JP7194584B2 - pneumatic tire - Google Patents

Description

The present invention relates to pneumatic tires.

The pneumatic tire carcass ply disclosed in Patent Document 1 includes a first ply that is continuous between a pair of bead portions and a discontinuous second ply that is arranged outside the first ply in the tire radial direction. . The second ply includes a pair of ply pieces extending from the tread portion to either one of the pair of bead portions. In the center of the tread portion, there is provided an area where neither of the two ply pieces exists, that is, a hollow portion. The hollow portion of the second ply is intended to achieve both of two fundamentally contradictory performances. One type of performance is rigidity (which contributes to improved steering stability) and cut resistance, and the other type of performance is weight reduction and thus rolling resistance reduction.

JP 2017-109517 A

The structure disclosed in Patent Literature 1 has room for further improvement in terms of weight reduction and thus reduction in rolling resistance while ensuring rigidity and cut resistance.

SUMMARY OF THE INVENTION An object of the present invention is to reduce the weight of a pneumatic tire including a carcass ply having a hollow portion while ensuring rigidity and cut resistance, thereby reducing rolling resistance.

A first aspect of the present invention is a tread portion, a pair of sidewall portions extending radially inward from both ends of the tread portion, and arranged at the radially inner end portions of the pair of sidewall portions. a center portion of the tread portion positioned radially inward of the tire; a pair of side portions extending radially inward of the tire from both ends of the central portion; and extending from the pair of side portions. a first ply having a pair of roll-up portions wound around the pair of bead cores respectively; a pair of ply pieces each having a side portion extending inward in the tire radial direction from the inner end portion and a roll-up portion provided continuously with the side portion and wound up on one of the pair of bead cores; and a discontinuous second ply, wherein the sidewall portion is formed at a maximum width position that protrudes most in the tire width direction and outside the maximum width position in the tire radial direction, and the thickness in the tire width direction is a buttress portion that is thicker than other portions, wherein the modulus of the first ply is lower than the modulus of the pair of ply pieces of the second ply, and The ply pieces are all wound up from the inside to the outside in the tire width direction with respect to the bead core, and the outer end portion, which is the end of the roll-up portion of the first ply, is the end of the roll-up portion of the ply piece. Provided is a pneumatic tire positioned radially outward of an outer end portion, which is an end, radially outward of the maximum width position, and radially inward of the buttress portion . A second aspect provides a pneumatic tire in which, instead of modulus, the breaking strength of the first ply is lower than the breaking strength of the pair of ply pieces of the second ply.

The second ply comprises a pair of ply pieces and is discontinuous. In other words, there is a hollow portion where no ply exists between the inner ends of the pair of ply pieces. By adopting the second ply having such a hollow portion, the weight can be reduced as compared with the case where the second ply is one continuous ply.

Carcass ply generally tends to be lighter as the modulus (stress generated when a certain strain is applied) and breaking strength (tensile load causing breakage) are lower, and as the modulus and breaking strength are higher, the weight tends to be heavier. . The second ply has a hollow portion while the first ply has a central portion in the tread portion. The central portion of the first ply contributes less to the improvement of rigidity and cut resistance than the side portions of the first ply and the ply pieces forming the second ply. The first ply having such a central portion has a lower modulus or lower breaking strength than the ply pieces of the second ply, and is relatively lightweight, thereby reducing weight without impairing rigidity and cut resistance. be able to.

Over the entire sidewall portion, two layers of plies are arranged, namely a side portion of a first ply and a side portion of a ply piece (second ply). In addition, in the bead core side region of the sidewall portion, two plies, that is, the winding portion of the first ply and the winding portion of the ply piece (second ply) are arranged. By providing two or four layers of plies in the sidewall portion in this way, the required cut resistance is ensured. In addition, by providing two or four layers of plies, the required rigidity in the sidewall portion is ensured.

As described above, according to the present invention, it is possible to reduce the weight and thereby reduce the rolling resistance while ensuring rigidity, steering stability and cut resistance.

