Abstract:
This manufacturing method of a pneumatic tire having a tread reinforcing layer reduces tire mass while maintaining the durability performance of the tire. A tread reinforcing layer formation step includes a winding step for winding belt-shape plies around an approximately cylindrical winding surface. The winding step involves: a first winding step in which, with the side edges of the belt-shape plies spaced from one another, said belt-shape plies are spirally wound from a first end located on one side of the tire in the axial direction, to a second end located on the other side of the tire in the axial direction; and a second winding step in which, with the side edges of the belt-shape plies spaced from one another, said belt-shape plies are spirally wound from the second end to the first end in the direction opposite that in the first winding step. A lattice-form tread reinforcing layer is formed that has gaps substantially rhombic in shape and bounded by the belt-shape plies.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a pneumatic tire manufacturing method that allows reduction in the amount of cord usage in a tread reinforcement layer while maintaining tire durability performance. 
       BACKGROUND ART 
       [0002]    Patent Literature 1 discloses a pneumatic tire including a carcass and a belt structure disposed outside the carcass in a tire radial direction. The belt structure is formed by winding a ribbon composed of a plurality of cords in a spiral manner at an angle of approximately 0 degree with respect to a tire equatorial plane. 
         [0003]    Unfortunately, the belt structure has the cords parallel to the tire circumferential direction, and tension acting on the cords in the area of a tread portion is absorbed in that area and is not transferred to cords in the adjacent areas. Accordingly, to reinforce the tread portion by the use of the belt structure as described in Patent Literature 1, it is necessary to wind the ribbon in parallel over the entire tread portion, causing increase in cord (material) costs. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. H09-118109 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    The present invention is devised in light of the foregoing circumstances described above. A major object of the present invention is to provide a pneumatic tire manufacturing method that basically improves the process for winding a belt-like ply and allows reduction in the amount of cord usage in the tread reinforcement layer while maintaining durability performance. 
       Solution to Problem 
       [0006]    The present invention provides a method for manufacturing a pneumatic tire including a carcass extending from a tread portion through sidewall portions to bead cores in bead portions and a tread reinforcement layer disposed radially outward of the carcass in the tread portion, the method including: a tread reinforcement layer formation step of forming the tread reinforcement layer, wherein the tread reinforcement layer formation step includes a winding step of winding a long belt-like ply formed by covering one or more reinforcement cords with a topping rubber around an approximately cylindrical winding surface, the winding step includes: a first winding step of winding the belt-like ply in a spiral manner from a first end portion located on one side in a tire axial direction to a second end portion located on the other side in the tire axial direction while separating side edges of the belt-like ply from each other in turn; and a second winding step of winding the belt-like ply in a spiral manner reversely with respect to the first winding step from the second end portion to the first end portion while separating the side edges of the belt-like ply from each other in turn to form a grid-shaped tread reinforcement layer having approximately diamond-shaped spaces surrounded by the belt-like ply. 
         [0007]    In the method for manufacturing a pneumatic tire according to the present invention, the winding step is preferably carried out with a single continuous belt-like ply. 
         [0008]    In the method for manufacturing a pneumatic tire according to the present invention, the winding step preferably includes a parallel winding step of winding the belt-like ply in parallel along a tire circumferential direction between the first winding step and the second winding step. 
         [0009]    In the method for manufacturing a pneumatic tire according to the present invention, in the winding step, a winding terminal end of the belt-like ply is preferably aligned with a winding start end of the belt-like ply. 
         [0010]    In the method for manufacturing a pneumatic tire according to the present invention, when the first winding step and the second winding step are set as one cycle, the winding step is preferably performed in at least two cycles. 
         [0011]    In the method for manufacturing a pneumatic tire according to the present invention, a width of the approximately diamond-shaped space in the tire axial direction is preferably larger than a width of the belt-like ply. 
         [0012]    In the method for manufacturing a pneumatic tire according to the present invention, a width of the approximately diamond-shaped space in the tire axial direction is preferably in a range of from 10% to 30% of the entire width of the grid tread reinforcement layer. 
