the angle of the carcass cord relative to the tire circumference, for example, at an angle of 20 to 70 degrees, preferably at an angle of 30 to 60 degrees, and more preferably at an angle of 40 to 50 degrees. The reinforcing cords are preferably organic fiber cords such as nylon, polyester or rayon, or steel cords. Preferably, the complex elastic modulus E*b of the reinforcing rubber of the bead reinforcement layer 9 is, for example, smaller than the complex elastic modulus E*1 of the bead apex rubber 8.

[0060] The bead reinforcement layer 9 includes a contact portion 17 where the first portion 9A and the second portion 9B are in contact. Such a contact portion 17 improves the bending rigidity of the bead portion 4 and suppresses an increase in the mass of the tire 1. In the present embodiment, the contact portion 17 is formed between the outer end 8e of the bead apex rubber 8 and the outer end 9e of the second portion 9B. Although not particularly limited, the length H2 of the contact portion 17 in the tire radial direction is preferably 15% or more of the tire cross-sectional height H, more preferably 20% or more, and preferably 35% or less, more preferably 30% or less.

[0061] Preferably, the outer end 9a of the first portion 9A in the tire radial direction is more than 5 mm away from the outer end 9e of the second portion 9B in the tire radial direction toward the outer side. This improves the effect of dispersing the deformation of the bead portion 4 during driving. The distance L2 in the tire radial direction between the outer end 9a of the first portion 9A and the outer end 9e of the second portion 9B is preferably less than 15 mm. The distance L2 between the outer end 9a of the first portion 9A and the outer end 9e of the second portion 9B is preferably equal to the distance L1 ( Figure 1 The term “substantially” means that the absolute value of the difference between the distance L1 and the distance L2 |L1-L2| is less than 2 mm.

[0062] Although not particularly limited, in this embodiment, the outer end 9a of the first portion 9A and the outer end 9e of the second portion 9B are located radially outward from the tire maximum width position M. In this specification, the tire maximum width position M refers to the position where the carcass 6 extends outwardly in the tire axial direction.

[0063] Figure 3 4 is an enlarged view of the tire bead portion 4. Figure 3 As shown, the outer end 9a of the bead reinforcement layer 9 in the tire radial direction (in the present embodiment, the outer end of the first portion 9A) is preferably located at 45% to 60% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction. Since the outer end 9a of the bead reinforcement layer 9 is located at more than 45% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, the durability of the bead portion 4 is improved. Since the outer end 9a of the bead reinforcement layer 9 is located at less than 60% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, it is possible to suppress an excessive increase in the mass of the tire 1. From this viewpoint, it is further preferred that the outer end 9a of the bead reinforcement layer 9 is located at more than 50% of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, and it is further preferred that it is located at less than 55%.

[0064] The tire 1 is provided with an outer apex 10 on the outer side of the folded portion 12 of each bead portion 4 in the tire axial direction. Such an outer apex 10 improves the bending rigidity of the carcass 6 and the bead reinforcing layer 9. The outer apex 10 is arranged, for example, between the folded portion 12 and the second carcass ply 6B.

[0065] The outer end 10e of the outer apex 10 in the tire radial direction is preferably located outward in the tire radial direction than the outer end 9e of the bead reinforcing layer 9. Such an outer apex 10 contributes to further improving the bending rigidity of the bead portion 4.

[0066] The outer end 10e of the outer apex rubber 10 is preferably 5 mm or more away from the outer end 9a of the bead reinforcing layer 9 toward the outer side in the tire radial direction. The distance L3 between the outer end 10e of the outer apex rubber 10 and the outer end 9a of the bead reinforcing layer 9 in the tire radial direction is preferably 15 mm or less. Thus, it is possible to improve durability and reduce tire quality in a balanced manner. In addition, in the present embodiment, since the distances L1, L2, and L3 are 5 mm or more in the tire radial direction, the deformation of the bead portion 4 during driving is effectively dispersed, and excellent durability is exerted.

[0067] In order to effectively exert the above-mentioned effects, the outer end 10e of the outer apex rubber 10 is preferably located at 55% or more of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, and more preferably located at 60% or more. In addition, the outer end 10e of the outer apex rubber 10 is preferably located at 70% or less of the tire cross-sectional height H from the bead base line BL toward the outer side in the tire radial direction, and more preferably located at 65% or less.

[0068] The inner end 10i of the outer apex 10 is located, for example, between the outer end 5e and the middle position 5c of the bead core 5. In this embodiment, the inner end 10i of the outer apex 10 in the tire radial direction is arranged at the same position as the inner end 14i of the second carcass ply 6B in the tire radial direction.

