Abstract:
The disclosed pneumatic tire ( 1 ) comprises a stiffener ( 31 ) and a rubber pad ( 32 ) which, disposed between a toroidal carcass body ( 21 ) and a folded-back carcass portion ( 22 ) folded back at a bead core ( 11 ), are arranged so as to be oriented radially outwards of the tire from the bead core ( 11 ). Further, from the rim baseline (BL), the height KSH to the end ( 31 A) of the stiffener ( 31 ), the height OWH to the maximum carcass width ( 20 W), and the height FH to the end ( 101 A) of the rim flange ( 101 ) fulfill 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a pneumatic tire comprising a carcass having a carcass body composed of a ply formed of a plurality of carcass cords, covered with a rubber material, toroidally extending between a pair of bead cores, and a carcass folded-back portion that the carcass body wound around the bead core from inside toward outside of the tire and extended outside in the tire radial direction. 
       BACKGROUND ART 
       [0002]    Stability in vehicle rolling and pitch depends on the strength of a part ranging from a bead portion to a sidewall portion of a pneumatic tire. Particularly, in a tire for a large-size vehicle compared with a vehicle for a passenger car, a sidewall portion located between a bead portion to a tread portion grounding a road surface is long, and is subjected to a heavy load. Thus, bending deformation is likely to occur in a sidewall portion falling outside in the width direction of a tire at a base point where a bead portion contacts a rim flange, thereby deteriorating the stability in rolling and pitch compared with a tire for a passenger car. 
         [0003]    To solve the above problem, the applicants have proposed measures to prevent a bending deformation (see Patent Literature 1). The patent document 1 has disclosed a pneumatic tire comprising a carcass having a carcass body composed of a ply formed of a plurality of carcass cords, covered with a rubber material, toroidally extending between a pair of bead cores, and the carcass folded-back portion that the carcass body wound around the bead core from inside toward outside of the tire and extended outside in the tire radial direction, wherein the rigidity of a bead portion is enhanced by providing a filling material called a stiffener with a 100% elongation modulus greater than that of a rubber material and a rubber with JIS A hardness of 50 degrees to 85 degrees between the carcass body and the carcass folded-back portion (see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Published Unexamined Application No. 2001-150910 
       SUMMARY OF INVENTION 
       [0005]    When a heavy load is applied in a conventional pneumatic tire, bending deformation occurs in a sidewall portion at a base point where a bead portion contacts a rim flange. When the sidewall portion falls outside in the tire width direction, in the sidewall portion, a rubber material located between a stiffener and a carcass cord and coating a carcass body is subjected to a tensile strain of pulling outside in the tire radial direction along a carcass body. 
         [0006]    Further, when a sidewall portion falls outside in the tire width direction, a stiffener located between a carcass body and a carcass folded-back portion is held and compressed between the carcass body and the carcass folded-back portion. A stiffener expands outside in the tire radial direction along the carcass body, and a rubber material is pulled outside in the tire radial direction along the carcass body, thereby promoting distortion. 
         [0007]    When a rubber material between a stiffener and a carcass cord is repeatedly subjected to distortion, a stiffener and a rubber material become easy to peel off, or a rubber material becomes easy to peel off from a carcass cord, causing deterioration in the durability of a part ranging from a bead portion to a sidewall portion. In other words, further improvements have been required to ensure the rigidity and durability of a part ranging from a bead portion to a sidewall portion, in a pneumatic tire. 
         [0008]    Accordingly, it is an object of the present invention to provide a pneumatic tire, which simultaneously ensures the rigidity and enhances the durability of a part ranging from a bead portion to a sidewall portion at a high level. 
         [0009]    The applicants of the present invention have found that in a region of a pneumatic tire subjected to a stress from a rim flange, an excessive distortion is applied to a rubber material coating a carcass cord by providing a first filling material in order to prevent falling of a sidewall portion, and have concluded that it is important not to provide a first filling material in a region of the tire subject to a stress from a rim flange. The applicants have minutely studied the relationship between the carcass body and first filling material, which can prevent shear distortion occurred in the rubber material contacting the first filling material of the carcass body without losing the essential function of the first filling material to prevent falling of the sidewall portion. 
         [0010]    As a result of the study, it has been proved that when a relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28 is satisfied, an index of distortion applied to the rubber material caused by deformation of a sidewall portion can be minimized. 