         [0013]    In the method for manufacturing a pneumatic tire according to the present invention, the method preferably further includes a tread rubber formation step of forming a tread rubber disposed outside the tread reinforcement layer in the tire radial direction, and the tread rubber formation step includes at least a step of forming a radially innermost layer portion to adhere to the grid-shaped tread reinforcement layer of the tread rubber by winding a long belt-like rubber strip in a spiral manner. 
       Advantageous Effects of Invention 
       [0014]    According to the pneumatic tire manufacturing method of the present invention, the winding step of winding a belt-like ply to form a tread reinforcement layer includes a first winding step of winding the belt-like ply in a spiral manner from a first end portion located on one side of a tire axial direction to a second end portion located on the other side of the tire axial direction while separating side edges of the belt-like ply from each other in turn, and a second winding step of winding the belt-like ply in a spiral manner reversely with respect to the first winding step from the second end portion to the first end portion while separating side edges of the belt-like ply from each other in turn. The tread reinforcement layer manufactured by the step forms a grid tread reinforcement layer having approximately diamond-shaped spaces surrounded by the belt-like ply. The grid tread reinforcement layer has no reinforcement cords in the approximately diamond-shaped spaces, and the material cost can be reduced by the non-use of cords. 
         [0015]    The belt-like ply is formed in an approximately diamond-shaped grid. Accordingly, when tension acts on the reinforcement cords in the area with the tread reinforcement layer, the tension is also transferred to the reinforcement cords in the adjacent areas via the grid belt-like ply. Therefore, the stress applied to the cords is decreased and sufficient strength and durability performance can be maintained only by a small number of cords. Accordingly, the present invention makes it possible to manufacture a pneumatic tire that allows reduction in the amount of cord usage in the tread reinforcement layer while maintaining durability performance. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a cross-sectional view of a pneumatic tire according to one embodiment of the present invention: 
           [0017]      FIG. 2  is a cross-sectional view of a manufacturing apparatus used in a winding step; 
           [0018]      FIG. 3  is a perspective view of one embodiment of a belt-like ply; 
           [0019]      FIG. 4  is a cross-sectional view illustrating conceptually a tread reinforcement layer forming step; 
           [0020]      FIGS. 5A and 5B  are developed plan views illustrating conceptually a tread reinforcement layer manufactured at a winding step of a first cycle; 
           [0021]      FIGS. 6A and 6B  are developed plan views illustrating conceptually a tread reinforcement layer manufactured at a winding step of a second cycle; 
           [0022]      FIG. 7  is a developed plan view illustrating conceptually the tread reinforcement layer of the embodiment; 
           [0023]      FIG. 8  is a cross-sectional view illustrating conceptually a manufacturing method of a base rubber part; 
           [0024]      FIG. 9  is a developed plan view illustrating conceptually winding of a rubber strip for forming the base rubber part; and 
           [0025]      FIG. 10  is a cross-sectional view illustrating conceptually a manufacturing method of a cap rubber part. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    An embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is a cross-sectional view of a pneumatic tire (hereinafter, also referred to simply as “tire”) manufactured by a manufacturing method according an embodiment of the present invention in a normal state taken along a tire meridian section including a tire axis. The normal state refers to a no-loaded state in which the tire is mounted on a normal rim and inflated with a normal inner pressure. Unless otherwise noted, hereinafter, the dimensions of components of the tire are measured in the normal state. 
         [0027]    The term “normal rim” is a rim specified for each tire by standards in a standard organization including the standards for the tire. For example, the normal rim refers to a “standard rim” under JATMA, a “design rim” under TRA, and a “measuring rim” under ETRTO. The term “normal inner pressure” refers to a pneumatic pressure specified for each tire by standards in a standard organization including the standards for the tire. The “normal inner pressure” is a “maximum pneumatic pressure” under JATMA, a maximum value described in the table “Tire Load Limits at Various Cold Inflation Pressures” under TRA, and an “inflation pressure” under ETRTO. 
         [0028]    The tire of the embodiment is a tire for motorcycles. Tires manufactured by the manufacturing method of the present invention are not limited to tires for motorcycles but include tires for passenger cars as well as for heavy-load vehicles such as trucks, and buses, for example. 
         [0029]    The tire of the embodiment includes a carcass  6 , a tread reinforcement layer  7 , and a tread rubber  2 G. The carcass  6  extends from a tread portion  2  through sidewall portions  3  to bead cores  5  of bead portions  4 . The tread reinforcement layer  7  is disposed outside the carcass  6  in a tire radial direction in the tread portion  2 . The tread rubber  2 G is disposed outside the tread reinforcement layer  7 . The tread portion  2  may be provided with a groove for drainage (not illustrated) as appropriate. 
