Patent Publication Number: US-2022234681-A1

Title: Sprocket support

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of the U.S. patent application Ser. No. 15/608,924 filed May 30, 2017. The contents of this application are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sprocket support. 
     Discussion of the Background 
     Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One bicycle component that has been extensively redesigned is a drive train. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, a sprocket support to which at least one sprocket of a bicycle rear sprocket assembly is attached comprises at least ten internal spline teeth configured to engage with a bicycle hub assembly. The at least ten internal spline teeth of the sprocket support includes at least ten internal-spline driving surfaces to transmit a driving rotational force to the bicycle hub assembly during pedaling. The at least ten internal-spline driving surfaces each include a radially outermost edge and a radially innermost edge. A radial length is defined from the radially outermost edge to the radially innermost edge. A total of the radial lengths of the at least ten internal-spline driving surfaces is equal to or larger than 7 mm. At least one internal-spline driving surface of the at least ten internal-spline driving surfaces has a first internal-spline-surface angle defined between the at least one internal-spline driving surface of the at least ten internal-spline driving surfaces and a first radial line extending from a rotational center axis of the bicycle rear sprocket assembly to the radially outermost edge of the at least one internal-spline driving surface of the at least ten internal-spline driving surfaces. The first internal-spline-surface angle ranges from 0 degree to 10 degrees. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is a schematic diagram of a bicycle drive train in accordance with an embodiment. 
         FIG. 2  is an exploded perspective view of the bicycle drive train illustrated in  FIG. 1 . 
         FIG. 3  is another perspective view of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the bicycle drive train taken along line IV-IV of  FIG. 2 . 
         FIG. 5  is an exploded perspective view of a bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 6  is an enlarged cross-sectional view of the bicycle drive train illustrated in  FIG. 4 . 
         FIG. 7  is a perspective view of a sprocket support body of the bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 8  is another perspective view of the sprocket support body of the bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 9  is a side elevational view of the sprocket support body illustrated in  FIG. 7 . 
         FIG. 10  is a side elevational view of a sprocket support body of the bicycle hub assembly in accordance with a modification. 
         FIG. 11  is an enlarged cross-sectional view of the sprocket support body illustrated in  FIG. 7 . 
         FIG. 12  is a cross-sectional view of the sprocket support body illustrated in  FIG. 7 . 
         FIG. 13  is a perspective view of the bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 14  is a side elevational view of the bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 15  is a rear view of the bicycle hub assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 16  is a cross-sectional view of the bicycle hub assembly taken along line XVI-XVI of  FIG. 5 . 
         FIG. 17  is a side elevational view of the bicycle rear sprocket assembly of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 18  is an exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 19  is a partial exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 20  is another partial exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 21  is another partial exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 22  is another partial exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 23  is a perspective cross-sectional view of the bicycle rear sprocket assembly taken along line XXIII-XXIII of  FIG. 17 . 
         FIG. 24  is a perspective view of a smallest sprocket of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 25  is another perspective view of the smallest sprocket of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 26  is a side elevational view of the smallest sprocket of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 27  is a side elevational view of a smallest sprocket in accordance with a modification. 
         FIG. 28  is an enlarged cross-sectional view of the smallest sprocket illustrated in  FIG. 24 . 
         FIG. 29  is a cross-sectional view of the smallest sprocket illustrated in  FIG. 24 . 
         FIG. 30  is a cross-sectional view of the sprocket support body and the smallest sprocket of the bicycle drive train illustrated in  FIG. 2 . 
         FIG. 31  is a partial exploded perspective view of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
         FIG. 32  is a perspective view of a sprocket support of the bicycle rear sprocket assembly illustrated in  FIG. 17 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiment(s) will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
     Referring initially to  FIG. 1 , a bicycle drive train  10  in accordance with an embodiment comprises a bicycle hub assembly  12  and a bicycle rear sprocket assembly  14 . The bicycle hub assembly  12  is secured to a bicycle frame BF. The bicycle rear sprocket assembly  14  is mounted on the bicycle hub assembly  12 . A bicycle brake rotor  16  is mounted on the bicycle hub assembly  12 . 
     The bicycle drive train  10  further comprises a crank assembly  18  and a bicycle chain  20 . The crank assembly  18  includes a crank axle  22 , a right crank atm  24 , a left crank arm  26 , and a front sprocket  27 . The right crank arm  24  and the left crank arm  26  are secured to the crank axle  22 . The front sprocket  27  is secured to at least one of the crank axle  22  and the right crank arm  24 . The bicycle chain  20  is engaged with the front sprocket  27  and the bicycle rear sprocket assembly  14  to transmit a pedaling force from the front sprocket  27  to the bicycle rear sprocket assembly  14 . The crank assembly  18  includes the front sprocket  27  as a single sprocket in the illustrated embodiment. However, the crank assembly  18  can include a plurality of front sprockets. The bicycle rear sprocket assembly  14  is a rear sprocket assembly. However, structures of the bicycle rear sprocket assembly  14  can be applied to the front sprocket. 
