Pneumatic tires

Abstract

A pneumatic tire is provided that improves handling stability and durability without compromising detachability from a wheel rim. The pneumatic tire includes a tread portion, a pair of sidewall portions, a pair of bead portions each having a bead core embedded therein, and a toroidal carcass. The carcass includes a folded-back cord ply, the folded-back cord ply including: a main portion extending annularly between the bead cores; and a pair of folded-back portions folded back around the bead core from the axially inner side to the outer side of the tire. An inner apex and an outer apex are provided in the bead portion. The inner apex extends from the bead core to the radially outer side of the tire between the main portion and the folded-back portion, and the outer apex is adjacent to the axially outer side of the folded-back portion. The height of the inner apex in the radial direction of the tire is 18 mm to 30 mm. The tire wall thickness D, the maximum width thickness E and the tire bead thickness F satisfy the relationships (1) to (4): E≧4.5mm…(1); F≧9.0mm…(2); E / D=0.6~0.9…(3); F / E=1.7~2.2…(4).

Description

Technical Field

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

[0002] Patent Document 1 below describes a pneumatic tire having a cushion with cushion cords arranged in a bead portion. Patent Document 2 below describes a pneumatic tire having a cushion made of rubber arranged in a bead portion.

[0003] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-147567

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-39276

[0005] In a pneumatic tire, ease of removal from a wheel rim is required when replacing the tire, etc. However, in the tire of Patent Document 1, the bending rigidity of the bead portion is excessively increased due to the cushioning rubber having the cord, making it difficult to remove from the wheel rim.

[0006] On the other hand, although the pneumatic tire of Patent Document 2 has improved detachability from the wheel rim, there is room for improvement in terms of shaking during lane changes and durability, especially durability outside the outer end of the cushion rubber in the tire radial direction. Summary of the Invention

[0007] 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 capable of improving steering stability and durability without impairing detachability from a rim.

[0008] The tire is constructed so that when the tire is in a state of being rotated relative to the tire, the tire can be easily moved along the tire's outer edges and into the tire's center of gravity, thereby ensuring that the tire is in a state of being rotated relative to the tire's outer edges.

[0009] E≧4.5mm…(1)

[0010] F≧9.0mm…(2)

[0011] E / D=0.6~0.9…(3)

[0012] F / E=1.7~2.2…(4)

[0013] The sidewall thickness D is the shortest distance from the outer surface of the tire to the carcass at position P1, which is 23% of the tire cross-section height away from the position of the maximum diameter of the tire in the radial direction of the tire. The maximum width thickness E is the shortest distance from the outer surface of the tire to the carcass at the position of the maximum width of the tire. The bead thickness F is the shortest distance from the outer surface of the tire to the carcass at position P2, which is 25 mm away from the bead baseline in the radial direction of the tire.

[0014] In another embodiment of the present invention, the outer apex rubber may be formed of a rubber composition having a loss tangent value tan δ of 0.13 or less.

[0015] In another embodiment of the present invention, the outer apex rubber may be formed of a rubber composition having a complex elastic modulus E* of 23 MPa or more.

[0016] In another embodiment of the present invention, the outer apex may have a thickness of 0.5 mm or more.

[0017] In another aspect of the present invention, the outer apex may be arranged in a range of 50% or more of an area in the tire radial direction from the position P2 to a position of the maximum tire width.

[0018] In another aspect of the present invention, a spacer rubber may be arranged between the main body portion and the folded portion of the folded carcass ply.

[0019] In another aspect of the present invention, the thickness of the insulation rubber may be 0.5 mm or more.

[0020] In another aspect of the present invention, the difference between the complex elastic modulus of the insulation rubber and the complex elastic modulus of the topping rubber of the turn-back ply may be 2 MPa or less.

[0021] In another aspect of the present invention, the height of the folded portion of the folded carcass ply from the bead base line may be equal to or greater than 50% of the tire cross-sectional height.

[0022] In another aspect of the present invention, the outer end of the outer apex rubber in the tire radial direction may be located further inward in the tire radial direction than the outer end of the folded portion in the tire radial direction.

[0023] In another aspect of the present invention, a distance in the tire radial direction between the outer end of the outer apex and an outer end in the tire radial direction of the folded portion may be 5 mm or more.

[0024] In another aspect of the present invention, the pneumatic tire may be a tire for a light truck.

