Abstract:
A multiple bicycle sprocket assembly is basically provided that is capable of creating a gear ratio in a wide range. The multiple bicycle sprocket assembly includes a first sprocket and a second sprocket. The first sprocket includes a first tooth number that is less than or equal to ten. The second sprocket includes a second tooth number that is more than or equal to forty-four.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. DE102014018568.0, filed on Dec. 15, 2014 and German Patent Application No. DE102015008454.2, filed on Jul. 1, 2015. The entire disclosures of German Patent Application Nos. DE102014018568.0 and DE102015008454.2 are hereby incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    This invention generally relates to a multiple bicycle sprocket assembly. More specifically, the present invention relates to a multiple bicycle sprocket assembly having a rotational central axis and configured to be mounted on a bicycle hub assembly. 
         [0004]    2. Background Information 
         [0005]    A plurality of rear sprockets are attached to a bicycle rear hub assembly (see EP1342657A2). The respective rear sprockets have different numbers of teeth. A combination of the numbers of teeth of the respective rear sprockets, that is, a tooth combination of the rear sprockets is set according to a characteristic of a course, for example. 
         [0006]    In the case in which a rider attaches importance to riding at a high speed in a course having many flat roads or the like, generally, a sprocket having a small number of teeth is used for the rear sprocket on a top side. On the other hand, in the case in which the rider attaches importance to comfortable riding in a course having many uphills or the like, a sprocket having a large number of teeth is used for the rear sprocket on a low side. 
         [0007]    In the conventional rear sprocket, it is possible to constitute a gear ratio which attaches importance to a speed, but it is difficult to constitute the gear ratio at which pedal stepping is very light. On the other hand, in the conventional rear sprocket, it is possible to constitute the gear ratio at which the pedal stepping is very light, but it is difficult to constitute the gear ratio which attaches importance to the speed. In other words, the conventional rear sprocket does not have such a configuration as to simultaneously satisfy both of the gear ratio which attaches importance to the speed and the gear ratio at which the pedal stepping is light. 
         [0008]    In consideration of the problem, it is an object of the present invention to provide a multiple bicycle sprocket assembly capable of constituting a gear ratio in a wide range. 
       SUMMARY 
       [0009]    Generally, the present disclosure is directed to various features of a multiple bicycle sprocket assembly. 
         [0010]    A multiple bicycle sprocket assembly according to the present invention has a rotational central axis and is configured to be mounted on a bicycle hub assembly. The multiple bicycle sprocket assembly comprises a first sprocket and a second sprocket. The first sprocket has a first tooth number that is less than or equal to ten. The second sprocket has a second tooth number that is more than or equal to forty-four. 
         [0011]    In the multiple bicycle sprocket assembly, the first tooth number of the first sprocket is less than or equal to ten. The second tooth number of the second sprocket is more than or equal to forty-four. In the multiple bicycle sprocket assembly, consequently, it is possible to constitute a gear ratio in a wider range as compared with the conventional configuration. 
         [0012]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The first tooth number is ten that is the smallest tooth number. The second tooth number is forty-six that is the largest tooth number. In this preferred multiple bicycle sprocket assembly, consequently, it is possible to constitute a gear ratio in a wider range. 
         [0013]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The first tooth number is less than or equal to nine. In this preferred multiple bicycle sprocket assembly, consequently, it is possible to constitute a gear ratio in a wider range. 
         [0014]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The first tooth number is nine that is the smallest tooth number. The second tooth number is forty-four that is the largest tooth number. In this preferred multiple bicycle sprocket assembly, consequently, it is possible to constitute a gear ratio in a wider range. 
         [0015]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The first tooth number is ten that is the smallest tooth number. The second tooth number is one among forty-six, forty-eight and fifty that is the largest tooth number. In this preferred multiple bicycle sprocket assembly, consequently, it is possible to constitute a gear ratio in a wider range. 
         [0016]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises at least five additional sprockets. The at least five additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. With this structure, it is possible to constitute a gear ratio in a wide range, and furthermore, to smoothly change the gear ratio between the first sprocket and the second sprocket. 
         [0017]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises five additional sprockets. The five additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. The total sprocket number is seven. With this structure, it is possible to constitute a gear ratio in a wide range while still achieving a low profile design of the multiple sprocket assembly in the axial direction with respect to the rotational central axis, and furthermore, to smoothly change the gear ratio between the first sprocket and the second sprocket. 
         [0018]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises at least eight additional sprockets. The at least eight additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. With this structure, it is possible to constitute a gear ratio in a wide range, and furthermore, to smoothly change the gear ratio between the first sprocket and the second sprocket. 
         [0019]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises nine additional sprockets. The nine additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. The total sprocket number is eleven. With this structure, it is possible to constitute a gear ratio in a wider range, and furthermore, to change the gear ratio more smoothly between the first sprocket and the second sprocket. 
         [0020]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises at least ten additional sprockets. The at least ten additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. With this structure, it is possible to constitute a gear ratio in a wide range, and furthermore, to smoothly change the gear ratio between the first sprocket and the second sprocket. 
         [0021]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The multiple bicycle sprocket assembly further comprises ten additional sprockets. The ten additional sprockets are positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. The total sprocket number is twelve. With this structure, it is possible to constitute a gear ratio in a wider range, and furthermore, to change the gear ratio more smoothly between the first sprocket and the second sprocket. 
         [0022]    In one embodiment the multiple bicycle sprocket assembly may comprise first to twelfth sprockets. In such an embodiment the multiple bicycle sprocket assembly of the present invention may be configured as follows: The first sprocket has a first tooth number that is ten. The second sprocket has a second tooth number that is fifty. The third sprocket has a third tooth number that is twelve. The third sprocket is positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. The fourth sprocket has a fourth tooth number that is forty-four. The fourth sprocket is positioned between the second sprocket and the third sprocket in the axial direction. The fifth sprocket has a fifth tooth number that is fourteen. The fifth sprocket is positioned between the third sprocket and the fourth sprocket in the axial direction. The sixth sprocket has a sixth tooth number that is thirty-eight. The sixth sprocket is positioned between the fourth sprocket and the fifth sprocket in the axial direction. The seventh sprocket has a seventh tooth number that is sixteen. The seventh sprocket is positioned between the fifth sprocket and the sixth sprocket in the axial direction. The eighth sprocket has an eighth tooth number that is thirty-three. The eighth sprocket is positioned between the sixth sprocket and the seventh sprocket in the axial direction. The ninth sprocket has a ninth tooth number that is eighteen. The ninth sprocket is positioned between the seventh sprocket and the eighth sprocket in the axial direction. The tenth sprocket has a tenth tooth number that is twenty-eight. The tenth sprocket is positioned between the eighth sprocket and the ninth sprocket in the axial direction. The eleventh sprocket has an eleventh tooth number that is twenty-one. The tenth sprocket is positioned between the ninth sprocket and the tenth sprocket in the axial direction. The twelfth sprocket has a twelfth tooth number that is twenty-four. The twelfth sprocket is positioned between the tenth sprocket and the eleventh sprocket in the axial direction. The total sprocket number is twelve. 
         [0023]    In another embodiment where the multiple bicycle sprocket assembly comprises first to twelfth sprockets the multiple bicycle sprocket assembly of the present invention may be configured as follows. The first sprocket has a first tooth number that is ten. The second sprocket has a second tooth number that is forty-eight. The third sprocket has a third tooth number that is twelve. The third sprocket is positioned between the first sprocket and the second sprocket in an axial direction parallel to the rotational central axis. The fourth sprocket has a fourth tooth number that is forty-two. The fourth sprocket is positioned between the second sprocket and the third sprocket in the axial direction. The fifth sprocket has a fifth tooth number that is fourteen. The fifth sprocket is positioned between the third sprocket and the fourth sprocket in the axial direction. The sixth sprocket has a sixth tooth number that is thirty-six. The sixth sprocket is positioned between the fourth sprocket and the fifth sprocket in the axial direction. The seventh sprocket having a seventh tooth number that is sixteen. The seventh sprocket is positioned between the fifth sprocket and the sixth sprocket in the axial direction. The eighth sprocket has an eighth tooth number that is thirty-two. The eighth sprocket is positioned between the sixth sprocket and the seventh sprocket in the axial direction. The ninth sprocket has a ninth tooth number that is eighteen. The ninth sprocket is positioned between the seventh sprocket and the eighth sprocket in the axial direction. The tenth sprocket has a tenth tooth number that is twenty-eight. The tenth sprocket is positioned between the eighth sprocket and the ninth sprocket in the axial direction. The eleventh sprocket has an eleventh tooth number that is twenty-one. The eleventh sprocket is positioned between the ninth sprocket and the tenth sprocket in the axial direction. The twelfth sprocket has a twelfth tooth number that is twenty-four. The twelfth sprocket is positioned between the tenth sprocket and the eleventh sprocket in the axial direction. The total sprocket number is twelve. 