     In the present application, the following directional terms “front,” “rear,” “forward,” “rearward,” “left,” “right,” “transverse,” “upward” and “downward” as well as any other similar directional terms refer to those directions which are determined on the basis of a user (e.g., a rider) who sits on a saddle (not shown) of a bicycle with facing a handlebar (not shown). Accordingly, these terms, as utilized to describe the bicycle drive train  10 , the bicycle hub assembly  12 , or the bicycle rear sprocket assembly  14 , should be interpreted relative to the bicycle equipped with the bicycle drive train  10 , the bicycle hub assembly  12 , or the bicycle rear sprocket assembly  14  as used in an upright riding position on a horizontal surface. 
     As seen in  FIGS. 2 and 3 , the bicycle hub assembly  12  and the bicycle rear sprocket assembly  14  have a rotational center axis A 1 . The bicycle rear sprocket assembly  14  is rotatably supported by the bicycle hub assembly  12  relative to the bicycle frame BF ( FIG. 1 ) about the rotational center axis A 1 . The bicycle rear sprocket assembly  14  is configured to be engaged with the bicycle chain  20  to transmit a driving rotational force F 1  between the bicycle chain  20  and the bicycle rear sprocket assembly  14  during pedaling. The bicycle rear sprocket assembly  14  is rotated about the rotational center axis A 1  in a driving rotational direction D 11  during pedaling. The driving rotational direction D 11  is defined along a circumferential direction D 1  of the bicycle hub assembly  12  or the bicycle rear sprocket assembly  14 . A reverse rotational direction D 12  is an opposite direction of the driving rotational direction D 11  and is defined along the circumferential direction D 1 . 
     As seen in  FIG. 2 , the bicycle hub assembly  12  comprises a sprocket support body  28 . The bicycle rear sprocket assembly  14  is mounted on the sprocket support body  28  to transmit the driving rotational force F 1  between the sprocket support body  28  and the bicycle rear sprocket assembly  14 . The bicycle hub assembly  12  further comprises a hub axle  30 . The sprocket support body  28  is rotatably mounted on the hub axle  30  about the rotational center axis A 1 . The bicycle hub assembly  12  comprises a lock ring  32 . The lock ring  32  is secured to the sprocket support body  28  to hold the bicycle rear sprocket assembly  14  relative to the sprocket support body  28  in an axial direction D 2  parallel to the rotational center axis A 1 . 
     As seen in  FIG. 4 , the bicycle hub assembly  12  is secured to the bicycle frame BF with a wheel securing structure WS. The hub axle  30  has a through hole  30 A. A securing rod WS 1  of the wheel securing structure WS extends through the through hole  30 A of the hub axle  30 . The hub axle  30  includes a first axle end  30 B and a second axle end  30 C. The hub axle  30  extends between the first axle end  30 B and the second axle end  30 C along the rotational center axis A 1 . The first axle end  30 B is provided in a first recess BF 11  of a first frame BF 1  of the bicycle frame BF. The second axle end  30 C is provided in a second recess BF 21  of a second frame BF 2  of the bicycle frame BF. The hub axle  30  is held between the first frame BF 1  and the second frame BF 2  with the wheel securing structure WS. The wheel securing structure WS includes a structure which has been known in the bicycle filed. Thus, it will not be described in detail here for the sake of brevity. 
     As seen in  FIGS. 4 and 5 , the bicycle hub assembly  12  further comprises a brake-rotor support body  34 . The brake-rotor support body  34  is rotatably mounted on the hub axle  30  about the rotational center axis A 1 . The brake-rotor support body  34  is coupled to the bicycle brake rotor  16  ( FIG. 1 ) to transmit a braking rotational force from the bicycle brake rotor  16  to the brake-rotor support body  34 . 
     As seen in  FIG. 5 , the bicycle hub assembly  12  further comprises a hub body  36 . The hub body  36  is rotatably mounted on the hub axle  30  about the rotational center axis A 1 . In this embodiment, the sprocket support body  28  is a separate member from the hub body  36 . The brake-rotor support body  34  is integrally provided with the hub body  36  as a one-piece unitary member. However, the sprocket support body  28  can be integrally provided with the hub body  36 . The brake-rotor support body  34  can be a separate member from the hub body  36 . 