         [0011]    The present invention has following features. It is summarized as a pneumatic tire comprising a carcass having a carcass body composed of a ply formed of a plurality of carcass cords, covered with rubber material, toroidally extending between a pair of bead cores, and a carcass folded-back portion where the carcass body wound around the bead core from inside toward outside of the tire and extended outside in a tire radial direction, wherein a gradual decrease region is provided, in which a distance between the carcass body and the carcass folded-back portion along a line normal to the carcass body gradually decreases toward outside in the tire radial direction, a first filling material and a second filling material sequentially arranged from the bead core toward outside in the tire radial direction, are provided between the carcass body and the carcass folded-back portion located outside in a tire width direction than the carcass body, an end of the first filling material outside in the tire radial direction is located in the gradual decrease region, a part of the first filling material and the second filling material contacts with the rubber material forming the carcass body, the end of the first filling material outside in the tire radial direction and an end of the second filling material inside in the tire radial direction are overlapped in the tire width direction, a thickness in the tire width direction of the first filling material at the end outside in the tire radial direction decreases toward outside in the tire radial direction, an end of the second filling material inside in the tire radial direction is located more inside in the tire radial direction than a contact position in contact with a rim flange of a rim defined by standards for mounting the pneumatic tire in the bead portion of the pneumatic tire, a height CE from a rim base line, which is an axis line of the tire passing through a position in the rim defining a rim diameter, to an end of the carcass folded-back portion, and a height OWH from the rim base line to a carcass maximum width portion of the carcass body having a maximum width in the tire width direction, satisfy a relation of 0.85OWH≦CE≦1.2OWH, and a height KSH from the rim base line to the end of the first filling material outside in the tire radial direction, the height OWH, and a height FH from the rim base line to the end of the rim flange outside in the tire radial direction, satisfy a relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28. 
         [0012]    As described above, it is possible to prevent peel-off of the rubber material from the first filling material and from the carcass cord caused by deformation of a sidewall portion, and to prevent deterioration of the durability of a part ranging from a bead portion to a sidewall portion, without loosing the essential function of the first filling material to prevent falling of a sidewall portion. 
         [0013]    Therefore, according to the pneumatic tire of the present invention, it is possible to simultaneously ensure the rigidity and enhance the durability of a part ranging from a bead portion to a sidewall portion at a high level. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  shows sectional view in tire radial direction and tire width direction of a pneumatic tire according to a first embodiment. 
           [0015]      FIG. 2  is a schematic diagram illustrating a part ranging from a bead portion to a sidewall portion of the pneumatic tire according to the first embodiment. 
           [0016]      FIG. 3  is a magnified view of the region A in  FIG. 2 . 
           [0017]      FIG. 4  is a schematic diagram explaining aspects of a bead portion of a pneumatic tire being deformed. 
           [0018]      FIG. 5  is a magnified view of a deformed bead portion. 
           [0019]      FIG. 6  is a graph showing the results of calculation of an index of distortion with respect to the value of (KSH−FH)/(OWH−FH) based on a finite element method. 
           [0020]      FIG. 7  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to a second embodiment. 
           [0021]      FIG. 8  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to a third embodiment. 
           [0022]      FIG. 9  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to a fourth embodiment. 
           [0023]      FIG. 10  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a comparative example pneumatic tire. 
           [0024]      FIG. 11  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of another comparative example. 
           [0025]      FIG. 12  is a table showing the results of a durability test of a pneumatic tire. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Embodiments of a pneumatic tire according to the present invention will be described with reference to the accompanying drawings. In particular, (1) first embodiment, (2) second embodiment, (3) third embodiment, (4) fourth embodiment and (5) other embodiment will be explained. In the drawings, the same or like reference signs are given to the same or like parts. It is to be noted that the drawings are schematic and the dimensions or ratios are different from real values. Therefore, actual dimensions should be determined according to the following explanations. The drawings include parts of different dimensions or ratios. 
       First Embodiment 
       [0027]    A first embodiment will be explained according to the following sections, particularly, (1-1) General configuration of a pneumatic tire, (1-2) Configuration of a part ranging from a bead portion to a sidewall portion, and (1-3) Functions and effects. 
