Patent Publication Number: US-2023138983-A1

Title: Pneumatic tire

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pneumatic tire. 
     2. Description of the Related Art 
     For a purpose of improving high-speed durability of a tire, it is known that a belt reinforcing layer in which organic fiber cords such as nylon fiber cords are arranged substantially parallel to a tire circumferential direction is provided on an outer circumferential side of a belt layer (see JP-A-2005-239069, JP-A-2005-75289, JP-A-2003-237309, and JP-A-2017-81349 (Patent Literatures 1 to 4)). 
     SUMMARY OF THE INVENTION 
     In the belt layer, belt cords such as steel cords are arranged to be inclined with respect to the tire circumferential direction, and an angle of each belt cord with respect to the tire circumferential direction is generally set to about 20 degrees. When the angle of the belt cord is set to be larger than usual, for example, to be more than 30 degrees, braking performance on a wet road surface (wet braking performance) and handling stability can be improved. However, when the angle of the belt cord is increased, rigidity of the belt layer in the tire circumferential direction decreases, and thus a ground contact shape is deteriorated, which may lead to a decrease in high-speed durability, ride comfortability, and rolling resistance. 
     In view of the above points, an object of an aspect of the invention is to provide a pneumatic tire in which high-speed durability, ride comfortability, and rolling resistance are improved while maintaining wet braking performance and handling stability by increasing an angle of a belt cord. 
     A pneumatic tire according to an aspect of the invention is a pneumatic tire including: a belt layer in which a belt cord is arranged on an outer circumferential side of a carcass layer in a tread so as to be inclined with respect to a tire circumferential direction; and a belt reinforcing layer in which an organic fiber cord is arranged along the tire circumferential direction on an outer circumferential side of the belt layer, in which, in the belt layer, an angle of the belt cord with respect to the tire circumferential direction is more than 30 degrees and 40 degrees or less, the organic fiber cord is a double-twisted cord of a yarn made of an organic fiber, the belt reinforcing layer is formed by coating the organic fiber cord with rubber, and a ratio (Sr/Sc) of a rubber cross-sectional area (Sr) to a cord cross-sectional area (Sc) is 1.0 to 1.5, and a value obtained by dividing, by 1000, a sum of a product (A) of a load LASE5% (N) at 5% elongation of the organic fiber cord, a cord count (per 25 mm), and the number of belt reinforcing layers, and a product (B) of a load (N) at 0.5% elongation of the belt cord, cos θ in which a belt angle is defined as θ, a cord count (per inch), and the number of belt layers is 8.7 or more. 
     The organic fiber cord can be a double-twisted cord of a yarn made of nylon 66. A product of the load LASE5% (N) at 5% elongation of the organic fiber cord and the cord count (per 25 mm) can be 1000 (N/25 mm) or more. 
     According to the aspect of the invention, by setting the angle of the belt cord to be more than 30 degrees and 40 degrees or less, high-speed durability, ride comfortability, and rolling resistance can be improved while maintaining wet braking performance and handling stability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a half cross-sectional view of a pneumatic radial tire according to an embodiment; and 
         FIG.  2    is a diagram schematically illustrating a part of a cross section of a belt reinforcing layer according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the invention will be described in detail. 
     A pneumatic tire according to the present embodiment is characterized by including a belt layer and a belt reinforcing layer disposed on an outer circumferential side of the belt layer. 
     The belt layer includes at least one belt ply in which belt cords are arranged so as to be inclined with respect to a tire circumferential direction on an outer circumferential side (that is, an outer side in a tire radial direction) of a carcass layer in a tread. 
     The belt reinforcing layer is formed of organic fiber cords arranged along the tire circumferential direction (equatorial plane) on the outer circumferential side (that is, the outer side in the tire radial direction) of the belt layer. The organic fiber cords of the belt reinforcing layer extend substantially parallel to the tire circumferential direction, that is, at an angle of approximately 0° (preferably an angle of 5° or less), and the cords are arranged at predetermined intervals in a tire width direction. Such a belt reinforcing layer may be a cap ply that covers the entire belt layer in a width direction, or may be an edge ply that covers an end of the belt. 
       FIG.  1    is a half cross-sectional view of a passenger vehicle pneumatic radial tire that is an example of the pneumatic tire. The tire includes a pair of left and right beads ( 1 ) and a pair of left and right sidewalls ( 2 ), and a tread ( 3 ) provided between the two sidewalls ( 2 ), and a carcass layer ( 4 ) extending in a toroidal shape is provided between the pair of beads ( 1 ). 
     The carcass layer ( 4 ) passes through the sidewalls ( 2 ) from the tread ( 3 ), and is folded back from an inner side to an outer side at a bead core ( 5 ) of the bead ( 1 ) so as to be locked. The carcass layer ( 4 ) is implemented by at least one ply in which carcass cords made of organic fibers are arranged substantially at right angles with respect to the tire circumferential direction. 