     The hub body  36  includes a first flange  36 A and a second flange  36 B. First spokes (not shown) are coupled to the first flange  36 A. Second spokes (not shown) are coupled to the second flange  36 B. The second flange  36 B is spaced apart from the first flange  36 A in the axial direction D 2 . The first flange  36 A is provided between the sprocket support body  28  and the second flange  36 B in the axial direction D 2 . The second flange  36 B is provided between the first flange  36 A and the brake-rotor support body  34  in the axial direction D 2 . 
     The lock ring  32  includes an externally threaded part  32 A. The sprocket support body  28  includes an internally threaded part  28 A. The externally threaded part  32 A is threadedly engaged with the internally threaded part  28 A in a state where the lock ring  32  is secured to the sprocket support body  28 . 
     As seen in  FIG. 6 , the bicycle hub assembly  12  further comprises a ratchet structure  38 . The sprocket support body  28  is operatively coupled to the hub body  36  with the ratchet structure  38 . The ratchet structure  38  is configured to couple the sprocket support body  28  to the hub body  36  to rotate the sprocket support body  28  along with the hub body  36  in the driving rotational direction D 11  ( FIG. 5 ) during pedaling. The ratchet structure  38  is configured to allow the sprocket support body  28  to rotate relative to the hub body  36  in the reverse rotational direction D 12  ( FIG. 5 ) during coasting. Accordingly, the ratchet structure  38  may be paraphrased into a one-way clutch structure  38 . The ratchet structure  38  includes structures which have been known in the bicycle field. Thus, they will not be described in detail here for the sake of brevity. 
     The bicycle hub assembly  12  includes a first bearing  39 A and a second bearing  39 B. The first bearing  39 A and the second bearing  39 B are provided between the sprocket support body  28  and the hub axle  30  to rotatably support the sprocket support body  28  relative to the hub axle  30  about the rotational center axis A 1 . 
     In this embodiment, each of the sprocket support body  28 , the brake-rotor support body  34 , and the hub body  36  is made of a metallic material such as aluminum, iron, or titanium. However, at least one of the sprocket support body  28 , the brake-rotor support body  34 , and the hub body  36  can be made of a non-metallic material. 
     As seen in  FIGS. 7 and 8 , the sprocket support body  28  includes at least one external spline tooth  40  configured to engage with the bicycle rear sprocket assembly  14  ( FIG. 6 ). The sprocket support body  28  includes a plurality of external spline teeth  40  configured to engage with the bicycle rear sprocket assembly  14  ( FIG. 6 ). Namely, the at least one external spline tooth  40  includes a plurality of external spline teeth  40 . The sprocket support body  28  includes at least nine external spline teeth  40  configured to engage with the bicycle rear sprocket assembly  14  ( FIG. 6 ). The sprocket support body  28  includes at least ten external spline teeth  40  configured to engage with the bicycle rear sprocket assembly  14  ( FIG. 6 ). 
     The sprocket support body  28  includes a base support  41  having a tubular shape. The base support  41  extends along the rotational center axis A 1 . The external spline tooth  40  extends radially outwardly from the base support  41 . The sprocket support body  28  includes a larger-diameter part  42 , a flange  44 , and a plurality of helical external spline teeth  46 . The larger-diameter part  42  and the flange  44  extend radially outwardly from the base support  41 . The larger-diameter part  42  is provided between the plurality of external spline teeth  40  and the flange  44  in the axial direction D 2 . The larger-diameter part  42  and the flange  44  are provided between the plurality of external spline teeth  40  and the plurality of helical external spline teeth  46  in the axial direction D 2 . As seen in  FIG. 6 , the bicycle rear sprocket assembly  14  is held between the larger-diameter part  42  and a lock flange  32 B of the lock ring  32  in the axial direction D 2 . The larger-diameter part  42  may have an interior cavity so that a drive structure such as a one-way clutch structure can be contained within the interior cavity. The larger-diameter part  42  can be omitted from the bicycle hub assembly  12  according to need. 
     As seen in  FIG. 9 , a total number of the at least ten external spline teeth  40  is equal to or larger than 20. The total number of the at least ten external spline teeth  40  is equal to or larger than 25. In this embodiment, the total number of the at least ten external spline teeth  40  is 26. However, a total number of the external spline teeth  40  is not limited to this embodiment and the above ranges. 
     The at least ten external spline teeth  40  have a first external pitch angle PA 11  and a second external pitch angle PA 12 . At least two external spline teeth of the plurality of external spline teeth  40  are circumferentially arranged at the first external pitch angle PA 11  with respect to the rotational center axis A 1  of the bicycle hub assembly  12 . At least two external spline teeth of the plurality of external spline teeth  40  are circumferentially arranged at the second external pitch angle PA 12  with respect to the rotational center axis A 1  of the bicycle hub assembly  12 . In this embodiment, the second external pitch angle PA 12  is different from the first external pitch angle PA 11 . However, the second external pitch angle PA 12  can be substantially equal to the first external pitch angle PA 11 . 