       (1-1) General Configuration of a Pneumatic Tire 
       [0028]    Hereinafter, a general configuration of a pneumatic tire will be explained with reference to the drawings.  FIG. 1  is an illustration a configuration of a pneumatic tire  1 . The pneumatic tire  1  comprises a pair of bead portions  12  having a bead core  11 , a pair of sidewall portions  13 , and a tread portion  14  continuous to the sidewall portion.  FIG. 1  shows a bead core  11 , a bead portion  12 , and a sidewall portion  13  of only one side with respect to an equator line CL in the pneumatic tire  1 . The pneumatic tire  1  is provided with a carcass  20  toroidally extending between a pair of bead cores  11 . A plurality of belt layers  15  is provided between a carcass  20  and a grounding surface  14 A of a tread portion  14  contacting a road surface. 
         [0029]    The carcass  20  has a carcass body  21  and a carcass folded-back portion  22 . The carcass folded-back portion  22  is rewound around the bead core  11  from inside toward outside of the tire, and is extended outside in the tire radial direction. In the embodiment, an end  22   a  of the carcass folded-back portion  22  extends up to a carcass maximum width portion  20 W in the width direction W of the tire. 
         [0030]    Between the toroidally carcass body  21  and the carcass folded-back portion  22  folded back from the bead core  11 , there are provided a stiffener  31  and a pad rubber  32  arranged sequentially from the bead core  11  outside in the tire radial direction. In the embodiment, the stiffener  31  is configured to a first filling material, and the pad rubber  32  is configured to a second filling material. 
         [0031]    An end  31 A of the stiffener  31  outside in the tire radial direction and an end  32 A of the pad rubber  32  inside in the tire radial direction are overlapped in the width direction W of the tire. The stiffener  31  decreases the thickness d in the width direction W of the tire as it moves outside in the tire radial direction. The end  32 A of the pad rubber  32  inside in the tire radial direction is located more inside in the tire radial direction in the bead portion  12  of the pneumatic tire  1  than a point P 1  where a rim flange  101  of a standard rim  100  defined by standards for mounting the pneumatic tire  1  contacts with the bead potion  12  of the pneumatic tire  1 . 
         [0032]    A 100% elongation modulus of the stiffener  31  is greater than a 100% elongation modulus of a rubber material  24 , and a 100% elongation modulus of the rubber material  24  is greater a 100% elongation modulus of the pad rubber  32 . In other words, the 100% elongation modulus Mn 1  of the stiffener  31 , the 100% elongation modulus Mn 2  of the pad rubber  32  and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2   
         [0033]    The height KSH from the rim base line BL, which is an axis line direction of the tire passing through a position to define a rim diameter in the standard rim  100 , to the end  31 A of the stiffener  31  outside in the tire radial direction, the height OWH from the rim base line BL to the carcass maximum width portion  20 W, and the height FH from the rim base line BL to the end  101 A of the rim flange  101  outside in the tire radial direction satisfy the relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28 
         [0034]    The height CH from the rim base line BL, which is an axis line direction of a tire passing through a position to define a rim diameter in the standard rim  100 , to the end  22   a  of the carcass folded-back portion  22 , and the height OWH from the rim base line BL to the carcass maximum width portion  20 W satisfy the relation of 0.85OWH≦CH≦1.2OWH 
         [0035]    Therefore, the end  22   a  of the carcass folded-back portion  22  extends to the vicinity of the carcass maximum width portion  20 W in the width direction W of the tire. In the embodiment, the height CE from the rim base line BL to the end  22   a  of the carcass folded-back portion  22  is substantially equal to the height OWH from the rim base line BL to the carcass maximum width portion  20 W. The fact that the height CE is substantially equal to the height OWH means at least that the relation of |CE−OWH|×100/OWH≦15% is satisfied. 
         [0036]    The height CE from the rim base line BL to the end  22   a  of the carcass folded-back portion  22  and the height SH from the rim base line BL to the carcass  20  on the equator line CL of the pneumatic tire  1  satisfy the relation of 0.4SH≦CE≦0.6SH. 
         [0037]    In the embodiment, an end  32 B of the pad rubber  32  outside in the tire radial direction is located in the vicinity of the carcass maximum width portion  20 W. In other words, the height PSH from the rim base line BL to the end  32 B of the pad rubber  32  outside in the tire radial direction is substantially equal to the height OWH from the rim base line BL to the carcass maximum width portion  20 W. The fact that the height PSH is substantially equal to the height OWH means at least that the relation of |PSH−OWH|×100/OWH≦15% is satisfied. 
         [0038]    The height KSH, the height OWH, the height FH, the height CE, and the height SH are measured along the tire radial direction. 
