Abstract:
A tubeless-tire spoke wheel with spokes threaded directly into integral bores of the wheel rim. The integral bores have closed ends which allow for a large degree of tubeless-tire design flexibility while also providing enhanced strength characteristics. This results in stiffer, stronger designs while providing for lighter, more energy efficient wheels.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an improvement of a wheel for a tubeless tire which does not include a tube. 
     BACKGROUND OF THE INVENTION 
     For a motorcycle, combinations have heretofore been adopted in which a tubeless tire is fitted to a cast wheel, and a tube tire containing a tube inside is fitted to a spoke wheel. This is because of a structural reason, that is, since spokes penetrate a rim, there is difficulty in using the tubeless tire. 
     However, a spoke wheel to which a tubeless tire can be fitted has been proposed in Japanese Patent Laid-Open No. 2000-6601, the spoke wheel having the aim of combining the advantages of a tubeless tire and the advantages of a spoke wheel. FIG. 2 of Japanese Patent Laid-Open No. 2000-6601 is a cross section along the radial direction of a conventional tubeless-tire spoke wheel. A plurality of spokes  30  (with regard to reference numerals, ones used in the publication are used hereinbelow) which are attached to a hub, which is at the center of the wheel, in a state where the spokes are outwardly directed from the hub, are attached to a rim  11 , and a tire T is fitted to the rim  11 . 
     The rim  11  includes a pair of tubular hollow portions  12  and  13  integrally, and the tubular hollow portions  12  and  13  are disposed between a plane P at the middle of the wheel and flanges  24  and  25 , respectively, the flanges supporting a bead portion of the tire T. 
     In addition, an end of the spoke  30  is attached to a seat portion  33  in the rim  11  via a fastening nipple  31 . This is one in which through holes, through which spokes  30  are passed, are made in the seat portions  32  and  33  along outer walls  22  and  23  of the tubular hollow portions  12  and  13 . 
     However, since, as is apparent from FIG. 2, the seat portions  32  and  33  have to be disposed more outward than the flanges  24  and  25 , the positions of the seat portions  32  and  33  are limited, and thus, it has been difficult to freely select the attachment position of the spoke  30 . That is, the degree of flexibility in the design for the attachment position of the spoke is small. 
     Therefore, an object of the present invention is to provide a tubeless-tire spoke wheel capable of increasing the degree of flexibility in the design for the attachment positions of spokes. 
     SUMMARY OF THE INVENTION 
     A tubeless-tire wheel is provided which includes a hub attached to an axle, a rim to which a tubeless tire is fitted, and a plurality of spokes connecting the rim to the hub, the tubeless-tire wheel comprising an external thread portion formed in an end portion of the spoke on the rim side; an internal thread portion into which the external thread portion can be screwed formed in the rim and one end of the spoke connected to the rim by screwing the external thread portion into the internal thread portion. 
     In a conventional nipple structure, it is necessary to provide a through hole to a rim. Therefore, the attachment position of the spoke is limited to each edge of the rim, and the degree of flexibility in the design will be small. 
     In this respect, the internal thread portion may be formed in the rim, and it is possible to provide the internal thread portion to an arbitrary position in the rim. As a result, it is possible to increase the degree of flexibility in the design for the attachment position of the spoke. 
     Further, the rim may include a bottom portion, inclined portions obliquely extended from the bottom portion, and base portions flatly, outwardly extended from outer edges of these inclined portions and the internal thread portion formed in the inclined portion. 
     An internal thread portion formed in the inclined portion which is provided between the bottom portion and the base portion also serves as a strengthening part. 
     The internal thread portion may be formed in any of the bottom portion, the inclined portion, and the base portion of the rim. Among them, while the bottom portion and the base portion are substantially orthogonal to the spoke, it is possible to make the inclined portion be in line with the spoke. If the internal thread portion is formed in such an inclined portion, it is possible to form the internal thread portion with a sufficient length, and it is not necessary to increase the thickness of the inclined portion so much. 
     That is, it is possible to form a sufficient length of screw hole in the inclined portion which has relatively thin thickness. As a result, there is an advantage that it is possible to achieve reduction in the weight of the rim. 