     In this embodiment, the external spline teeth  40  are arranged at the first external pitch angle PA 11  in the circumferential direction D 1 . Two external spline teeth of the external spline teeth  40  are arranged at the second external pitch angle PA 12  in the circumferential direction D 1 . However, at least two external spline teeth of the external spline teeth  40  can be arranged at another external pitch angle in the circumferential direction D 1 . 
     The first external pitch angle PA 11  ranges from 10 degrees to 20 degrees. The first external pitch angle PA 11  ranges from 12 degrees to 15 degrees. The first external pitch angle PA 11  ranges from 13 degrees to 14 degrees. In this embodiment, the first external pitch angle PA 11  is 13.3 degrees. However, the first external pitch angle PA 11  is not limited to this embodiment and the above ranges. 
     The second external pitch angle PA 12  ranges from 5 degrees to 30 degrees. In this embodiment, the second external pitch angle PA 12  is 26 degrees. However, the second external pitch angle PA 12  is not limited to this embodiment and the above range. 
     The external spline teeth  40  have substantially the same shape as each other. The external spline teeth  40  have substantially the same spline size as each other. The external spline teeth  40  have substantially the same profile as each other when viewed along the rotational center axis A 1 . As seen in  FIG. 10 , however, at least one of the at least ten external spline teeth  40  can have a first spline shape different from a second spline shape of another of the at least ten external spline teeth  40 . At least one of the at least ten external spline teeth  40  can have a first spline size different from a second spline size of another of the at least ten external spline teeth  40 . At least one of the at least ten external spline teeth  40  can have a profile different from a profile of another of the at least ten external spline teeth  40  when viewed along the rotational center axis A 1 . In  FIG. 10 , one of the external spline teeth  40  has a spline shape different from a spline shape of the other teeth of the external spline teeth  40 . One of the external spline teeth  40  has a spline size different from a spline size of the other teeth of the external spline teeth  40 . One of the external spline teeth  40  has a profile different from a profile of the other teeth of the external spline teeth  40  when viewed along the rotational center axis A 1 . 
     As seen in  FIG. 11 , each of the at least ten external spline teeth  40  has an external-spline driving surface  48  and an external-spline non-driving surface  50 . The plurality of external spline teeth  40  includes a plurality of external-spline driving surfaces  48  to receive the driving rotational force F 1  from the bicycle rear sprocket assembly  14  ( FIG. 6 ) during pedaling. The plurality of external spline teeth  40  includes a plurality of external-spline non-driving surfaces  50 . The external-spline driving surface  48  is contactable with the bicycle rear sprocket assembly  14  to receive the driving rotational force F 1  from the bicycle rear sprocket assembly  14  ( FIG. 6 ) during pedaling. The external-spline driving surface  48  faces in the reverse rotational direction D 12 . The external-spline non-driving surface  50  is provided on a reverse side of the external-spline driving surface  48  in the circumferential direction D 1 . The external-spline non-driving surface  50  faces in the driving rotational direction D 11  not to receive the driving rotational force F 1  from the bicycle rear sprocket assembly  14  during pedaling. 
     The at least ten external spline teeth  40  respectively have circumferential maximum widths MW 1 . The external spline teeth  40  respectively have circumferential maximum widths MW 1 . The circumferential maximum width MW 1  is defined as a maximum width to receive a thrust force F 2  applied to the external spline tooth  40 . The circumferential maximum width MW 1  is defined as a straight distance based on the external-spline driving surface  48 . 
     The plurality of external-spline driving surfaces  48  each includes a radially outermost edge  48 A and a radially innermost edge  48 B. The external-spline driving surface  48  extends from the radially outermost edge  48 A to the radially innermost edge  48 B. A first reference circle RC 11  is defined on the radially innermost edge  48 B and is centered at the rotational center axis A 1 . The first reference circle RC 11  intersects with the external-spline non-driving surface  50  at a reference point  50 R. The circumferential maximum width MW 1  extends straight from the radially innermost edge  48 B to the reference point  50 R in the circumferential direction D 1 . 
     The plurality of external-spline non-driving surfaces  50  each includes a radially outermost edge  50 A and a radially innermost edge  50 B. The external-spline non-driving surface  50  extends from the radially outermost edge  50 A to the radially innermost edge  50 B. The reference point  50 R is provided between the radially outermost edge  50 A and the radially innermost edge  50 B. However, the reference point  50 R can coincide with the radially innermost edge  50 B. 