     A belt layer ( 7 ) is disposed on an outer circumferential side of the carcass layer ( 4 ) in the tread ( 3 ). The belt layer ( 7 ) is provided so as to overlap an outer circumference of a crown of the carcass layer ( 4 ), and can be implemented by one or a plurality of belt plies. In this example, the belt layer ( 7 ) is implemented by two belt plies, that is, a first belt ply ( 7 A) on an inner side and a second belt ply ( 7 B) on an outer side. These belt plies are formed by covering belt cords such as steel cords with rubber. The belt cords are each inclined at a constant angle with respect to the tire circumferential direction and arranged at predetermined intervals in the tire width direction. The belt cords are disposed between the two belt plies ( 7 A) and ( 7 B) so as to intersect one another (that is, so as to be inclined in a left-right symmetrical manner with respect to the tire circumferential direction). 
     On an outer circumferential side of the belt layer ( 7 ), a belt reinforcing layer ( 9 ) is provided between the belt layer ( 7 ) and a tread rubber ( 8 ). In this example, the belt reinforcing layer ( 9 ) is a cap ply covering an entire width of the belt layer ( 7 ). The belt reinforcing layer ( 9 ) is formed of organic fiber cords arranged substantially parallel to the tire circumferential direction, and is formed by coating the organic fiber cords with rubber. The belt reinforcing layer ( 9 ) tightens the belt layer ( 7 ) in the tire circumferential direction so as to exhibit a hoop effect of improving rigidity in the tire circumferential direction and radial direction and improving a belt binding force, thereby preventing belt lifting, diameter growth, and belt edge distortion caused by a centrifugal force during high-speed traveling and thus improving durability and handling stability at a high speed. 
     In the present embodiment, in the belt layer, the angle of the belt cord with respect to the tire circumferential direction (hereinafter, also simply referred to as a belt angle) is set to be more than 30 degrees and 40 degrees or less. That is, in a case where the belt layer is formed of one belt ply, a belt angle of the one belt ply is set to be more than 30 degrees and 40 degrees or less, and in a case where the belt layer is formed of a plurality of belt plies, belt angles of the plurality of belt plies in which belt cords are disposed so as to intersect one another are all set to be more than 30 degrees and 40 degrees or less with respect to the tire circumferential direction. By setting the belt angle to be more than 30 degrees, wet braking performance and handling stability can be improved. By setting the belt angle to 40 degrees or less, a decrease in rigidity in the tire circumferential direction can be prevented, and thus a decrease in high-speed durability can be prevented. The belt angle is more preferably 31 degrees or more and 37 degrees or less, and still more preferably 32 degrees or more and 35 degrees or less. 
     A load LASE0.5% (N) at 0.5% elongation of the belt cord is not particularly limited, and may be, for example, 100 N to 400 N or 150 N to 400 N. The value of the LASE0.5% can be adjusted by, for example, the number of filaments, diameters of the filaments, and carbon contents (mass %) of the filaments. 
     A cord count E of the belt cord is not particularly limited, and may be, for example, 10 to 30 per inch, 10 to 28 per inch, or 10 to 26 per inch. 
     A type of the organic fiber for the organic fiber cord used in the belt reinforcing layer according to the present embodiment is not particularly limited, and various organic fibers such as a nylon fiber, an aramid fiber, a polyester fiber, and a rayon fiber may be used. Among these, the nylon fiber is preferable. A twisted structure of the cord may be a double-twisted structure, and when the twisted structure of the cord is a double-twisted structure, convergence is improved, filaments constituting the cord do not easily buckle locally against compression and bending deformation, and are thus excellent in fatigue resistance. 
     Examples of the nylon fiber include nylon 6, nylon 66, and nylon 46. The aramid fiber may be a para-aramid fiber or a meta-aramid fiber, and a known aramid fiber can be used. 
     A fineness D of the organic fiber cord is not particularly limited, and may be, for example, 1000 dtex to 4000 dtex, 1500 dtex to 3500 dtex, or 1800 dtex to 3000 dtex. A twist level T of the organic fiber cord is not particularly limited as well, and may be, for example, 20 to 60 per 10 cm, or 25 to 55 per 10 cm. A twist level of a primary twist may be set to the same value as a twist level of a secondary twist. 
     In the present embodiment, in the belt reinforcing layer, a product (that is, LASE5%×E) of a load LASE5% (N) at 5% elongation of the organic fiber cord and the cord count E (per 25 mm) of the organic fiber cord is preferably 1000 N or more, more preferably 1100 N or more, and still more preferably 1200 N or more. An upper limit thereof is not particularly limited, and may be 2500 N or less, 2000 N or less, or 1500 N or less. When the product of the LASE5% and the cord count E is 1000 N or more, the belt binding force is improved, and excellent high-speed durability, handling stability, and rolling resistance are easily obtained. 
     The LASE5% of the organic fiber cord is not particularly limited, and may be, for example, 30 N to 100 N, 35 N to 90 N, or 40 N to 80 N. The value of the LASE5% can be adjusted by, for example, selecting the type of the fiber constituting the organic fiber cord, and adjusting the twist level and cord treatment conditions. For example, the LASE5% can be increased by reducing the twist level. In addition, examples of the cord treatment conditions include conditions of a dip treatment in which the organic fiber cord is immersed in a resin solution for an adhesion treatment with rubber (resin solution formulation, treatment temperature, tension, time, and the like). Accordingly, physical properties of the organic fiber cord can be adjusted. For example, when the dip treatment is performed by using a resin solution such as resorcinol formaldehyde latex (RFL) or a blocked isocyanate aqueous solution, the LASE5% can be increased by using a low temperature bath and setting a tension applied to the organic fiber cord to be high. Here, the LASE5% is measured according to JIS L1017. 