[0025] The pneumatic tire of the present invention can improve steering stability and durability without impairing detachability from a rim. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a cross-sectional view showing a pneumatic tire according to one embodiment of the present invention.

[0027] Figure 2 It shows Figure 1 A partial enlarged view of the right half.

[0028] Figure 3 yes Figure 2 A magnified view of the tire near its maximum width.

[0029] Description of labels

[0030] 1: Pneumatic tire; 2: Tread; 3: Sidewall; 4: Bead; 5: Bead core; 6: Carcass; 6A: Turned-back cord layer; 6a: Main body; 6b: Turned-back portion; 8: Inner apex rubber; 9: Outer apex rubber; 50: Isolation rubber; BL: Bead baseline; D: Sidewall thickness; E: Maximum width thickness; F: Bead thickness; H: Tire section height. DETAILED DESCRIPTION

[0031] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0032] exist Figure 1 1 is a cross-sectional view of a pneumatic tire 1 showing one embodiment of the present invention. Figure 2 It will Figure 1 The right half is enlarged to show the main parts.

[0033] [Normal state of pneumatic tires]

[0034] exist Figure 1 and 2 The normal state of the pneumatic tire 1 is shown in FIG. The normal state of the pneumatic tire 1 uniquely defines the posture of the pneumatic tire 1 and is defined as the unloaded state of the pneumatic tire 1 mounted on a normal rim (not shown) at a normal internal pressure. Unless otherwise specified in this specification, the dimensions of various components of the pneumatic tire 1 are understood to be values measured in this normal state.

[0035] Furthermore, in this specification, a regular rim refers to a rim having a rim width suitable for effectively exhibiting the performance of the pneumatic tire 1. Specifically, a "regular rim" is defined for each standard to which the pneumatic tire 1 complies. For example, a "standard rim" may be defined for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.

[0036] "Normal internal pressure" refers to the air pressure determined for each tire in the standard system including the standard based on which the pneumatic tire 1 is based. For JATMA, it is the maximum air pressure. For TRA, it is the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". For ETRTO, it is "INFLATION PRESSURE".

[0037] [Basic structure of tires]

[0038] like Figure 1 and Figure 2 As shown, the pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each having a bead core 5 embedded therein, and a toroidal carcass 6. An inner liner rubber 10 is disposed inside the carcass 6 for retaining air.

[0039] In this embodiment, a light truck tire having a relatively large tire section height H and a relatively large operating load is exemplified as the pneumatic tire 1. Light truck tires are regulated by, for example, Chapter B of the JATMA YEAR BOOK.

[0040] [Tread]

[0041] The tread portion 2 defines a ground contact surface 2a that contacts the ground when the tire is running. The tread portion 2 of this embodiment includes a tread rubber 20 that constitutes the ground contact surface 2a. A belt layer 7 is disposed between the tread rubber 20 and the carcass 6 in the tread portion 2.

[0042] The ground contact surface 2a refers to the surface with which the tread portion 2 contacts the ground when the pneumatic tire 1, in a normal state, is grounded on a flat surface at a camber angle of 0° and a normal load is applied. Furthermore, in this specification, "normal load" refers to the load determined for each tire within the standards system, including the standards to which the pneumatic tire 1 conforms. For JATMA, this refers to the "maximum load capacity," for TRA, the maximum value specified in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, "LOAD CAPACITY."

[0043] [Belt]

[0044] The belt layer 7 is composed of, for example, multiple (two in this embodiment) belt plies 7A and 7B arranged with steel cords. The belt plies 7A and 7B have multiple belt cords oriented at an angle of, for example, 15° to 35° relative to the tire equatorial plane C. Steel cords are preferred as the belt cords. The belt plies 7A and 7B overlap so that their respective belt cords intersect with each other. This belt layer 7 improves the flexural and torsional rigidity of the tread portion 2.

[0045] [Sidewall]

[0046] The sidewall portion 3 extends radially inward from both ends of the tread portion 2, forming the tire's sidewall. The sidewall portion 3 of this embodiment primarily comprises a carcass 6 and sidewall rubber 30 disposed axially outward of the tire. The radially outer end of the sidewall rubber 30 extends, for example, to the radially inner surface 20i of the tread rubber 20. Reference numeral 60 denotes a belt cushion rubber. Furthermore, the radially inner end of the sidewall rubber 30 extends to the bead portion 4.

