Pneumatic tires and molds for tire molding.

Abstract

To provide a pneumatic tire that can be improved in wet performance and steering stability performance.SOLUTION: A pneumatic tire 10 comprises a tread 20 including a block 30 having sipes 40 formed therein. A portion from a surface side of the block to a bottom surface side thereof, of a wall surface 41 at least either of the sipes 40, is formed in a waveform constituted of a plurality of bent parts 42 when viewed from a tire radial direction Z. The bent part 42 includes an inward bent portion 42A swelled inward in the sipe 40 and an outward bent portion 42B swelled outward in the sipe 40, where a curvature radius of the inward bent portion 42A is the same as a curvature radius of the outward bent portion 42B, at the surface side of the block in the tire radial direction Z and the curvature radiuses of the inward bent portion 42A is different from the curvature radius of and the outward bent portion 42B, at the bottom surface side of the block.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire having a tread including blocks on which sipes are formed, and a mold for molding the pneumatic tire. [Background technology]

[0002] A pneumatic tire has a tread, which is the part that contacts the road surface. The tread contains multiple blocks. Each block has sipes formed on it. Sipes provide an edge effect and water-removal effect on icy and snowy roads. The sipes on a pneumatic tire are formed using a sipe blade equipped on a tire molding die.

[0003] For example, Patent Document 1 discloses a technique in which the amplitude of the wave-like shape of the sipe gradually decreases as it moves from the block surface side to the bottom side in the tire radial direction. Patent Document 2 also discloses a technique in which a depression is provided on one block surface of the wall of the sipe, and the cross-sectional area of ​​the depression is reduced as it moves from the block surface side to the bottom side in the tire radial direction. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2003-118322 [Patent Document 2] Japanese Patent Publication No. 2010-202009 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the pneumatic tires disclosed in Patent Documents 1 and 2 still have room for improvement in terms of wet performance and handling stability.

[0006] (Accordingly, the present invention aims to provide a pneumatic tire and a tire molding mold that can improve wet performance and steering stability performance. [Means for Solving the Problems]

[0007] The pneumatic tire according to the present invention is a pneumatic tire having a tread including blocks formed with sipes, wherein at least one wall surface of the sipe is formed in a wave shape consisting of a plurality of bent portions from the block surface side to the bottom surface side when viewed in the tire radial direction, the bent portions include an inward bent portion bulging inward in the sipe and an outward bent portion bulging outward in the sipe, the radii of curvature of the inward bent portion and the outward bent portion are equal on the block surface side in the tire radial direction, and the radii of curvature of the inward bent portion and the outward bent portion are different on the bottom surface side. [Effects of the Invention]

[0008] According to the pneumatic tire of the present invention, wet performance and steering stability performance can be improved. [Brief Description of the Drawings]

[0009] [Figure 1] It is a schematic plan view showing a block of a pneumatic tire as an example of an embodiment. [Figure 2] It is an enlarged view of region A in Figure 1. [Figure 3] It is an enlarged view of region B in Figure 2. [Figure 4] It is a schematic diagram showing the wave shape on the block surface side and the wave shape on the bottom surface side. [Figure 5] It is a schematic diagram showing a tire molding mold as an example of an embodiment. [Figure 6] It is a perspective view showing a sipe blade as an example of an embodiment. [Modes for Carrying Out the Invention]

[0010] An example of an embodiment of the present invention will be described in detail below. In the following description, specific shapes, materials, directions, numerical values, etc., are examples provided to facilitate understanding of the present invention and can be appropriately modified according to the application, purpose, specifications, etc.

[0011] [Air-filled tires] An example of an embodiment, a pneumatic tire 10, will be described using Figure 1.

[0012] As shown in Figure 1, the pneumatic tire 10 has a tread 20 including blocks 30. Sipes 40 are formed on the blocks 30. As will be described in more detail later, the pneumatic tire 10 can improve wet performance and handling stability.

[0013] In the following sections, each component will be described according to the tire axial direction X, tire circumferential direction Y, and tire radial direction Z. Furthermore, in the tire axial direction X, the equator CL may be used to describe the tire width. Additionally, in the tire radial direction Z, the block surface and bottom surface may be used to describe the tire depth. Note that in the figures, the block surface SF and bottom surface BM are indicated.