     The spoke may be inclined parallel to the inclined portion of the rim. Since the spoke may be inclined parallel to the inclined portion, it is possible to make the internal thread for fastening the spoke by use of the thickness of the inclined portion. 
     If the inclination of the inclined portion and the inclination of the spoke coincide with each other, it is possible to further reduce the thickness of the inclined portion, and an advantage that it is possible to achieve further reduction in the weight of the rim can be brought about. 
     The thickness of the inclined portion may be set thicker than those of the adjacent bottom portion and base portion. Since the thickness of the inclined portion may be thicker than those of the bottom portion and the base portion, it is possible to inhibit the local deformation of the inclined portion which is the part on which force is exerted. At the same time, since it is possible to make the adjacent bottom portion and base portion thin, it is possible to achieve reduction in the weight of the rim. 
     In the inclined portion, a part to which the internal thread portion is provided may be made thick, and the other part may be set thin to the extent that the thickness thereof is substantially equal to those of the bottom portion and the base portion. 
     If the inclined portion were made evenly thick, the weight of the rim would increase. Accordingly, the needed portion (part to which the internal thread portion is provided) in the inclined portion can be made thick, and the other part thereof can be made thin to the extent that the thickness thereof is substantially equal to those of the bottom portion and the base portion, thereby reducing the unnecessary thickness, and thus an advantage that reduction in the weight of the rim can be achieved can be brought about. 
     The tubeless tire wheel may further comprise an inner circumference of a tire brought into contact with the base portion and the extension of the spoke disposed to run along a side portion of the tire. Since an inner circumference of a tire is brought into contact with the base portion, and the extension of the spoke can be disposed to run along a side portion of the tire, there is no need to arrange the spoke unnecessarily widely, so that a compact structure can be realized. In addition, there is an advantage that the load exerted from the spoke can be effectively received by the tire which runs along the extension of the axis of the spoke. 
     The rim of the tubeless tire wheel may include a bottom portion in the middle thereof in the width direction of the cross section, a protruding portion protruding in the direction away from the hub provided to the bottom portion, and the internal thread portion formed in the protruding portion. Thus, it is possible to dispose the heavy portion at the rotation center. As a result, an advantage that the cornering ability of the wheel can be improved can be brought about. 
     Further, the rim may include a bottom portion, inclined portions obliquely extended from the bottom portion, base portions flatly, outwardly extended from outer edges of these inclined portions, and flanges extended from outer edges of these base portions in the direction away from the hub and the internal thread portion formed in the flange. Since the internal thread portion is formed in the flange, and the flange is formed thick for connection with the spoke, it is possible to increase stiffness. The flange becomes resistant to deformation, and, even when the flange receives impact force from the outside, air leak can be reduced. 
     The rim may be made as a hollow-cross-section structure including a hollow portion and the internal thread portion formed in a wall portion surrounding the hollow portion. Since the rim is made as a hollow-cross-section structure including a hollow portion, it is possible to reduce the weight of the rim. In addition, by forming the internal thread portion in a wall portion surrounding the hollow portion, and devising the cross sectional shape of the hollow portion, an advantage can be brought about that it is made possible to easily increase the section modulus, and to achieve increase in the stiffness of the wheel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a tubeless-tire wheel according to a first embodiment. 
         FIG. 2  is a diagram for explaining a state of spokes attached to the wheel according to the first embodiment. 
         FIG. 3  is a main-part cross section of  FIG. 2 . 
         FIG. 4  is a perspective view of a tubeless-tire wheel according to a second embodiment. 
         FIG. 5  is a diagram for explaining a state of spokes attached to the wheel according to the second embodiment. 
         FIG. 6  is a main-part cross section of  FIG. 5 . 
         FIG. 7  is a perspective view of a tubeless-tire wheel according to a third embodiment. 
         FIG. 8  is a diagram for explaining a state of spokes attached to the wheel according to the third embodiment. 
         FIG. 9  is a cross section of a wheel portion according to the third embodiment. 
         FIG. 10  is a cross section of a wheel portion according to a fourth embodiment. 
