pneumatic tires

Abstract

Pneumatic tire (1) that can be mounted on a predetermined rim tapered by 15°, wherein the pneumatic tire (1) comprises the following: a pair of bead sections (20) arranged on each side of a tire equatorial plane (CL) in a tire transverse direction; a tire bead core (21) provided in each pair of bead sections (20); a carcass (6) which is supported by the pair of tire bead cores (21), wherein the carcass (6) comprises a carcass body part (61) and a carcass refold section (62) formed by the carcass (6) which refolds back on the tire bead core (21); a steel cord reinforcement layer (35) arranged on an outer surface of the carcass (6) which is folded back on the tire bead core (21), and a bead rubber layer (K) wherein at least one section thereof is arranged between the carcass body part (61) and the carcass refolding section (62);wherein, when the pneumatic tire (1) is not mounted on the specified rim, a distance (A) from a second line segment (J) to a third line segment (F) is 4 mm to 8 mm, wherein a first line segment (D) passing through an outermost projection point of the tire bead core (21) in the transverse direction of the tire and parallel to a longest side of the tire bead core (21), a side (P) of a bead base section (26) closer to a bead heel (27), which is a section of the bead section that comes into contact with the specified rim, a curved line (G) of a tire outer surface (40), which is a section of the bead section that is arranged outwards in the transverse direction of the tire from the bead base section (26), a first intersection (H) of the side (P) and the curved line (G), the second line segment (J) passing through the first intersection (H) runs and is perpendicular to the first line segment (D), and the third PS:SI:hm ; Line segment (F) passing through the projection point (E) and perpendicular to the first line segment (D) are specified. wherein the ratio R2 / R1 is from 0.935 to 0.975, where R2 is a tire radius at a bead toe (28) of the bead base section (26) and R1 is a tire radius at the bead heel (27), and wherein the ratio R1 / R3 is from 0.985 to 0.995, where R3 is a tire radius at the tire bead core (21) and R1 is the tire radius at the bead heel (27).

Description

Technical area

[0001] The invention relates to a pneumatic tire. State of the art

[0002] A pneumatic tire includes a bead portion with a bead core on each side in the tire transverse direction. A pneumatic tire is mounted on a rim wheel by the engagement of the bead portion and the rim wheel. JP 28 553 27 B describes a technology designed to improve the durability of a bead portion through a specific relationship between a tire bead core (tire bead wire) and a bead base portion. List of citations

[0003] US 2010 / 0 224 300 A1 discloses a heavy-duty radial tire. The heavy-duty radial tire is mounted on a 15° tapered rim and has bead portions arranged on both sides of a tire equatorial plane in a tire width direction, each bead portion including a bead core. Furthermore, the heavy-duty radial tire has a carcass including a carcass body portion and a carcass fold-back portion, a bead reinforcing cord layer, and a bead tip rubber having a lower tip portion.

[0004] JP 2002 - 254 908 A discloses a tubeless heavy-duty tire that provides both resistance to rim deflection and a consistent fit on the rim. The heavy-duty tire has bead sections, each bead section enclosing a bead core.

[0005] JP 2005 - 329 796 A discloses a pneumatic tire with bead portions comprising a bead core and a carcass layer. The carcass layer is folded back on the bead core. Summary of the inventionTechnical problem

[0006] Uneven wear can occur in a pneumatic tire if a bead portion is not correctly positioned and is eccentrically engaged with a rim wheel. Particularly under low-wear usage conditions such as long-haul (high-haul) haulage, the likelihood of uneven wear occurring in an eccentrically engaged pneumatic tire is significant.

[0007] An object of the present invention is to provide a pneumatic tire which can prevent eccentric engagement of a bead portion on a rim wheel. Solving the problems

[0008] The object of the invention is achieved by a pneumatic tire having the features of claim 1. Advantageous further developments are defined in the dependent claims.