[0014] The tread 20 is the portion of the pneumatic tire 10 that contacts the road surface. The tread 20 has a plurality of blocks 30 separated by main grooves 21 and sub-grooves 22. Each block 30 is formed in a rectangular shape, with the length in the tire axis direction X decreasing as it approaches the equator CL in a plan view, and is aligned on the tread 20. However, the shape of the blocks 30 is not limited to that of this embodiment; as long as the blocks 30 are separated by the main grooves 21 and sub-grooves 22, they may be rhombic or parallelograms, and their shape is not particularly limited.

[0015] The main groove 21 is a groove that extends along the tire circumferential direction Y. The main groove 21 is formed in a straight line along the tire circumferential direction Y. The secondary groove 22 is a groove that extends along the tire axial direction X. The secondary groove 22 is formed in a straight line along the tire axial direction X. However, the shape of the main groove 21 or secondary groove 22 is not limited to that of this embodiment, and the main groove 21 may be formed inclined with respect to the tire circumferential direction Y, and the secondary groove 22 may be formed inclined with respect to the tire axial direction X.

[0016] [Sipe] Figure 2 will be used to explain sipe 40.

[0017] As shown in Figure 2, sipes 40 are formed on the block 30. The sipes 40 are grooves that extend along the tire axis direction X. The wall surface 41 of the sipes 40 is formed in a wavy shape along the tire axis direction X, although this will be described in detail later. Three sipes 40 are formed at equal intervals in the tire circumferential direction Y of the block 30. The depth of the grooves of the sipes 40 is preferably 60 to 80% of the length of the block 30 in the tire radial direction Z.

[0018] However, the number and shape of the sipes 40 are not limited to those of this embodiment, and 3 to 5 sipes 40 may be formed on the block 30. Also, the sipes 40 may be formed at an angle with respect to the tire axis X. Furthermore, the sipes 40 may be open sipes that penetrate the end side of the block 30, or closed sipes that do not penetrate the end side of the block 30.

[0019] The sipes 40 soften the blocks 30, increasing the contact surface with the road and improving friction. Furthermore, the sipes 40 provide an edge effect and a water-removal effect on icy and snowy roads. The edge effect refers to the ability of the corners of the blocks 30 or sipes 40 to scratch the road surface, increasing grip. The water-removal effect refers to the ability of the sipes 40 to trap water in the voids between them on icy and snowy roads.

[0020] [Wavy pattern of sipes] The wave shape of sipe 40 will be explained using Figures 3 and 4.

[0021] As shown in Figure 3, the wall surface 41 of the sipe 40 is formed in a corrugated shape from the block surface side to the bottom side when viewed from the tire radial direction Z. In other words, the wall surface 41 of the sipe 40 is formed in a corrugated shape in a cross-sectional view perpendicular to the tire radial direction Z. Here, the wall surface 41 of the sipe 40 is the wall (surface) of the sipe 40 perpendicular to the tire circumferential direction Y. By forming the wall surface 41 of the sipe 40 in a corrugated shape, the edge effect described above can be further increased.

[0022] However, the configuration is not limited to the sipe 40 of this embodiment in which one wall surface 41 and the other wall surface 41 are formed in a corrugated shape. The sipe 40 may have only one wall surface 41 formed in a corrugated shape, or only the other wall surface 41 may have a corrugated shape.

[0023] More specifically, the wall surface 41 of the sipe 40 is formed in a wave shape consisting of multiple curved portions 42 when viewed from the tire radial direction Z. Here, the multiple curved portions 42 include inwardly curved portions 42A that bulge inward in the sipe 40 and outwardly curved portions 42B that bulge outward in the sipe 40. Furthermore, the inwardly curved portions 42A and the outwardly curved portions 42B are formed alternately to form the wave shape. In addition, a straight portion 43 is formed between the inwardly curved portions 42A and the outwardly curved portions 42B.