     The cord count (end count) E of the organic fiber cord is not particularly limited, and can be appropriately set according to the value of the LASE5% such that the product of the LASE5% and the cord count E is in the above range. The cord count E may be, for example, 15 to 50 per 25 mm, 20 to 40 per 25 mm, or 25 to 35 per 25 mm. 
     In the present embodiment, the organic fiber cord obtained in this way is disposed in the belt reinforcing layer such that a ratio (Sr/Sc) of a rubber cross-sectional area (Sr) to a cord cross-sectional area (Sc) is 1.0 to 1.5. When the ratio is 1.0 or more, excellent high-speed durability is easily obtained. In addition, when the ratio is 1.5 or less, an amount of the rubber is reduced, and excellent rolling resistance is easily obtained. 
     Here, as shown in  FIG.  2   , the cord cross-sectional area (Sc) and the rubber cross-sectional area (Sr) are cross-sectional areas of an organic fiber cord ( 10 ) and a rubber ( 11 ), respectively, in a member width direction cross section obtained by cutting the belt reinforcing layer ( 9 ) along a width direction thereof. The member width direction cross section is a cross section obtained by cutting the belt reinforcing layer ( 9 ) perpendicularly to an extending direction of the organic fiber cord ( 10 ). In addition, the ratio (Sr/Sc) can be obtained by dividing the rubber cross-sectional area (Sr) by the cord cross-sectional area (Sc). For example, Sr/Sc per cord (Sr/Sc for each cord partitioned by dotted lines in  FIG.  2   ) is calculated by calculating a cord cross-sectional area per 25 mm width of the belt reinforcing layer ( 9 ) from a cord count and a cord diameter of the organic fiber cord ( 10 ), calculating a rubber cross-sectional area per 25 mm width from a cross-sectional area of the belt reinforcing layer calculated from a thickness (t) of the belt reinforcing layer ( 9 ) and the cord cross-sectional area, and dividing the rubber cross-sectional area by the cord cross-sectional area. When the cord count of the organic fiber cord ( 10 ) is constant in the width direction of the belt reinforcing layer ( 9 ), the value per cord is used as Sr/Sc of the belt reinforcing layer ( 9 ). When the cord count of the organic fiber cord ( 10 ) changes in the width direction of the belt reinforcing layer ( 9 ), an average value of Sr/Sc of the respective cords calculated as described above may be calculated. 
     In the present embodiment, the belt layer and the belt reinforcing layer are set such that a value obtained by dividing, by 1000, a sum of a product (A) of the load LASE5% (N) at 5% elongation of the organic fiber cord, the cord count (per 25 mm) and the number of the belt reinforcing layers, and a product (B) of the load LASE0.5% (N) at 0.5% elongation of the belt cord, cos θ in which the belt angle is defined as θ, the cord count, and the number of the belt layers is 8.7 or more, preferably 8.9 or more, and more preferably 9.2 or more. An upper limit thereof is not particularly limited, and may be 11.0 or less, or may be 10.5 or less. When this value is in the above range, a binding force in a belt circumferential direction is improved, a ground contact shape is improved, and thus excellent handling stability, wet braking performance, ride comfortability, and rolling resistance are easily obtained. 
     Using the belt cord and the organic fiber cord described above, a raw tire (green tire) is prepared in a state in which the belt reinforcing layer is wound around the outer circumferential side of the belt layer, and the obtained raw tire is vulcanized and molded to obtain a pneumatic tire. When the belt reinforcing layer is formed on the belt layer, one or a plurality of organic fiber cords may be aligned and covered with rubber, spirally wound on the belt layer of the raw tire, or a wide rubberized sheet in which the organic fiber cords are aligned may be wound once on the belt layer. Preferably, the belt reinforcing layer is wound in a spiral shape in the former manner. 
     EXAMPLES 
     Hereinafter, the invention will be described in more detail with reference to Examples, but the invention is not limited to these Examples. 
     [Measurement Method and Test Method] 
     Measurement methods and test methods in Examples are as follows. 
     (Cord Test Method)
         Cord diameter: One organic fiber cord was bent into four portions such that a twist thereof did not untwist, and the four portions were aligned so as not to be slackened and were arranged in parallel, then a measurement was performed using a predetermined dial gauge (a diameter of a leg (measuring element) was 9.5±0.03 mm, a load was 1666±29.4 mN) by dropping the leg from a height of about 6.5 mm.   Cord strength: A load under which a sample was broken was obtained for the organic fiber cord when the organic fiber cord was left to stand for 24 hours under a constant temperature condition of 20° C. and 65% RH and then subjected to a tensile test at 20° C. according to JIS L1017. A load under which a sample was broken was obtained for the belt cord when a tensile test was performed according to JIS G3510.   LASE5%: A load at 5% elongation was obtained when the organic fiber cord was left to stand for 24 hours under a constant temperature condition of 20° C. and 65% RH and then subjected to a tensile test at 20° C. according to JIS L1017.   LASE0.5%: A load at 0.5% elongation was obtained when a tensile test was performed according to JIS G3510.       