         [0030]    The tread rubber  2 G is disposed on an area between tread ends TE and TE. The tread rubber  2 G of the embodiment has a base rubber  2   a  including a radially innermost layer portion to be overlapped with the tread reinforcement layer  7  and a cap rubber  2   b  disposed outside the base rubber  2   a  in the tire radial direction and forming a tread surface  2 S. The form of the tread rubber  2 G can be changed as appropriate. 
         [0031]    The carcass  6  includes one carcass ply  6 A, for example. The carcass ply  6 A includes a main body part  6   a  extending in a troidal form between a pair of the bead cores  5  and  5  and turn-up parts  6   b  that connect with the both ends of the main body part  6   a  and are turned up around the bead cores  5  from the inside to the outside in a tire axial direction. 
         [0032]    The carcass ply  6 A is a cord ply including carcass cords coated with a topping rubber. The carcass cords are oriented at an angle of from 70 to 90 degrees with respect to the tire equator C, for example. The carcass cords are preferably made of organic fibers selected from, for example, aramid, polyethylene naphthalate (PEN), nylon, rayon, and the like. 
         [0033]    A bead apex rubber  8  made of a hard rubber extends from the bead cores  5  outward in the tire radial direction between the main part  6   a  and the turn-up parts  6   b  of the carcass ply  6 A. 
         [0034]    The tread reinforcement layer  7  is formed of at least one reinforcement ply  7 A in which reinforcement cords are arranged with an inclination with respect to the tire circumferential direction. The reinforcement cords of the reinforcement ply  7 A are preferably made of steel cords or organic fiber cords, for example. The tread reinforcement layer  7  tightens the carcass  6  to enhance the rigidity of the tread portion  2  and improve durability performance. 
         [0035]    Next, an embodiment of a manufacturing method for the foregoing tire will be described.  FIG. 2  illustrates a manufacturing apparatus T having a known structure used for manufacture of the tread reinforcement layer  7 . The manufacturing apparatus T of the embodiment includes a base stand  13 , an approximately cylindrical drum  14  rotatably supported by the base stand  13 , and an applicator  15  capable of supplying a belt-like ply  11  to the drum  14 . 
         [0036]    The base stand  13  includes a rotation shaft  13   c  rotatably holding the drum  14 . The base stand  13  also includes a power transmission device for rotating the rotation shaft  13   c,  a control device for controlling the rotation (not illustrated), and the like. 
         [0037]    The drum  14  includes a circular ring-shaped core body  16 , a scaling device  17 , and a holding device  18 . The core body  16  includes an outer peripheral surface  16   a  approximated to a tire tread surface  2 S. The scaling device  17  extends and contracts the core body  16  inward and outward in the tire radial direction. The scaling device  17  is composed of a rubber member, for example. The holding device  18  holds a raw tire base body K around which the belt-like ply  11  is to be wound. The scaling device  17  may be a reciprocating member such as an air cylinder, for example. 
         [0038]    The raw tire base body K has a cylindrical shape and includes the bead cores  5  and the carcass  6 . Rubber members (not illustrated) such as inner liner rubber and sidewall rubber are attached as appropriate to the raw tire base body K, for example. 
         [0039]    The applicator  15  is formed in a conveyor shape, for example. The applicator  15  supplies the belt-like ply  11  on its conveyance surface to a circumferential surface  14   a  of the drum  14 . On the upstream side of the applicator  15 , a rubber extruder or the like for continuously extruding the belt-like ply  11 , for example is provided (not illustrated). The applicator  15  is supported by a three-dimensional moving device (not illustrated) capable of reciprocating in an axial direction and a radial direction with respect to the drum  14 , for example. 
         [0040]      FIG. 3  is a perspective view of the belt-like ply  11 . As illustrated in  FIG. 3 , the belt-like ply  11  has an approximately rectangular cross section and is formed by covering with a topping rubber  10  one or more reinforcement cords  9  arranged in parallel with approximately equal intervals therebetween. 
         [0041]    The width W 1  and the thickness t 1  of the belt-like ply  11  can be determined as appropriate by custom. The width W 1  of the belt-like ply  11  is preferably in a range of from 3.0 to 12.0 mm, for example. The thickness t 1  of the belt-like ply  11  is preferably in a range of from 0.6 to 1.5 mm. The number of the reinforcement cords  9  included in the belt-like ply  11  is preferably two to five. 
         [0042]    A tire manufacturing method of the embodiment includes a step of preparing the raw tire base body K, a tread reinforcement layer formation step of forming the tread reinforcement layer  7 , and a tread rubber formation step of forming the tread rubber  2 G. The raw tire base body K is manufactured by a known manufacturing method. 