[0024] In other words, when a reference line RL is drawn along the longitudinal direction of the sipe 40 at the center of the width of the sipe 40 (length Y in the tire circumferential direction), the inward curved portion 42A is a curved portion 42 that bulges toward the reference line RL, and the outward curved portion 42B is a curved portion 42 that bulges toward the opposite side of the reference line RL.

[0025] As shown in Figure 4, on the block surface side (section AA in the figure) in the tire radial direction Z, the radius of curvature R1 of the inward curved portion 42A and the radius of curvature R2 of the outward curved portion 42B are the same, while on the bottom side (section BB in the figure), the radius of curvature R1 of the inward curved portion 42A and the radius of curvature R2 of the outward curved portion 42B are different. Furthermore, in the tire radial direction Z, from the block surface side toward the bottom side, the wave pattern changes continuously from one where the radius of curvature R1 of the inward curved portion 42A and the radius of curvature R2 of the outward curved portion 42B are the same to one where the radius of curvature R1 of the inward curved portion 42A and the radius of curvature R2 of the outward curved portion 42B are different.

[0026] Here, the block surface side in the tire radial direction Z is preferably the range from the block surface SF to 30 when the sipe depth (from the block surface SF to the bottom surface BM) is set to 100. Furthermore, the bottom surface side in the tire radial direction Z is preferably the range from 70 to the bottom surface BM when the sipe depth is set to 100.

[0027] Furthermore, on the bottom side, the radius of curvature R1 of the inward curved portion 42A is formed to be larger than the radius of curvature R2 of the outward curved portion 42B. A larger radius of curvature indicates a gentler curve.

[0028] More specifically, on the bottom side, if P is the distance between the center of the inward curved portion 42A and the center of the outward curved portion 42B (the pitch of the wave pattern), t is the thickness of the sipe 40 (the length in the circumferential direction of the tire), and R1 is the radius of curvature of the inward curved portion 42A, then the following equation holds: [Math 1] 0.5 × P - 0.5 × t ≤ R1 ≤ 0.6 × P

[0029] Here, if the radius of curvature R1 of the inward curved portion 42A is greater than 0.6 × P, the wave shape becomes smaller, the restraining force on the wall surface 41 of the sipe 40 decreases, and the anti-collapse performance deteriorates. Also, if the radius of curvature R1 of the inward curved portion 42A is less than 0.5 × P - 0.5 × t, the gap between the inward curved portion 42A and the outward curved portion 42B becomes smaller, and the wet performance, which will be described later, deteriorates.

[0030] Furthermore, when the radius of curvature of the outward curved portion 42B is R2, the radius of curvature R2 is within the range of the following formula. [Math 2] 1.1 ≤ R1 / R2 ≤ 6.0 Furthermore, the radius of curvature R2 is preferably within the range of the following formula. [Math 3] 1.5 ≤ R1 / R2 ≤ 4.0

[0031] If the gap between the inward curved portion 42A and the outward curved portion 42B becomes too large, the restraining force on the wall surface 41 of the sipe 40 will decrease.

[0032] [effect] The pneumatic tire 10 can improve wet performance and handling stability. More specifically, the sipes 40 of the pneumatic tire 10 can increase the rigidity (surface rigidity) of the block surface SF by forming the sipes 40 such that the radius of curvature R1 of the corrugated inner curve portion 42A on the block surface side and the radius of curvature R2 of the outer curve portion 42B are the same. On the other hand, by forming the sipes 40 such that the radius of curvature R1 of the corrugated inner curve portion 42A on the bottom side and the radius of curvature R2 of the outer curve portion 42B are different, a gap is created in the sipes 40, which can reduce the in-plane rigidity.

[0033] The increased surface rigidity improves the contact pressure per unit area of ​​the block 30, thereby improving the driving force. On the other hand, the decreased in-plane rigidity increases the contact area of ​​the block 30, removing water from the wet road surface and increasing the coefficient of friction between the block 30 and the road surface, thereby improving the braking performance of the pneumatic tire 10. In other words, with the pneumatic tire 10, by increasing the surface rigidity and decreasing the in-plane rigidity, it is possible to achieve a balance between wet performance and handling stability.

[0034] [Tire mold] Using Figure 5, we will describe a mold 50, which is an example of an embodiment.