[0069] The maximum rubber thickness Ha of the outer apex rubber 10 is preferably 3 mm or more, more preferably 3.5 mm or more, and preferably 6 mm or less, more preferably 5.5 mm or less. In this specification, the maximum rubber thickness Ha of the outer apex rubber 10 refers to the length in a direction orthogonal to the outer side surface 10a of the outer apex rubber 10 in contact with the second carcass ply 6B in the tire axial direction.

[0070] The complex elastic modulus E*2 of the outer apex rubber 10 is preferably equal to or greater than the complex elastic modulus E*1 of the bead apex rubber 8. Such an outer apex rubber 10 can further increase the bending rigidity of the bead portion 4, thereby significantly improving durability.

[0071] When the complex elastic modulus E*2 of the outer apex rubber 10 is too large, the rigidity difference increases in the inner and outer sides of the outer end 8e of the bead apex rubber 8 in the tire radial direction, so the durability may be deteriorated. Therefore, the complex elastic modulus E*2 of the outer apex rubber 10 is more preferably 125% or more of the complex elastic modulus E*1 of the bead apex rubber 8, more preferably 135% or more, and preferably 175% or less, more preferably 170% or less.

[0072] In addition, the tire 1 includes, for example, a sidewall rubber 3G, which is arranged on the outer side of the second carcass ply 6B in the tire axial direction. The sidewall rubber 3G of this embodiment is not in direct contact with the outer apex rubber 10, but is arranged on the outer side of the outer apex rubber 10 in the tire axial direction via the second carcass ply 6B. As a result, air can be effectively discharged during tire molding. In this embodiment, the sidewall rubber 3G forms the outer surface 1a of the tire 1.

[0073] Although not particularly limited, the rubber thickness Hb of the sidewall rubber 3G is 0.8 mm to 2.0 mm.

[0074] Figure 4 FIG. 4 is a cross-sectional view of a bead portion 4 of another embodiment. The same reference numerals are given to the same structures as those of the present embodiment and their description is omitted. Figure 4 As shown, in this embodiment, the angle θ1 of the outer side surface 8b of the bead apex rubber 8 is formed larger than the angle θ1 of the outer side surface 8b of this embodiment. Such an outer side surface 8b applies greater traction to the second portion 9B and the return portion 12 during cornering. In addition, the outer side surface 8b can make the maximum rubber thickness Ha of the outer apex rubber 10 larger.

[0075] Figure 5 FIG. 2 is a cross-sectional view of a tire 1 according to another embodiment. The same reference numerals are given to the same structures as those of the present embodiment, and the description thereof is omitted. Figure 5 As shown, in this embodiment, the carcass 6 includes a second carcass ply 6B arranged on the inner side of the first carcass ply 6A in the tire radial direction. In this embodiment, the second carcass ply 6B includes: a main body portion 14 extending between the bead cores 5; and a folded portion 16 folded around each bead core 5 from the inner side to the outer side in the tire axial direction and extending to the outer side in the tire radial direction.

[0076] The outer end 16e in the tire radial direction of the folded portion 16 of the second carcass ply 6B is offset in the tire radial direction from the outer end 10e in the tire radial direction of the outer apex 10. This can more effectively disperse the deformation during running.

[0077] The outer end 16e of the folded portion 16 is located on the outer side in the tire radial direction than the outer end 9a of the bead reinforcing layer 9. This further improves durability.

[0078] As mentioned above, although the particularly preferred embodiment of the present invention has been described in detail, the present invention is not limited to the illustrated embodiment, and can be implemented in various modified forms.

[0079] [Example]

[0080] have Figure 1 or Figure 5The pneumatic tires for racing with the basic structure size (front wheel: 270 / 660R18, rear wheel: 310 / 710R18) were trial-produced based on the specifications in Table 1. Then, the durability, grip and tire quality of each test tire were tested. The common specifications and test methods of each test tire are as follows.

[0081] <Durability>

[0082] The test tire for the front wheel was run on a drum under the following conditions, and the running distance until the bead portion was damaged was measured. The result was expressed as an index with the running distance of Comparative Example 1 being 100. The larger the value, the better.

[0083] Internal pressure: 200kPa

[0084] Load: 9.0kN

[0085] Speed: 200km / h

[0086] <Grip>

[0087] Each test tire was mounted on the front and rear wheels of a 3800cc racing car under the following conditions. The test driver drove the car on a test course that was a lap course on a dry asphalt road, and evaluated the responsiveness, rigidity, and grip related to stability at this time through the senses of the test driver. The results were expressed as a score with Comparative Example 1 being 100. The larger the value, the better.