         [0039]    The standard rim  100  means a rim defined by standards. The standards are determined by industrial standards valid in districts where a tire is manufactured or used. For example, “YEAR BOOK OF THE TIRE AND RIM ASSOCIATION INC” in U.S.A, “STANDARDS MANUAL OF THE EUROPEAN TIRE AND RIM TECHNICAL ORGANIZATION” in Europe, and “JATMA YEAR BOOK OF JAPAN AUTOMOBILE AND TIRE ASSOCIATION” in Japan. 
         [0000]    (1-2) Configuration of Part Ranging from a Bead Portion to a Sidewall Portion 
         [0040]      FIG. 2  is a schematic diagram illustrating the bead portion  12  to a sidewall portion  13  of the pneumatic tire  1 .  FIG. 3  is a magnified view of the region A in  FIG. 2 , that is, a magnified sectional view of a stiffener and a carcass in the radial direction and the tread width direction of the pneumatic tire of the first embodiment. 
         [0041]    A carcass  20  comprises a ply  25  composed of a plurality of carcass cords  23  coated with a rubber material  24  toroidally extending between a pair of bead cores  11 . A part of the stiffener  31  and the pad rubber  32  contacts at least the rubber material  24  that constitute the carcass body  21 . The carcass  20  has a parallel region Sp, where the distance G between the centers of the cords of the carcass body  21  and the carcass folded-back portion  22  on a line H normal to the carcass body  21  becomes substantially constant. The substantially constant distance G means that when a minimum value of the distance G is assumed to be Gs, the following relation is at least satisfied: Gs≦G≦1.2Gs 
         [0000]    The end  31 A of the stiffener  31  outside in the tire radial direction is located in the parallel region Sp. 
         [0042]    In the embodiment, when defining a line H 1  normal to the carcass body  21  passing through a point P 2  equivalent to 1.2FH in the bead portion  12  from a rim base line toward outside in the tire radial direction, the distance G 1  between the carcass body  21  and the carcass folded-back portion  22  on the normal line H 1  and the length BW of the bead core  11  in the tire width direction satisfy the relation of 0.3BW≦G 1 ≦0.4BW 
         [0043]    Further, in the embodiment, the distances G and G 1  between the carcass body  21  and the carcass folded-back portion  22  are the distances between the centers of the carcass cords  23  that constitute the carcass body  21  and the carcass folded-back portion  22 . 
       (1-3) Functions and Effects 
       [0044]      FIG. 4  is a schematic diagram explaining aspects of the sidewall portion  13  of the pneumatic tire  1  being deformed. When simulating aspects of the sidewall portion  13  of the pneumatic tire  1  being deformed by using a finite element analysis method, the following deformation can be simulated. When a heavy load is applied to the pneumatic tire  1 , bending deformation occurs in the sidewall portion  13  at a base point of a part where the bead portion  12  contacts the rim flange  101 . In  FIG. 4 , a chain line indicates the sidewall portion  13  before being deformed, and a solid line indicates the wall portion  13  after being deformed. When the sidewall portion  13  falls outside in the tire width direction, a force indicated by the arrow direction is applied to the part where the bead portion  12  continues to the sidewall portion  13 . 
         [0045]    At this time, the carcass body  21  becomes a neutral axis and deforms a little, and the stiffener  31  and pad rubber  32  arranged between the carcass body  21  and carcass folded-back portion  22  are pressed and deformed as being compressed between the carcass body  21  and the carcass folded-back portion  22 . 
         [0046]      FIG. 5  is a magnified view showing the states of the carcass  20  and stiffener  31  in the deformed sidewall portion  13 . When the sidewall portion  13  falls outside in the tire width direction at a base point (a neutral axis) of the part where the bead portion  12  contacts the rim flange  101 , inside the sidewall portion  13 , the rubber material  24  located between the stiffener  31  and carcass cord  23  suffers distortion of pulling toward in the outside in tire radial direction along the carcass body  21  (indicated by the black arrow f 1  in  FIG. 5 ). The rubber material  24  located more inside in the tire width direction than the carcass cord  23  suffers distortion of pulling inside in the tire radial direction along the carcass body  21  (indicated by the black arrow f 2  in  FIG. 5 ). 
         [0047]    The stiffener  31  is pressed and compressed between the carcass body  21  and the carcass folded-back portion  22 , and is expanded outside in the tire radial direction along the carcass body  21 . As a result, the rubber material  24  is pulled outside in the tire radial direction along the carcass body, and the distortion indicated by the black arrow f 1  direction is increased. 