[0035] The mold 50, used as a mold for molding tires, is a mold for molding the pneumatic tire 10 described above. The pneumatic tire 10 has a tread 20 including blocks 30 on which sipes 40 are formed, as described above, and a sidewall (not shown) that forms the side surface. The mold 50 makes it possible to mold a pneumatic tire 10 that can improve wet performance and handling stability.

[0036] In the following, each component will be described according to the tire axial direction X, tire circumferential direction Y, and tire radial direction Z of the pneumatic tire 10 molded by the mold 50.

[0037] The mold 50 includes a tread mold 51 for molding the surface of the tread 20 of the pneumatic tire 10, and a pair of side molds 52 for molding the surface of the sidewall.

[0038] The tread mold 51 includes a main body 54 having a tread molding surface 53, protrusions 55 protruding from the tread molding surface 53, and sipe blades 60 protruding from the tread molding surface 53 and provided between the protrusions 55.

[0039] The main body 54 is made of a metal material, for example, an aluminum alloy. Suitable aluminum alloys include, for example, AC4 series and AC7 series. The projection 55 is the part that forms the main groove 21 in the pneumatic tire 10. The projection 55 is made of the same metal material as the main body 54.

[0040] [Siped Blade] An example of an embodiment, a sipe blade 60, will be described using Figure 6.

[0041] The sipe blade 60 forms the sipes 40 of the pneumatic tire 10. The sipe blade 60 protrudes from the tread forming surface 53 in the radial direction Z of the tire between the projections 55. The sipe blade 60 is flat and made of a metal material, which may be stainless steel, for example. Suitable stainless steels include SUS303, SUS304, SUS630, SUS631, etc. When using a 3D molding machine, SUS304L, SUS630 equivalent material 17-4PH, etc., are suitable.

[0042] A common method for processing the sipe blade 60 is to form its shape using a press molding machine. For sipe blades 60 of this embodiment, where the shape changes in the thickness direction, machining is used to form the shape through cutting. Alternatively, a 3D modeling machine may be used to form complex shapes that are difficult to achieve with machining alone.

[0043] The side surface 61 of the sipe blade 60 is formed in a wavy shape when viewed from the tire radial direction Z. More specifically, the side surface 61 of the sipe blade 60 is formed in a wavy shape consisting of multiple curved portions 62 when viewed from the tire radial direction Z. Here, the multiple curved portions 62 include inwardly curved portions 62A that bulge inward in the sipe blade 60 and outwardly curved portions 62B that bulge outward in the sipe blade 60. Furthermore, the inwardly curved portions 62A and outwardly curved portions 62B are formed alternately to form the wavy shape.

[0044] On the block surface side (section AA in the figure) in the tire radial direction Z, the radius of curvature R1 of the inward curved portion 62A and the radius of curvature R2 of the outward curved portion 62B are the same, while on the bottom side (section BB in the figure), the radius of curvature R1 of the inward curved portion 62A and the radius of curvature R2 of the outward curved portion 62B are different. Furthermore, in the tire radial direction Z, from the block surface side toward the bottom side, the wave pattern changes continuously from one where the radius of curvature R1 of the inward curved portion 62A and the radius of curvature R2 of the outward curved portion 62B are the same to one where the radius of curvature R1 of the inward curved portion 62A and the radius of curvature R2 of the outward curved portion 62B are different.

[0045] Here, the block surface side in the tire radial direction Z is preferably the range from the block surface SF to 30 when the sipe depth (from the block surface SF to the bottom surface BM) is set to 100. Furthermore, the bottom surface side in the tire radial direction Z is preferably the range from 70 to the bottom surface BM when the sipe depth is set to 100.