[0009] To solve the above-described problems and achieve the above-described object, a pneumatic tire according to an embodiment of the present invention is a pneumatic tire mountable on a predetermined rim tapered by 15°, the pneumatic tire including: a pair of bead portions arranged on either side of a tire equatorial plane in a tire transverse direction; a tire bead core provided in each pair of bead portions; a carcass supported by the pair of tire bead cores, the carcass including a carcass body part and a carcass fold-back portion formed by the carcass and folded back on the tire bead core; a steel cord reinforcing layer disposed on an outer surface of the carcass folded back on the tire bead core, and a bead rubber layer, at least a portion of which is disposed between the carcass body part and the carcass fold-back portion; if the pneumatic tire is not mounted on the specified rim, wherein a distance from a second line segment to a third line segment is from 4 mm to 8 mm, wherein a first line segment passing through an outermost protrusion point of the tire bead core in the tire transverse direction and being parallel to a longest side of the tire bead core, a side of a bead base portion closer to a bead heel, which is a portion of the bead portion that comes into contact with the predetermined rim, a curved line of a tire outer surface, which is a portion of the bead portion located outward from the bead base portion in the tire transverse direction, a first intersection point of the side and the curved line, the second line segment passing through the first intersection point and being perpendicular to the first line segment, and the third line segment passing through the protrusion point and being perpendicular to the first line segment are indicated, and wherein a ratio R2 / R1 of from 0.935 to 0.975, where R2 is a tire radius at a bead toe of the bead base portion and R1 is a tire radius at the bead heel.

[0010] In the pneumatic tire according to the present invention, a ratio R1 / R3 is from 0.985 to 0.995, where R3 is a tire radius at the tire bead core and R1 is the tire radius at the bead heel.

[0011] In a pneumatic tire according to an embodiment of the present invention, preferably, the bead base portion includes an outer portion including the bead heel and an inner portion including the bead toe, and an angle of a side of the outer portion with respect to a line perpendicular to the tire equatorial plane is from 18° to 23°, and an angle of a side of the inner portion is from 27° to 33°.

[0012] In a pneumatic tire according to an embodiment of the present invention, an angle of the bead base portion side with respect to a line perpendicular to the tire equatorial plane is preferably from 15° to 20°. Advantageous effects of the invention

[0013] The present invention provides a pneumatic tire capable of preventing eccentric engagement of a bead portion on a rim wheel. Brief description of the drawings Fig. 1 is a meridian cross-sectional view illustrating a main portion of a pneumatic tire according to the present embodiment. Fig. 2 is a detailed view of a section G of Fig. 1. Fig. 3 is an enlarged view of a section of Fig. 2. Fig. 4 is a meridian cross-sectional view illustrating a pneumatic tire according to a modified example of the present embodiment. Fig. 5 is a table showing results of performance tests of pneumatic tires according to the present embodiments. Fig. 6 is a table showing results of performance tests of pneumatic tires according to the present embodiments. Fig. 7 is a table showing results of performance tests of pneumatic tires according to the present embodiments. Fig. 8 is a table showing results of performance tests of pneumatic tires according to the present embodiments. Description of embodiments

[0014] Embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, components described in the following embodiments may be combined, and one or more components may be omitted.

[0015] Herein, "tire transverse direction" refers to the direction parallel to a tire rotation axis of a pneumatic tire. "Tire transverse inward" refers to the direction toward a tire equatorial plane in the tire transverse direction. "Tire transverse outward" refers to the direction away from the tire equatorial plane in the tire transverse direction. Furthermore, "tire radial direction" refers to the direction perpendicular to the tire rotation axis. "Tire radial inward" refers to the direction toward the tire rotation axis in the tire radial direction. "Tire radial outward" refers to the direction away from the tire rotation axis in the tire radial direction. "Tire circumferential direction" refers to the direction of rotation around the tire rotation axis.

[0016] "Tire equatorial plane" refers to a plane perpendicular to the tire's axis of rotation and passing through the tire's transverse center. "Tire equatorial line" refers to a centerline where the tire equatorial plane and the surface of a tread portion of the pneumatic tire meet.

[0017] Fig. 1 is a meridian cross-sectional view illustrating a main portion of a tire 1 according to an embodiment. "Meridian cross-section" refers to a cross section passing through the tire rotation axis. The tire 1 is a pneumatic tire and a tubeless tire. The tire 1 is a heavy-duty tire mountable on a truck or bus. A tire (heavy-duty tire) for a truck or bus refers to a tire specified in Chapter C of the JATMA Yearbook (Standards of the Japan Automobile Tire Manufacturers Association, Inc.) published by the Japan Automobile Tire Manufacturers Association, Inc. (JATMA). Note that the tire 1 may be mountable on a passenger car or may be mountable on a light truck.