         [0048]    According to the analysis of deformation by a finite element method, the applicants minutely studied the relationship between the stiffener  31  and carcass  20 , which can prevent shear distortion in the rubber material  24  close to the stiffener  31  of the carcass body  21  without loosing the essential function of the stiffener  31  to prevent falling of the sidewall portion  13 . 
         [0049]      FIG. 6  is a graph showing the results of analysis of deformation based on a finite element method. An index that represents the distortion is calculated by changing the value of (KSH−FH)/(OWH−FH) to 0.15 to 0.35. As a result of the analysis, it is proved that an index of distortion applied to the rubber material  24  due to deformation of the sidewall portion  13  can be decreased when the height KSH from the rim base line BL to the end  31 A outside in the tire radial direction of the stiffener  31 , the height OWH from the rim base line BL to the carcass maximum width portion  20 W, and the height FH from the rim base line BL to the end  101 A of the rim flange  101  outside in the tire radial direction satisfy the relation of 0.2≦[(KSH−FH)/(OWH−FH)≦]0.28. 
         [0050]    As the distortion applied to the rubber material  24  due to deformation of the sidewall portion  13  can be decreased, it is possible to prevent peel-off of the rubber material  24  from the stiffener  31  due to deformation of the sidewall portion  13 , peel-off of the rubber material  24  from the carcass cord  23 , and to prevent deterioration in the durability of the part ranging from the bead portion  12  to the sidewall portion  13 . 
         [0051]    Further, in the embodiment, when the 100% elongation modulus Mn 1  of the stiffener  31 , the 100% elongation modulus Mn 2  of the pad rubber  32 , and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2 . 
         [0052]    Even if deformation occurs in the rubber material  24  contacting the stiffener  31  due to deformation of the sidewall portion  13 , is easy to follow the deformation, and the rubber material  24  can be prevented from being damaged by a shear stress. It is thus possible to ensure the rigidity and to improve the durability of the part ranging from the bead portion  12  to the sidewall portion  13  at a high level in a pneumatic tire. 
         [0053]    In the pneumatic tire  1 , the end  22   a  of the carcass folded-back portion  22  is arranged at a position at the height CE from the rim base line BL, and the height CE and the height SH from the rim base line BL to the carcass on the equator line CL of the tire satisfy the relation of 0.4SH≦CE≦0.6SH. By arranging the end  22   a  of the carcass folded-back portion  22  to satisfy this relationship, it is possible to prevent cracks in a surrounding rubber due to the end  22   a  of the carcass folded-back portion  22 . 
         [0054]    Further, in the pneumatic tire  1 , when defining a line H normal to the carcass body  21  passing through a point equivalent to  1 . 2 FH in the bead portion  12  from the rim base line BL toward outside in the tire radial direction, the distance G between the carcass body  21  and the carcass folded-back portion  22  on the normal line H and the length BW of the bead core  11  in the tire width direction satisfy the relation of 0.3BW≦G≦0.4BW. 
         [0055]    At the point P 2  equivalent to 1.2FH from the rim base line BL to outside in the tire radial direction, bending deformations of the carcass body  21  and the carcass folded-back portion  22  become maximized. By setting the distance G between the carcass body  21  and the carcass folded-back portion  22  close to the above-mentioned range in this part, a compression strain produced in the carcass folded-back portion  22  can be decreased. 
       (2) Second Embodiment 
       [0056]    A second embodiment will be explained with reference to the drawings. Particularly, explanations will be given of (2-1) configuration of a part ranging from a bead portion to a sidewall portion, and (2-2) Functions and effects.  FIG. 7  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to a second embodiment. In the second embodiment, the same reference signs are given to the same parts as those in the first embodiment, and detailed description thereof is omitted. 
         [0000]    (2-1) Configuration of a Part Ranging from a Bead Portion to a Sidewall Portion 
         [0057]    In a pneumatic tire  2  shown as a second embodiment, the space between the carcass body  21  and the carcass folded-back portion  22  varies outside in the tire radial direction. In the pneumatic tire  2  of the second embodiment, a stiffener  131  and a pad rubber  132  are provided between a carcass body  21  and a carcass folded-back portion  22 . 
         [0058]    In the pneumatic tire  2  shown as a second embodiment, the height KSH from a rim base line BL to an end  131 A of the stiffener  131  outside in the tire radial direction, the height OWH from the rim base line BL to the carcass maximum width portion  20 W, and the height FH from the rim base line BL to an end  101 A of a rim flange  101  outside in the tire radial direction satisfy the relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28. 