[0047] The sidewall rubber 30 is made of a rubber composition having excellent damage resistance and flexural properties. In a preferred embodiment, the sidewall rubber 30 is made of a rubber composition having a complex elastic modulus E* of about 3.0 MPa to 4.0 MPa.

[0048] In the present specification, the viscoelastic properties (complex elastic modulus E* and loss tangent tan δ) of the rubber composition are measured in accordance with the provisions of JIS K6394 using a viscoelasticity spectrometer under the following conditions.

[0049] Initial strain: 10%

[0050] Amplitude: ±1%

[0051] Frequency: 10Hz

[0052] Deformation Mode: Stretch

[0053] Measurement temperature: 70°C

[0054] [Bead section]

[0055] The bead portion 4 is formed on the radially inner end of each sidewall portion 3 and is used to mount the pneumatic tire 1 on a wheel rim (not shown). A non-extensible bead core 5, such as a steel wire, is embedded in the bead portion 4. Furthermore, a hard rubber bead edge rubber 40 is disposed on the axially outer side of the bead portion 4 that contacts the rim. Furthermore, a hard rubber chafer rubber 41 is disposed on the portion of the bead portion 4 that contacts the rim seat.

[0056] [Carcass]

[0057] In this embodiment, the carcass 6 includes at least one turn-back ply 6A. For example, the carcass 6 in this embodiment includes multiple (two in this embodiment) turn-back plies 6A. In other embodiments, the carcass 6 may be constructed by combining the turn-back ply 6A with a non-turn-back ply (not shown).

[0058] Each turnup ply 6A comprises, for example, a cord ply formed by covering a plurality of longitudinally aligned carcass cords with topping rubber. Examples of the carcass cords include organic fiber cords such as nylon, polyester, rayon, and polyethylene terephthalate. Furthermore, steel cords may be used as needed.

[0059] Each turnup ply 6A includes a main portion 6a extending annularly between the bead cores 5, 5, and a pair of turnup portions 6b that are folded around the bead cores 5 from the axially inner side to the outer side of the tire. The carcass cords of each turnup ply 6A are oriented at an angle of, for example, 80° to 90° relative to the tire equator. In other words, the carcass 6 of this embodiment has a radial construction.

[0060] The height of the turn-up portion 6b of the turn-up ply 6A from the bead base line BL is preferably at least 50% of the tire cross-sectional height H. This strengthens not only the bead portion 4 but also the sidewall portion 3, contributing to improved steering stability. Furthermore, when multiple turn-up plies 6A are present, the height of the turn-up portion 6b is determined by the highest turn-up portion.

[0061] In this specification, the "bead base line" refers to the tire's axial line passing through the rim diameter of a regular rim. Furthermore, the "tire cross-section height" refers to the distance in the tire's radial direction from the bead base line to the tire's maximum diameter. The tire's maximum diameter position Hmax is determined based on the contour of the contact patch 2a of the tread portion 2. If the tread portion 2 has a recess such as a groove, the contour is determined as a hypothetical contour that fills the recess.

[0062] An inner apex rubber 8 and an outer apex rubber 9 are provided in each of the pair of bead portions 4 .

[0063] [Inner triangle rubber]

[0064] The inner apex rubber 8 is positioned between the main body 6a and the turn-up portion 6b of the turn-up ply 6A, extending radially outward from the bead core 5. The inner apex rubber 8 moderately increases the flexural rigidity of the bead portion 4, while also improving steering stability and durability. From this perspective, the complex elastic modulus E* of the inner apex rubber 8 is preferably 18 MPa or greater, more preferably 22 MPa or greater, and even more preferably 24 MPa or greater.

[0065] On the other hand, if the complex elastic modulus E* of the inner apex rubber 8 becomes too large, the removal efficiency from the rim may be impaired. From this point of view, the complex elastic modulus E* of the inner apex rubber 8 is preferably 36 MPa or less, more preferably 32 MPa or less, and even more preferably 30 MPa or less.

[0066] In this embodiment, the inner apex 8 extends tapered outward in the tire radial direction, for example. Accordingly, the turn-back portion 6b of the turn-back ply 6A of this embodiment includes a portion curved along the axially outer side of the inner apex 8 into an arcuate shape convex toward the inner apex 8. This structure of the turn-back portion 6b is preferred for reducing the compressive strain acting on the carcass cords in the turn-back portion 6b during tire travel, thereby preventing damage originating from the turn-back portion 6b.