         [0024]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The axial length of each space between axially adjacent sprockets is 2.18 mm. 
         [0025]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The axial length of each space between axially adjacent sprockets is 2.2 mm when the bicycle is to be equipped with a thick tire. 
         [0026]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The axial thickness of each of the first sprocket, the second sprocket and the additional sprockets is 1.6 mm. 
         [0027]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The total axial length between the first sprocket and the second sprocket is 24.28 mm when the total sprocket number is seven. 
         [0028]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The total axial length between the first sprocket and the second sprocket is 39.4 mm when the total sprocket number is eleven. 
         [0029]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The total axial length between the first sprocket and the second sprocket is 43.4 mm when the total sprocket number is twelve. 
         [0030]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The second sprocket includes at least one shift assist projection. Consequently, it is possible to smoothly move a chain from a smaller adjacent sprocket to the second sprocket. 
         [0031]    The multiple bicycle sprocket assembly of the present invention may be configured as follows. The first sprocket is configured to be mounted to the bicycle hub assembly via a mounting adapter. Even if the number of the sprockets is increased, consequently, the sprockets can easily be attached to the hub assembly. 
         [0032]    In the multiple bicycle sprocket assembly according to the present invention, it is possible to constitute a gear ratio in a wider range. In the multiple bicycle sprocket assembly according to the present invention, moreover, it is possible to change the gear ratio more smoothly between the first sprocket and the second sprocket. 
         [0033]    Also other objects, features, aspects and advantages of the disclosed a multiple bicycle sprocket assembly will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses selected illustrative embodiments of the multiple bicycle sprocket assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Referring now to the attached drawings which form a part of this original disclosure: 
           [0035]      FIG. 1  is a side elevational view of a bicycle that is equipped with a multiple bicycle sprocket assembly in accordance with first to fifth illustrated embodiments; 
           [0036]      FIG. 2  is a detailed view of a rear hub assembly according to the first to the fifth embodiments; 
           [0037]      FIG. 3  is an exploded view of a first tubular member and a second tubular member on the rear hub assembly according to the first to the fifth embodiments; 
           [0038]      FIG. 4  is a front view and a side view of a rear sprocket assembly according to the first embodiment; 
           [0039]      FIG. 5  is a front view and a side view of a rear sprocket assembly according to the second embodiment; 
           [0040]      FIG. 6  is a front view and a side view of a rear sprocket assembly according to the third embodiment; 
           [0041]      FIG. 7  is a front view and a side view of a rear sprocket assembly according to the fourth embodiment; 
           [0042]      FIG. 8  is a front view of a rear sprocket assembly according to the fifth embodiment; and 
           [0043]      FIG. 9  is a side view of a rear sprocket assembly according to the fifth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0044]    Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the bicycle field from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
       First Embodiment 
       [0045]    Referring initially to  FIG. 1 , a bicycle  1  is illustrated that is configured in accordance with a first embodiment. The bicycle  1  mainly includes a frame  11 , a handle  13 , a front hub assembly  15 , a rear hub assembly  29 , front and rear wheels  17 ,  19 , front and rear brake devices  21 ,  23 , a gear change portion  30 , and a driving portion  25 . 
         [0046]    The frame  11  has a frame body  11   a  and a front fork  11   b . The front fork  11   b  is rotatably attached to the frame body  11   a . The handle  13  is fixed to the front fork  11   b.    
         [0047]    The front hub assembly  15  is supported on the front fork  11   b . The front hub assembly  15  mainly has a front hub shaft  15   a  and a front hub shell (not shown). Both ends of the front hub shaft  15   a  are held on the front fork  11   b . The front hub shell is provided rotatably with respect to the front hub shaft  15   a . The front wheel  17  (e.g. spokes) is attached to the front hub shell. 
         [0048]    The front and rear wheels  17 ,  19  are rotatably attached to the front fork  11   b  and a rear portion of the frame  11  through the front hub assembly  15  and the rear hub assembly  29 , respectively. 
         [0049]    The front and rear brake devices  21 ,  23  are operated by manipulation of a brake lever  14 . Since the front and rear brake devices  21 ,  23  have the same configuration as those in the conventional configuration, description will be omitted. 
         [0050]    The gear change portion  30  is attached to the frame  11 . The gear change portion  30  includes a front derailleur  31  and a rear derailleur  33 . The front derailleur  31  moves a bicycle chain  9  from a front sprocket to an adjacent front sprocket by a shift operation of a shift lever (not shown) attaching to, e.g. the left side of the handle  13 . The front derailleur  31  is attached to a seat tube of the frame  11  in the illustrated embodiment. The rear derailleur  33  moves the bicycle chain  9  from a rear sprocket to an adjacent rear sprocket by a shift operation of a shift lever  33   a  attaching to, e.g. the right side of the handle  13 . The rear derailleur  33  is attached to a connecting portion of a chain stay and a seat stay of the frame  11 . 
         [0051]    The driving portion  25  mainly has a crank assembly  27 , a rear hub assembly  29  and a rear sprocket assembly  50  (an example of a multiple bicycle sprocket assembly). 
         [0052]    The crank assembly  27  includes a crank shaft (not shown), a right crank arm  27   a  and a left crank arm (not shown). The crank shaft is roratably supported on a lower portion of the frame  11 , for example, on a bottom bracket hanger portion. Base ends of the right crank arm  27   a  and the left crank arm are attached unrotatably to both ends of the crank shaft, respectively. A pedal  34  is attached to distal end of the right crank arm  27   a  and distal end of the left crank arm. A front sprocket assembly  27   b  having the same configuration as that in the conventional configuration is attached to the right crank arm  27   a  so as to be integrally rotatable. The front sprocket assembly  27   b  has at least one front sprocket. For example, the front sprocket assembly  27   b  has two front sprockets in the illustrated embodiment. 
         [0053]    As shown in  FIGS. 1 and 2 , the rear hub assembly  29  is supported on the rear part of the frame  11 . The rear hub assembly  29  has a rear hub shaft  35 , a rear hub shell  37 , a first tubular member  41  and a second tubular member  43  (an example of a mounting adapter). 
         [0054]    The rear hub shaft  35  is held on the rear part of the frame  11  with a conventional wheel securing mechanism  49 . The wheel securing mechanism  49  is the same as the conventional mechanism. The wheel securing mechanism  49  has a draw bar  49   a , a stationary nut  49   b  and a movable nut  49   c , for example. The draw bar  49   a  is extended along the rear hub shaft  35 . The stationary nut  49   b  is screwed at one of ends of the draw bar  49   a . The movable nut  49   c  is disposed on the other end of the draw bar  49   a . The movable nut  49   c  is movable in an axial direction by a conventional cam mechanism. The stationary nut  49   b  and the movable nut  49   c  clamp the rear hub shaft  35  to the frame  11  when a lever  49   d  is operated. 
         [0055]    The rear hub shell  37  is supported rotatably with respect to the rear hub shaft  35 . The rear wheel  19  (e.g. spokes) is attached to the rear hub shell  37 . 
         [0056]    The rear hub shell  37  is rotatable around a shaft center C (an example of a rotational central axis) of the rear hub shaft  35 . One of ends (a left side in  FIG. 2 ) of the rear hub shell  37  is rotatably supported on the rear hub shaft  35  through a bearing assembly  39 . An outer race  39   a  of the bearing assembly  39  is fixed to an inner peripheral surface at one of the ends of the rear hub shell  37 . An inner race  39   b  of the bearing assembly  39  is fixed to the rear hub shaft  35  by a lock nut  48  and spacer  48   a . Ball bearings  39   c  are disposed between the outer race  39   a  of the bearing assembly  39  and the inner race  39   b  of the bearing assembly  39 . 