         [0043]    As illustrated in  FIG. 2 , at the step of preparing the raw tire base body K, first, the raw tire base body K is placed on the diameter-reduced circumferential surface  14   a  of the drum  14  in the manufacturing apparatus T. 
         [0044]    Next, as illustrated in  FIG. 4 , the scaling device  17  is pressurized to increase the diameter of the core body  16  and bulge the raw tire base body K, for example. 
         [0045]    Next, the tread reinforcement layer formation step is carried out. The tread reinforcement layer formation step includes a winding step of winding the belt-like ply  11  around a winding surface  6   e  of the carcass  6  of the raw tire base body K on the outside in the tire radial direction. At the winding step, the conveyance surface of the applicator  15  is preferably held in parallel to the outer peripheral surface  16   a  of the core body  16  around which the belt-like ply  11  is to be wound. 
         [0046]    The winding step includes a first winding step, a parallel winding step, and a second winding step. When the first winding step and the second winding step are set as one cycle, the winding step is desirably performed in at least two cycles. In the embodiment, the winding step is carried out in two cycles. 
         [0047]      FIGS. 5A and 5B  are developed plan views illustrating conceptually the tread reinforcement layer  7  manufactured at the winding step of the first cycle.  FIGS. 6A and 6B  are developed plan views illustrating conceptually the tread reinforcement layer  7  manufactured at the winding step of the second cycle. In  FIGS. 5 and 6 , the vertical axis indicates the angle of the tread reinforcement layer  7  in the tire circumferential direction, and the lateral axis indicates entire width Wt of the tread reinforcement layer  7 . The entire width Wt of the tread reinforcement layer  7  refers to a developed length along the tread surface  2 S (illustrated in  FIG. 1 ). 
         [0048]    As illustrated in  FIGS. 4 and 5A , at the first winding step of the first cycle, a winding start end  11   a  of the belt-like ply  11  guided by the applicator  15  is fastened at a first end portion  7   e  of the tread reinforcement layer  7  on one side in the tire axial direction. A pressure roller (not illustrated) is desirably used to fasten the belt-like ply  11  in a reliable manner, for example. 
         [0049]    Next, the drum  14  is rotated and the applicator  15  is moved from the first end portion  7   e  to a second end portion  7   i  of the tread reinforcement layer  7  on the other side in the tire axial direction. At that time, the belt-like ply  11  is wound in a spiral manner such that side edges  11   s  of the belt-like ply  11  are continuously separated from each other in turn. Accordingly, at the first winding step of the first cycle, a first one-side inclined portion  20   a  and a first non-winding portion  21   a  are formed. At the first one-side inclined portion  20   a,  the belt-like ply  11  is inclined to one side with respect to the tire circumferential direction. The first non-winding portion  21   a  is a portion around which the belt-like ply  11  is not wound. The angle of inclination of the belt-like ply  11  is freely adjusted by controlling the moving speed of the applicator  15  in the tire axial direction or the rotation speed of the drum  14 . 
         [0050]    Next, the parallel winding step of the first cycle is carried out. At the parallel winding step, the drum  14  is rotated while the applicator  15  is fixed at the second end portion  7   i.  Accordingly, at the parallel winding step of the first cycle, a first parallel portion  22   a  where the belt-like ply  11  extends along the tire circumferential direction is provided at the second end portion  7   i.    
         [0051]    Next, the second winding step of the first cycle is carried out. At this step, the belt-like ply  11  is wound in connection with the first parallel portion  22   a.  At the second winding step, the applicator  15  is moved from the second end portion  7   i  to the first end portion  7   e.  At that time, the belt-like ply  11  is wound in a spiral manner such that the side edges  11   s  are continuously separated from each other in turn. Accordingly, at the second winding step of the first cycle, as illustrated in  FIG. 5( b ) , a first other-side inclined portion  20   b  and a second non-winding portion  21   b  are formed. At the first other-side inclined portion  20   b,  the belt-like ply  11  is inclined to the other side with respect to the tire circumferential direction. The second non-winding portion  21   b  is a portion around which the belt-like ply  11  is not wound. 
         [0052]    Next, the parallel winding step is carried out between the first cycle and the second cycle. At the parallel winding step, the drum  14  is rotated while the applicator  15  is fixed at the first end portion  7   e.  Accordingly, a second parallel portion  22   b  where the belt-like ply  11  extends along the tire circumferential direction is provided at the first end portion  7   e.    