[0067] The height 8h of the inner apex 8 in the tire radial direction is, for example, 18 mm to 30 mm. The height 8h of the inner apex 8 is the height in the tire radial direction from the outer surface of the bead core 5 in the tire radial direction to the outer end of the inner apex 8 in the tire radial direction.

[0068] If the height 8h of the inner apex 8 is less than 18 mm, the basic bending rigidity of the bead portion 4 cannot be ensured, and there is a tendency for steering stability to decrease. From this point of view, the height 8h of the inner apex 8 is preferably 19 mm or more, more preferably 20 mm or more, and even more preferably 21 mm or more.

[0069] On the other hand, if the height 8h of the inner apex 8 exceeds 30 mm, the outer end of the inner apex 8 approaches an area subject to significant strain during driving, potentially causing damage originating from the outer end of the inner apex 8 and potentially deteriorating durability. From this perspective, the height 8h of the inner apex 8 is preferably 29 mm or less, more preferably 28 mm or less, and even more preferably 27 mm or less.

[0070] [Outer triangle]

[0071] The outer apex rubber 9 is positioned adjacent to the outer side of the turn-up portion 6b of the turn-up cord ply 6A in the axial direction of the tire and extends in the radial direction of the tire. By supporting the turn-up portion 6b from the outer side of the tire in the axial direction, the outer apex rubber 9 can further increase the bending rigidity of the bead portion 4, thereby reducing the bending strain of the bead portion 4 during tire travel.

[0072] In this embodiment, the outer apex 9 is formed of, for example, a rubber sheet having a substantially constant thickness t1. The thickness t1 of the outer apex 9 is, for example, smaller than the maximum axial width 8W of the inner apex 8. This contributes to reducing the weight of the bead portion 4.

[0073] As described above, the bead portion 4 of the present embodiment is reinforced by the inner apex 8 and the outer apex 9 having no cords and has no cushion cords, thereby preventing deterioration in detachability from the wheel rim.

[0074] [Thickness of each tire part]

[0075] To improve the handling stability and durability during lane changes (particularly the durability of the tire radially outward from the outer end of the inner apex rubber 8), it is necessary to further determine the thickness of each part of the tire based on the structure of the bead portion 4. In this embodiment, from this perspective, the sidewall thickness D, the maximum width thickness E, and the bead thickness F are configured to satisfy the following relationships (1) to (4).

[0076] E≧4.5mm…(1)

[0077] F≧9.0mm…(2)

[0078] E / D=0.6~0.9…(3)

[0079] F / E=1.7~2.2…(4)

[0080] Here, "sidewall thickness D" is the shortest distance from the tire's outer surface to the carcass 6 at position P1, which is 23% of the tire's cross-sectional height H, radially inward from the tire's maximum diameter position Hmax. Furthermore, "maximum width thickness E" is the shortest distance from the tire's outer surface to the carcass 6 at position Wmax, which is the tire's maximum width. Furthermore, "bead thickness F" is the shortest distance from the tire's outer surface to the carcass 6 at position P2, which is 25 mm radially outward from the bead base line BL.

[0081] The position Wmax of the maximum tire width and the position P2 of the pneumatic tire 1 are representative locations where bending strain is large during running. Formulas (1) and (2) maintain the durability of the pneumatic tire 1 by defining the thickness of these locations.

[0082] Specifically, the maximum width thickness E is E≧4.5 mm or greater (Equation (1)), more preferably E≧4.8 mm, and even more preferably E≧5.0 mm. On the other hand, if the maximum width thickness E is too large, heat generation during driving tends to increase. From this perspective, the maximum width thickness E may be, for example, E≦6.0 mm, and preferably E≦5.5 mm.

[0083] The position P2 where the bead thickness F is specified corresponds to the outer end of the flange of the wheel rim in the radial direction of the tire, and is subject to significant deformation when turning or changing lanes. Therefore, specifying the thickness at this position is important for improving the durability of the pneumatic tire 1. From this point of view, the bead thickness F is F≧9.0mm (Formula (2)), preferably F≧9.5mm. On the other hand, when the bead thickness F becomes too large, there is a tendency for the bead portion 4 to heat up more during driving. From this point of view, the bead thickness F is, for example, F≦10.5mm, preferably F≦10.0mm.