One and the other of said pair of ply pieces have the same modulus or breaking strength. According to this aspect, since the mounting direction to the vehicle (wheel) is not specified, the functionality and design of the pneumatic tire can be improved.

One of the pair of ply pieces has a different modulus or breaking strength than the other. In general, a sidewall portion located on the outside of a vehicle is more likely to be damaged than an inside sidewall portion, and its rigidity tends to affect steering stability. Therefore, in the case of this aspect, it is preferable that, of the pair of ply pieces, the one having the higher modulus or breaking strength is used for the outside, and the one having the lower modulus or breaking strength is used for the inside. By doing so, it is possible to further reduce the weight and thereby reduce the rolling resistance while ensuring the cut resistance and rigidity of the outside of the pair of sidewalls, which is easily damaged and affects the steering stability. I can do it.

In order to make the modulus or breaking strength different, the pair of ply pieces of the first ply and the second ply have at least one of cord material, cord diameter, number of ends, rubber hardness, and rubber thickness. can be different.

The tread portion further includes a belt layer disposed radially outward of the central portion of the first ply, wherein the inner end portion of the ply piece is connected to the belt layer and the central portion of the first ply. is placed between. According to this aspect, since the inner ends of the ply pieces are firmly held by the belt layer, the rigidity of the second ply can be ensured more reliably.

Advantageous Effects of Invention According to the present invention, in a pneumatic tire provided with a carcass ply having a hollow portion, it is possible to reduce weight and thereby reduce rolling resistance while ensuring rigidity and cut resistance.

1 is a meridional cross-sectional view of a pneumatic tire according to an embodiment of the present invention; FIG. 1 is a meridional cross-sectional view of a tread portion of a pneumatic tire according to an embodiment of the present invention and its surroundings. FIG. 2 is a partially enlarged view of FIG. 1;

Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
1 to 3 show a rubber pneumatic tire (hereinafter referred to as "tire") 1 according to an embodiment of the present invention.

As shown in FIGS. 1 and 2 , the tire 1 includes a tread portion 2 , a pair of sidewall portions 3 , and a pair of ring-shaped bead portions 4 .

The tread portion 2 extends in the tire width direction (indicated by symbol TW in FIG. 1). Grooves 2a are provided on the surface of the tread portion 2, that is, on the tread surface.

The pair of sidewall portions 3 extend inward from both ends of the tread portion 2 in the tire radial direction (indicated by symbol TR in FIG. 1).

The pair of bead portions 4 are arranged at the inner end portions of the pair of sidewall portions 3 in the tire radial direction, respectively. Each bead portion 4 comprises a bead core 5 and a bead filler 6 . The bead core 5 comprises a large number of steel wires bundled into a ring. The bead filler 6 is ring-shaped and made of rubber harder than the rubber forming the tread portion 2 and the sidewall portion 3 . The bead filler 6 has a base end 6a arranged adjacent to the outer side of the bead core 5 in the tire radial direction, and a tip end 6b opposite to the base end 6a. It tapers outward. Each bead portion 4 comprises a strip rubber 7 provided so as to wrap a bead core 5 and a bead filler 6 .

The tire 1 includes a carcass 10 that is toroidally spanned between the bead portions 4 . The carcass 10 of this embodiment includes a first carcass ply (hereinafter referred to as “first ply”) 11 and a second carcass ply (hereinafter referred to as “second ply”) 12 . The second ply 12 is a ply having a hollow portion 13b, while the first ply 11 is a normal ply having no hollow portion. Both plies 11 and 12 will be described in detail later. An inner liner 8 is provided inside the carcass 10 , that is, on the innermost peripheral surface of the tire 1 .