         [0053]    Next, the first winding step of the second cycle is carried out. At this step, the belt-like ply  11  is wound in connection with the second parallel part  22   b.  At the first winding step of the second cycle, as at the first winding step of the first cycle, the applicator  15  is moved from the first end portion  7   e  to the second end portion  7   i.  As illustrated in  FIG. 6A , at the first winding step of the second cycle, a second one-side inclined portion  20   c  and a third non-winding portion  21   c  are formed. At the second one-side inclined portion  20   c,  the belt-like ply  11  is inclined to one side with respect to the tire circumferential direction. The third non-winding portion  21   c  is a portion where the belt-like ply  11  is not wound. The second one-side inclined portion  20   c  of the embodiment is provided at the first non-winding portion  21   a.    
         [0054]    Next, the parallel winding step of the second cycle is carried out. Accordingly, a third parallel portion  22   c  where the belt-like ply  11  extends in the tire circumferential direction is provided at the second end portion  7   i.  In the embodiment, the first parallel portion  22   a  in the first cycle and the third parallel portion  22   c  in the second cycle are shifted in position from each other in the tire circumferential direction. 
         [0055]    Next, the second winding step of the second cycle is carried out. At this step, the belt-like ply  11  is wound in connection with the third parallel portion  22   c.  At the second winding step of the second cycle, the applicator  15  is moved from the second end portion  7   i  to the first end portion  7   e.  As illustrated in  FIG. 6B , at the second winding step, a second other-side inclined portion  20   d  and a fourth non-winding portion  21   d  are formed. At the second other-side inclined portion  20   d,  the belt-like ply  11  is inclined to the other side with respect to the tire circumferential direction. The fourth non-winding portion  21   d  is a portion where the belt-like ply  11  is not wound. The second other-side inclined portion  20   d  of the embodiment is provided at the second non-winding portion  21   b.    
         [0056]    Next, the step for forming a fourth parallel portion  22   d  where the belt-like ply  11  extends in the circumferential direction with the applicator  15  fixed at the first end portion  7   e  is carried out. 
         [0057]    Next, a winding terminal end  11   b  of the belt-like ply  11  guided by the applicator  15  is fastened at the first end portion  7   e  in alignment with the winding start end  11   a  (illustrated in  FIG. 5A ). In the embodiment, the winding terminal end  11   b  is formed at the fourth parallel portion  22   d.    
         [0058]    In this manner, the winding process is performed on the one long continuous belt-like ply  11 . That is, the tread reinforcement layer  7  is formed from the one belt-like ply  11 . The tread reinforcement layer  7  has high rigidity and produces the enhanced effect of reinforcing the carcass  6 . 
         [0059]      FIG. 7  is a developed plan view illustrating conceptually the tread reinforcement layer  7  manufactured in the winding process described above. As illustrated in  FIG. 7 , the tread reinforcement layer  7  of the embodiment is formed as a grid tread reinforcement layer  19  having almost diamond-shaped spaces  24  surrounded by the belt-like ply  11 . The grid tread reinforcement layer  7  does not have the reinforcement cords  9  (illustrated in  FIG. 3 ) in the almost diamond-shaped spaces  24 , which decreases the amount of cord usage and leads to reduction in material costs. The belt-like ply  11  is formed in an almost diamond-shaped grid. Accordingly, when tension acts on the reinforcement cords  9  in the area with the tread reinforcement layer  7 , the tension is also transferred to the reinforcement cords  9  in the adjacent areas via the grid belt-like ply  11 . Therefore, stress applied to the cords is decreased and sufficient strength and durability performance can be maintained even with a small number of cords. The spaces  24  of the embodiment are surrounded by the one-side inclined portions  20   a  and  20   c  and the other-side inclined portions  20   b  and  20   d  (hereinafter, also referred to simply as “one-side inclined portion  20 A” and “other-side inclined portion  20 B”). 
         [0060]    Since the winding terminal end  11   b  is fastened in alignment with the winding start end  11   a,  the rigidity of the tread reinforcement layer  7  is ensured to further improve the durability performance of the tire. The state in which “the winding start end  11   a  and the winding terminal end  11   b  are aligned with each other” indicates the state in which the winding start end  11   a  and the winding terminal end  11   b  are in contact with each other. In addition, the state in which “the winding start end  11   a  and the winding terminal end  11   b  are aligned with each other” includes the state in which the winding start end  11   a  and the winding terminal end  11   b  overlap in the tire circumferential direction and the length of the overlapping portion in the tire circumferential direction (not illustrated) is 10 mm or less. 
         [0061]    The width (maximum width) Wa of the almost diamond-shaped space  24  in the tire axial direction is desirably larger than the width W 1  of the belt-like ply  11 . This effectively reduces the amount of cord usage. From the viewpoint of maintaining the rigidity of the tread reinforcement layer  7 , the width Wa of the space  24  in the tire axial direction is more preferably 3 to 10 times larger than the width W 1  of the belt-like ply. The width Wa of the space  24  is a developed length along the tread surface  2 S. 