     A total of the circumferential maximum widths MW 1  is equal to or larger than 55 mm. The total of the circumferential maximum widths MW 1  is equal to or larger than 60 mm. The total of the circumferential maximum widths MW 1  is equal to or larger than 65 mm. In this embodiment, the total of the circumferential maximum widths MW 1  is 68 mm. However, the total of the circumferential maximum widths MW 1  is not limited to this embodiment and the above ranges. 
     As seen in  FIG. 12 , the at least one external spline tooth  40  has an external-spline major diameter DM 11 . The external-spline major diameter DM 11  is equal to or larger than 25 mm. The external-spline major diameter DM 11  is equal to or larger than 29 mm. The external-spline major diameter DM 11  is equal to or smaller than 30 mm. In this embodiment, the external-spline major diameter DM 11  is 29.6 mm. However, the external-spline major diameter DM 11  is not limited to this embodiment and the above ranges. 
     The at least one external spline tooth  40  has an external-spline minor diameter DM 12 . The at least one external spline tooth  40  has an external-spline root circle RC 12  having the external-spline minor diameter DM 12 . However, the external-spline root circle RC 12  can have another diameter different from the external-spline minor diameter DM 12 . The external-spline minor diameter DM 12  is equal to or smaller than 28 mm. The external-spline minor diameter DM 12  is equal to or larger than 25 mm. The external-spline minor diameter DM 12  is equal to or larger than 27 mm. In this embodiment, the external-spline minor diameter DM 12  is 27.2 mm. However, the external-spline minor diameter DM 12  is not limited to this embodiment and the above ranges. 
     The larger-diameter part  42  has an outer diameter DM 13  larger than the external-spline major diameter DM 11 . The outer diameter DM 13  ranges from 32 mm to 40 mm. In this embodiment, the outer diameter DM 13  is 35 mm. However, the outer diameter DM 13  is not limited to this embodiment. 
     As seen in  FIG. 11 , the plurality of external-spline driving surfaces  48  each includes a radial length RL 11  defined from the radially outermost edge  48 A to the radially innermost edge  48 B. A total of the radial lengths RL 11  of the plurality of external-spline driving surfaces  48  is equal to or larger than 7 mm. The total of the radial lengths RL 11  is equal to or larger than 10 mm. The total of the radial lengths RL 11  is equal to or larger than 15 mm. In this embodiment, the total of the radial lengths RL 11  is 19.5 mm. However, the total of the radial lengths RL 11  is not limited to this embodiment. 
     The plurality of external spline tooth  40  has an additional radial length RL 12 . The additional radial lengths RL 12  are respectively defined from the external-spline root circle RC 12  to radially outermost ends  40 A of the plurality of external spline teeth  40 . A total of the additional radial lengths RL 12  is equal to or larger than 12 mm. In this embodiment, the total of the additional radial lengths RL 12  is 31.85 mm. However, the total of the additional radial lengths RL 12  is not limited to this embodiment. 
     At least one of the at least nine external spline teeth  40  has an asymmetric shape with respect to a circumferential tooth-tip center line CL 1 . The circumferential tooth-tip center line CL 1  is a line connecting the rotational center axis A 1  and a circumferential center point CP 1  of the radially outermost end  40 A of the external spline tooth  40 . However, at least one of the external spline teeth  40  can have a symmetric shape with respect to the circumferential tooth-tip center line CL 1 . The at least one of the at least nine external spline teeth  40  comprises the external-spline driving surface  48  and the external-spline non-driving surface  50 . 
     The external-spline driving surface  48  has a first external-spline-surface angle AG 11 . The first external-spline-surface angle AG 11  is defined between the external-spline driving surface  48  and a first radial line L 11 . The first radial line L 11  extends from the rotational center axis A 1  of the bicycle hub assembly  12  to the radially outermost edge  48 A of the external-spline driving surface  48 . The first external pitch angle PA 11  or the second external pitch angle PA 12  is defined between the adjacent first radial lines L 11  (see, e.g.,  FIG. 9 ). 
     The external-spline non-driving surface  50  has a second external-spline-surface angle AG 12 . The second external-spline-surface angle AG 12  is defined between the external-spline non-driving surface  50  and a second radial line L 12 . The second radial line L 12  extends from the rotational center axis A 1  of the bicycle hub assembly  12  to the radially outermost edge  50 A of the external-spline non-driving surface  50 . 
     In this embodiment, the second external-spline-surface angle AG 12  is different from the first external-spline-surface angle AG 11 . The first external-spline-surface angle AG 11  is smaller than the second external-spline-surface angle AG 12 . However, the first external-spline-surface angle AG 11  can be equal to or larger than the second external-spline-surface angle AG 12 . 
     The first external-spline-surface angle AG 11  ranges from 0 degree to 10 degrees. The second external-spline-surface angle AG 12  ranges from 0 degree to 60 degrees. In this embodiment, the first external-spline-surface angle AG 11  is 5 degrees. The second external-spline-surface angle AG 12  is 45 degrees. However, the first external-spline-surface angle AG 11  and the second external-spline-surface angle AG 12  are not limited to this embodiment and the above ranges. 