With reference to FIGS. 2 and 3 , an endless belt layer 20 is provided between the tread portion 2 , more specifically the carcass 10 and the tread portion 2 . In this embodiment, the belt layer 20 has two belts 21 and 22 . The belt 21 is arranged adjacent to the outer side of the carcass 10 in the tire radial direction, and the belt 22 is arranged adjacent to the outer side of the belt 21 in the tire radial direction. In addition, in the present embodiment, the dimension of the lower belt 21 in the tire width direction is larger than the dimension of the upper belt 22 in the tire width direction, and the end 21a of the belt 21 is closer to the tire than the end 22a of the belt 22. It is positioned on the outside in the width direction. The tread portion 2 is located on the inner side in the tire width direction of the end portion 21 a of the widest belt 21 . The belts 21 and 22 are formed by coating steel or organic fiber belt cords with rubber. The belt layer 20 may be composed of one belt, or may be provided with three or more belts.

An endless cap layer 30 is provided adjacent to the outer side of the belt layer 20 in the tire radial direction. The cap layer 30 of this embodiment comprises a pair of narrow edge plies 31 directly covering either of the ends 21a, 22a of the belts 21, 22, respectively. In addition, the cap layer 30 of the present embodiment includes a wide cap ply 32 that is arranged adjacent to the edge ply 31 in the tire radial direction and covers the entire belts 21 and 22 including the ends 21a and 22a with one sheet. . Cap layer 30 may comprise one or more plies. Alternatively, the cap layer 30 may be omitted.

A pair of endless rubber pads 40 are arranged between the outer end portions of the belt layer 20 in the tire width direction and the carcass layer 10 . The cross-sectional shape of the pad 40 is a flat triangular shape. The positions of the ends 21a and 22a of the belts 21 and 22, the outer end 31a of the edge ply 31 in the tire width direction, and the end 32a of the cap ply 32 in the tire width direction correspond to the outer ends of the pad 40 in the tire width direction. It is set in the area between the portion 40a and the inner end portion 40b, that is, the area where the pad 40 exists. Pad 40 may be eliminated.

The first ply 11 and the second ply 12 constituting the carcass 10 will be described below.

As described above, the first ply 11 is a single ply, while the second ply 12 is a discontinuous ply having a hollow portion 13b and is composed of a pair of ply pieces 13. As shown in FIG. Each of the ply pieces 13 of the first ply 11 and the second ply 12 is a belt-shaped sheet in which a plurality of cords arranged side by side with a gap are covered with rubber.

The first ply 11 includes a central portion 11a, a pair of side portions 11b, and a pair of roll-up portions 11c. The central portion 11a is arranged inside the tread portion 2 in the tire radial direction. The pair of side portions 11b are arranged on the sidewall portion 3 so as to extend inward in the tire radial direction from both ends of the central portion 11a in the tire width direction. The pair of roll-up portions 11c are respectively continuous with the inner end portions in the tire radial direction of the pair of side portions 11b. Each roll-up portion 11 c is rolled up from the inner side to the outer side in the tire width direction with respect to one of the pair of bead cores 5 and terminates at the sidewall portion 3 .

The second ply 12 is arranged adjacent to the first ply 11 on the radially outer side of the tire, and is a discontinuous ply made up of a pair of ply pieces 13 . The ply piece 13 has an inner end portion 13a located between the belt layer 20 and the central portion 11a of the first ply 11 . A pad 40 is interposed between the inner end portion 13 a and the belt layer 20 . The position of the inner end portion 13a of the ply piece 13 in the tire width direction is located in the outer region in the tire width direction of the tread portion 2, more specifically, the end portions 21a and 22a of the belts 21 and 22 forming the belt layer 20. It is set in a region on the inner side in the tire width direction than any of them. A central area of the tread portion 2 in the tire width direction, more specifically, an area between the inner end portions 13a of the pair of ply pieces 13, is provided with a hollow portion 13b. The second ply 12 does not exist in the hollow portion 13b, and only the central portion 11a of the first ply 11 exists.