         [0057]    On the other hand, the other end (a right side in  FIG. 2 ) of the rear hub shell  37  is unrotatably supported on an inner member  47  disposed on an inner peripheral side of the first tubular member  41  (described later) by a spline structure  38 . The spline structure  38  comprises splines on an inner peripheral surface at the other end of the rear hub shell  37  and splines on an outer peripheral surface at one of ends (the left side in  FIG. 2 ) of the inner member  47 . 
         [0058]    The inner member  47  is rotatable around the shaft center C of the rear hub shaft  35 . For example, the other end (the right side in  FIG. 2 ) of the inner member  47  is rotatably supported on the rear hub shaft  35  through the bearing assembly  69 . An outer race  69   a  of the bearing assembly  69  is fixed to an outer peripheral surface at the other end of the inner member  47 . An inner race  69   b  of the bearing assembly  69  is fixed to the rear hub shaft  35  by a lock nut  71  and a spacer  71   b . Ball bearings  69   c  are disposed between the outer race  69   a  of the bearing assembly and the inner race  69   b  of the bearing assembly. Thus, the other end of the rear hub shell  37  and the inner member  47  are rotatably supported on the rear hub shaft  35  through the bearing assembly  69 . Ratchet pawls  47   a  are formed on the outer peripheral portion of the inner member  47 . 
         [0059]    The first tubular member  41  is rotatable around the shaft center C of the rear hub shaft  35  as shown in  FIG. 3 . The first tubular member  41  has a first body portion  41   a , a plurality of first splines  41   b , a plurality of ratchet teeth  41   c  and a first female screw portion  41   d . The first body portion  41   a  is formed in a tubular shape. The first splines  41   b  are formed integrally with the outer peripheral portion of the first body portion  41   a . A rear sprocket assembly  50  (a first rear sprocket assembly  51 ; described later) is mounted to the first splines  41   b.    
         [0060]    The ratchet teeth  41   c  are formed integrally with the inner peripheral portion of the first body portion  41   a . The ratchet teeth  41   c  are engaged with the ratchet pawls  47   a  of the inner member  47 . A one-way clutch used conventionally is configured by the engagement of the ratchet teeth  41   c  and the ratchet pawls  47   a.    
         [0061]    The first female screw portion  41   d  is formed on an inner peripheral surface at the end of the first body portion  41   a , for example, an inner peripheral surface at the end of the second tubular member  43  side. A second male screw portion  43   e  (described later) of the second tubular member  43  is screwed with the first female screw portion  41   d . Moreover, a screw hole portion  41   e  is formed at the end where the first female screw portion  41   d  is formed on the first body portion  41   a . The screw hole portion  41   e  penetrates from the outer peripheral surface toward the inner peripheral surface. 
         [0062]    The first body portion  41   a  is rotatably supported on the inner member  47  through ball bearings  42   a ,  42   b . For example, the ball bearings  42   a ,  42   b  are disposed on both sides of the ratchet teeth  41   c  in a direction along the rotation axis of the first body portion  41   a . The ball bearings  42   a  are disposed between the inner peripheral surface of the first body portion  41   a  and one end side (the left side in  FIG. 2 ) of the outer peripheral portion of the inner member  47 . Moreover, the ball bearings  42   b  are disposed between the inner peripheral surface of the first body portion  41   a  and an outer race  69   a  of the bearing assembly  69 . 
         [0063]    The second tubular member  43  is rotatable around the shaft center C of the rear hub shaft  35 . The second tubular member  43  has a second body portion  43   a , a coupling portion  43   b , a plurality of second splines  43   c , and a first male screw portion  43   d . The second body portion  43   a  is formed in a tubular shape. The outside diameter of the second body portion  43   a  is smaller than the outside diameter of the first body portion  41   a . The coupling portion  43   b  is coupled to the first tubular member  41  (the first body portion  41   a ). The coupling portion  43   b  is formed in a flange shape and is provided integrally with one of the ends (the left side in  FIG. 2 ) of the second body portion  43   a . The second male screw portion  43   e  is formed on the outer peripheral portion of the coupling portion  43   b . Moreover, a groove portion  43   f  extended in a circumferential direction is formed on the outer peripheral portion of the coupling portion  43   b.    
         [0064]    The second male screw portion  43   e  is screwed into the first female screw portion  41   d  of the first tubular member  41  (the first body portion  41   a ). In this condition, a clamping member such as a screw member  44  is screwed into the screw hole portion  41   e  of the first tubular member  41  (the first body portion  41   a ) and is engaged with the groove portion  43   f . Thus, the first tubular member  41  and the second tubular member  43  are coupled to each other. 
         [0065]    The second splines  43   c  are formed integrally with the outer peripheral portion of the second body portion  43   a . A rear sprocket assembly  50  (a second rear sprocket assembly  52 ; described later) is attached to the second splines  43   c.    
         [0066]    The first male screw portion  43   d  is formed on the outer peripheral surface (the right side in  FIG. 2 ) at the other end of the second body portion  43   a . A second female screw portion  71   a  of a lock nut  71  is screwed to the first male screw portion  43   d . For example, the second female screw portion  71   a  of the lock nut  71  is screwed to the first male screw portion  43   d  of the second tubular member  43  in a state in which the rear sprocket assembly  50  is mounted to the rear hub assembly  29  (the first tubular member  41  and the second tubular member  43 ). 
         [0067]    The rear sprocket assembly  50  is configured to be mounted on the rear hub assembly  29 . The rear sprocket assembly  50  has a rotational central axis. The rotational central axis corresponds to the rear hub shaft  35  or the shaft center C of the rear hub shaft  35 . 
         [0068]    The rear sprocket assembly  50  is mounted to the first tubular member  41  and the second tubular member  43 . The rear sprocket assembly  50  has a plurality of rear sprockets  50 A- 50 K. 
         [0069]    As shown in  FIG. 4 , the rear sprocket assembly  50  has a first rear sprocket assembly  51  and a second rear sprocket assembly  52 . 
         [0070]    The first rear sprocket assembly  51  is mounted to the first tubular member  41  (the first body portion  41   a ). The first rear sprocket assembly  51  has first to ninth rear sprockets  50 A- 50 I. The first to ninth rear sprockets  50 A- 50 I are arranged on the outer peripheral portion of the first tubular member  41  in an axial direction parallel to the shaft center C of the rear hub shaft  35 . The first rear sprocket  50 A is disposed on the outer peripheral portion of the first tubular member  41  on a side of the rear hub shell  37 . A spacer (not shown) is disposed between two sprockets which are adjacent to each other in the first to ninth rear sprockets  50 A- 50 I. Instead of such a spacer, some of the first to ninth rear sprockets  50 A- 50 I may be fixed to a sprocket support member (not shown) such that the sprockets fixed to the sprocket support member are mounted to the first tubular member  41  through the sprocket support member. 
         [0071]    More specifically, first hole portions  53  are formed on the respective inner peripheral portions of the first to ninth rear sprockets  50 A- 50 I. A plurality of third splines  53   a  are formed on each of the first hole portions  53 . The third splines  53   a  are engaged with the first splines  41   b  (see  FIG. 3 ) on the first tubular member  41 , respectively. Thus, the first to ninth rear sprockets  50 A- 50 I are engaged with the first tubular member  41  so that the first to ninth rear sprockets  50 A- 50 I are arranged on the outer peripheral portion of the first tubular member  41 . 
         [0072]    The second rear sprocket assembly  52  is attached to the second tubular member  43  (the second body portion  43   a ). The second rear sprocket assembly  52  has tenth and eleventh rear sprockets  50 J,  50 K. The tenth and eleventh rear sprockets  50 J,  50 K are arranged on the outer peripheral portion of the second tubular member  43  in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The tenth rear sprocket  50 J is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the ninth rear sprocket  50 I in the axial direction. The eleventh rear sprocket  50 K is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the tenth rear sprocket  50 J at the most distant position from the first rear sprocket  50 A in the axial direction. A spacer (not shown) is disposed between the two sprockets which are adjacent to each other in the tenth and eleventh rear sprockets  50 J,  50 K. 