[0084] In this embodiment, to improve steering stability, the maximum width thickness E is defined in association with the sidewall thickness D. The position P1 where the sidewall thickness D is defined is located near the boundary between the tread portion 2 and the sidewall portion 3. Therefore, by linking the maximum width thickness E with the sidewall thickness D, the rigidity balance in the area from position P1 of the sidewall portion 3 to the position Wmax of the maximum tire width can be improved. In this embodiment, to improve steering stability during lane changes, E / D is set to 0.6 to 0.9 (Equation (3)).

[0085] When the E / D ratio is less than 0.6, the rigidity near the tire's maximum width position Wmax is relatively reduced, primarily resulting in reduced handling stability during cornering. From this perspective, the E / D ratio is more preferably 0.7 or greater. On the other hand, when the E / D ratio exceeds 0.9, the rigidity near the sidewall (position P1) is relatively reduced, primarily resulting in reduced responsiveness and convergence during lane changes. From this perspective, the E / D ratio is more preferably 0.8 or less.

[0086] In this embodiment, in order to further improve the durability of the bead portion 4, the bead thickness F is specified in association with the maximum width thickness E. That is, the ratio F / E of these thicknesses is F / E=1.7~2.2 (Formula (4)). Here, when the ratio F / E is lower than 1.7, there is a tendency for the strain of the bead portion 4 during driving to increase, and damage is likely to occur in the bead portion 4. From such a viewpoint, it is particularly preferred that the ratio F / E is greater than 1.8. On the other hand, when the ratio F / E exceeds 2.2, the strain is likely to concentrate near the position Wmax of the maximum width of the tire, and damage is likely to occur in the interval from the vicinity to the position P2. From such a viewpoint, the ratio F / E is preferably less than 2.1, and more preferably less than 2.0.

[0087] The pneumatic tire 1 of the present embodiment as described above can improve steering stability and durability without impairing detachability from the rim by balancing the rigidity of the tire side portions.

[0088] The outer apex rubber 9 is preferably made of a rubber composition having a loss tangent value tanδ of, for example, 0.13 or less, more preferably 0.12 or less. Such an outer apex rubber 9 suppresses heat generation during running and further improves the durability of the bead portion 4.

[0089] Furthermore, the outer apex rubber 9 is preferably composed of a rubber composition having a complex elastic modulus E* of 23 MPa or greater, preferably 26 MPa or greater. Such an outer apex rubber 9 reduces bending strain and other factors in the bead portion 4, further improving the durability of the bead portion 4. On the other hand, if the complex elastic modulus E* of the outer apex rubber 9 is too high, it may deteriorate ride comfort and reduce removal ease from the rim. Therefore, it is preferably 30 MPa or less.

[0090] The thickness t1 of the outer apex rubber 9 is preferably, for example, 0.5 mm or greater, more preferably 1.0 mm or greater. Such an outer apex rubber 9 not only further improves the durability of the bead portion 4 but also further suppresses wobbling during lane changes. On the other hand, if the thickness t1 of the outer apex rubber 9 is too large, it will not only make it difficult to remove from the rim, but may also deteriorate the thermal durability of the bead portion 4. In this regard, the thickness t1 of the outer apex rubber 9 is, for example, 2.0 mm or less, more preferably 1.5 mm or less.

[0091] The outer apex rubber 9 is preferably positioned over 50% or more of the tire's radial area Hu, from position P2 to position Wmax, where the tire has the largest width. Such an outer apex rubber 9 can distribute or mitigate strain within the area from position P2 to position Wmax, further improving durability. In a more preferred embodiment, the outer apex rubber 9 is preferably positioned over 60% or more, and more preferably over 65% or more, of the tire's radial area from position P2 to position Wmax, where the tire has the largest width.

[0092] The inner end of the outer apex rubber 9 in the tire radial direction is preferably located further inward in the tire radial direction than position P2. As described above, when the pneumatic tire 1 is mounted on a wheel rim, position P2 corresponds to a position near the outer end of the rim flange. Therefore, the bead portion 4 tends to flex during driving, starting from near position P2. Therefore, the inner end of the outer apex rubber 9 is preferably defined so as to reinforce the bead portion 4 near position P2.