     (Tire Test Method)
         Belt angle: An angle of the belt cord with respect to the tire circumferential direction on a tire equator (at a center position in the width direction) of the tread was measured for a tire not filled with air.   Tire high-speed durability: The FMVSS 109 (UTQG) standard was used. A steel drum tester having a smooth surface and a diameter of 1700 mm was used, a tire internal pressure was 220 kPa, and a load was 88% of a maximum load specified by JATMA. After break-in traveling at 80 km/h for 60 minutes, the tire was allowed to cool, and after an air pressure was adjusted again, formal traveling was performed. The formal traveling was started from 120 km/h, the speed was increased stepwise by 8 km/h every 30 minutes, and the traveling was continued until a failure occurred. A traveling distance until the occurrence of the failure was expressed as an index with a tire in Comparative Example 1 being 100. A larger number indicates better high-speed durability.   Rolling resistance: Rolling resistance of the tire was measured by using a rolling resistance tester under conditions of a tire internal pressure of 250 KPa, a rim size of 19×7.5 J, a load of 5.6 kN, and a speed of 80 km/h. A reciprocal thereof is expressed as an index with a related example being 100, and a larger index indicated smaller rolling resistance and better fuel economy.   Ride comfortability: Each tire was adjusted to have an internal pressure of 260 kPa using a standard rim of JIS standard, four tires of the same type were mounted on a 2000 cc passenger vehicle made in Japan, ride comfortability was sensory-evaluated by three test drivers on a test course with smooth roads and rough roads, and the evaluation was performed based on Comparative Example 1. Those equivalent to Comparative Example 1 are indicated by “Good”, those worse are indicated by “Poor”, and those better are indicated by “Excellent”.   Actual vehicle handling stability: Test tires each assembled at an internal pressure of 260 kPa were mounted on a test vehicle having an engine displacement of 2000 cc and driven on a test course by three trained test drivers to perform a sensory evaluation. Scores were evaluated on a scale of 1 to 10, and a relative comparison was performed with the tire in Comparative Example 1 being 6 points, and an average point of the three test drivers was expressed as an index with the tire in Comparative Example 1 being 100. A larger index indicates better handling stability.   Wet braking performance: Test tires each assembled at an internal pressure of 260 kPa were mounted on a test vehicle having an engine displacement of 2000 cc, and a water depth on a road surface was set to 1 mm. A distance from when a brake pedal was stepped on at a speed of 100 km/h to when the vehicle stopped was measured, and a reciprocal thereof was expressed as an index with the tire in Comparative Example 1 being 100. A larger index indicates better wet braking performance.       