         [0073]    More specifically, a second hole portion  55  is formed on the respective inner peripheral portions of the tenth and eleventh rear sprockets  50 J,  50 K. A plurality of fourth splines  55   a  are formed on the second hole portion  55 . The fourth splines  55   a  are engaged with the second splines  43   c  of the second tubular member  43 , respectively. Thus, the tenth and eleventh rear sprockets  50 J,  50 K are engaged with the second tubular member  43  so that the tenth and eleventh rear sprockets  50 J,  50 K are arranged on the outer peripheral portion of the second tubular member  43 . 
         [0074]    As described above, the first rear sprocket assembly  51  is attached to the first tubular member  41  (the first body portion  41   a ). Moreover, the second rear sprocket assembly  52  is attached to the second tubular member  43  (the second body portion  43   a ). In this condition, the lock nut  71  (the second female screw portion  71   a ; see  FIG. 2 ) is screwed with the second tubular member  43  (the first male screw portion  43   d ) so that the rear sprocket assembly  50  (the first rear sprocket assembly  51  and the second rear sprocket assembly  52 ) is fixed to the rear hub assembly  29 . 
         [0075]    The first rear sprocket  50 A is an example of a second rear sprocket. The second to ten rear sprockets  50 B- 50 J are an example of at least five additional sprockets, at least eight additional sprockets, and nine additional sprockets. The eleventh rear sprocket  50 K is an example of a first sprocket. 
         [0076]    Layouts of the first to eleventh rear sprockets  50 A- 50 K will be described below in detail. The first to eleventh rear sprockets  50 A- 50 K are arranged on the first tubular member  41  and the second tubular member  43  in alphabetical order. 
         [0077]    Specifically, the second to tenth rear sprockets  50 B- 50 J are positioned between the first rear sprocket  50 A and the eleventh rear sprocket  50 K in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The second rear sprocket  50 B is positioned between the first rear sprocket  50 A and the third rear sprocket  50 C in the axial direction. The third rear sprocket  50 C is positioned between the second rear sprocket  50 B and the fourth rear sprocket  50 D in the axial direction. The fourth rear sprocket  50 D is positioned between the third rear sprocket  50 C and the fifth rear sprocket  50 E in the axial direction. The fifth rear sprocket  50 E is positioned between the fourth rear sprocket  50 D and the sixth rear sprocket  50 F in the axial direction. 
         [0078]    The sixth rear sprocket  50 F is positioned between the fifth rear sprocket  50 E and the seventh rear sprocket  50 G in the axial direction. The seventh rear sprocket  50 G is positioned between the sixth rear sprocket  50 F and the eighth rear sprocket  50 H in the axial direction. The eighth rear sprocket  50 H is positioned between the seventh rear sprocket  50 G and the ninth rear sprocket  50 I in the axial direction. The ninth rear sprocket  50 I is positioned between the eighth rear sprocket  50 H and the tenth rear sprocket  50 J in the axial direction. The tenth rear sprocket  50 J is positioned between the ninth rear sprocket  50 I and the eleventh rear sprocket  50 K in the axial direction. 
         [0079]    In other words, the second rear sprocket  50 B is positioned between the first rear sprocket  50 A and the tenth rear sprocket  50 J in the axial direction. The third rear sprocket  50 C is positioned between the second rear sprocket  50 B and the ninth rear sprocket  50 I in the axial direction. The fourth rear sprocket  50 D is positioned between the third rear sprocket  50 C and the eighth rear sprocket  50 H in the axial direction. The fifth rear sprocket  50 E is positioned between the fourth rear sprocket  50 D and the seventh rear sprocket  50 G in the axial direction. 
         [0080]    The sixth rear sprocket  50 F is positioned between the fifth rear sprocket  50 E and the seventh rear sprocket  50 G in the axial direction. The seventh rear sprocket  50 G is positioned between the fourth rear sprocket  50 D and the eighth rear sprocket  50 H in the axial direction. The eighth rear sprocket  50 H is positioned between the third rear sprocket  50 C and the ninth rear sprocket  50 I in the axial direction. The ninth rear sprocket  50 I is positioned between the second rear sprocket  50 B and the tenth rear sprocket  50 J in the axial direction. The tenth rear sprocket  50 J is positioned between the first rear sprocket  50 A and the eleventh rear sprocket  50 K in the axial direction. 
         [0081]    Finally, the configuration and the tooth combination of the first to eleventh rear sprocket  50 A- 50 K will be described in detail. A root circle diameter of the first rear sprocket  50 A is the largest in the first to eleventh rear sprocket  50 A- 50 K. Root circle diameters of the second to tenth sprockets  50 B- 50 J are gradually reduced in order of the second to tenth sprockets  50 B- 50 J. A root circle diameter of the eleventh sprocket is the smallest in the first to eleventh rear sprocket  50 A- 50 K. 
         [0082]    The first rear sprocket  50 A preferably includes at least one shift assist projection  54 . The shift assist projection  54  catches the chain prior to sprocket teethe of the first sprocket  50 A when the rear derailleur  33  moves the chain from the second rear sprocket  50 B to the first rear sprocket  50 A. For example, the first rear sprocket  50 A includes two shift assist projections  54 . The two shift assist projections  54  are provided on the outer peripheral portion of the first rear sprocket  50 A on the side of the second rear sprocket  50 B. The two shift assist projections  54  are disposed at a predetermined interval around the rear hub shaft  35  (in a circumferential direction). 
         [0083]    The axial thickness T 1  of each of the first to the eleventh rear sprockets  50 A- 50 K is 1.6 mm. The axial length L 1  of each space between the axially adjacent rear sprockets is 2.18 mm. The total axial length TL 1  between the first rear sprocket  50 A and the eleventh rear sprocket  50 K is 39.4 mm. The total axial length TL 1  represents a distance between a surface of the first rear sprocket  50 A on an opposite side of the second rear sprocket  50 B and a surface of the eleventh rear sprocket  50 K on an opposite side to the tenth rear sprocket  50 J. 
         [0084]    The first rear sprocket  50 A has a first tooth number (an example of a second tooth number). The first tooth number is more than or equal to forty-four. In the embodiment, for example, the first tooth number is forty-four that is the largest tooth number. 
         [0085]    The second rear sprocket  50 B has a second tooth number. The second tooth number is thirty eight. The third rear sprocket  50 C has a third tooth number. The third tooth number is thirty two. The fourth rear sprocket  50 D has a fourth tooth number. The fourth tooth number is twenty seven. The fifth rear sprocket  50 E has a fifth tooth number. The fifth tooth number is twenty three. The sixth rear sprocket  50 F has a sixth tooth number. The sixth tooth number is twenty. The seventh rear sprocket  50 G has a seventh tooth number. The seventh tooth number is seventeen. The eighth rear sprocket  50 H has an eighth tooth number. The eighth tooth number is fifteen. The ninth rear sprocket  50 I has a ninth tooth number. The ninth tooth number is thirteen. The tenth rear sprocket  50 J has a tenth tooth number. The tenth tooth number is eleven. 
         [0086]    The eleventh rear sprocket  50 K has an eleventh tooth number (an example of a first tooth number). The eleventh tooth number is less than or equal to ten. Specifically, the eleventh tooth number is less than or equal to nine. In the embodiment, for example, the eleventh tooth number is nine that is the smallest tooth number. 
       Second Embodiment 
       [0087]    A configuration of a bicycle employing a second embodiment according to the present invention is substantially identical to that of the first embodiment except for a configuration of a rear sprocket assembly  150 . For this reason, in the second embodiment, the rear sprocket assembly  150  will be described in detail and explanation of the other configuration will be omitted. The configurations omitted herein conform to the configuration according to the first embodiment. The same configurations as those in the first embodiment have the same reference numerals. 
         [0088]    As shown in  FIGS. 2 and 5 , the rear sprocket assembly  150  is configured to be mounted on the rear hub assembly  29 . The rear sprocket assembly  150  has a rotational central axis. The rotational central axis corresponds to the rear hub shaft  35  or the shaft center C of the rear hub shaft  35 . 
         [0089]    The rear sprocket assembly  150  is attached to the first tubular member  41  (the first body portion  41   a ) and the second tubular member  43  (the second body portion  43   a ). The rear sprocket assembly  150  has a plurality of rear sprockets  150 A- 150 G. 