[0018] The Fig. The tire 1 illustrated in FIG. 1 is provided with a tread portion 2 in the outermost portion in the tire radial direction when viewed in a meridian cross-section. The surface of the tread portion 2, that is, the portion that comes into contact with the road surface when a vehicle on which the tire 1 is mounted runs, is formed as a tread surface 3. A plurality of circumferential main grooves 15 extending in the tire circumferential direction and a plurality of lug grooves (not illustrated) intersecting the circumferential main grooves 15 are formed in the tread surface 3. A plurality of land portions 10 are defined in the tread surface 3 by the circumferential main grooves 15 and the lug grooves.Note that the number of circumferential main grooves 15, the pitches between the lug grooves in the tire circumferential direction, the length and angle of the lug grooves, the groove width and groove depth of each groove, and the like are preferably adjusted as needed. In other words, a tread pattern formed in the tread surface 3 is preferably adjusted appropriately.

[0019] Both ends of the tread portion 2 in the tire transverse direction are formed as shoulder portions 4. Sidewall portions 5 are arranged inwardly of the shoulder portions 4 at predetermined positions in the tire radial direction. In other words, the sidewall portions 5 are arranged at two positions on each side of the pneumatic tire 1 in the tire transverse direction.

[0020] Furthermore, a bead portion 20 is located inward of each sidewall portion 5 in the tire radial direction. The bead portions 20 are arranged at two positions on either side of a tire equatorial plane CL in a similar manner to the sidewall portions 5. In other words, the pair of bead portions 20 are arranged on either side of the tire equatorial plane CL in the tire transverse direction. The pair of bead portions 20 each includes a bead core 21. The bead core 21 is formed by winding a bead wire, which is a steel wire, into a ring shape.

[0021] The bead portion 20 is configured to be mounted on a predetermined rim tapered at a 15° angle. Herein, "prescribed rim" refers to an "applicable rim" as defined by JATMA, a "design rim" as defined by the Tire and Rim Association (TRA), or a "measuring rim" as defined by the European Tire and Rim Technical Organization (ETRTO). In other words, the tire 1 according to the present embodiment can be mounted on the predetermined rim, including an engaging portion for the bead portion 20 inclined at an angle of 15° with respect to the rotation axis.

[0022] A belt layer 7 is provided inside the tread portion 2 in the tire radial direction. The belt layer 7 has, for example, a multi-layer structure including laminated four belts 71, 72, 73, 74, which are produced by a process of covering a plurality of belt cords made of steel or an organic fiber material such as polyester, rayon, and nylon, followed by a rolling process. Furthermore, the belts 71, 72, 73, 74 have a different set of belt cords, defined as the inclination angle of the fiber direction of the belt cords with respect to the tire circumferential direction, and the belts are laminated such that the fiber directions of the belt cords cross each other, that is, in a cross-ply structure.

[0023] A carcass 6 including cords from a radial ply is provided continuously inward of the belt layer 7 in the tire radial direction and along one side of the sidewall portion 5 closer to the tire equatorial plane CL. The carcass 6 is supported by the pair of bead cores 21. The carcass 6 has a single-layer structure made of one carcass ply or a multi-layer structure made of a plurality of carcass plies and extends between the bead cores 21 arranged on both sides in the tire transverse direction in a toroidal shape, thereby forming the support structure for the tire.Specifically, the carcass 6 is arranged from one bead portion 20 to the other bead portion 20, with the set of bead portions 20 arranged on both sides in the tire transverse direction, and bends back outward in the tire transverse direction along the bead cores 21 at the bead portions 20, wrapping around the bead cores 21. In other words, the carcass 6 is folded back around the bead cores 21 at the bead portions 20, so that the carcass 6 is arranged inward of the bead cores 21 in the tire transverse direction, and extends inward of the bead core 21 in the tire transverse direction, and then outward of the bead core 21 in the tire transverse direction. The carcass ply of the carcass 6 arranged in this manner is manufactured by a process of covering a plurality of carcass cords made of steel or an organic fiber material such as aramid, nylon, polyester and rayon, and then a rolling process.

[0024] Hereinafter, the carcass 6, which folds back on the bead core 21 arranged on the bead portion 20, includes a portion appropriately located inward from the bead core 21 in the tire transverse direction, which is referred to as a carcass body part 61, and a portion formed by folding back the carcass 6 on the bead core 21 appropriately located outward from the bead core 21 in the tire transverse direction, which is referred to as a carcass fold-back portion 62.

[0025] In addition, an inner liner 8 is formed along the carcass 6 on the inside of the carcass 6 or on the inner side of the tire 1 of the carcass 6.