[0093] Furthermore, strain tends to concentrate on the outer end of the folded portion 6b during driving. On the other hand, the outer apex rubber 9 is made of a rubber composition with relatively high rigidity, and therefore tends to have difficulty fully following the deformation of the folded portion 6b during driving. Therefore, the outer apex rubber 9 is preferably configured so as not to be subjected to large strains during driving. That is, the outer end of the outer apex rubber 9 is preferably located radially inward of the outer end of the folded portion 6b in the tire direction, so as not to cover the outer end of the folded portion 6b. Thus, the folded portion 6b is covered by the sidewall rubber 30, which has a smaller complex elastic modulus than the outer apex rubber 9, thereby suppressing peeling damage, etc., starting from the folded portion 6b.

[0094] And, as Figure 1 As shown, the distance G in the tire radius between the outer end of the outer apex 9 and the outer end of the folded portion 6b is preferably 5 mm or greater. This allows the outer end of the outer apex 9 to be sufficiently away from locations subject to significant strain. Consequently, damage originating from the outer end of the outer apex 9 is effectively suppressed.

[0095] During high-load driving, large shear strains are repeatedly generated between the main body 6a and the turn-back portion 6b of the turn-back ply 6A, potentially causing damage such as loosening of the ply and cords. To suppress this loosening, an insulation rubber 50 is preferably disposed between the main body 6a and the turn-back portion 6b. In this embodiment, the insulation rubber 50 is formed from a sheet-like rubber composition.

[0096] Figure 3 yes Figure 2 A partial enlarged view of the tire's maximum width position Wmax. Figure 3 As shown, the isolation rubber 50 can ensure a sufficient distance d between the carcass cords 6c, 6c between the main body portion 6a and the turnback portion 6b, thereby alleviating the shear stress acting therebetween and suppressing loosening. From this perspective, the thickness t2 of the isolation rubber 50 is preferably, for example, 0.5 mm or greater. On the other hand, increasing the thickness t2 of the isolation rubber 50 may deteriorate heat resistance and rolling resistance. Therefore, the thickness t2 of the isolation rubber 50 is preferably, for example, 1.5 mm or less.

[0097] The insulation rubber 50 may be composed of the same rubber composition as the topping rubber 6t of the turn-back ply 6A, or a different rubber composition. In the latter case, the difference in complex elastic modulus between the insulation rubber 50 and the topping rubber 6t of the turn-back ply 6A is preferably 2 MPa or less to eliminate the difference in rigidity between the main body 6a and the turn-back 6b. By limiting the difference in complex elastic modulus between the topping rubber 6t and the insulation rubber 50, strain is effectively distributed between the carcass cords 6c, 6c of the main body 6a and the turn-back 6b, further improving durability by suppressing loosening and other factors.

[0098] The spacer rubber 50 of this embodiment is positioned throughout the entire area between the main body 6a and the turnback portion 6b of the turnup ply 6A. Furthermore, the spacer rubber 50 extends radially outward beyond the outer end of the turnback portion 6b. More specifically, the radially outer end of the spacer rubber 50 is sandwiched between the belt layer 7 and the carcass 6. This arrangement prevents damage originating from the outer end of the spacer rubber 50, further improving durability.

[0099] Furthermore, the inner end of the spacer rubber 50 in the tire radial direction of this embodiment terminates between the inner side surface of the inner apex rubber 8 in the tire axial direction and the main body 6a. In this manner, since the inner end of the spacer rubber 50 is located in an area with low strain, damage originating from the inner end of the spacer rubber 50 can be suppressed, further improving durability.

[0100] As mentioned above, although one embodiment of the present invention has been described in detail, the present invention is not limited to the above specific disclosure, and can be implemented with various modifications within the scope of the technical concept described in the claims.

[0101] [Example]

[0102] Next, more detailed examples of the present invention will be described, but the present invention is not limited to these examples.

[0103] Based on the specifications in the table below, we have produced Figure 1 The performance of pneumatic radial tires for small trucks with a basic structure of the present invention was tested. Furthermore, for comparison, comparative tires not having the structure of the present invention were also tested in the same manner. The main common specifications are as follows.

[0104] Tire size: 205 / 85R16 117 / 115N

[0105] Rim: 5.5J

[0106] Height of folded portion: 0.63H

[0107] Complex elastic modulus E* of sidewall rubber: 3.4MPa

[0108] Complex elastic modulus E* of inner triangle rubber: 26MPa

[0109] Height of outer triangle: 0.37H

[0110] The test content is as follows.

[0111] [Rim removal workability]

[0112] Each tire was mounted and removed from the rim 10 times using a tire changer. Afterwards, an observer visually inspected the bead area of each tire and evaluated the degree of damage to the bead area on a 10-point scale, termed "rim removal performance." A higher value indicates better performance.