[0046] Furthermore, on the bottom side, the radius of curvature R1 of the inwardly curved portion 62A is formed to be larger than the radius of curvature R2 of the outwardly curved portion 62B. [Examples]

[0047] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0048] <Comparative Example 1> A pneumatic tire A1 (tire size: 205 / 55R16, rim size: 16×6.5JJ) was fabricated with curved sections formed on the walls of the sipes shown in Figures 1 to 4. The thickness t of each sipe, the pitch P of the wave-like pattern formed on the wall of each sipe, and the radius of curvature R of the inward curved section on the block surface were all determined. SF 1. Radius of curvature R of the outer curved portion on the surface side of the block SF 2. Radius of curvature R of the inwardly curved portion on the bottom side BM 1. Radius of curvature R of the outward curved portion on the bottom side BM 2. is as follows: Wave pattern pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1:0.75 Radius of curvature R of the outward curved portion on the surface side of the block SF 2:1.25 Radius of curvature R of the inwardly curved portion on the bottom side BM 1:0.75 Radius of curvature R of the outward curved portion on the bottom side BM 2:1.25

[0049] <Comparative Example 2> Radius of curvature R of the inner curved portion on the block surface side SF 1, Radius of curvature R of the outer curved portion on the block surface side SF 2 was changed, a pneumatic tire B2 was produced in the same manner as in Comparative Example 1. Wavy pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inner curved portion on the block surface side SF 1:1.2 Radius of curvature R of the outer curved portion on the block surface side SF 2:0.75 Radius of curvature R of the inner curved portion on the bottom surface side BM 1:0.75 Radius of curvature R of the outer curved portion on the bottom surface side BM 2:1.25

[0050] <Example 1> Radius of curvature R of the outer curved portion on the block surface side SF 2 was changed, a pneumatic tire A1 was produced in the same manner as in Comparative Example 1. Wavy pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inner curved portion on the block surface side SF 1:0.75 Radius of curvature R of the outer curved portion on the block surface side SF 2:0.75 Radius of curvature R of the inner curved portion on the bottom surface side BM 1:0.75 Radius of curvature R of the outer curved portion on the bottom surface side BM 2:1.25

[0051] <Example 2> Radius of curvature R of the inner curved portion on the block surface side SF 1, Radius of curvature R of the outer curved portion on the block surface side SF 2, Radius of curvature R of the outer curved portion on the bottom surface side BM 2 were changed, a pneumatic tire A2 was produced in the same manner as in Comparative Example 1. Wavy pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1:0.5 Radius of curvature R of the outward curved portion on the surface side of the block SF 2:0.5 Radius of curvature R of the inwardly curved portion on the bottom side BM 1:0.75 Radius of curvature R of the outward curved portion on the bottom side BM 2:0.5

[0052] <Example 3> Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1. Radius of curvature R of the outer curved portion on the surface side of the block SF 2. Radius of curvature R of the outward curved portion on the bottom side BM Except for changing component 2, the pneumatic tire A3 was manufactured in the same manner as in Comparative Example 1. Wave pattern pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1:0.3 Radius of curvature R of the outward curved portion on the surface side of the block SF 2:0.3 Radius of curvature R of the inwardly curved portion on the bottom side BM 1:0.75 Radius of curvature R of the outward curved portion on the bottom side BM 2:0.3

[0053] <Example 4> Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1. Radius of curvature R of the outer curved portion on the surface side of the block SF 2. Radius of curvature R of the inwardly curved portion on the bottom side BM 1. Radius of curvature R of the outward curved portion on the bottom side BM Except for changing component 2, the pneumatic tire A4 was manufactured in the same manner as in Comparative Example 1. Wave pattern pitch P: 2.0mm Sipe thickness t: 0.5mm Radius of curvature R of the inwardly curved portion on the surface side of the block SF 1:0.3 Radius of curvature R of the outward curved portion on the surface side of the block SF2:0.3 Radius of curvature R of the inwardly curved portion on the bottom side BM 1:1.2 Radius of curvature R of the outward curved portion on the bottom side BM 2:0.3

[0054] For pneumatic tires A1-A4 and B1-B2, the tires were fitted to all wheels of a test vehicle (front-wheel drive, 2000cc engine) at an air pressure of 230kPa, and wet performance and handling stability were evaluated using the method described below. The evaluation results are shown in Table 1.

[0055] [Evaluation of wet performance] The above test vehicle was driven on a wet surface (water-sprayed asphalt road) and the braking distance from an initial speed of 40 km / h was measured. The results are expressed as an index with Comparative Example 1 set to 100, and a higher value indicates a shorter braking distance and superior wet performance.