         [0062]    The width Wa of the space  24  in the tire axial direction is preferably in a range of from 10% to 30% of the entire width Wt of the grid tread reinforcement layer  19 . This makes it possible to reduce the amount of cord usage and maintain the durability performance of the tire in a balanced manner. 
         [0063]    An angle θ 1  of the inclined portions  20   a  to  20   d  (hereinafter, also referred to simply as “inclined portion  20 ”) of the belt-like ply  11  with respect to the tire circumferential direction is preferably two to ten degrees. When the angle θ 1  of the belt-like ply  11  is less than two degrees, the spaces  24  become smaller in size and there is the possibility that the amount of usage of the reinforcement cords  9  cannot be reduced. When the angle  01  of the belt-like ply  11  is more than ten degrees, there is the possibility that the effect of reinforcing the carcass  6  becomes lower. 
         [0064]    A pitch P of the belt-like ply  11  between the one-side inclined portion  20 A and the other-side inclined portion  20 B adjacent to each other in the tire axial direction in turn is preferably constant. Accordingly, it is possible to effectively reduce stress applied to the reinforcement cords  9  by transferring tension acting on the reinforcement cords  9  in the area with the tread reinforcement layer  7  to the reinforcement cords  9  in the adjacent areas in a balanced manner. 
         [0065]    To reduce the amount of usage of the reinforcement cords  9  and maintain the sufficient strength of the tread reinforcement layer  7  in a balanced manner, a length Lp of the one pitch P of the belt-like ply  11  in the tire circumferential direction is preferably 150 to 300 mm. 
         [0066]    The one-side inclined portion  20 A is connected to any one of ends of the parallel portions  22   a  to  22   d  (hereinafter, also referred to simply as “parallel portion  22 ”) in the tire circumferential direction, and the other-side inclined portion  20 B is connected to the other end of the parallel portion  22 . Accordingly, an angle θ 2  (smaller than 180 degrees) between the inclined portion  20  and the parallel portion  22  becomes larger than an angle (smaller than 180 degrees) formed by connecting directly the one-side inclined portion  20 A and the other-side inclined portion  20 B. This reduces bending stress acting on the reinforcement cords  9  to keep high joint strength between the reinforcement cords  9  and the carcass  6 , thereby prevent the collapse of the wound belt-like ply  11 . 
         [0067]    The length La of the parallel portion  22  with respect to the tire circumferential direction is preferably 10 mm or more. Accordingly, the foregoing actions can be effectively exerted to reduce bending stress on the reinforcement cords  9 . When the length La of the parallel portion  22  is larger than 100 mm, the amount of cord usage increases and there is the possibility that the effect of reducing the material costs becomes lower. Accordingly, the length La of the parallel portion  22  is more preferably in a range of from 13 to 50 mm. 
         [0068]    Next, the tread rubber formation step is carried out. As illustrated in  FIGS. 8 to 10 , at the tread rubber formation step of the embodiment, a strip winding method is employed to wind a long belt-like rubber strip  25  in a spiral manner. The drum  14  is used at the tread rubber formation step of the embodiment. 
         [0069]    The rubber strip  25  is unvulcanized and is rectangular in cross section with its width larger than its thickness (not illustrated), for example. The thickness of the rubber strip  25  of the embodiment is decided as customary. The thickness of the rubber strip  25  is preferably about 0.5 to 2.0 mm. 
         [0070]    The tread rubber formation step of the embodiment includes a base rubber formation step of forming base rubber  2   a  and a cap rubber formation step of forming cap rubber  2   b.  In this manner, the rubber strip  25  of the embodiment includes a first rubber strip  25 A for forming the base rubber  2   a  and a second rubber strip  25 B for forming cap rubber  2   b.    
         [0071]    As illustrated in  FIGS. 8 and 9 , a winding start end  25   a  of the first rubber strip  25 A continuously supplied from the applicator  15  is fastened on the outer peripheral surface of the raw tire base body K around which the belt-like ply  11  is wound. After that, the applicator  15  is moved as appropriate while the drum  14  is rotated to wind the first rubber strip  25 A up to its winding terminal end (not illustrated). In the embodiment, the winding start end  25   a  is disposed at the first end portion  7   e  of the tread reinforcement layer  7 . The applicator supplying the rubber strip  25  may be different from the applicator  15  supplying the belt-like ply  11 . 
         [0072]    As described above, in the embodiment, the narrow first rubber strip  25 A is wound on the outer side of the raw tire base body K having the grid tread reinforcement layer  19 . Accordingly, the first rubber strip  25 A can be easily embedded into the spaces  24  in the grid tread reinforcement layer  19 . Therefore, the air between the spaces  24  and the tread rubber  2 G is effectively discharged. Although there is no particular limitation, the width of the first rubber strip  25 A is preferably in a range of from 50% to 100% of the width Wa of the space  24  in the tire axial direction. 