[0026] Fig. 2 is a detailed view of a section G of Fig. 1. A steel cord reinforcing layer 35 made of steel cords is disposed in a portion where the carcass 6 folds back around the bead core 21. The steel cord reinforcing layer 35 is disposed in contact with the outer surface of the carcass 6 folded back on the bead core 21 and reinforces the carcass 6. The steel cord reinforcing layer 35 is arranged in layers on the carcass 6 on the outer side of the carcass 6 at the portion where the carcass 6 is folded back, and is folded back around the bead core 21 from the inside to the outside in the tire transverse direction in a manner similar to the carcass 6 and is continuously arranged in the tire circumferential direction.In other words, the steel cord reinforcing layer 35 is arranged at the portion where the carcass 6 is arranged inward in the tire transverse direction from the bead core 21, and at the portion where the carcass 6 is arranged outward in the tire transverse direction from the carcass 6.

[0027] In addition, the tire bead core 21, which is formed by winding a tire bead wire into an annular shape, has a shape that is substantially hexagonal when viewed in a meridian cross section. Specifically, the tire bead core 21, when viewed as a whole, has a substantially hexagonal shape and includes an inner peripheral surface 22 and an outer peripheral surface 23 having a substantially parallel orientation, which, as they extend from the outside to the inside in the tire transverse direction, are inclined inward in the tire radial direction, a corner portion 24 protruding outward in the tire transverse direction at an outer position in the tire transverse direction, and a corner portion 25 protruding inward in the tire transverse direction at an inner position in the tire transverse direction.It should be noted that the inner peripheral surface 22 is a surface of the tire bead core 21 facing inward in the tire radial direction, and the outer peripheral surface 23 is another surface of the tire bead core 21 facing outward in the tire radial direction.

[0028] In the present embodiment, of the six sides of the hexagonal shape of the tire bead core 21, the side designated as the outer peripheral surface 23 is the longest when viewed in a meridian cross-section. Note that the side designated as the inner peripheral surface 22 may be the longest, or the side designated as the outer peripheral surface 23 and the side designated as the inner peripheral surface 22 may be the same length.

[0029] Similarly, a bead base portion 26, which is the inner peripheral surface of the bead portion 20, slopes in an inward direction in the tire radial direction while extending from outside to inside in the tire transverse direction. Note that the inner peripheral surface of the bead portion 20 is a surface of the bead portion 20 facing inward in the tire radial direction. In other words, at the bead base portion 26, a bead toe 28, which is an inner end portion of the bead base portion 26 in the tire transverse direction, slopes more in an inward direction in the tire radial direction than a bead heel 27, which is an outer end portion of the bead base portion 26 in the tire transverse direction. The bead base portion 26 is provided as an engagement portion that engages and comes into contact with the given rim when the tire 1 according to the present embodiment is mounted on the given rim.

[0030] The bead base portion 26 includes a rim cushion rubber 29. The rim cushion rubber 29 is arranged inward of the tire bead core 21 and the carcass fold-back portion 62 in the tire radial direction and outward therefrom in the tire transverse direction. The rim cushion rubber 29 is a rubber layer that forms the contact surface that contacts a given rim. The bead base portion 26 is made of the rim cushion rubber 29.

[0031] In the bead portion 20, a tire outer surface 40 is shaped to be curved, projecting outward in the tire transverse direction. In other words, the portion of the tire outer surface 40 at the bead portion 20, where the outer surface 40 is a surface on the side of the tire 1 exposed to the outside air, is curved, projecting outward in the tire transverse direction. The bead heel 27, i.e., an end portion of the bead base portion 26, is the intersection point between the tire outer surface 40 and the bead base portion 26.

[0032] In the bead portion 20, a tire inner surface 50 is formed to be curved, projecting inward in the tire transverse direction. In other words, the portion of the tire inner surface 50 at the bead portion 20, where the inner surface 50 is a surface on the side of the tire 1 that is filled with air, is curved, projecting inward in the tire transverse direction. The bead toe 28, that is, the other end portion of the bead base portion 26, is the intersection point between the tire inner surface 50 and the bead base portion 26.

[0033] Furthermore, the bead portion 20 is provided with a bead rubber layer K. At least a portion of the bead rubber layer K is disposed between the carcass body part 61 and the carcass fold-back portion 62. The bead rubber layer K is also known as a bead filler.