[0056] [Evaluation of handling stability performance] The handling stability performance of the above test vehicle when driving on a dry surface was evaluated subjectively by the driver. It was evaluated on a 7-point scale, from "very poor," "poor," "somewhat poor," "equivalent," "somewhat good," "good," to "very good," compared to the handling stability performance of Comparative Example 1.

[0057] [Table 1]

[0058] As shown in Table 1, Comparative Example 1 used a typical corrugated sipe.

[0059] In Comparative Example 2, the radius of curvature of the inwardly curved portion and the radius of curvature of the outwardly curved portion of the sipe on the block surface are different, preventing the sipe from closing. As a result, the surface rigidity decreases, and the steering stability performance is reduced.

[0060] In Example 1, the radius of curvature of the inward curved portion and the radius of curvature of the outward curved portion of the corrugated shape were made the same on the block surface side, and the same as in Comparative Example 1 on the bottom side. As a result, the surface pressure when the sipe collapses increases, the surface rigidity increases, and thus the steering stability performance is improved.

[0061] In Examples 2 and 3, the surface rigidity is increased and steering stability is improved by reducing the radius of curvature on the block surface side compared to Example 1. On the other hand, compared to Comparative Examples 1 and 2 and Example 1, the radius of curvature on the bottom surface side is configured in the opposite way, which reduces the in-plane rigidity and increases the contact area, thus improving wet performance.

[0062] In Example 4, the effects are the same as in Examples 2 and 3, but the in-plane rigidity is lower compared to Examples 2 and 3, resulting in reduced steering stability.

[0063] It should be noted that the present invention is not limited to the embodiments and their modifications described above, and various changes and improvements are possible within the scope of the claims of this application. [Explanation of symbols]

[0064] 10 Pneumatic tire, 20 Tread, 21 Main groove, 22 Secondary groove, 30 Block, 40 Sipe, 41 Wall surface, 42 Curved section, 42A Inner curved section, 42B Outer curved section, 42C Straight section, 50 Mold, 51 Tread mold, 52 Side mold, 53 Tread molding surface, 54 Main body, 55 Protrusion, 60 Sipe blade, 61 Side, 62 Curved section, 62A Inner curved section, 62B Outer curved section

Claims

1. A pneumatic tire having a tread that includes blocks in which sipes are formed, Both walls of the aforementioned sipe are formed in a corrugated shape consisting of multiple curved sections from the block surface side to the bottom side when viewed from the tire radial direction. The curved portion includes an inwardly curved portion that bulges inward in the sipe and an outwardly curved portion that bulges outward in the sipe. On the block surface side in the tire radial direction, the radii of curvature of the inward curved portion and the outward curved portion are the same, while on the bottom surface side in the tire radial direction, the radii of curvature of the inward curved portion and the outward curved portion are different. Pneumatic tires.

2. A pneumatic tire according to claim 1, On the bottom side, the radius of curvature of the inward curved portion is greater than the radius of curvature of the outward curved portion. Pneumatic tires.

3. A pneumatic tire according to claim 1 or 2, On the bottom side, when the pitch of the wave pattern is P, the thickness of the sipe is t, and the radius of curvature of the inner curved portion is R1, the following equation holds: Pneumatic tires. [Mathematics 1] 0.5 × P - 0.5 × t ≤ R1 ≤ 0.6 × P

4. A pneumatic tire according to claim 3, On the bottom side, when the radius of curvature of the outward curved portion is R2, the following equation holds: Pneumatic tires. [Mathematics 2] 1.1 ≤ R1 / R2 ≤ 6.0

5. A tire molding die equipped with a sipe blade for forming sipes in the tread blocks of a tire, Both sides of the aforementioned sipe blade are formed in a wave-like shape consisting of multiple curved portions when viewed from the radial direction of the tire. The curved portion includes an inwardly curved portion that bulges inward in the sipe blade and an outwardly curved portion that bulges outward in the sipe blade. On the block surface side in the tire radial direction, the radii of curvature of the inward curved portion and the outward curved portion are the same, while on the bottom side, the radii of curvature of the inward curved portion and the outward curved portion are different. Mold for tire molding.

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