         [0059]    Further, the 100% elongation modulus Mn 1  of the stiffener  131 , the 100% elongation modulus Mn 2  of the pad rubber  132 , and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2 . 
         [0060]    Further, a carcass  20  has a gradual decrease region Sd, where the distance G 0  between the carcass body  21  and the carcass folded-back portion  22  on the line OH normal to the carcass body  21  gradually decreases toward outside in the tire radial direction, and the end  131 A of the stiffener  131  outside in the tire radial direction is located in the gradual decrease region Sd. 
         [0061]    Further, in the second embodiment, the carcass  20  has a shortest part  201 , where the distance G from the carcass body  21  to the carcass folded-back portion  22  becomes minimum in the gradual decrease region Sd, in a part outside the gradual decrease region Sd outside in the tire radial direction. The distance from the carcass body  21  to the carcass folded-back portion  22  in the shortest portion is expressed as Gmin. 
         [0062]    In a part outside the shortest part  201  outside in the tire radial direction, there is provided a longest part  202  where the distance G from the carcass body  21  to the carcass folded-back portion  22  becomes maximum. The distance from the carcass body  21  to the carcass folded-back portion  22  in the longest part  202  is expressed as Gmax. 
         [0063]    In the embodiment  2 , there is an outer gradual decrease region Sdo where the distance from the carcass body  21  to the carcass folded-back portion  22  gradually decreases from the longest part  202  toward outside in the tire radial direction. When defining a line H 2  normal to the carcass body  21  passing through the longest part  202  and a point P 3  intersecting the surface of the sidewall portion  13 , the height HP 3  from the rim base line BL to the intersection point P 3  satisfies the relation of HP 3 ≦3.75FH. 
         [0064]    In the embodiment, the distances Gmin, Gmax, and G 0  between the carcass body  21  and the carcass folded-back portion  22  are the distances between the centers of the carcass cords  23  that constitute the carcass body  21  and the carcass folded-back portion  22 . 
       (2-2) Functions and Effects 
       [0065]    In the pneumatic tire  2 , a shortest part  201 , where the distance G from the carcass body  21  to the carcass folded-back portion  22  becomes minimum in the gradual decrease region Sd, is provided in a part outside the gradual decrease region Sd outside in the tire radial direction. In the gradual decrease region Sd where the distances between the cords forming the carcass body  21  and carcass folded-back portion  22  gradually decreases, deformation due to compression occurred in the carcass folded-back portion  22  is decreased. 
         [0066]    As the longest part  202  is provided by gradually increasing the distance between the carcass body  21  and the carcass folded-back portion  22  from the shortest part  201  outside in the tire radial direction, the carcass folded-back portion  22  separates from a position (a neutral axis) that is a base point of bending the carcass folded-back portion  22 , the carcass folded-back portion  22  is pulled outside in the tire radial direction, and deformation due to compression occurred in the carcass folded-back portion  22  is decreased. 
         [0067]    Therefore, it is possible to prevent peel-off of the rubber material  24  from the stiffener  131  due to deformation of the sidewall portion  13 , peel-off of the rubber material  24  from the carcass cord  23 , and deterioration in the durability of the part ranging from the bead portion  12  to the sidewall portion  13 . It is thus possible to ensure at a high level, the rigidity and to improve the durability of the part ranging from the bead portion  12  to the sidewall portion  13  in the pneumatic tire. By setting the longest part  202  between to 3.75FH from the rim base line BL, it is possible to increase the ratio of the pad rubber and to prevent a large shear distortion in the rubber material  24 . 
       (3) Third Embodiment 
       [0068]    A third embodiment will be explained with reference to the drawings. Particularly, explanations will be given of (3-1) Configuration of a part ranging from a bead portion to a sidewall portion, and (3-2) Functions and effects.  FIG. 8  shows a magnified sectional view in tire radial direction and tire width direction illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to a third embodiment. In the third embodiment, the same reference signs are given to the same parts as those in the first and second embodiments, and detailed description thereof is omitted. 
         [0000]    (3-1) Configuration of Part Ranging from a Bead Portion to a Sidewall Portion 
         [0069]    In a pneumatic tire  3  shown as a third embodiment, a stiffener  133  and a pad rubber  134  are provided between a carcass body  21  and a carcass folded-back portion  22 . 