[0034] Fig. 3 is an enlarged view of a section of Fig. 2. Specified values ​​such as the respective dimensions of the components of the bead portion 20 according to the present embodiment will be described below with reference to Fig. 2 and Fig. 3. The specified values ​​described below are specified values ​​when the tire 1 is not mounted on the specified rim. In other words, the specified values ​​are specified values ​​of the tire 1 in a state before being mounted on the specified rim, and are specified values ​​in a meridian cross section of the tire 1 after vulcanization molding via a mold. For convenience, the specified values ​​are in a meridian cross section of the tire 1 defined by the linear distance between imaginary intersection points H (the distance between the imaginary intersection points H of the pair of bead portions 20) as described below when the tire stands upright alone.

[0035] As in Fig. 3, in a meridian cross section of the bead portion 20, a first line segment D passing through an outermost protrusion point E of the tire bead core 21 in the tire transverse direction and being parallel to the longest side of the tire bead core 21, a side P of the bead base portion 26 closer to the bead heel 27, the side P being a portion of the bead portion 20 being formed to come into contact with the predetermined rim, a curved line G of the tire outer surface 40, the curved line G being a portion of the bead portion 20 being located outward from the bead base portion 26 in the tire transverse direction, a first intersection point H of the side P and the curved line G, a second line segment J passing through the first intersection point H and being perpendicular to the first line segment D, and a third line segment F passing through the projection point E and is perpendicular to the first line segment D,specified.,

[0036] The protrusion point E includes the corner portion 24. The protrusion point E is a point in a meridian cross-section where the first line segment D passing through the center of the outermost bead wire in the tire transverse direction of the bead wires of the tire bead core 21 and parallel to the longest side of the tire bead core 21 meets the profile of the tire bead wires. The longest side is designated by the outer circumferential surface 23. The first intersection point H includes the bead heel 27.

[0037] In the present embodiment, a distance A between the second line segment J and the third line segment F is from 4 mm to 8 mm.

[0038] Furthermore, in the present embodiment, the bead base portion 26 includes an outer portion 26A including the bead heel 27 and an inner portion 26B including the bead toe 28. The side of the outer portion 26A in the meridian cross section is the P side. The side of the inner portion 26B in the meridian cross section is an M side.

[0039] The side P and the side M are connected by a curvature point L. In other words, the side P and the side M each have different angles with respect to the tire rotation axis, and the side P and the side M are bent at the curvature point L. The curvature point L is located from 8 mm to 18 mm in the tire transverse direction from the first intersection point H.

[0040] An angle θ1 of the side P of the outer portion 26A with respect to a line AX perpendicular to the tire equatorial plane CL (which is a line AX parallel to the tire rotation axis) is from 18° to 23°, and an angle θ2 of the side M of the inner portion 26B with respect to the line AX is from 27° to 33°.

[0041] As in Fig. 2, a tire radius R2 at the bead toe 28 and a tire radius R1 at the bead heel 27 of the bead base portion 26 have a ratio R2 / R1 in the range of 0.935 to 0.975. The tire radius R1 is the distance in the tire radial direction from the tire rotation axis to the bead heel 27. The tire radius R2 is the distance in the tire radial direction from the tire rotation axis to the bead toe 28.

[0042] Furthermore, a tire radius R3 at the bead core 21 and the tire radius R1 at the bead heel 27 have a ratio R1 / R3 in the range of 0.985 to 0.995. "Tire radius R3" at the bead core 21 is the distance in the tire radial direction from the innermost tip in the tire radial direction of the tips (six in the present embodiment) of the polygonal (hexagonal in the present embodiment) bead core 21 to the tire rotation axis in a meridian cross section.

[0043] As described above, the distance A according to the present embodiment is from 4 mm to 8 mm. This allows an angle α (see Fig. 3) formed by the carcass body part 61 and the outer peripheral surface 23 of the bead core 21. In other words, by setting the distance A from 4 mm to 8 mm, the position of the bead core 21 is offset inward in the tire transverse direction. As a result, in the tire 1, before and after inflation, the amount of position change of the carcass 6 located near the bead portion 20 is reduced. Furthermore, the ratio between the tire radius R2 at the bead toe 28 and the tire radius R1 at the bead heel 27 can be adjusted, and thus eccentric engagement after inflation can be suppressed.