         FIG. 11  is a perspective view of a tubeless-tire wheel according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective view of a tubeless-tire wheel according to a first embodiment. The tubeless-tire wheel  10  is provided with a plurality of holder portions  13  . . . (hereinafter, “ . . . ” indicates plurality) for attaching spokes  12  . . . around a hub  11  which is at the center of the wheel. The spokes  12  . . . are extended from the holder portions  13  . . . toward the inner circumferential face  14   a  of a circular-wheel-shaped rim  14 . One ends  15   a  . . . of the spokes  12  . . . are attached to the inner circumferential face  14   a  of the rim. 
     Moreover, a tubeless tire is fitted onto the outer circumferential face  14   b  of the rim  14 . 
     In other words, the tubeless-tire wheel  10  is a member which includes the hub  11  for attachment to an axle, the rim  14  onto which the tubeless tire is fitted, and the plurality of spokes  12  . . . for connecting the rim  14  and the hub  11 . 
     The holder portions  13  . . . have two rows of holders  17  in the axis direction of the hub  11 . The rows of holders  17  consist of a left side row  17 L and a right side row  17 R. Moreover, the holder portions  13  . . . constituting the rows of holders  17  include two hole portions  19   s  . . . and  19   u  . . . constituted of the outer ones and the inner ones, respectively. 
     The spokes  12  . . . attached around the hub  11  are members which are arranged in a state where a plurality of types of attachment directions are given to the spokes  12 . 
     Forces of at least three kinds of directions are exerted on the spokes  12  . . . , the forces being exerted, for example, when a vehicle is at rest, when a driving force is applied to the wheel, and when a braking force is applied to the rotating wheel. Since the other irregular forces due to the influences of the road surface irregularities and the like are additionally exerted on the wheel  10 , a function of supporting the forces exerted from various directions is required of the wheel  10 . 
     For supporting these forces effectively, the plurality of spokes  12  . . . extended toward the inner circumferential face  14   a  of the rim  14  are attached with a plurality of types of attachment directions given thereto. 
       FIG. 2  is a diagram for explaining a state of the spokes attached to the wheel according to the first embodiment, and shows the relative arrangement of the spokes  12  . . . . 
     As attachment portions of the spokes  12  . . . , there are the hole portions  19   s  . . . and  19   u  . . . which the holder portions  13  . . . constituting the left side row  17 L in the hub  11  have, and internal thread portions  21  . . . made in the rim  14 . Moreover, the spokes  12  . . . are extended from the hole portions  19   s  . . . and  19   u  . . . of the holder portions  13  . . . to the rim  14 , and attached thereto. 
     In  FIG. 2 , shown is the arrangement of the spokes  12  . . . extended from the holder portions  13  . . . of the left side row  17 L out of two rows of holders  17 L and  17 R included in the hub  11 . The spokes extended from the right side row  17 R are the same as those extended from the left side row  17 L with the exception that the spokes extended from the right side row  17 R are arranged with a some phase difference between 1° and 15° given thereto with respect to the spokes of the left side row  17 L, and therefore will be omitted. 
     Next, by taking as an example one holder portion  13  out of the holder portions  13  . . . arranged in the left side row  17 L, a description concerning attachment relation at the start and end points of the two spokes  12 ,  12  extended from the holder portion  13  will be given. 
     The upper left part of  FIG. 2  is a diagram showing that the spoke  12  is extended from the inner hole  19   u  included in the holder portion  13  to an inclined portion  25  disposed in the inner side of the rim  14 , and attached thereto. 
     On the other hand, the upper right part of  FIG. 2  is a diagram showing that the spoke  12  is extended from the outer hole  19   s  in the holder portion  13  to the inclined portion  25  disposed in the inner side of the rim  14 , and attached thereto. 
     Thus, in the present embodiment, each spoke  12 , which protrudes from the holder portion  13  included in the left side row  17 L, is extended to the inclined portion  25  provided in the inner side of the rim  14 , and attached thereto. 
     Similarly, each spoke  12 , which protrudes from the holder portion  13  included in the right side row  17 R (not shown), is extended to the inclined portion  25  provided to the outer side of the rim  14 , and attached thereto. 