The ply piece 13 includes a side portion 13c extending inward in the tire radial direction from the inner end portion 13a, and a roll-up portion 13d provided continuously with the side portion 13c. The side portion 13c is arranged to overlap the side portion 11b of the first ply 11 on the outside in the tire width direction. The roll-up portion 13 d rolls up from the inner side to the outer side in the tire width direction with respect to the bead core 5 a and terminates at the sidewall portion 3 . The roll-up portion 13d is arranged on the inner side of the roll-up portion 11c of the first ply 11 in the tire width direction, and is arranged on the outer side of the bead filler 6 in the tire radial direction so as to overlap the side portion 13c on the outer side in the tire radial direction.

In this embodiment, the material of the first ply 11 and the material of the pair of ply pieces 13 of the second ply 12 are different. Specifically, the ply pieces 13 of the first ply 11 and the second ply 12 have different moduli (stress generated when a certain strain is applied), and the modulus of the first ply 11 is different from that of the second ply. lower than the modulus of 12 ply pieces 13; Further, the ply pieces 13 of the first ply 11 and the ply pieces 13 of the second ply 12 have different breaking strengths (tensile loads at which breakage occurs), and the breaking strength of the first ply 11 is the same as that of the ply pieces 13 of the second ply 12. Lower than breaking strength. One and the other of the pair of ply pieces 13 have the same modulus and breaking strength.

By varying at least one of cord material, cord diameter, number of ends, rubber hardness, and rubber thickness, the modulus of the first ply 11 is set lower than the modulus of the ply pieces 13 of the second ply 12. Alternatively, the breaking strength of the first ply 11 can be set lower than the breaking strength of the ply pieces 13 of the second ply 12 .

The cord diameter, number of ends, rubber hardness, and rubber thickness generally have the following tendencies. First, the thicker the cord diameter, the higher the modulus and breaking strength. Also, the greater the number of ends, the higher the modulus and breaking strength. Furthermore, the higher the rubber hardness, the higher the modulus and breaking strength. Furthermore, the thicker the rubber, the higher the modulus and breaking strength.

As for cord materials, metal (steel), aramid, rayon, polyester, and nylon have the highest modulus in that order. The cord to be used is set so that the modulus of the first ply 11 is lower than that of the ply piece 13 based on this order of modulus. Specifically, the first ply 11 does not use a metal cord, but uses one of aramid, rayon, polyester, and nylon cords. The ply piece 13 does not use a nylon cord, but uses a cord having a higher modulus than the first ply 11 among metal, aramid, rayon, and polyester cords.

Regarding cord materials, metal (steel), aramid, nylon, polyester, and rayon have the highest breaking strength in that order. The cords to be used are set so that the breaking strength of the first ply 11 is lower than that of the ply piece 13 based on the breaking strength order. Specifically, the first ply 11 does not use a metal cord, but uses one of aramid, nylon, polyester, and rayon cords. The ply piece 13 does not use a nylon cord, but uses a cord having higher breaking strength than the first ply 11 among metal, aramid, rayon, and polyester cords.

Further, in this embodiment, the arrangement of the outer end portion 11d of the first ply 11 and the outer end portion 13e of the ply piece 13 and the arrangement of the inner end portion 13a of the ply piece 13 are optimized.

Specifically, as shown in FIG. 1 , the outer end portion 11 d of the first ply 11 is positioned radially outward of the tip 6 b of the bead filler 6 and radially inward of the tread portion 2 . do. More specifically, the outer end portion 11d is arranged outside the maximum width position 3a of the sidewall portion 3 in the tire radial direction and near the end portion of the buttress portion 9 on the inside in the tire radial direction. The buttress portion 9 is a portion that is formed on the outer side of the sidewall portion 3 in the tire radial direction, protrudes outward in the tire width direction, and has a greater rubber thickness than other portions.