     As seen in  FIGS. 13 and 14 , the brake-rotor support body  34  includes at least one additional external spline tooth  52  configured to engage with the bicycle brake rotor  16  ( FIG. 4 ). In this embodiment, the brake-rotor support body  34  includes an additional base support  54  and a plurality of additional external spline teeth  52 . The additional base support  54  has a tubular shape and extends from the hub body  36  along the rotational center axis A 1 . The additional external spline tooth  52  extends radially outwardly from additional base support  54 . A total number of the additional external spline teeth  52  is 52. However, the total number of the additional external spline teeth  52  is not limited to this embodiment. 
     As seen in  FIG. 14 , the at least one additional external spline tooth  52  has an additional external-spline major diameter DM 14 . As seen in  FIG. 15 , the additional external-spline major diameter DM 14  is larger than the external-spline major diameter DM 11 . The additional external-spline major diameter DM 14  is substantially equal to the outer diameter DM 13  of the larger-diameter part  42 . However, the additional external-spline major diameter DM 14  can be equal to or smaller than the external-spline major diameter DM 11 . The additional external-spline major diameter DM 14  can be different from the outer diameter DM 13  of the larger-diameter part  42 . 
     As seen in  FIG. 16 , the hub axle  30  includes an axially contact surface  30 B 1  to contact the bicycle frame BF. In this embodiment, the axially contact surface  30 B 1  is contactable with the first frame BF 1  of the bicycle frame BF. The first frame BF 1  includes a frame contact surface BF 12 . The axially contact surface  30 B 1  is in contact with the frame contact surface BF 12  in a state where the bicycle hub assembly  12  is secured to the bicycle frame BF with the wheel securing structure WS. 
     A first axial length AL 11  is defined from the axially contact surface  30 B 1  to the larger-diameter part  42  in the axial direction D 2  with respect to the rotational center axis A 1 . The first axial length AL 11  ranges from 35 mm to 41 mm. The first axial length AL 11  can be equal to or larger than 39 mm. The first axial length AL 11  can also range from 35 mm to 37 mm. In this embodiment, the first axial length AL 11  is 36.2 mm. However, the first axial length AL 11  is not limited to this embodiment and the above ranges. 
     The larger-diameter part  42  has an axial end  42 A which is the farthest from the axially contact surface  30 B 1  in the axial direction D 2 . A second axial length AL 12  is defined from the axially contact surface  30 B 1  to the axial end  42 A in the axial direction D 2 . The second axial length AL 12  ranges from 38 mm to 47 mm. The second axial length AL 12  can range from 44 mm to 45 mm. The second axial length AL 12  can also range from 40 mm to 41 mm. In this embodiment, the second axial length AL 12  is 40.75 mm. However, the second axial length AL 12  is not limited to this embodiment and the above ranges. 
     An axial length AL 13  of the larger-diameter part  42  ranges from 3 mm to 6 mm. In this embodiment, the axial length AL 13  is 4.55 mm. However, the axial length AL 13  is not limited to this embodiment and the above ranges. 
     As seen in  FIG. 17 , the bicycle rear sprocket assembly  14  comprises at least one sprocket. The at least one sprocket includes a smallest sprocket SP 1  and a largest sprocket SP 12 . The smallest sprocket SP 1  can also be referred to as a sprocket SP 1 . The largest sprocket SP 12  can also be referred to as a sprocket SP 12 . In this embodiment, the at least one sprocket further includes sprockets SP 2  to SP 11 . The sprocket SP 1  corresponds to top gear. The sprocket SP 12  corresponds to low gear. A total number of the sprockets of the bicycle rear sprocket assembly  14  is not limited to this embodiment. 
     The smallest sprocket SP 1  includes at least one sprocket tooth SP 1 B. A total number of the at least one sprocket tooth SP 1 B of the smallest sprocket SP 1  is equal to or smaller than 10. In this embodiment, the total number of the at least one sprocket tooth SP 1 B of the smallest sprocket SP 1  is 10. However, the total number of the at least one sprocket tooth SP 1 B of the smallest sprocket SP 1  is not limited to this embodiment and the above range. 
     The largest sprocket SP 12  includes at least one sprocket tooth SP 12 B. A total number of the at least one sprocket tooth SP 12 B of the largest sprocket SP 12  is equal to or larger than 46. The total number of the at least one sprocket tooth SP 12 B of the largest sprocket SP 12  is equal to or larger than 50. In this embodiment, the total number of the at least one sprocket tooth SP 12 B of the largest sprocket SP 12  is 51. However, the total number of the at least one sprocket tooth SP 12 B of the largest sprocket SP 12  is not limited to this embodiment and the above ranges. 