       FIG. 3  is a main-part cross section of  FIG. 2 , showing the attachment structure of the spoke on the hub side and the rim side. 
     The spoke  12  is a member which engages with the hole portion  19  included in the holder portion  13  of the hub  11  via an adjustment member  26  and, in a state where the internal thread portion  21  is made in the inclined portion  25  included in the rim  14 , which is attached to the rim  14  by screwing an external thread portion  28  of the spoke  12  into the internal thread portion  21 . 
     The rim  14  includes a bottom portion  29 , the inclined portions  25 ,  25 , which are inclined toward a tire from the bottom portion  29 , base portions  31 ,  31 , which are extended from these inclined portions  25 ,  25  to the outside, and flanges  34 ,  34  which include hollow portions  33 ,  33  and are extended from the base portions  31 ,  31  toward the tire  32 . The tire  32  is fitted in a state where bead portions  32   b ,  32   b  of the tire  32  is abutted against outer surfaces  31   g ,  31   g  of the base portions  31 ,  31  and inner surfaces  34   n ,  34   n  of the flanges  34 ,  34 . Incidentally,  32   a  is a tire side portion. 
     With regard to the portions of the spoke  12 ,  36  indicates a collar portion;  37 , a fastening portion; and  38 , an external thread portion which also serves as an end portion on the rim side. 
     The fastening portion  37  to which to apply a tool when the spoke  12  is screwed into the rim  14  is provided. Reference numeral  26  indicates the adjustment member provided separately from the spoke  12 . The adjustment member  26  has, in one end portion, a connection portion  39  which is screwed together with the external thread portion  38  of the spoke  12 , and, in the other end portion, a head portion  35  which engages with the holder portion  13 , the head portion  35  provided with a socket portion  35 A into which a tool such as an Allen wrench can be inserted. Thus, it is possible to perform tension adjustment of the spoke  12  by screwing the adjustment member  26  to the spoke  12  or loosening. 
     In this embodiment, the rim  14  is an aluminum extruded material, and the hollow portions  33 ,  33 , are provided to the flanges  34 ,  34  for weight reduction. 
     In other words, in the tubeless-tire wheel  10 , the external thread portion  28  is formed in the end portion  38  of the spoke  12  on the rim side, the internal thread portion  21  into which this external thread portion  28  can be screwed is formed in the rim, and the one end  15  of the spoke is connected to the rim  14  by screwing the external thread portion  28  into the internal thread portion  21 . 
     Specifically, the rim  14  is characterized in that the rim  14  includes the bottom portion  29 ; the inclined portions  25 ,  25  obliquely extended from the bottom portion  29 ; and the base portions  31 ,  31  flatly, outwardly extended from outer edges  25   s ,  25   s  of these inclined portions  25 ,  25 , and that the internal thread portion  21  is formed in the inclined portion  25 . 
     It should be noted that the internal thread portion  21  is formed in a state where the rim  14  is not penetrated. 
     The internal thread portion  21  may be formed in any of the bottom portion  29 , the inclined portion  25 , and the base portion  31  of the rim  14 . Among them, while the bottom portion  29  and the base portion  31  are substantially orthogonal to the spoke  12 , it is possible to make the inclined portion  25  be in line with the spoke  12 . If the internal thread portion  21  is formed in such an inclined portion  25 , it is possible to form the internal thread portion  22  with a sufficient length, and it is not necessary to increase the thickness of the inclined portion  25  so much. 
     In other words, it is possible to form a sufficient length of screw hole in the inclined portion  25  which has relatively thin thickness. Thus, it is possible to achieve reduction in the weight of the rim  14 . 
     The rim includes the bottom portion  29 , the inclined portion  25  obliquely extended from the bottom portion  29 , and the base portions  31 ,  31  flatly, outwardly extended from the outer edges of these inclined portions  25 ,  25 . The internal thread portion  21  is formed in the inclined portion  25  which is provided between the bottom portion  29  and the base portion  31  and also serves as a strengthening part. 