         [0070]    In the pneumatic tire  3  shown as a third embodiment, the height KSH from a rim base line BL to an end  133 A of the stiffener  133  outside in the tire radial direction, the height OWH from the rim base line BL to the carcass maximum width portion  20 W, and the height FH from the rim base line BL to an end  101 A of a rim flange  101  outside in the tire radial direction satisfy the relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28. 
         [0071]    Further, the 100% elongation modulus Mn 1  of the stiffener  133 , the 100% elongation modulus Mn 2  of the pad rubber  134 , and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2 . 
         [0072]    On a line H 4  normal to the carcass body  21  passing through the end  133 A of the stiffener  133  outside in the tire radial direction, when the distance between the centers of the cords of the carcass body  21  and carcass folded-back portion  22  is defined as DA, and the distance between the carcass body  21  and the carcass folded-back portion  22  on the normal line H 4  as G 3 , the end  133 A of the stiffener  133  is within a range of 0.25G 3  to 0.75G 3 . 
       (3-2) Functions and Effects 
       [0073]    In the pneumatic tire  3 , the carcass body  21  does not directly contact the end  133 A of the stiffener  133 , and it is possible to decrease distortion of the rubber material  24  of the carcass body  21  due to the end  133 A of the stiffener  133 . Therefore, it is possible to prevent peel-off of the rubber material  24  from the stiffener  133  due to deformation of the sidewall portion  13 , peel-off of the rubber material  24  from the carcass cord  23 , and reduction in the durability of the part from the bead portion  12  to the sidewall portion  13 . When the distance G 3  between the carcass body  21  and the carcass folded-back portion  22  on the normal line H 4  of the carcass body  21  does not satisfy the relation of 0.25G 3 ≦DA≦0.75G 3 , the thickness of the pad rubber  134  decreases, distortion concentrates on the pad rubber  134 , and the rubber material becomes easy to peel off from the pad rubber  134 . This is unsuitable. 
       (4) Fourth Embodiment 
       [0074]    A fourth embodiment will be explained with reference to the drawings. Particularly, explanations will be given of (4-1) configuration of a part ranging from a bead portion to a sidewall portion, and (4-2) Functions and effects.  FIG. 9  shows a magnified sectional view in direction of the tire and width directions of the tire illustrating a part ranging from a bead portion to a sidewall portion of a pneumatic tire according to the fourth embodiment. In the fourth embodiment, the same reference signs are given to the same parts as those in the first to third embodiments, and detailed description thereof is omitted. 
         [0000]    (4-1) Configuration of a Part Ranging from a Bead Portion to a Sidewall Portion 
         [0075]    In a pneumatic tire  4  shown as the fourth embodiment, a stiffener  135  and a pad rubber  136  are provided between a carcass body  21  and a carcass folded-back portion  22 . 
         [0076]    In the pneumatic tire  4  shown as the fourth embodiment, the height KSH from a rim base line BL to an end  135 A of the stiffener  135  outside in the tire radial direction, the height OWH from the rim base line BL to the carcass maximum width portion  20 W, and the height FH from the rim base line BL to an end  101 A of a rim flange  101  outside in the tire radial direction satisfy the relation of 0.2≦[(KSH−FH)/(OWH−FH)]≦0.28. 
         [0077]    Further, the 100% elongation modulus Mn 1  of the stiffener  135 , the 100% elongation modulus Mn 2  of the pad rubber  136 , and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2 . 
         [0078]    Further, a buffer rubber  140  is provided between the end  135 A of the stiffener  135  outside in the tire radial direction and the carcass body  21 , and between the end  136 A of the pad rubber  136  inside in the tire radial direction and the carcass body  21 . The 100% elongation modulus Mn 4  of the buffer rubber  140  is 0.7 to 1.0 times of the 100% elongation modulus of the pad rubber  136 , that is, satisfying the relation of 0.7×Mn 2 ≦Mn 4 ≦Mn 2 . 
       (4-2) Functions and Effects 
       [0079]    In the pneumatic tire  4 , as the buffer rubber  140  is provided in a part likely to receive a reactive force from a rim flange, the rigidity difference between the carcass body  21  and stiffener  135  can be decreased, and distortion of the rubber material  24  can be decreased. When the 100% elongation modulus of the buffer rubber decreases to lower than 70% of the 100% elongation modulus of the pad rubber  136 , distortion concentrates on the buffer rubber, and the buffer rubber is likely suffer damage. This is unsuitable. 