The outer end portion 13 e of the ply piece 13 is located between the tip 6 b of the bead filler 6 and the outer end portion 11 d of the first ply 11 . More specifically, the outer end portion 13e is located near the maximum width position 3a of the sidewall portion 3, and the distance between the outer end portion 13e and the outer end portion 11d of the first ply 11 in the tire radial direction is 5 mm or more and 60 mm or less. are arranged as If the distance between the outer end portion 13e of the ply piece 13 and the outer end portion 11d of the first ply 11 is excessively reduced, the outer end portions 11d and 13e are brought close to each other, and the difference in level between the outer ends 11d and 13e causes contact with the rubber of the sidewall portion 3. There is a risk that a large gap will be formed between them (process failure). On the other hand, if the interval is excessively increased, the degree of contribution of the roll-up portion 13d of the second ply 12 to improving the rigidity of the sidewall portion 3 becomes low. In order to prevent these inconveniences and secure the rigidity and cut resistance of the sidewall portion 3, it is preferable to set the distance between the outer ends 11d and 13e within the above range.

Referring to FIG. 3, the inner end portion 13a of the ply piece 13 is located inside the end portion 21a of the belt 21 in the tire width direction, and the inner end portion 13a side of the ply piece 13 is positioned relative to the belt 21. They overlap in the tire width direction. The overlapping ratio is preferably set to be higher than 0% (that is, not including 0) and 30% or less with respect to the width of the belt 21 in the tire width direction. If the overlap ratio is 0% or less (that is, if there is no overlap), the belt 21 cannot position the inner end 13a of the ply piece 13 via the pad 40, so the ply piece 13 ensures the rigidity of the sidewall portion 3. Can not. When the overlapping ratio is higher than 30%, the degree of contribution to weight reduction and rolling resistance reduction in the tread portion 12 is low. In order to prevent these inconveniences, it is preferable to set the overlapping ratio of the ply pieces 13 and the belt 21 within the above range.

Next, the features of the pneumatic tire 1 of this embodiment will be described.

The second ply 12 is a discontinuous ply having a pair of ply pieces 13. Between the inner ends 13b of the pair of ply pieces 13 is a hollow portion 13b where no ply exists. By adopting the second ply 12 having such a hollow portion 13b, the weight can be reduced as compared with the case where the second ply 12 is one continuous ply.

The modulus of the first ply 11 is lower than the modulus of the ply pieces 13 of the second ply 12 . The second ply 12 has a hollow portion 13b, while the first ply 11 has a central portion 11a in the tread portion 2. As shown in FIG. Compared to the side portions 11b of the first ply 11 and the ply pieces 13 of the second ply 12, the central portion 11a of the first ply 11 contributes less to improving rigidity and cutting resistance. The first ply 11 having such a central portion 11a has a lower modulus than the ply pieces 13 of the second ply 12 and is relatively lightweight, thereby further reducing the weight without impairing the rigidity and cut resistance. can be planned.

The breaking strength of the first ply 11 is lower than the breaking strength of the ply pieces 13 of the second ply 12 . The second ply 12 has a hollow portion 13b, while the first ply 11 has a central portion 11a in the tread portion 2. As shown in FIG. Compared to the side portions 11b of the first ply 11 and the ply pieces 13 of the second ply 12, the central portion 11a of the first ply 11 contributes less to improving rigidity and cutting resistance. The first ply 11 having such a central portion 11a has a lower breaking strength than the ply piece 13 of the second ply 12 and is relatively lightweight, thereby further reducing the weight without impairing the rigidity and cut resistance. can be improved.

Over the entire sidewall portion 3, two layers of plies, that is, the side portion 11b of the first ply 11 and the side portion 13c of the ply piece 12 are arranged. Further, in the region of the sidewall portion 3 on the bead core 5 side, two plies, that is, the roll-up portion 11c of the first ply 11 and the roll-up portion 13d of the ply piece 13 are arranged. By providing two or four layers of plies in the sidewall portion 3 in this way, the required cut resistance is ensured. Moreover, the required rigidity in the sidewall portion 3 is ensured by providing two or four layers of plies.

As described above, according to the present embodiment, it is possible to reduce the weight and thereby reduce the rolling resistance while ensuring rigidity, steering stability and cut resistance.