         [0090]    The first to sixth rear sprockets  150 A- 150 F are disposed on the outer peripheral portion of the first tubular member  41  in an axial direction parallel to the shaft center C of the rear hub shaft  35 . The first rear sprocket  150 A is disposed on the outer peripheral portion of the first tubular member  41  at the rear hub shell  37  side. The first to sixth rear sprockets  150 A- 150 F are arranged on the outer peripheral portion of the first tubular member  41  by the same spline coupling as that in the first embodiment. 
         [0091]    The seventh rear sprockets  150 G are disposed on the outer peripheral portion of the second tubular member  43  in an axial direction parallel to the shaft center C of the rear hub shaft  35 . The seventh rear sprocket  150 G is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the sixth rear sprocket  150 F at the most distant position from the first rear sprocket  150 A in the axial direction. The seventh rear sprocket  150 G is arranged on the outer peripheral portion of the second tubular member  43  by the same spline coupling as that in the first embodiment. 
         [0092]    The first rear sprocket  150 A is an example of a second sprocket. The second to sixth rear sprockets  150 F are an example of five additional sprockets. The seventh rear sprocket  150 G is an example of a first sprocket. 
         [0093]    In the second embodiment, the first tubular member  41  is formed so as to be shorter than that of the first embodiment in the axial direction. The second tubular member  43  is formed so as to be shorter than that of the first embodiment in the axial direction. Total number of the first to sixth rear sprockets  150 A- 150 F is smaller than total number of the first to ninth rear sprockets  50 A- 50 I in the first embodiment. Also, number of the seventh rear sprocket  150 G is smaller than number of the tenth and eleventh rear sprockets  50 J,  50 K in the first embodiment. 
         [0094]    Layouts of the first to seventh rear sprockets  150 A- 150 G will be described below in detail. The first to seventh rear sprockets  150 A- 150 G are arranged on the first tubular member  41  in alphabetical order. 
         [0095]    Specifically, the second to sixth rear sprockets  150 B- 150 F are positioned between the first rear sprocket  150 A and the seventh rear sprocket  150 G in the axial direction parallel to the shaft center C of the rear hub shaft  35 . 
         [0096]    The second rear sprocket  150 B is positioned between the first rear sprocket  150 A and the third rear sprocket  150 C in the axial direction. The third rear sprocket  150 C is positioned between the second rear sprocket  150 B and the fourth rear sprocket  150 D in the axial direction. The fourth rear sprocket  150 D is positioned between the third rear sprocket  150 C and the fifth rear sprocket  150 E in the axial direction. The fifth rear sprocket  150 E is positioned between the fourth rear sprocket  150 D and the sixth rear sprocket  150 F in the axial direction. The sixth rear sprocket  150 F is positioned between the fifth rear sprocket  150 E and the seventh rear sprocket  150 G in the axial direction. 
         [0097]    In other words, the sixth rear sprocket  150 F is positioned between the first rear sprocket  150 A and the seventh rear sprocket  150 G in the axial direction. The second rear sprocket  150 B is positioned between the first rear sprocket  150 A and the sixth rear sprocket  150 F in the axial direction. The fifth rear sprocket  150 E is positioned between the second rear sprocket  150 B and the sixth rear sprocket  150 F in the axial direction. The third rear sprocket  150 C is positioned between the second rear sprocket  150 B and the fifth rear sprocket  150 E in the axial direction. The fourth rear sprocket  150 D is positioned between the third rear sprocket  150 C and the fifth rear sprocket  150 E in the axial direction. 
         [0098]    Finally, a configuration and a tooth combination of the first to seventh rear sprockets  150 A- 150 G will be described in detail. A root circle diameter of the first rear sprocket  150 A is the largest in the first to seventh rear sprockets  150 A- 150 G. Root circle diameters of the second to sixth sprockets  150 B- 150 F are gradually reduced in order of the second to sixth sprockets  150 B- 150 F. A root circle diameter of the seventh sprocket  150 G is the smallest in the first to seventh rear sprockets  150 A  150 G. 
         [0099]    The first rear sprocket  150 A preferably includes at least one shift assist projection  154 . For example, the first rear sprocket  150 A includes two shift assist projections  154 . The two shift assist projections  154  are provided on the outer peripheral portion of the first rear sprocket  150 A. The two shift assist projections  154  are disposed at a predetermined interval around the rear hub shaft  35  (in a circumferential direction). 
         [0100]    The axial thickness T 2  of each of the first to the seventh rear sprockets  150 A- 150 G is 1.6 mm. The axial length L 2  of each space between the axially adjacent rear sprockets is 2.18 mm. The total axial length TL 2  between the first rear sprocket  150 A and the seventh rear sprocket  150 G is 24.28 mm. The total axial length TL 2  represents a distance between a surface of the first rear sprocket  150 A on an opposite side to the second rear sprocket  150 B and a surface of the seventh rear sprocket  150 G on an opposite side to the sixth rear sprocket  150 F. 
         [0101]    The first rear sprocket  150 A has a first tooth number (an example of a second tooth number). The first tooth number is more than or equal to forty-four. In the embodiment, for example, the first tooth number is forty-six that is the largest tooth number. 
         [0102]    The second rear sprocket  150 B has a second tooth number. The second tooth number is thirty six. The third rear sprocket  150 C has a third tooth number. The third tooth number is twenty eight. The fourth rear sprocket  150 D has a fourth tooth number. The fourth tooth number is twenty two. The fifth rear sprocket  150 E has a fifth tooth number. The fifth tooth number is seventeen. The sixth rear sprocket  150 F has a sixth tooth number. The sixth tooth number is thirteen. 
         [0103]    The seventh rear sprocket  150 G has a seventh tooth number (an example of a first tooth number). The seventh tooth number is less than or equal to ten. In the embodiment, for example, the seventh tooth number is ten that is the smallest tooth number. 
       Third Embodiment 
       [0104]    A configuration of a bicycle employing a third embodiment according to the present invention is substantially identical to that of the first embodiment except for a configuration of a rear sprocket assembly  250 . Moreover, the configuration of the rear sprocket assembly  250  is substantially identical to that of the second embodiment except for configuration of rear sprockets  250 A- 250 G. 
         [0105]    For this reason, in the third embodiment, layouts of the rear sprockets  250 A- 250 G will be described in detail and explanation of the other configuration will be omitted. The configurations omitted herein conform to the configuration according to the first and second embodiments. The same configurations as those in the first and second embodiments have the same reference numerals. 
         [0106]    As shown in  FIG. 2  and  FIG. 6 , the rear sprocket assembly  250  is attached to the first tubular member  41  (the first body portion  41   a ) and the second tubular member  43  (the second body portion  43   a ). The rear sprocket assembly  250  has a plurality of rear sprockets  250 A- 250 G. 
         [0107]    The first to sixth rear sprockets  150 A- 150 F are disposed on the outer peripheral portion of the first tubular member  41  in the same manner as the second embodiment. The seventh rear sprocket  150 G is disposed on the outer peripheral portion of the second tubular member  43  in the same manner as the second embodiment. 
         [0108]    The first to seventh rear sprockets  150 A- 150 G is arranged respectively on the outer peripheral portions of the first and second tubular member  41 ,  43  by the same spline coupling as that in the first embodiment. 
         [0109]    A root circle diameter of the first rear sprocket  250 A is the largest in the first to seventh rear sprockets  250 A- 250 G. Root circle diameters of the second to sixth sprockets  250 B- 250 F are gradually reduced in order of the second to sixth sprockets  250 B- 250 F. A root circle diameter of the seventh rear sprocket  250 G is the smallest in the first to seventh rear sprockets  250 A- 250 G. 
         [0110]    The first rear sprocket  250 A preferably includes at least one shift assist projection  254 . For example, the first rear sprocket  250 A includes two shift assist projections  254 . The two shift assist projections  254  are provided on the outer peripheral portion of the first rear sprocket  250 A. The two shift assist projections  254  are disposed at a predetermined interval around the rear hub shaft  35  (in a circumferential direction). 