       (5) Other Embodiments 
       [0080]    Although the present invention has been described in terms of preferred embodiments, the foregoing discussion and drawings are not to be understood as restrictive of the invention. It will be appreciated that various alternative embodiments, examples might be made by those skilled in the art. For example, the embodiments of the present invention may be modified as follows. 
         [0081]    In the embodiments, the 100% elongation modulus Mn 1  of the stiffener  31 , the 100% elongation modulus Mn 2  of the pad rubber  32 , and the 100% elongation modulus Mn 3  of the rubber material  24 , respectively, satisfy the relation of Mn 1 &gt;Mn 3 &gt;Mn 2 , but this is not restrictive. For example, it may satisfy the relation of Mn 1 &gt;Mn 2 &gt;Mn 3 . 
         [0082]    In the embodiments, the height PSH from the rim base line BL to the end  32 B of the pad rubber  32  outside in the tire radial direction has been defined substantially equal to the height OWH from the rim base line BL to the carcass maximum width portion  20 W. However, for example, the heights may be PSH&lt;OWH. The end of the pad rubber outside in the tire radial direction may be closer to inside in the tire radial direction than the height CE. In this case, a hard-to-crack rubber may be provided adjacent to the end  22   a  of the carcass folded-back portion  22 . As a result, it is possible to prevent a crack in the surrounding rubber caused by the end  22   a  of the carcass folded-back portion  22 . As a hard-to-crack rubber, it is permitted to use a rubber with the 100% elongation modules lower than the 100% elongation modules of the pad rubber  32 . 
         [0083]    As described above, many embodiments not disclosed herein are to be understood as included in the present invention. The scope of the invention should, therefore, be defined by the appended claims. 
       EXAMPLES 
       [0084]    We have manufactured pneumatic tires of examples 1-4 and comparative examples 1-4 by changing conditions, and conducted durability tests to examine the durability of a part from a bead portion to a sidewall portion under the following conditions. The example 1 is a pneumatic tire  1  having the structure shown in  FIG. 2 , the example 2 is a pneumatic tire  2  having the structure shown in  FIG. 7 , the example 3 is a pneumatic tire  3  having the structure shown in  FIG. 8 , and the example 4 is a pneumatic tire  4  having the structure shown in  FIG. 9 , respectively. 
         [0085]    The structure of the comparative example 1 is shown in  FIG. 10 . The structure of the comparative example 2 is shown in  FIG. 11 . The structures of the comparative examples 1 and 2 are similar to those shown in  FIGS. 2 and 7 , except that the end of the stiffener outside in the tire radial direction is more outside in the tire radial direction than the pneumatic tires  1  and  2  shown in  FIGS. 2 and 7 . In the comparative example 3, the ratio of the distance DA to the distance G 3  in the pneumatic tire  3  shown in  FIG. 8  is changed. 
         [0086]    Tire size: 59/80R63 
         [0087]    Inside pressure: Set to 500 kPa. 
         [0088]    Rim: TRA standard rim 
         [0089]    Drum tester: Drum diameter 7 m 
         [0090]    Drum rotation speed: 8 km/h 
         [0091]    Drum load: 150% to 180% of standard load 999.6 kN (Step load system) A step load system sets a standard load of 150% at a startup when applying a drum load to an object pneumatic tire for 12 hours, thereafter, add 10% of the standard load, and finally applies 180% of the standard load. 
         [0092]    After 12 hours, we have cut out a part ranging from a bead portion to a sidewall portion of the pneumatic tire, and visually checked the cord and rubber material for cracks. The durability test results are shown in  FIG. 12 . The test results are expressed by indexes assuming a comparative example to be 100. 
         [0093]    According to the results shown in  FIG. 12 , the pneumatic tire of the examples 1 to 4, it is proved that the cord of the carcass folded-back portion is not cracked, the distortion index of the rubber material  24  is decreased, and the rubber material contacting the stiffener is not cracked. 
         [0094]    According to the above results, it is proved that in the pneumatic tire of the example, the rigidity of the part ranging from the bead portion to sidewall portion is ensured, and the durability of that part can be enhanced at a high level. 
         [0095]    It should be noted by reference the entire contents of Japanese Patent Application No. 2010-207946 (filed Sep. 16, 2010) is incorporated the specification of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0096]    As described above, according to the pneumatic tire of the present invention, it is possible to ensure the rigidity and enhance the durability of a part ranging from a bead portion to sidewall portion at a high level.