     Since the internal thread portion  21  is exclusively provided to the inclined portion  25  which also serves as a strengthening part, the force exerted from the spoke  12  is wholly received by the inclined portion, and thus not received by the bottom portion  29  nor the base portion  31 . 
     Since there is no need for the force exerted from the spoke  12  to be received by the bottom portion  29  and the base portion  31 , it is possible to make the thicknesses of the bottom portion  29  and the base portion  31  thinner than that of the inclined portion  25 . 
     As a result, making the thicknesses of the bottom portion  29  and the base portion  31  thin effectuates an advantage that reduction in the weight of the rim  14  can be achieved. 
     Since the fixation portion on the rim side is the internal thread portion  21 , and the one end of the spoke  12  is connected to the rim  14  by screwing the external thread portion  28  into the internal thread portion  21 , generally, a plurality of through holes which would otherwise be made by the number of spokes  12  for fixing the spoke  12  in the rim will be unnecessary, and the internal thread portion  21  can be completed with a blind hole. 
     Since the internal thread portion  21  can be completed with a blind hole, it is possible to eliminate a through hole made in the rim. 
     The elimination of the through hole significantly increases the stiffness of the rim  14 . 
     Since the increase in the rim stiffness allows for easily obtaining certain stiffness, it is possible to make the thickness of the rim  14  thinner than that of the conventional one. As a result, it is made possible to achieve reduction in the weight of the rim  14 . 
     In addition, the spoke  12  is inclined parallel to the inclined portion  25 . 
     Since the spoke  12  is inclined parallel to the inclined portion  25 , it is possible to make the internal thread for fastening the spoke  12  by use of the thickness of the inclined portion  25 . 
     If the inclination of the inclined portion  25  and the inclination of the spoke  12  coincide with each other, it is possible to further reduce the thickness of the inclined portion  25 , and thus it is possible to achieve further reduction in the weight of the rim  14 . 
     In addition, since the rim  14  is so configured that the rim  14  receives force from the spoke  12  in the direction of the inclination angle of the rim  14 , it is possible to ensure stiffness effectively while the increase in the thickness of the rim  14  is inhibited. 
     As a result, it is made possible to increase the stiffness of the rim  14 , and it is possible to ensure the connection stiffness between the rim  14  and the spoke  12 . 
     Moreover, the thickness of the inclined portion  25  is set thicker than those of the adjacent bottom portion  29  and base portion  31 . 
     Since the thickness of the inclined portion  25  is thicker than those of the bottom portion  29  and the base portion  31 , it is possible to inhibit the local deformation of the inclined portion  25  which is the part on which force is exerted. At the same time, since it is possible to make the adjacent bottom portion and base portion  31  thin, it is possible to achieve reduction in the weight of the rim  14 . 
     By making the inclined portion  25  thick, it is possible to tap a thread of a larger size as needed. 
     In the inclined portion  25 , a part to which the internal thread portion  21  is provided is made thick, and the other part is set thin to the extent that the thickness thereof is substantially equal to those of the bottom portion  29  and the base portion  31 . 
     If the inclined portion  25  were made evenly thick, the weight of the rim  14  would increase. Accordingly, the needed portion (part to which the internal thread portion is provided) in the inclined portion  25  is expanded inward or outward to be made thick, and the other part thereof is made thin to the extent that the thickness thereof is substantially equal to those of the bottom portion  29  and the base portion  31 , thereby reducing the unnecessary thickness, and achieving reduction in the weight of the rim  14 . 
     Alternatively, as shown by the imaginary line in  FIG. 3 , by removing what is called a pad portion, which is other part than that to which the internal thread portion is provided, by removal machining such as cutting to effect formation of the cross section as shown by the solid line, it is made possible to achieve reduction in thickness. 
     In addition, by casting or forging the rim to form the inclined portion  25 , to which the internal thread portion  27  is not provided, with a thin thickness, it is also made possible to omit a cutting process. 
     As described above, the external thread portion  28  is formed in the end portion of the spoke  12  on the rim side, the internal thread portion  21  into which this external thread portion  28  can be screwed is formed in the rim, and the one end of the spoke  12  is connected to the rim  14  by screwing the external thread portion  28  into the internal thread portion  21 . 