         [0111]    The axial thickness T 3  of each of the first to the seventh rear sprockets  250 A- 250 G is 1.6 mm. The axial length L 3  of each space between the axially adjacent rear sprockets is 2.18 mm. The total axial length TL 3  between the first rear sprocket  250 A and the eleventh rear sprocket  250 K is 24.28 mm. The total axial length TL 3  represents a distance between a surface of the first rear sprocket  250 A on an opposite side to the second rear sprocket  250 B and a surface of the seventh rear sprocket  250 G on an opposite side to the sixth rear sprocket  250 F. 
         [0112]    The first rear sprocket  250 A has a first tooth number (an example of a second tooth number). The first tooth number is more than or equal to forty-four. In the embodiment, for example, the first tooth number is fifty that is the largest tooth number. 
         [0113]    The second rear sprocket  250 B has a second tooth number. The second tooth number is thirty eight. The third rear sprocket  250 C has a third tooth number. The third tooth number is twenty nine. The fourth rear sprocket  250 D has a fourth tooth number. The fourth tooth number is twenty two. The fifth rear sprocket  250 E has a fifth tooth number. The fifth tooth number is seventeen. The sixth rear sprocket  250 F has a sixth tooth number. The sixth tooth number is thirteen. 
         [0114]    The seventh rear sprocket  250 G has a seventh tooth number (an example of a first tooth number). The seventh tooth number is less than or equal to ten. In the embodiment, for example, the seventh tooth number is ten that is the smallest tooth number. 
       Fourth Embodiment 
       [0115]    A configuration of a bicycle employing a fourth embodiment according to the present invention is substantially identical to that of the first embodiment except for a configuration of a rear sprocket assembly  350 . For this reason, in the fourth embodiment, the rear sprocket assembly  350  will be described in detail and explanation of the other configuration will be omitted. The configurations omitted herein conform to the configuration according to the first embodiment. The same configurations as those in the first embodiment have the same reference numerals. 
         [0116]    As shown in  FIGS. 2 and 7 , the rear sprocket assembly  350  is configured to be mounted on the rear hub assembly  29 . The rear sprocket assembly  350  has a rotational central axis. The rotational central axis corresponds to the rear hub shaft  35  or a shaft center C of the rear hub shaft  35 . 
         [0117]    The rear sprocket assembly  350  is attached to a first tubular member  41  and a second tubular member  43 . The rear sprocket assembly  350  has a plurality of rear sprockets  350 A- 350 L. 
         [0118]    For example, the rear sprocket assembly  350  has a first rear sprocket assembly  351  and a second rear sprocket assembly  352 . 
         [0119]    The first rear sprocket assembly  351  is attached to the first tubular member  41  (the first body portion  41   a ). The first rear sprocket assembly  351  has first to ninth rear sprockets  350 A- 350 I. The first to ninth rear sprockets  350 A- 350 I are arranged on the outer peripheral portion of the first tubular member  41  in an axial direction parallel to the shaft center C of the rear hub shaft  35 . The first rear sprocket  350 A is disposed on the outer peripheral portion of the first tubular member  41  at a rear hub shell  37  side. The first to ninth rear sprockets  350 A- 350 I are arranged on the outer peripheral portion of the first tubular member  41  by the same spline coupling as that in the first embodiment. 
         [0120]    The second rear sprocket assembly  352  is attached to the second tubular member  43  (the second body portion  43   a ). The second rear sprocket assembly  352  has tenth to twelfth rear sprockets  350 J- 350 L. The tenth to twelfth rear sprockets  350 J- 350 L are arranged on the outer peripheral portion of the second tubular member  43  in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The tenth rear sprocket  350 J is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the ninth rear sprocket  350 I in the axial direction. The eleventh rear sprocket  350 K is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the tenth rear sprocket  350 J in the axial direction. The twelfth rear sprocket  350 K is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the eleventh rear sprocket  350 K at the most distant position from the first rear sprocket  350 A in the axial direction. 
         [0121]    The first rear sprocket  350 A is an example of a second sprocket. The second to eleventh rear sprockets  350 B- 350 K are an example of at least five additional sprockets, and at least eight additional rear sprockets. The twelfth rear sprocket  350 L is an example of a first sprocket. 
         [0122]    Layouts of the first to twelfth rear sprockets  350 A- 350 L will be described below in detail. The first to twelfth rear sprockets  350 A- 350 L are arranged on the first tubular member  41  and the second tubular member  43  in alphabetical order. 
         [0123]    Specifically, the second to eleventh rear sprockets  350 B- 350 K are positioned between the first rear sprocket  350 A and the twelfth rear sprocket  350 L in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The second rear sprocket  350 B is positioned between the first rear sprocket  350 A and the third rear sprocket  350 C in the axial direction. The third rear sprocket  350 C is positioned between the second rear sprocket  350 B and the fourth rear sprocket  350 D in the axial direction. The fourth rear sprocket  350 D is positioned between the third rear sprocket  350 C and the fifth rear sprocket  350 E in the axial direction. The fifth rear sprocket  350 E is positioned between the fourth rear sprocket  350 D and the sixth rear sprocket  350 F in the axial direction. 
         [0124]    The sixth rear sprocket  350 F is positioned between the fifth rear sprocket  350 E and the seventh rear sprocket  350 G in the axial direction. The seventh rear sprocket  350 G is positioned between the sixth rear sprocket  350 F and the eighth rear sprocket  350 H in the axial direction. The eighth rear sprocket  350 H is positioned between the seventh rear sprocket  350 G and the ninth rear sprocket  350 I in the axial direction. The ninth rear sprocket  350 I is positioned between the eighth rear sprocket  350 H and the tenth rear sprocket  350 J in the axial direction. The tenth rear sprocket  350 J is positioned between the ninth rear sprocket  350 I and the eleventh rear sprocket  350 K in the axial direction. The eleventh rear sprocket  350 K is positioned between the tenth rear sprocket  350 J and the twelfth rear sprocket  350 L in the axial direction. 
         [0125]    In other words, the second rear sprocket  350 B (an example of a fourth sprocket) is positioned between the first rear sprocket  350 A (an example of a second sprocket) and the eleventh rear sprocket  350 K (an example of a third sprocket) in the axial direction. The third rear sprocket  350 C (an example of a sixth sprocket) is positioned between the second rear sprocket  350 B (an example of a fourth sprocket) and the tenth rear sprocket  350 J (an example of a fifth sprocket) in the axial direction. The fourth rear sprocket  350 D (an example of an eighth sprocket) is positioned between the third rear sprocket  350 C (an example of a sixth sprocket) and the ninth rear sprocket  350 I (an example of a seventh sprocket) in the axial direction. The fifth rear sprocket  350 E (an example of a tenth sprocket) is positioned between the fourth rear sprocket  350 D (an example of an eighth sprocket) and the eighth rear sprocket  350 H (an example of a ninth sprocket) in the axial direction. 
         [0126]    The sixth rear sprocket  350 F (an example of a twelfth sprocket) is positioned between the fifth rear sprocket  350 E (an example of a tenth sprocket) and the seventh rear sprocket  350 G (an example of an eleventh sprocket) in the axial direction. The seventh rear sprocket  350 G (an example of an eleventh sprocket) is positioned between the fifth rear sprocket  350 E (an example of a tenth sprocket) and the eighth rear sprocket  350 H (an example of a ninth sprocket) in the axial direction. The eighth rear sprocket  350 H (an example of a ninth sprocket) is positioned between the fourth rear sprocket  350 D (an example of an eighth sprocket) and the ninth rear sprocket  350 I (an example of a seventh sprocket) in the axial direction. The ninth rear sprocket  350 I (an example of a seventh sprocket) is positioned between the third rear sprocket  350 C (an example of a sixth sprocket) and the tenth rear sprocket  350 J (an example of a fifth sprocket) in the axial direction. The tenth rear sprocket  350 J (an example of a fifth sprocket) is positioned between the second rear sprocket  350 B (an example of a fourth sprocket) and the eleventh rear sprocket  350 K (an example of a third sprocket) in the axial direction. The eleventh rear sprocket  350 K (an example of a third sprocket) is positioned between the first rear sprocket  350 A (an example of a second sprocket) and the twelfth rear sprocket  350 L (an example of a first sprocket) in the axial direction. 