         [0073]    The temperature at which the first rubber strip  25 A is attached to the raw tire base body K is preferably of from 70 to 80 degrees. The first rubber strip  25 A is in a low-viscosity state and is deformable in accordance with the shape of the belt-like ply  11  forming the spaces  24  in the grid tread reinforcement layer  19  as illustrated in  FIG. 8 . This makes it easy to discharge the air from the narrow portions  24   a  and  24   a  of the spaces  24  on the both sides in the tire circumferential direction. 
         [0074]    The first rubber strip  25 A is desirably directly moved by a conveyor or the like to the drum  14  without winding high-temperature rubber discharged from a gear pump not illustrated around a roll body or the like, for example. 
         [0075]    The first rubber strip  25 A of the embodiment includes a circumferential portion  26   a  and an inclined portion  26   b.  The circumferential portion  26   a  extends in parallel to the tire circumferential direction. The inclined portion  26   b  connects to the circumferential portion  26   a  and inclines with respect to the tire circumferential direction to move the first rubber strip  25 A in the tire axial direction. The first rubber strip  25 A is not limited to this mode but may be substantially formed only from the inclined portion to move the rubber strip  25 A in the tire axial direction. 
         [0076]    Next, as illustrated in  FIG. 10 , the cap rubber formation step is carried out to form the cap rubber  2   b  using the second rubber strip  25 B. For the second rubber strip  25 B, it is desired that a pre-formed rubber strip is rewound from a roll body and is wound by the applicator on the outer side of the base rubber  2   a  via a festoon (not illustrated) holding the rubber strip loosened in a U shape. The second rubber strip  25 B may be formed by moving directly rubber discharged from the gear pump similar to the first rubber strip  25 A. The rubber strip  25  of the embodiment is wound with side edges in contact with each other. However, the rubber strip  25  is not limited to this mode but the rubber strip  25  adjacent in the tire axial direction may be overlapped in the tire radial direction, for example. 
         [0077]    The pneumatic tire manufacturing method of the present invention has been explained so far. The present invention is not limited to the foregoing embodiment but can be modified in various manners. 
       EXAMPLES 
       [0078]    Pneumatic tires for motorcycles with a size of 190/50ZR17 having the basic structure illustrated in  FIG. 1  were prototyped in accordance with the specifications in Table 1. The sample tires were tested for durability performance and evaluated for the amount of usage of reinforcement cords. Common specifications and test method for the sample tires are as follows: 
         [0079]    The entire width Wt of the tread reinforcement layer: 200 mm 
         [0080]    The length of the tread reinforcement layer on the tire equation in the tire circumferential direction: 610 mm 
         [0081]    The length of the tread reinforcement layer at the first and second end portions in the tire circumferential direction: 500 mm 
         [0082]    The width W 1  of the belt-like ply: 4.2 mm 
         [0083]    The thickness t 1  of the belt-like ply: 1.0 mm 
         [0084]    The number of reinforcement cords in the belt-like ply: three 
         [0085]    Durability performance: 
         [0086]    The sample tires were measured in the number of remaining airs between the tread reinforcement layer and the tread rubber by shearography as an optical non-destructive inspection technique using a plurality of semiconductor lasers and a CCD camera. An X-ray CT scan device was used to take cross-sectional images of the tires to check for the presence or absence of collapse of the wound belt-like ply at the first and second end portions. When the number of remaining airs per pitch of the belt-like ply is larger than 10, the durability performance of the tire is influenced. When the collapse of the wound belt-like ply has occurred at more than three places, the durability performance of the tire is influenced. Table 1 shows the test results. 
         [0087]    The term “extrusion” appearing in Table 1 means a manufacturing method for attaching cap rubber composed of a rubber sheet with a width equal to the length between the tread ends. 
         [0088]    The term “STW-1” means a manufacturing method for attaching rubber strip from a roll body through a festoon. 
         [0089]    The term “STW-2” means a manufacturing method for attaching rubber strip directly from a gear pump. 
         [0090]    The term “film attachment” means a manufacturing method for attaching base rubber composed of a thin rubber sheet to cap rubber. 
         [0091]    The number of remaining airs per pitch in the belt-like ply of example 3 was two. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Ref. 1 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
                 Ex. 7 
                 Ex. 8 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Shape of spaces in tread reinforcement 
                 None 
                 Grid 
                 Grid 
                 Grid 
                 Grid 
                 Grid 
                 Grid 
                 Grid 
                 Grid 
               