[0113] [Handling stability]

[0114] A small truck equipped with each test tire was driven on a test route, and the driver evaluated the degree of truck roll when changing lanes. The results were evaluated on an index scale of 10, with the roll level of Example 1 being 10, with higher values indicating better performance.

[0115] Internal pressure: 600kPa

[0116] Small truck load capacity: 2 tons

[0117] Durability

[0118] Each test tire was run continuously using a roller tester under the following conditions, and the distance until the tire was damaged was measured. The results were evaluated using the running distance of Example 1 as 10, with larger values indicating better results.

[0119] Internal pressure: 600kPa

[0120] Longitudinal load: 20kN

[0121] Driving speed: 80km / h

[0122] The test results are shown in Tables 1 and 2.

[0123]

Table 1

[0124]

[0125]

Table 2

[0126]

[0127] As a result of the test, it was confirmed that the tire of the example had improved steering stability and durability without impairing detachability from the rim.

Claims

1. A pneumatic tire comprising: tread; a pair of sidewalls; a pair of bead portions, each of which has a bead core embedded therein; and Ring-shaped carcass, The carcass comprises at least one folded-back cord layer, The folded ply comprises: a main body portion extending annularly between the bead cores; and A pair of folded portions folded from the inner side to the outer side of the tire axial direction around the bead core, An inner apex rubber and an outer apex rubber are provided in each of the pair of bead parts, wherein the inner apex rubber extends from the bead core to the outer side in the radial direction of the tire between the main body of the folded-back cord layer and the folded-back part, and the outer apex rubber is adjacent to the outer side of the folded-back part in the tire axial direction. The height of the inner apex in the tire radial direction from the outer surface of the bead core in the tire radial direction to the outer end of the inner apex in the tire radial direction is 18 mm to 30 mm. The tire wall thickness D, the maximum width thickness E and the bead thickness F satisfy the following relationships (1) to (4), E≧4.5mm…(1) F≧9.0mm…(2) E / D=0.6~0.9…(3) F / E=1.7~2.2…(4) The sidewall thickness D is the shortest distance from the tire outer surface to the carcass at a position P1 that is 23% of the tire cross-section height inward in the tire radial direction from the position of the maximum tire diameter. The maximum width thickness E is the shortest distance from the outer surface of the tire to the carcass at the position of the maximum width of the tire. The bead thickness F is the shortest distance from the tire outer surface to the carcass at a position P2 25 mm outward in the tire radial direction from the bead base line.

2. The pneumatic tire according to claim 1, wherein The outer apex rubber is composed of a rubber composition having a loss tangent value tan δ of 0.13 or less.

3. The pneumatic tire according to claim 1 or 2, wherein: The outer apex rubber is composed of a rubber composition having a complex elastic modulus E* of 23 MPa or more.

4. The pneumatic tire according to claim 1 or 2, wherein: The thickness of the outer apex rubber is greater than 0.5 mm.

5. The pneumatic tire according to claim 1 or 2, wherein: The outer apex is disposed over a range of 50% or more of the tire radial area from the position P2 to the position of the maximum tire width.

6. The pneumatic tire according to claim 1 or 2, wherein: An insulation rubber is arranged between the main body portion and the turn-back portion of the turn-back ply.

7. The pneumatic tire according to claim 6, wherein: The thickness of the isolation rubber is greater than 0.5 mm.

8. The pneumatic tire according to claim 6, wherein: The folded ply is a cord ply formed by covering a plurality of carcass cords aligned along the length direction with rubberized rubber. The difference between the complex elastic modulus of the insulation rubber and the complex elastic modulus of the topping rubber of the turn-back cord ply is 2 MPa or less.

9. The pneumatic tire according to claim 1 or 2, wherein: The height of the folded portion of the folded ply from the bead base line is greater than or equal to 50% of the tire cross-sectional height.

10. The pneumatic tire according to claim 1 or 2, wherein: An outer end of the outer apex rubber in the tire radial direction is located inward in the tire radial direction relative to an outer end of the folded portion in the tire radial direction.

11. The pneumatic tire according to claim 10, wherein: A distance in the tire radial direction between the outer end of the outer apex and the outer end of the folded portion in the tire radial direction is 5 mm or more.

12. The pneumatic tire according to claim 1 or 2, wherein: This pneumatic tire is a tire for small trucks.

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