         [0127]    Finally, a configuration of the first to twelfth rear sprockets  350 A- 350 L will be described in detail. A root circle diameter of the first rear sprocket  350 A is the largest in the first to twelfth rear sprockets  350 A- 350 L. Root circle diameters of the second to eleventh sprockets  350 B- 350 K are gradually reduced in order of the second to eleventh sprockets  350 B- 350 K. A root circle diameter of the twelfth sprocket  350 L is the smallest in the first to twelfth rear sprockets  350 A- 350 L. 
         [0128]    The first rear sprocket  350 A preferably includes at least one shift assist projection  354 . For example, the first rear sprocket  350 A includes two shift assist projections  354 . The two shift assist projections  354  are provided on the outer peripheral portion of the first rear sprocket  350 A. The two shift assist projections  354  are disposed at a predetermined interval around the rear hub shaft  35  (in a circumferential direction). 
         [0129]    The axial thickness T 4  of each of the first to the twelfth rear sprockets  350 A- 350 L is 1.6 mm. The axial length L 4  of each space between the axially adjacent rear sprockets is 2.2 mm. The total axial length TL 4  between the first rear sprocket  350 A and the twelfth rear sprocket  350 L is 43.4 mm. The total axial length TL 4  represents a distance between a surface of the first rear sprocket  350 A on an opposite side to the second rear sprocket  350 B and a surface of the twelfth rear sprocket  350 L on an opposite side to the eleventh rear sprocket  350 K. 
         [0130]    The first rear sprocket  350 A has a first tooth number (an example of a second tooth number). The first tooth number is more than or equal to forty-four. In the embodiment, for example, the first tooth number is fifty that is the largest tooth number. 
         [0131]    The second rear sprocket  350 B has a second tooth number. The second tooth number is forty four. The third rear sprocket  350 C has a third tooth number. The third tooth number is thirty eight. The fourth rear sprocket  350 D has a fourth tooth number. The fourth tooth number is thirty three. The fifth rear sprocket  350 E has a fifth tooth number. The fifth tooth number is twenty eight. The sixth rear sprocket  350 F has a sixth tooth number. The sixth tooth number is twenty four. The seventh rear sprocket  350 G has a seventh tooth number. The seventh tooth number is twenty one. The eighth rear sprocket  350 H has an eighth tooth number. The eighth tooth number is eighteen. The ninth rear sprocket  350 I has a ninth tooth number. The ninth tooth number is sixteen. The tenth rear sprocket  350 J has a tenth tooth number. The tenth tooth number is fourteen. The eleventh rear sprocket  350 K has an eleventh tooth number. The eleventh tooth number is twelve. 
         [0132]    The twelfth rear sprocket  350 L has a twelfth tooth number (an example of a first tooth number). The twelfth tooth number is less than or equal to ten. In the embodiment, for example, the twelfth tooth number is ten that is the smallest tooth number. 
       Fifth Embodiment 
       [0133]    A configuration of a bicycle employing a fifth embodiment according to the present invention is substantially identical to that of the first embodiment except for a configuration of a rear sprocket assembly  450 . For this reason, in the fifth embodiment, the rear sprocket assembly  450  will be described in detail and explanation of the other configuration will be omitted. The configurations omitted herein conform to the configuration according to the first embodiment. The same configurations as those in the first embodiment have the same reference numerals. 
         [0134]    As shown in  FIGS. 2 and 8 , the rear sprocket assembly  450  is configured to be mounted on the rear hub assembly  29 . The rear sprocket assembly  450  has a rotational central axis. The rotational central axis corresponds to the rear hub shaft  35  or a shaft center C of the rear hub shaft  35 . 
         [0135]    The rear sprocket assembly  450  is attached to a first tubular member  41  and a second tubular member  43 . The rear sprocket assembly  450  has a plurality of rear sprockets  450 A- 450 L. 
         [0136]    For example, the rear sprocket assembly  450  has a first rear sprocket assembly  451  and a second rear sprocket assembly  452 . 
         [0137]    The first rear sprocket assembly  451  is attached to the first tubular member  41  (the first body portion  41   a ). The first rear sprocket assembly  451  has first to ninth rear sprockets  450 A- 450 I. The first to ninth rear sprockets  450 A- 450 I are arranged on the outer peripheral portion of the first tubular member  41  in an axial direction parallel to the shaft center C of the rear hub shaft  35 . The first rear sprocket  450 A is disposed on the outer peripheral portion of the first tubular member  41  at a rear hub shell  37  side. The first to ninth rear sprocket s  450 A- 450 I are arranged on the outer peripheral portion of the first tubular member  41  by the same spline coupling as that in the first embodiment. 
         [0138]    The second rear sprocket assembly  452  is attached to the second tubular member  43  (the second body portion  43   a ). The second rear sprocket assembly  452  has tenth to twelfth rear sprockets  450 J- 450 L. The tenth to twelfth rear sprockets  450 J- 450 L are arranged on the outer peripheral portion of the second tubular member  43  in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The tenth rear sprocket  450 J is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the ninth rear sprocket  450 I in the axial direction. The eleventh rear sprocket  450 K is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the tenth rear sprocket  450 J in the axial direction. The twelfth rear sprocket  450 K is disposed on the outer peripheral portion of the second tubular member  43  so as to be adjacent to the eleventh rear sprocket  450 K at the most distant position from the first rear sprocket  450 A in the axial direction. 
         [0139]    The first rear sprocket  450 A is an example of a second sprocket. The second to eleventh rear sprockets  450 B- 450 K are an example of at least five additional sprockets, and at least eight additional rear sprockets. The twelfth rear sprocket  450 L is an example of a first sprocket. 
         [0140]    Layouts of the first to twelfth rear sprockets  450 A- 450 L will be described below in detail. The first to twelfth rear sprockets  450 A- 450 L are arranged on the first tubular member  41  and the second tubular member  43  in alphabetical order. 
         [0141]    Specifically, the second to eleventh rear sprockets  450 B- 450 K are positioned between the first rear sprocket  450 A and the twelfth rear sprocket  450 L in the axial direction parallel to the shaft center C of the rear hub shaft  35 . The second rear sprocket  450 B is positioned between the first rear sprocket  450 A and the third rear sprocket  450 C in the axial direction. The third rear sprocket  450 C is positioned between the second rear sprocket  450 B and the fourth rear sprocket  450 D in the axial direction. The fourth rear sprocket  450 D is positioned between the third rear sprocket  450 C and the fifth rear sprocket  450 E in the axial direction. The fifth rear sprocket  450 E is positioned between the fourth rear sprocket  450 D and the sixth rear sprocket  450 F in the axial direction. 
         [0142]    The sixth rear sprocket  450 F is positioned between the fifth rear sprocket  450 E and the seventh rear sprocket  450 G in the axial direction. The seventh rear sprocket  450 G is positioned between the sixth rear sprocket  450 F and the eighth rear sprocket  450 H in the axial direction. The eighth rear sprocket  450 H is positioned between the seventh rear sprocket  450 G and the ninth rear sprocket  450 I in the axial direction. The ninth rear sprocket  450 I is positioned between the eighth rear sprocket  450 H and the tenth rear sprocket  450 J in the axial direction. The tenth rear sprocket  450 J is positioned between the ninth rear sprocket  450 I and the eleventh rear sprocket  450 K in the axial direction. The eleventh rear sprocket  450 K is positioned between the tenth rear sprocket  450 J and the twelfth rear sprocket  450 L in the axial direction. 
         [0143]    In other words, the second rear sprocket  450 B (an example of a fourth sprocket) is positioned between the first rear sprocket  450 A (an example of a second sprocket) and the eleventh rear sprocket  450 K (an example of a third sprocket) in the axial direction. The third rear sprocket  450 C (an example of a sixth sprocket) is positioned between the second rear sprocket  450 B (an example of a fourth sprocket) and the tenth rear sprocket  450 J (an example of a fifth sprocket) in the axial direction. The fourth rear sprocket  450 D (an example of an eighth sprocket) is positioned between the third rear sprocket  450 C (an example of a sixth sprocket) and the ninth rear sprocket  450 I (an example of a seventh sprocket) in the axial direction. The fifth rear sprocket  450 E (an example of a tenth sprocket) is positioned between the fourth rear sprocket  450 D (an example of an eighth sprocket) and the eighth rear sprocket  450 H (an example of a ninth sprocket) in the axial direction. 