     When the internal thread portion  21  into which the external thread portion  28  can be screwed is made as a blind hole as described in the embodiment, there is no need to be afraid of air leak from the tire, and it is possible to provide the internal thread portion  21  to an arbitrary position in the rim  14 . As a result, it is made possible to increase the degree of flexibility in the design for the attachment position of the spoke  12 . Alternatively, with selection of position, the internal thread portion  28  may be made as a through hole. 
     An inner circumference  32   c  of the tire  32  abuts against the base portion  31 , and the extension C of the spoke  12  is disposed along an inner circumference  32   d  of the tire side portion  32   a . Thus, there is no need to arrange the spoke  12  unnecessarily widely, so that a compact structure can be realized, and the load exerted from the spoke  12  can be effectively received by the tire  32  which runs along the extension of the axis of the spoke  12 . 
       FIG. 4  is a perspective view of a tubeless-tire wheel according to a second embodiment. The tubeless-tire wheel  50  is one in which a plurality of holder portions  53  . . . for attaching spokes  52  . . . around a hub  51  which is the center of a wheel are provided, and the spokes  52  . . . are extended from these holder portions  53  . . . to an inner circumference  54   u  of a circular-wheel-shaped rim  54 , and are attached to the inner circumference  54   u  of the rim  54 . 
     The holder portions  53  . . . have two rows of holders  57  in the axis direction of the hub  51 . The rows of holders  57  consist of a left side row  57 L and a right side row  57 R. Moreover, one row of holders includes eight holder portions  53  . . . . 
     The holder portions  53  . . . includes two hole portions  59   s  and  59   u  constituted of the outer ones and the inner ones, respectively. 
     In addition, a connection member  62  for adjusting tension of the spoke  52  is interposed at a position in the spoke  52  to the rim  54  side. The detail is explained in  FIGS. 5 and 6 . 
       FIG. 5  is a diagram for explaining a state of the spokes attached to the wheel according to the second embodiment, and shows the relative arrangement of the spokes  52  . . . . 
     As attachment portions of the spokes  52  . . . , there are the hole portions  59  . . . which the holder portions  53  . . . constituting the left side row  57 L in the hub  51  have, and an internal thread portion  61  made in the rim  54 . Moreover, the spoke  52  is extended from the hole portion  59  of the holder portion  53  to the rim  54 , and attached thereto. 
     In  FIG. 5 , shown is the arrangement of the spoke  52  extended from the holder portions  53  . . . of the left side row  57 L out of two rows of holders  57 L and  57 R included in the hub  51 . The spokes extended from the right side row  57 R are the same as those extended from the left side row  57 L with the exception that the spokes extended from the right side row  57 R are arranged with a some phase difference between 1° and 15° given thereto with respect to the spokes of the left side row  17 L, and therefore will be omitted. 
     Next, by taking as an example one holder portion  53  out of the holder portions  53  . . . arranged in the left side row  57 L, a description concerning attachment relation at the start and end points of the two spokes  52 ,  52  extended from the holder portion  53  will be given. 
     The upper left part of  FIG. 5  is a diagram showing that the spoke  52  is extended from the inner hole  59   u  out of the two holes included in the holder portion  53  to a bottom portion  69  provided to the substantially middle portion of the rim  54 , and attached thereto. 
     On the other hand, the upper right part of  FIG. 5  is a diagram showing that the spoke  52  is extended from the outer hole  59   s  in the holder portion  53  to the bottom portion  69  provided to the substantially middle portion of the rim  54 , and attached thereto. 
     Thus, in the present embodiment, each spoke  52 , which protrudes from the holder portion  53  included in the left side row  57 L, is extended to the bottom portion  69  provided to the substantially middle portion of the rim  54 , and attached thereto. 
     Similarly, each spoke  52 , which protrudes from the holder portion  53  included in the right side row  57 R (not shown), is extended to the bottom portion  69  provided to the substantially middle portion of the rim  54 , and attached thereto. 