     EXAMPLES AND COMPARATIVE EXAMPLES 
     A passenger vehicle pneumatic radial tire having a tire size of 225/45ZR19 96Y and including the belt reinforcing layer ( 9 ) as shown in  FIG.  1    was experimentally prepared. A belt angle of a belt layer and a configuration of organic fiber cords constituting the belt reinforcing layer (cap ply) were as shown in Table 1 below for each of tires in Examples and Comparative Examples, and the other configurations were common to all of the tires. 
     Specifically, as the belt layer, two steel cords of 2+2×0.25 mm were disposed at a belt angle and with a cord count shown in Table 1. 
     Regarding a cord structure, “1400 dtex/2” means a double-twisted structure obtained by twisting together two twisted yarns each having a nominal fineness of 1400 dtex. 
     The obtained tires were used to evaluate tire high-speed durability, rolling resistance, ride comfortability, actual vehicle handling stability, and wet braking performance. Results are shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                   
                 Comparative 
                   
                   
                   
                   
                   
               
               
                   
                   
                 Example 1 
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
               
               
                   
               
               
                 Belt 
                 Cord material 
                 Nylon 
                 Nylon 
                 Nylon 
                 Nylon 
                 Nylon 
                 Nylon 
               
               
                 reinforcing 
                 Cord structure 
                 1400 
                 1400 
                 1400 
                 1400 
                 1400 
                 1400 
               
               
                 layer 
                   
                 dtex/2 
                 dtex/2 
                 dtex/2 
                 dtex/2 
                 dtex/2 
                 dtex/2 
               
               
                   
                 Nominal fineness (dtex) 
                 2800 
                 2800 
                 2800 
                 2800 
                 2800 
                 2800 
               
               
                   
                 Twist level (per 10 cm) 
                 38 
                 27 
                 27 
                 27 
                 27 
                 27 
               
               
                   
                 Cord diameter (mm) 
                 0.67 
                 0.65 
                 0.65 
                 0.65 
                 0.65 
                 0.65 
               