As described above, one of the pair of ply pieces 13 and the other have the same modulus and breaking strength. As a result, the direction of attachment to the vehicle (wheel) is not specified, so the functionality and design of the tire 1 can be improved.

As described above, the outer end portion 11d of the first ply 11 and the outer end portion 13e of the ply piece 13 are located outside the tip 6b of the bead filler 6 in the tire radial direction, and are radially outside the tread portion 2 in the tire radial direction. located inside. With this configuration, the side fall portion 3 has four plies, that is, the side portion 11b of the first ply 11, the side portion 13c of the ply piece 13, the roll-up portion 13d of the ply piece 13, and the roll-up portion 11c of the first ply 11. The existing area is sufficiently secured. As a result, rigidity and cut resistance can be ensured more reliably.

As described above, the outer end portion 11d of the first ply 11 and the outer end portion 13e of the ply piece 13 are arranged with a predetermined gap therebetween. With this configuration, compared to the case where the positions of the outer ends 11d and 13e are aligned, it is possible to minimize the step caused by them. Further, since the outer end portion 13e of the ply piece 13 can be covered with the roll-up portion 11c of the first ply 11, the number of steps between the ply piece 13 and the rubber of the sidewall portion 3 can be minimized.

As described above, the inner end portion 13a of the ply piece 13 is positioned between the belt layer 20 and the central portion 11a of the first ply 11 . With this configuration, the inner end portion 13a of the ply piece 13 is firmly held by the belt layer 20, so that the rigidity of the second ply 12 can be ensured more reliably.

(Second embodiment)
The tire 10 of the second embodiment has the same basic structure as the tire 10 of the first embodiment shown in FIGS. 1-3. In the second embodiment, the material (modulus or breaking strength) of one of the pair of ply pieces 13 is different from that of the other. That is, the modulus or breaking strength is increased in the order of the first ply 11, the ply piece 13 on one side (for example, the left side in FIG. 2), and the ply piece 13 on the other side (the right side in FIG. 2). The method of varying the modulus or breaking strength is the same as in the first embodiment.

In general, the sidewall portion 3 is more likely to be damaged when placed on the outside of the vehicle than when placed on the inside, and the rigidity of the outside tends to affect steering stability. Therefore, of the pair of ply pieces 13, the one with a higher modulus or breaking strength is used for the outside, and the one with a lower modulus or breaking strength is used for the inside, and the tire 1 including the tread pattern is designed.

In the second embodiment, as in the first embodiment, the second ply 12 is a discontinuous ply having a pair of ply pieces 13, so the rigidity of the tire 10 and the resulting steering stability and cut resistance are improved. It is possible to reduce the weight and thereby reduce the rolling resistance while ensuring the Moreover, since the modulus and breaking strength of one of the pair of ply pieces 13 are different from that of the other, cut resistance and rigidity are ensured at the outside sidewall portion 3, which is easily damaged and affects steering stability. At the same time, it is possible to further reduce the weight of the inner side wall portion 3 and thereby reduce the rolling resistance.

In addition, the pneumatic tire 10 of the present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible.

For example, the pneumatic tire 10 may have a three-ply structure including two first plies 11 and a second ply 12 having a pair of ply pieces 13, and the number of laminated plies can be changed as necessary. be.

1 pneumatic tire 2 tread portion 2a groove 3 sidewall portion 3a maximum width position 4 bead portion 5 bead core 6 bead filler 6a base end 6b tip end 7 strip rubber 8 inner liner 9 buttress portion 10 carcass 11 first carcass ply (first ply )
11a central portion 11b side portion 11c winding portion 11d outer end portion 12 second carcass ply (second ply)
13 ply piece 13a inner end portion 13b hollow portion 13c side portion 13d winding portion 13e outer end portion 20 belt layer 21 belt 21a end portion 22 belt 22a end portion 30 cap layer 31 edge ply 31a end portion 32 cap ply 32a end portion 40 Pad 40a End 40b End TR Tire radial direction TW Tire width direction