     Since the connection members  62  . . . are interposed at positions to the rim  54  side for adjusting tension of the spokes  52  . . . , each engagement portion of the spokes  52  . . . attached to the holder portion  53  can be made more simple and lightweight. Specifically, it is possible to omit the adjustment member  26  (see  FIG. 3 ) having the thread portion which is shown in the first embodiment. 
       FIG. 6  is a main-part cross section of  FIG. 5 , showing the attachment structure of the spoke  52  to the rim. 
     The spoke  52  is a member which connects the hub  51  and the rim  54  in such a way that a protruding portion  76  protruding in the direction away from the hub  51  (see  FIG. 5 ) is provided to the bottom portion  69  of the rim  54 , and an external thread portion  68  of the spoke  52  is screwed into the internal thread portion  61  provided to the protruding portion  76 . 
     Significantly different features from the first embodiment are that each spoke  52  is extended to the bottom portion  69  provided to the substantially middle portion of the rim  54  and attached thereto, and that the connection member  62  for adjusting the tension of the spoke  52  is provided to the spoke  52  to the rim side. Reference numeral  73  indicates a first connection thread portion,  74  indicates a second connection thread portion, and  75  indicates an internal thread portion. It should be noted that a bend portion  55  is provided to the spoke  52  to the holder portion  53  side (see  FIG. 5 ) in order to prevent the connection member  62  from rotating together at the time of adjustment. 
     Specifically, the rim  54  includes the bottom portion  69  in the middle thereof in the width direction of the cross section, the protruding portion  76  protruding in the direction away from the hub  51  (see  FIG. 5 ) is provided to the bottom portion  69 , and the internal thread portion  61  is formed in the protruding portion  76 . 
     It is made possible to dispose the heavy portion at the rotation center because the rim  54  includes the bottom portion  69  in the middle thereof in the width direction of the cross section, the protruding portion  76  protruding in the direction away from the hub  51  is provided to the bottom portion  69 , and the internal thread portion  61  is formed in the protruding portion  76 . As a result, the cornering ability of the wheel  50  can be improved. 
     In addition, the internal thread portion  61  provided to the rim  54  is provided to the bottom portion  69 , which internal thread portion  61  is made as a blind hole. That is, while the internal thread portion  61  is formed to the center side of a base portion  81  of the rim supporting a bead portion  78   b  of a tubeless tire  78 , one end  77  is made blind, so that the spoke  52  can be arranged without consideration of air leak. As a result, the degree of flexibility in the arrangement of the spoke  52  can be increased. 
     In this embodiment, with regard to the position of the connection member  62 , while the connection member  62  is disposed near the rim  54 , it is possible to dispose the connection member  62  at an arbitrary position in the spoke  52 . Preferably, the connection member  62  is disposed near to the hub  51  (see  FIG. 5 ), so that the moment of inertia is reduced. 
     Incidentally,  83  indicates a hollow portion which is provided in order to reduce weight and to increase stiffness, and  84  indicates a flange. 
     Back to  FIG. 4 , by use of the connection member  62 , the structure of the engagement portion of the holder portion  53 , which engagement portion is one end of the spoke  52 , can be made simple and lightweight compared to that of the first embodiment shown in  FIG. 1 . That is, in  FIG. 3 , the adjustment member  26  can be omitted. 
       FIG. 7  is a perspective view of a tubeless-tire wheel according to a third embodiment. The tubeless-tire wheel  110  is one in which a plurality of holder portions  113  . . . each of which is for attaching a spoke  112  around a hub  111  which is the center of a wheel are provided, and the plurality of spokes  112  . . . are extended from these holder portions  113  . . . toward an inner circumference  114   a  of a circular-wheel-shaped rim  114 , and are attached to the inner circumference  114   a  of the rim  114 . 
     The holder portions  113  . . . have two rows of holders  117  in the axis direction of the hub  111 . The rows of holders  117  consist of a left side row  117 L and a right side row  117 R. Moreover, the holder portions  113  . . . constituting the rows of holders  117  include two hole portions  119   s  . . . and  119   u  . . . constituted of the outer ones and the inner ones, respectively. 
     In addition, connection members  122  . . . are interposed at midpoints of the spokes  112  . . . to the rim  114  side. 