[0044] If the distance A is greater than 8 mm, the volume of the bead rubber layer K increases to a level that degrades the heat buildup and durability of the bead portion 20. If the distance A is less than 4 mm, the angle α cannot be made sufficiently small, and effective suppression of eccentric engagement becomes difficult. Thus, the distance A is preferably from 4 mm to 8 mm, and more preferably from 5 mm to 7 mm.

[0045] In the present embodiment, the ratio R2 / R1 is from 0.935 to 0.975. If the ratio R2 / R1 is less than 0.935, the tire mounting workability of the tire 1 is impaired. If the ratio R2 / R1 is greater than 0.975, the probability of eccentric engagement is high. Thus, the ratio R2 / R1 is preferably from 0.935 to 0.975.

[0046] Furthermore, in the present embodiment, the tire radius R3 at the bead core 21 and the tire radius R1 at the bead heel 27 have the ratio R1 / R3 in the range of 0.985 to 0.995. This can further suppress eccentric engagement. If the ratio R1 / R3 is less than 0.985, the effect of eliminating eccentric engagement is not sufficiently achieved. If the ratio R1 / R3 is greater than 0.995, the tire mounting workability is deteriorated. Thus, the ratio R1 / R3 is preferably from 0.985 to 0.995.

[0047] In the present embodiment, the bead base portion 26 has a two-stage tapered structure including the P side and the M side bent at the curvature point L. The angle θ1 of the P side of the outer portion 26A is from 18° to 23°. The angle θ2 of the M side of the inner portion 26B is from 27° to 33°. When the angle θ1 is less than 18° and the angle θ2 is less than 27°, an effect of eliminating eccentric engagement is not sufficiently achieved. When the angle θ1 is greater than 23° and the angle θ2 is greater than 33°, the tire mounting workability is deteriorated. Thus, the angle θ1 is preferably from 18° to 23°, and the angle θ2 is preferably from 27° to 33°.

[0048] It should be noted that in the present embodiment, the bead base portion 26 has a two-stage tapered structure. As shown in Fig. 4, the bead base portion 26 may have a single tapered structure. Fig. The bead base portion 26 illustrated in FIG. 4 does not include the curvature point L, and the side of the bead base portion 26 is linear in a meridian cross section. In such a configuration, in order to suppress eccentric engagement, an angle θ of the side of the bead base portion 26 with respect to the line AX perpendicular to the tire equatorial plane CL is preferably from 15° to 20°. If the angle θ is less than 15°, an effect of eliminating eccentric engagement is not sufficiently achieved. If the angle θ is greater than 20°, tire mounting workability is deteriorated. Thus, the angle θ is preferably from 15° to 20°. Examples

[0049] Fig. 5 to 8 are tables showing results of performance tests of tire 1. With respect to the tires 1 described above, performance evaluation tests conducted on tires 1 of a prior art example and comparative examples, and on the tires 1 according to embodiments of the present invention will be described below. The performance evaluation tests were conducted with respect to eccentric engagement, which indicates the degree to which a tread portion is eccentrically engaged with a rim wheel, and tire mounting workability, which indicates the ease with which a tire 1 can be mounted on a rim.

[0050] As in Fig. 5 to 8, the evaluation test was conducted on the tire 1 of the prior art example, the tires 1 of Comparative Examples 1 to 4, and the tires 1 of Examples 1 to 16, which are embodiments of the present invention.

[0051] In the eccentric engagement performance evaluation test, tires 1, measuring 11R22.5, were mounted on 22.5 × 7.50 rims and inflated to the specified maximum air pressure (700 kPa). The distance from the rim flange to the circumferential vent was measured at eight circumferential positions on one side, and the area around one tire was compared and evaluated. Smaller areas indicate better eccentric engagement, meaning the degree of eccentric engagement is low.

[0052] In the tire mounting feasibility evaluation test, tires 1, measuring 11R22.5, were manually mounted on 22.5 × 7.50 rim wheels using two tire levers. The time required and ease of mounting were evaluated. For the tire mounting feasibility evaluation, the results are expressed and evaluated as index values. Higher values ​​indicate better tire mounting feasibility.

[0053] As in Fig. As shown in Figure 5, the distance A and the ratio R2 / R1 of tire 1 of the prior art example are outside the technical scope of the present invention. The tires 1 of Comparative Examples 1 to 4 all have a component outside the technical scope of the present invention.