Claims (9)

a tread portion;
a pair of sidewall portions extending radially inward from both ends of the tread portion;
a pair of bead cores respectively arranged at the tire radial direction inner end portions of the pair of sidewall portions;
A central portion positioned radially inward of the tread portion, a pair of side portions extending inward in the tire radial direction from both ends of the central portion, and a pair of bead cores extending from the pair of side portions, respectively. a first ply having a pair of rolled-up rolls;
a side portion disposed radially outwardly of the first ply, having an inner end positioned at the tread portion, and extending radially inward from the inner end; and being continuous with the side portion. a discontinuous second ply comprising a pair of ply pieces each having a roll-up portion wound on one of said pair of bead cores;
The sidewall portion has a maximum width position that protrudes most in the tire width direction, and a buttress portion formed outside the maximum width position in the tire radial direction and having a thickness in the tire width direction that is thicker than other portions. ,
the modulus of the first ply being lower than the modulus of the pair of ply pieces of the second ply;
The pair of ply pieces of the first ply and the second ply are both wound up from the inside to the outside in the tire width direction with respect to the bead core,
The outer end portion of the first ply, which is the end of the roll-up portion, is positioned radially outward of the outer end portion of the ply piece, which is the end of the roll-up portion of the ply piece, and is positioned further in the tire radial direction than the maximum width position. A pneumatic tire arranged outside and inside the buttress portion in the tire radial direction . 2. The pneumatic tire of claim 1, wherein the modulus of one and the other of said pair of ply pieces are the same. 2. The pneumatic tire according to claim 1, wherein the modulus of one and the other of said pair of ply pieces are different. a tread portion;
a pair of sidewall portions extending radially inward from both ends of the tread portion;
a pair of bead cores respectively arranged at the tire radial direction inner end portions of the pair of sidewall portions;
A central portion positioned radially inward of the tread portion, a pair of side portions extending inward in the tire radial direction from both ends of the central portion, and a pair of bead cores extending from the pair of side portions, respectively. a first ply having a pair of rolled-up rolls;
a side portion disposed radially outwardly of the first ply, having an inner end positioned at the tread portion, and extending radially inward from the inner end; and being continuous with the side portion. a discontinuous second ply comprising a pair of ply pieces each having a roll-up portion wound on one of said pair of bead cores;
The sidewall portion has a maximum width position that protrudes most in the tire width direction, and a buttress portion formed outside the maximum width position in the tire radial direction and having a thickness in the tire width direction that is thicker than other portions. ,
The breaking strength of the first ply is lower than the breaking strength of the pair of ply pieces of the second ply,
The pair of ply pieces of the first ply and the second ply are both wound up from the inside to the outside in the tire width direction with respect to the bead core,
The outer end portion of the first ply, which is the end of the roll-up portion, is positioned radially outward of the outer end portion of the ply piece, which is the end of the roll-up portion of the ply piece, and is positioned further in the tire radial direction than the maximum width position. A pneumatic tire arranged outside and inside the buttress portion in the tire radial direction . 5. The pneumatic tire according to claim 4, wherein one and the other of said pair of ply pieces have the same breaking strength. 5. The pneumatic tire according to claim 4, wherein one of the pair of ply pieces and the other have different breaking strengths. 7. The first ply and the pair of ply pieces of the second ply differ in at least one of cord material, cord diameter, number of ends, rubber hardness, and rubber thickness. 1. The pneumatic tire according to 1. Further comprising a belt layer disposed radially outward of the central portion of the first ply in the tread portion,
8. The pneumatic tire according to any one of claims 1 to 7, wherein the inner ends of the ply pieces are arranged between the belt layer and the central portion of the first ply. A bead filler disposed adjacent to the outer side of the pair of bead cores in the tire radial direction and extending in a tapered shape outward in the tire radial direction,
The outer end of the ply piece is arranged between the outer end of the bead filler in the tire radial direction and the outer end of the first ply so as to be positioned near the maximum width position. A pneumatic tire according to any one of claims 1 to 8.

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