     The sprocket SP 2  includes at least one sprocket tooth SP 2 B. The sprocket SP 3  includes at least one sprocket tooth SP 3 B. The sprocket SP 4  includes at least one sprocket tooth SP 4 B. The sprocket SP 5  includes at least one sprocket tooth SP 5 B. The sprocket SP 6  includes at least one sprocket tooth SP 6 B. The sprocket SP 7  includes at least one sprocket tooth SP 7 B. The sprocket SP 8  includes at least one sprocket tooth SP 8 B. The sprocket SP 9  includes at least one sprocket tooth SP 9 B. The sprocket SP 10  includes at least one sprocket tooth SP 10 B. The sprocket SP 11  includes at least one sprocket tooth SP 11 B. 
     A total number of the at least one sprocket tooth SP 2 B is 12. A total number of the at least one sprocket tooth SP 3 B is 14. A total number of the at least one sprocket tooth SP 4 B is 16. A total number of the at least one sprocket tooth SP 5 B is 18. A total number of the at least one sprocket tooth SP 6 B is 21. A total number of the at least one sprocket tooth SP 7 B is 24. A total number of the at least one sprocket tooth SP 8 B is 28. A total number of the at least one sprocket tooth SP 9 B is 33. A total number of the at least one sprocket tooth SP 10 B is 39. A total number of the at least one sprocket tooth SP 11 B is 45. The total number of the sprocket teeth of each of the sprockets SP 2  to SP 11  is not limited to this embodiment. 
     As seen in  FIG. 18 , the sprockets SP 1  to SP 12  are separate members from each other. However, at least one of the sprockets SP 1  to SP 12  can be at least partly provided integrally with another of the sprockets SP 1  to SP 12 . The bicycle rear sprocket assembly  14  comprises a sprocket support  56 , a plurality of spacers  58 , a first ring  59 A, and a second ring  59 B. The sprockets SP 1  to SP 12  are attached to the sprocket support  56  in the illustrated embodiment. 
     As seen in  FIG. 19 , the sprocket SP 1  includes a sprocket body SP 1 A and the plurality of sprocket teeth SP 1 B. The plurality of sprocket teeth SP 1 B extends radially outwardly from the sprocket body SP 1 A. The sprocket SP 2  includes a sprocket body SP 2 A and the plurality of sprocket teeth SP 2 B. The plurality of sprocket teeth SP 2 B extends radially outwardly from the sprocket body SP 2 A. The sprocket SP 3  includes a sprocket body SP 3 A and the plurality of sprocket teeth SP 3 B. The plurality of sprocket teeth SP 3 B extends radially outwardly from the sprocket body SP 3 A. The sprocket SP 4  includes a sprocket body SP 4 A and the plurality of sprocket teeth SP 4 B. The plurality of sprocket teeth SP 4 B extends radially outwardly from the sprocket body SP 4 A. The sprocket SP 5  includes a sprocket body SP 5 A and the plurality of sprocket teeth SP 5 B. The plurality of sprocket teeth SP 5 B extends radially outwardly from the sprocket body SP 5 A. The first ring  59 A is provided between the sprockets SP 3  and SP 4 . The second ring  59 B is provided between the sprockets SP 4  and SP 5 . 
     As seen in  FIG. 20 , the sprocket SP 6  includes a sprocket body SP 6 A and the plurality of sprocket teeth SP 6 B. The plurality of sprocket teeth SP 6 B extends radially outwardly from the sprocket body SP 6 A. The sprocket SP 7  includes a sprocket body SP 7 A and the plurality of sprocket teeth SP 7 B. The plurality of sprocket teeth SP 7 B extends radially outwardly from the sprocket body SP 7 A. The sprocket SP 8  includes a sprocket body SP 8 A and the plurality of sprocket teeth SP 8 B. The plurality of sprocket teeth SP 8 B extends radially outwardly from the sprocket body SP 8 A. 
     As seen in  FIG. 21 , the sprocket SP 9  includes a sprocket body SP 9 A and the plurality of sprocket teeth SP 9 B. The plurality of sprocket teeth SP 9 B extends radially outwardly from the sprocket body SP 9 A. The sprocket SP 10  includes a sprocket body SP 10 A and the plurality of sprocket teeth SP 10 B. The plurality of sprocket teeth SP 10 B extends radially outwardly from the sprocket body SP 10 A. The sprocket SP 11  includes a sprocket body SP 11 A and the plurality of sprocket teeth SP 11 B. The plurality of sprocket teeth SP 11 B extends radially outwardly from the sprocket body SP 11 A. The sprocket SP 12  includes a sprocket body SP 12 A and the plurality of sprocket teeth SP 12 B. The plurality of sprocket teeth SP 12 B extends radially outwardly from the sprocket body SP 12 A. 