               
                   
                 Cord strength (N) 
                 220 
                 237 
                 237 
                 237 
                 237 
                 237 
               
               
                   
                 Modulus at 5% elongation (LASE5%) 
                 30.0 
                 48.0 
                 48.0 
                 48.0 
                 48.0 
                 48.0 
               
               
                   
                 (N) 
               
               
                   
                 LASE5% × cord count (N/25 mm) 
                 915 
                 1464 
                 1464 
                 1440 
                 1248 
                 1584 
               
               
                   
                 Member thickness of belt reinforcing 
                 1.00 
                 1.00 
                 0.90 
                 0.80 
                 0.85 
                 1.00 
               
               
                   
                 layer (mm) 
               
               
                   
                 Cord count (per 25 mm) 
                 30.5 
                 30.5 
                 30.5 
                 30.0 
                 26.0 
                 33.0 
               
               
                   
                 Ratio (Sr/Sc) of rubber cross-sectional 
                 1.32 
                 1.47 
                 1.22 
                 1.01 
                 1.46 
                 1.28 
               
               
                   
                 area (Sr) to cord cross-sectional area 
               
               
                   
                 (Sc) 
               
               
                   
                 Number of belt reinforcing layers 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 Belt 
                 Belt angle (°) 
                 33 
                 33 
                 38 
                 33 
                 33 
                 33 
               
               
                 layer 
                 Cord strength (N) 
                 617 
                 617 
                 617 
                 617 
                 617 
                 617 
               
               
                   
                 Modulus at 0.5% elongation 
                 180 
                 180 
                 180 
                 180 
                 180 
                 180 
               
               
                   
                 (LASE0.5%) (N) 
               
               
                   
                 Number of belt layers 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                   
                 Cord count (per inch) 
                 21 
                 21 
                 21 
                 21 
                 21 
                 21 
               
               
                   
                 LASE0.5% × cos[belt angle] × cord 
                 3170 
                 3170 
                 2979 
                 3170 
                 3170 
                 3170 
               
               
                   
                 count (N/inch) 
               
               
                   
                 (A + B)/1000 
                 8.2 
                 9.3 
                 8.9 
                 9.2 
                 8.8 
                 9.5 
               
               
                   
                 A = LASE5% × cord count × 
               
               
                   
                 number of belt reinforcing layers 
               
               
                   
                 B = LASE0.5% × cos[belt angle] × 
               
               
                   
                 cord count × number of belt layers 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Tire high-speed durability 
                 100 
                 109 
                 105 
                 107 
                 101 
                 110 
               
               
                 Rolling resistance 
                 100 
                 104 
                 105 
                 105 
                 102 
                 104 
               
               
                 Ride comfortability 
                 Good 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
               
               
                 Actual vehicle handling stability 
                 100 
                 111 
                 106 
                 111 
                 106 
                 111 
               
               
                 Wet braking performance 
                 100 
                 102 
                 102 
                 103 
                 101 
                 104 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                   
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
                 Example 6 
               
               
                   
               
               
                 Belt 
                 Cord material 
                 Nylon 
                 Nylon 
                 Nylon 
                 Nylon 
                 Nylon 
               
               
                 reinforcing 
                 Cord structure 
                 1400 
                 1400 
                 1400 
                 1400 
                 1400 
               
               
                 layer 
                   
                 dtex/2 
                 dtex/2 
                 dtex/2 
                 dtex/2 
                 dtex/2 
               
               
                   
                 Nominal fineness (dtex) 
                 2800 
                 2800 
                 2800 
                 2800 
                 2800 
               
               
                   
                 Twist level (per 10 cm) 
                 27 
                 27 
                 27 
                 51 
                 27 
               
               
                   
                 Cord diameter (mm) 
                 0.65 
                 0.65 
                 0.65 
                 0.68 
                 0.65 
               
               
                   
                 Cord strength (N) 
                 237 
                 237 
                 237 
                 213 
                 237 
               
               
                   
                 Modulus at 5% elongation (LASE5%) 
                 48.0 
                 48.0 
                 48.0 
                 37.0 
                 48.0 
               