               
                 layer 
               
               
                 Number of drum rotations for application 
                 50 
                 32 
                 32 
                 32 
                 32 
                 32 
                 32 
                 32 
                 24 
               
               
                 of belt-like ply (times) 
               
               
                 Manufacturing method of cap rubber 
                 Extrusion 
                 Extrusion 
                 Extrusion 
                 Extrusion 
                 STW-1 
                 STW-1 
                 STW-1 
                 STW-1 
                 STW-1 
               
               
                 Manufacturing method of base rubber 
                 Film 
                 Film 
                 STW-1 
                 STW-2 
                 STW-2 
                 STW-2 
                 STW-2 
                 STW-2 
                 STW-2 
               
               
                   
                 attachment 
                 attachment 
               
               
                 Tire circumferential length of belt-like ply 
                 — 
                 195 
                 195 
                 195 
                 195 
                 195 
                 195 
                 195 
                 260 
               
               
                 per pitch Lp: (mm) 
               
               
                 Tire circumferential length of third portion 
                 — 
                 15 
                 15 
                 15 
                 0 
                 5 
                 10 
                 15 
                 15 
               
               
                 La: (mm) 
               
               
                 Tire circumferential angle of belt-like 
                 0.15 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
               
               
                 ply θ: (degrees) 
               
               
                 Number of collapses of wound belt-like 
                 0 
                 0 
                 0 
                 0 
                 2 
                 1 
                 0 
                 0 
                 0 
               
               
                 ply at first and second end portions: 
               
               
                 (units) 
               
               
                 Number of remaining airs in belt-like ply 
                 0 
                 8 
                 2 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 per pitch: (units) 
               
               
                 Amount of usage of reinforcement cords 
                 100 
                 64 
                 64 
                 64 
                 64 
                 64 
                 64 
                 64 
                 50 
               
               
                 [index: better with smaller values] 
               
               
                   
               
             
          
         
       
     
         [0092]    According to the test results, it has been confirmed that the tire of the examples have decreased the amount of usage of the reinforcement cords as compared to the tire of the comparative example and maintained durability performance. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           7  Tread reinforcement layer 
           7   e  First end portion 
           7   i  Second end portion 
           11  Belt-like ply 
           11   s  Side edge 
           19  Grid tread reinforcement layer 
           24  Space