[0054] As in Fig. As shown in Figure 5, the tires 1 of Examples 1 to 4 exhibit better eccentric engagement compared to the tires 1 of the prior art example and the comparative examples. In other words, in the tires 1 of Examples 1 to 4, the bead portions engage with the rim wheels with correct positioning, and the likelihood of uneven wear is reduced.

[0055] As in Fig. As indicated in Figure 6, the ratio R1 / R3 was varied for the tires of Examples 5 to 8. When the value of the ratio R1 / R3 is from 0.985 to 0.995, the eccentric engagement and the operability of tire mounting are even better.

[0056] As in Fig. As indicated in Example 7, the values ​​of the angles θ1, θ2 were varied for the two-stage tapered structure of the bead base portion 26. As indicated by Examples 9 to 12, when the angle θ1 is from 18° to 23° and the angle θ2 is from 27° to 33°, the eccentric engagement and tire mounting workability are even better.

[0057] As in Fig. 8, the value of the angle θ was varied for the single tapered structure of the bead base portion 26. As indicated by Examples 13 to 16, when the angle θ is from 15° to 20°, the eccentric engagement and tire mounting workability are even better. List of reference symbols 1 tire (pneumatic tire) 2 Tread section 3 Tread surface 4 shoulder section 5 Side wall section 6 Carcass 7 belt layer 8 Inner core 10 bridge section 15 Main circumferential groove 20 bead section 21 Tire bead core 22 Inner circumferential surface 23 Outer peripheral surface 24 corner section 25 corner section 26 Bead base section 27 Bead heel 28 bulge toe 35 steel cord reinforcement layer 40 Tire outer surface 50 tire inner surface 61 Carcass body part 62 Carcass fold-back section 71, 72, 73, 74 Belts A distance CL Tire equatorial plane D First line segment F Third line segment G Curved line H First intersection point J Second line segment K Bead rubber layer L Curvature point P Page

Claims

[1] A pneumatic tyre (1) mountable on a predetermined rim tapered by 15°, the tyre (1) comprising: a pair of bead portions (20) arranged on each side of a tire equatorial plane (CL) in a tire transverse direction; a tire bead core (21) provided in each pair of bead portions (20); a carcass (6) supported by the pair of tire bead cores (21), the carcass (6) comprising a carcass body part (61) and a carcass fold-back portion (62) formed by the carcass (6) and folded back on the tire bead core (21); a steel cord reinforcing layer (35) arranged on an outer surface of the carcass (6) folded back on the tire bead core (21), and a bead rubber layer (K), at least a portion of which is disposed between the carcass body part (61) and the carcass fold-back portion (62);wherein, when the pneumatic tire (1) is not mounted on the predetermined rim, a distance (A) from a second line segment (J) to a third line segment (F) is from 4 mm to 8 mm, wherein a first line segment (D) passing through an outermost protrusion point of the tire bead core (21) in the tire transverse direction and being parallel to a longest side of the tire bead core (21), a side (P) of a bead base portion (26) closer to a bead heel (27), which is a portion of the bead portion that comes into contact with the predetermined rim, a curved line (G) of a tire outer surface (40), which is a portion of the bead portion that is located outward from the bead base portion (26) in the tire transverse direction, a first intersection point (H) of the side (P) and the curved line (G), the second line segment (J) passing through the first intersection point (H) and is perpendicular to the first line segment (D), and the third PS:SI:hm ; Line segment (F) passing through the projection point (E) and perpendicular to the first line segment (D), wherein a ratio R2 / R1 is from 0.935 to 0.975, where R2 is a tire radius at a bead toe (28) of the bead base portion (26) and R1 is a tire radius at the bead heel (27), and wherein a ratio R1 / R3 is from 0.985 to 0.995, where R3 is a tire radius at the tire bead core (21) and R1 is the tire radius at the bead heel (27). [2] Pneumatic tire (1) according to claim 1, wherein the bead base portion (26) comprises an outer portion (26A) comprising the bead heel (27) and an inner portion (26B) comprising the bead toe (28), and wherein an angle (θ1) of a side of the outer portion (26A) with respect to a line (AX) perpendicular to the tire equatorial plane (CL) is from 18° to 23°, an angle (θ2) of a side of the inner portion (26B) is from 27° to 33°. [3] A pneumatic tire (1) according to claim 1, wherein an angle of the side of the bead base portion (26) with respect to a line (AX) perpendicular to the tire equatorial plane (CL) is from 15° to 20°.

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