       FIG. 8  is a diagram for explaining a state of the spokes attached to the wheel according to the third embodiment, and shows the relative arrangement of the spokes. 
     Significantly different features from the first embodiment of  FIG. 2  are that each spoke  112  is extended to a flange  134  provided to either the left or the right of the rim  114  and attached thereto, and that the connection member  122  is interposed in the spoke  112  to the rim  114  side in order to adjust the tension of the spoke  112 . 
       FIG. 9  is a cross section of the wheel portion according to the third embodiment, showing the attachment structure of the spoke  112  to the rim. 
     Significantly different features from the first embodiment are that the spokes  112  . . . are extended to the flange  134  provided to either edge of the rim  114  and attached thereto, and that the connection member  122  for adjusting the tension of the spoke  112  is interposed in the spoke  112  to the rim side. Reference numeral  135  indicates a first connection thread portion,  136  indicates a second connection thread portion, and  137  indicates an internal thread portion. 
     Specifically, the rim  114  of the tubeless-tire wheel  110  (see  FIG. 7 ) includes a bottom portion  129 ; a base portion  131  flatly, outwardly extended from this bottom portion  129 ; and the flange  134  extended from an outer edge  131   g  of the base portion  131  in the direction away from the hub  111 . An internal thread portion  121  is formed in the flange  134 . 
     Since the internal thread portion  121  is formed in the flange  134 , and the flange  134  is formed thick in order to fix the spoke  112 , it is possible to increase stiffness. 
     As a result, even when the rim  114  receives impact force from the outside, air leak can be reduced. 
       FIG. 10  is a cross section of a wheel portion according to a fourth embodiment, the embodiment characterized in that a rim  154 B is made as a hollow-cross-section structure including a hollow portion  155 , and that an internal thread portion  157  is formed in a wall portion  156  surrounding the hollow portion  155 . Reference numeral  152  indicates a spoke, and  168  indicates an external thread portion. 
     Since the rim  154 B is made as a hollow-cross-section structure including the hollow portion  155 , and the internal thread portions  157 ,  157  are formed in the wall portions  156 ,  156  surrounding the hollow portion  155 , it is possible to reduce the weight of the rim  154 B. Moreover, by forming the internal thread portions  157 ,  157  in the wall portions  156 ,  156  surrounding the hollow portion  155 , and devising the cross sectional shape of the hollow portion  155 , it is made possible to easily increase the section modulus, and to achieve increase in the stiffness of the wheel. As a result, it is made possible to achieve both of the reduction in the weight and the increase in the stiffness of the wheel  110  (see  FIG. 7 ). 
     Incidentally, reference numeral  158  indicates an extension portion covering the bead portion of the tire from the outside in the axle direction, and the extension portion  158  is disposed substantially collinearly with the wall portion  156 . 
       FIG. 11  is a perspective view of a tubeless-tire wheel according to a fifth embodiment. With regard to the arrangement of spokes  152 B . . . extended from a hub  151 B to a rim  154 B and attached thereto, it is shown that the spokes  152 B are stretched in the substantially radial direction of the rim  154 B. Since the spokes  152 B are stretched in the substantially radial direction of the rim  154 B, it is possible to increase the strength of the whole wheel. 
     It should be noted that the internal thread portion formed in the rim does not have to be formed in the inclined portion. That is, the position at which the internal thread portion formed in the rim is disposed can be freely chosen. 
     Also, the inclined portion provided to the rim does not have to be inclined parallel to the spoke. That is, the inclination angle of the inclined portion can be freely chosen. 
     The thickness of the inclined portion may be formed thinner than those of the adjacent bottom portion and base portion. That is, the thickness of the inclined portion can be freely chosen. 
     In addition, while the present invention is applied to a two-wheeled vehicle such as a motorcycle and a bicycle in the embodiments, the present invention may be applied to general vehicles. 
     Moreover, the present structure may be used for a tube tire. The present structure is effective in being able to eliminate nipples. 
     Although embodiments of the present invention have been described thus far, the present invention is not limited to the examples in the drawings and the embodiments described above, and various modification may be made without departing the scope of the present invention, as a matter of course.