               
                   
                 (N) 
               
               
                   
                 LASE5% × cord count (N/25 mm) 
                 1464 
                 1464 
                 1464 
                 962 
                 1248 
               
               
                   
                 Member thickness of belt reinforcing 
                 1.10 
                 0.80 
                 1.00 
                 0.90 
                 0.85 
               
               
                   
                 layer (mm) 
               
               
                   
                 Cord count (per 25 mm) 
                 30.5 
                 30.5 
                 30.5 
                 26.0 
                 26.0 
               
               
                   
                 Ratio (Sr/Sc) of rubber cross-sectional 
                 1.72 
                 0.98 
                 1.47 
                 1.38 
                 1.46 
               
               
                   
                 area (Sr) to cord cross-sectional area 
               
               
                   
                 (Sc) 
               
               
                   
                 Number of belt reinforcing layers 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 Belt 
                 Belt angle (°) 
                 33 
                 33 
                 41 
                 33 
                 40 
               
               
                 layer 
                 Cord strength (N) 
                 617 
                 617 
                 617 
                 617 
                 617 
               
               
                   
                 Modulus at 0.5% elongation 
                 180 
                 180 
                 180 
                 180 
                 180 
               
               
                   
                 (LASE0.5%) (N) 
               
               
                   
                 Number of belt layers 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                   
                 Cord count (per inch) 
                 21 
                 21 
                 21 
                 21 
                 21 
               
               
                   
                 LASE0.5% × cos[belt angle] × cord 
                 3170 
                 3170 
                 2853 
                 3170 
                 2896 
               
               
                   
                 count (N/inch) 
               
               
                   
                 (A + B)/1000 
                 9.3 
                 9.3 
                 8.6 
                 8.3 
                 8.3 
               
               
                   
                 A = LASE5% × cord count × 
               
               
                   
                 number of belt reinforcing layers 
               
               
                   
                 B = LASE0.5% × cos[belt angle] × 
               
               
                   
                 cord count × number of belt layers 
               
            
           
           
               
               
               
               
               
               
            
               
                 Tire high-speed durability 
                 105 
                 98 
                 97 
                 100 
                 100 
               
               
                 Rolling resistance 
                 97 
                 103 
                 100 
                 100 
                 100 
               
               
                 Ride comfortability 
                 Excellent 
                 Excellent 
                 Good 
                 Good 
                 Good 
               
               
                 Actual vehicle handling stability 
                 106 
                 111 
                 100 
                 100 
                 100 
               
               
                 Wet braking performance 
                 101 
                 101 
                 99 
                 100 
                 100 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, Comparative Example 2 is an example in which the ratio (Sr/Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) exceeds the upper limit value, and rolling resistance thereof is worse than that of Comparative Example 1. 
     Comparative Example 3 is an example in which the ratio (Sr/Sc) of the rubber cross-sectional area (Sr) to the cord cross-sectional area (Sc) is less than the lower limit value, and high-speed durability thereof is worse than that of Comparative Example 1. 
     Comparative Example 4 is an example in which the belt angle exceeds the upper limit value, as compared to Comparative Example 1, Comparative Example 4 has worse high-speed durability and wet braking performance while rolling resistance and actual vehicle handling stability thereof are not improved. 
     Comparative Examples 5 and 6 are examples in which the value of (A+B)/1000 is less than the lower limit value, and all of evaluations thereof are not improved as compared with those of Comparative Example 1. 
     Although certain embodiments of the invention have been described above, these embodiments have been presented as examples only, and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and omissions, substitutions, modifications thereof are included in the invention described in the claims and equivalents thereof, as well as being included in the scope and gist of the invention. 
     INDUSTRIAL APPLICABILITY 
     The embodiment of the invention can be suitably used for various pneumatic tires such as a passenger vehicle tire. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : bead 
               2 : sidewall 
               3 : tread 
               4 : carcass layer 
               5 : bead core 
               7 : belt layer 
               8 : tread rubber 
               9 : belt reinforcing layer 
               10 : organic fiber cord 
               11 : rubber