[0088] Internal pressure: 200KPa (shared by front and rear wheels)

[0089] <Tire Quality>

[0090] The mass of each tire was measured. The result was expressed as an index with the value of Comparative Example 1 being 100. The smaller the value, the lighter it is.

[0091] The test results are shown in Table 1 and Table 2.

[0092] The “comprehensive evaluation” is expressed as durability × grip / tire quality, and the larger the value, the better.

[0093] "Outer apex height": the radial length of the tire between the outer end of the outer apex and the bead baseline / tire section height (%)

[0094] "Height of bead reinforcement layer": the radial length of the tire between the outer end of the bead reinforcement layer and the bead baseline / tire section height (%)

[0095] "Height of the folded portion": the length in the tire radial direction between the outer end of the folded portion of the first carcass ply and the bead base line / tire cross-sectional height (%)

[0096]

Table 1

[0097]

[0098]

Table 2

[0099]

[0100] According to the test results, the test tire of the embodiment is lighter and has improved durability compared to the test tire of the comparative example. In addition, it can be understood that the test tire of the embodiment has excellent grip compared to the test tire of the comparative example. In addition, the tire of Example 12 may have defects on the outer surface of the tire.

Claims

1. A pneumatic tire, wherein: The pneumatic tire comprises: A pair of bead parts, each of which has a bead core embedded therein; a carcass spanning between the pair of bead portions; A bead apex rubber extending from each bead core toward the outer side in the tire radial direction; as well as A bead reinforcement layer, which is composed of a cord ply arranged in each bead portion, The carcass comprises: a first carcass ply including a main body portion extending between the bead cores and a folded portion folded around each bead core from the inner side to the outer side in the tire axial direction; and A second carcass ply is disposed on the outer side of the first carcass ply, The height of the bead apex rubber in the tire radial direction from the bead base line is 15% to 25% of the tire cross-sectional height. The bead reinforcement layer includes: a first portion, which is arranged on the outer side of the main body in the tire axial direction; and a second portion, which passes through the inner side of the bead core in the tire radial direction and is folded back, and extends from the inner side of the folded portion in the tire axial direction to the outer side of the tire radial direction. The outer end of the second portion in the tire radial direction is more than 5 mm away from the outer end of the folded portion in the tire radial direction toward the outside. Among them, the bead portion is respectively provided with an outer apex rubber, which is arranged on the axially outside of the return portion and on the axially inside of the second carcass ply, and the radially outer end of the outer apex rubber is located radially outside of the radially outer end of the return portion and is sandwiched between the main body of the first carcass ply and the second carcass ply.

2. The pneumatic tire according to claim 1, wherein: The bead reinforcing layer includes a contact portion where the first portion contacts the second portion.

3. The pneumatic tire according to claim 1 or 2, wherein: An outer end of the first portion in the tire radial direction is more than 5 mm away from an outer end of the second portion in the tire radial direction toward the outside in the tire radial direction.

4. The pneumatic tire according to claim 1 or 2, wherein: The outer end of the bead reinforcement layer in the tire radial direction is located at 45% to 60% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

5. The pneumatic tire according to claim 1 or 2, wherein: The outer end of the folded portion in the tire radial direction is located at 30% to 45% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

6. The pneumatic tire according to claim 1 or 2, wherein: The bead portions are provided with outer apex rubbers on the outer sides of the folded portions in the tire axial direction.

7. The pneumatic tire according to claim 6, wherein: An outer end of the outer apex rubber in the tire radial direction is located further outward in the tire radial direction than an outer end of the bead reinforcing layer in the tire radial direction.

8. The pneumatic tire according to claim 6, wherein: An outer end of the outer apex rubber in the tire radial direction is more than 5 mm away from an outer end of the bead reinforcing layer in the tire radial direction toward the outside.

9. The pneumatic tire according to claim 6, wherein: The complex elastic modulus E*2 of the outer apex rubber is greater than or equal to the complex elastic modulus E*1 of the bead apex rubber.

10. The pneumatic tire according to claim 9, wherein: The complex elastic modulus E*2 of the outer apex rubber is 125% to 175% of the complex elastic modulus E*1 of the bead apex rubber.

11. The pneumatic tire according to claim 6, wherein: The outer end of the outer apex rubber in the tire radial direction is located at 55% to 70% of the tire cross-sectional height from the bead base line toward the outer side in the tire radial direction.

12. The pneumatic tire according to claim 1 or 2, wherein: The carcass includes a second carcass ply disposed on the outer side of the first carcass ply in the tire radial direction. The second carcass ply is composed of a main body portion extending between the bead cores.

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