         [0144]    The sixth rear sprocket  450 F (an example of a twelfth sprocket) is positioned between the fifth rear sprocket  450 E (an example of a tenth sprocket) and the seventh rear sprocket  450 G (an example of an eleventh sprocket) in the axial direction. The seventh rear sprocket  450 G (an example of an eleventh sprocket) is positioned between the fifth rear sprocket  450 E (an example of a tenth sprocket) and the eighth rear sprocket  450 H (an example of a ninth sprocket) in the axial direction. The eighth rear sprocket  450 H (an example of a ninth sprocket) is positioned between the fourth rear sprocket  450 D (an example of an eighth sprocket) and the ninth rear sprocket  450 I (an example of a seventh sprocket) in the axial direction. The ninth rear sprocket  450 I (an example of a seventh sprocket) is positioned between the third rear sprocket  450 C (an example of a sixth sprocket) and the tenth rear sprocket  450 J (an example of a fifth sprocket) in the axial direction. The tenth rear sprocket  450 J (an example of a fifth sprocket) is positioned between the second rear sprocket  450 B (an example of a fourth sprocket) and the eleventh rear sprocket  450 K (an example of a third sprocket) in the axial direction. The eleventh rear sprocket  450 K (an example of a third sprocket) is positioned between the first rear sprocket  450 A (an example of a second sprocket) and the twelfth rear sprocket  450 L (an example of a first sprocket) in the axial direction. 
         [0145]    Finally, a configuration of the first to twelfth rear sprockets  450 A- 450 L will be described in detail. A root circle diameter of the first rear sprocket  450 A is the largest in the first to twelfth rear sprockets  450 A- 450 L. Root circle diameters of the second to eleventh sprockets  450 B- 450 K are gradually reduced in order of the second to eleventh sprockets  450 B- 450 K. A root circle diameter of the twelfth sprocket  450 L is the smallest in the first to twelfth rear sprockets  450 A- 450 L. 
         [0146]    The first rear sprocket  450 A preferably includes at least one shift assist projection (not shown). For example, the first rear sprocket  450 A may include six shift assist projections. The six shift assist projections are provided on the outer peripheral portion of the first rear sprocket  450 A. The six shift assist projections are disposed at a predetermined interval around the rear hub shaft  35  (in a circumferential direction). 
         [0147]    The axial thickness T 4  of each of the first to the twelfth rear sprockets  450 A- 450 L is 1.6 mm. The axial length L 4  of each space between the axially adjacent rear sprockets is 2.2 mm. The total axial length TL 4  between the first rear sprocket  450 A and the twelfth rear sprocket  450 L is 43.4 mm. The total axial length TL 4  represents a distance between a surface of the first rear sprocket  450 A on an opposite side to the second rear sprocket  450 B and a surface of the twelfth rear sprocket  450 L on an opposite side to the eleventh rear sprocket  450 K. 
         [0148]    The first rear sprocket  450 A has a first tooth number (an example of a second tooth number). The first tooth number is more than or equal to forty-eight. In the embodiment, for example, the first tooth number is forty-eight that is the largest tooth number. 
         [0149]    The second rear sprocket  450 B has a second tooth number. The second tooth number is forty-two. The third rear sprocket  450 C has a third tooth number. The third tooth number is thirty-six. The fourth rear sprocket  450 D has a fourth tooth number. The fourth tooth number is thirty-two. The fifth rear sprocket  450 E has a fifth tooth number. The fifth tooth number is twenty eight. The sixth rear sprocket  450 F has a sixth tooth number. The sixth tooth number is twenty four. The seventh rear sprocket  450 G has a seventh tooth number. The seventh tooth number is twenty one. The eighth rear sprocket  450 H has an eighth tooth number. The eighth tooth number is eighteen. The ninth rear sprocket  450 I has a ninth tooth number. The ninth tooth number is sixteen. The tenth rear sprocket  450 J has a tenth tooth number. The tenth tooth number is fourteen. The eleventh rear sprocket  450 K has an eleventh tooth number. The eleventh tooth number is twelve. 
         [0150]    The twelfth rear sprocket  450 L has a twelfth tooth number (an example of a first tooth number). The twelfth tooth number is less than or equal to ten. In the embodiment, for example, the twelfth tooth number is ten that is the smallest tooth number. 
       Other Embodiments 
       [0151]    (a) In the first to fifth embodiments, the description has been given to the example of the case in which the present invention is applied to a bicycle of a road type. Instead of this, the present invention can be applied to a mountain bike and/or a city cycle etc. 
         [0152]    (b) In the first to fifth embodiments, the description has been given to the example of the case in which a plurality of rear sprockets is attached to the first tubular member  41  and one, two or three rear sprockets are disposed in the second tubular member  43 . The numbers of the rear sprockets to be disposed in the first tubular member  41  and the second tubular member  43  are not restricted to the first to fourth embodiments but can be set optionally. 
         [0153]    (c) In the first to fifth embodiments, the second tubular member  43  is provided separately from the first tubular member  41 . Instead of this, the second tubular member  43  may be formed integrally with the first tubular member  41 . 
         [0154]    (d) In the first to fifth embodiments, the description has been given to the example of the case in which the front sprocket assembly  27   b  has two front sprockets. The numbers of the front sprockets are not restricted to the first to fourth embodiments but can be set optionally such as one sprocket or three sprockets. 
         [0155]    (e) Although the first sprockets  50 A,  150 A,  250 A,  350 A and  450 A illustrated in the first to fifth embodiments include the shift assist projections  54 ,  154 ,  254   354  respectively, the shift assist projections can be omitted from the first sprocket in the first, fourth and fifth embodiment since the difference between the first tooth number and the tooth number of the adjacent sprocket is not so large in comparison with the second and third embodiments. The shift assist projections  154  and  254  can also be omitted from the first sprockets  150 A and  250 A according to need. 
         [0156]    (f) Although the shift assist projection  54 ,  154 ,  254   354  is provided to the first sprocket  50 A,  150 A,  250 A, and  350 A only in the first to fifth embodiments, such a shift assist projection  54 ,  154 ,  254   354  can also be provided to the other sprocket according to need. 
         [0157]    In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts unless otherwise stated. 
         [0158]    As used herein, the following directional terms “frame facing side”, “non-frame facing side”, “forward”, “rearward”, “front”, “rear”, “up”, “down”, “above”, “below”, “upward”, “downward”, “top”, “bottom”, “side”, “vertical”, “horizontal”, “perpendicular” and “transverse” as well as any other similar directional terms refer to those directions of a bicycle in an upright, riding position and equipped with the multiple bicycle sprocket assembly. Accordingly, these directional terms, as utilized to describe the multiple bicycle sprocket assembly should be interpreted relative to a bicycle in an upright riding position on a horizontal surface and that is equipped with the multiple bicycle sprocket assembly. The terms “left” and “right” are used to indicate the “right” when referencing from the right side as viewed from the rear of the bicycle, and the “left” when referencing from the left side as viewed from the rear of the bicycle. 
         [0159]    Also it will be understood that although the terms “first” and “second” may be used herein to describe various components these components should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, for example, a first component discussed above could be termed a second component and vice versa without departing from the teachings of the present invention. The term “attached” or “attaching”, as used herein, encompasses configurations in which an element is directly secured to another element by affixing the element directly to the other element; configurations in which the element is indirectly secured to the other element by affixing the element to the intermediate member(s) which in turn are affixed to the other element; and configurations in which one element is integral with another element, i.e. one element is essentially part of the other element. This definition also applies to words of similar meaning, for example, “joined”, “connected”, “coupled”, “mounted”, “bonded”, “fixed” and their derivatives. Finally, terms of degree such as “substantially”, “about” and “approximately” as used herein mean an amount of deviation of the modified term such that the end result is not significantly changed. 
         [0160]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, unless specifically stated otherwise, the size, shape, location or orientation of the various components can be changed as needed and/or desired so long as the changes do not substantially affect their intended function. Unless specifically stated otherwise, components that are shown directly connected or contacting each other can have intermediate structures disposed between them so long as the changes do not substantially affect their intended function. The functions of one element can be performed by two, and vice versa unless specifically stated otherwise. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.