     As seen in  FIG. 22 , the sprocket support  56  includes a hub engagement part  60  and a plurality of support arms  62 . The plurality of support arms  62  extends radially outwardly from the hub engagement part  60 . The support arm  62  includes first to eighth attachment parts  62 A to  62 H. The plurality of spacers  58  includes a plurality of first spacers  58 A, a plurality of second spacers  58 B, a plurality of third spacers  58 C, a plurality of fourth spacers  58 D, a plurality of fifth spacers  58 E, a plurality of sixth spacers  58 F, and a plurality of seventh spacers  58 G. 
     As seen in  FIG. 23 , the first spacers  58 A are provided between the sprockets SP 5  and SP 6 . The second spacers  58 B are provided between the sprockets SP 6  and SP 7 . The third spacers  58 C are provided between the sprockets SP 7  and SP 8 . The fourth spacers  58 D are provided between the sprockets SP 8  and SP 9 . The fifth spacers  58 E are provided between the sprockets SP 9  and SP 10 . The sixth spacers  58 F are provided between the sprockets SP 10  and SP 11 . The seventh spacers  58 G are provided between the sprockets SP 11  and SP 12 . 
     The sprocket SP 6  and the first spacer  58 A are attached to the first attachment part  62 A with a bonding structure such as an adhesive agent. The sprocket SP 7  and the second spacer  58 B are attached to the second attachment part  62 B with a bonding structure such as an adhesive agent. The sprocket SP 8  and the third spacer  58 C are attached to the third attachment part  62 C with a bonding structure such as an adhesive agent. The sprocket SP 9  and the fourth spacer  58 D are attached to the fourth attachment part  62 D with a bonding structure such as an adhesive agent. The sprocket SP 10  and the fifth spacer  58 E are attached to the fifth attachment part  62 E with a bonding structure such as an adhesive agent. The sprocket SP 11  and the sixth spacer  58 F are attached to the sixth attachment part  62 F with a bonding structure such as an adhesive agent. The sprocket SP 12  and the seventh spacer  58 G are attached to the seventh attachment part  62 G with a bonding structure such as an adhesive agent. The sprocket SP 5  and the second ring  59 B are attached to the eighth attachment part  62 H with a bonding structure such as an adhesive agent. The hub engagement part  60 , the sprockets SP 1  to SP 4 , the first ring  59 A, and the second ring  59 B are held between the larger-diameter part  42  and the lock flange  32 B of the lock ring  32  in the axial direction D 2 . 
     In this embodiment, each of the sprockets SP 1  to SP 12  is made of a metallic material such as aluminum, iron, or titanium. Each of the sprocket support  56 , the first to seventh spacers  58 A and to  58 G, the first ring  59 A, and the second ring  59 B is made of a non-metallic material such as a resin material. However, at least one of the sprockets SP 1  to SP 12  can be at least partly made of a non-metallic material. At least one of the sprocket support  56 , the first to seventh spacers  58 A and to  58 G, the first ring  59 A, and the second ring  59 B can be at least partly made of a metallic material such as aluminum, iron, or titanium. 
     The at least one sprocket includes at least one internal spline tooth configured to engage with the bicycle hub assembly  12 . As seen in  FIGS. 24 and 25 , the at least one sprocket includes at least ten internal spline teeth configured to engage with the bicycle hub assembly  12 . The at least one internal spline tooth includes a plurality of internal spline teeth. Thus, the at least one sprocket includes a plurality of internal spline teeth configured to engage with the bicycle hub assembly  12 . In this embodiment, the sprocket SP 1  includes at least ten internal spline teeth  64  configured to engage with the bicycle hub assembly  12 . In this embodiment, the sprocket SP 1  includes the internal spline teeth  64  configured to mesh with the external spline teeth  40  of the sprocket support body  28  of the bicycle hub assembly  12 . The sprocket body SP 1 A has an annular shape. The internal spline teeth  64  extend radially inwardly from the sprocket body SP 1 A. 
     As seen in  FIG. 26 , a total number of the at least ten internal spline teeth  64  is equal to or larger than 20. The total number of the at least ten internal spline teeth  64  is equal to or larger than 25. In this embodiment, the total number of the internal spline teeth  64  is 26. However, the total number of the internal spline teeth  64  is not limited to this embodiment and the above ranges. 
     The at least ten internal spline teeth  64  have a first internal pitch angle PA 21  and a second internal pitch angle PA 22 . At least two internal spline teeth of the plurality of internal spline teeth  64  is circumferentially arranged at a first internal pitch angle PA 21  with respect to the rotational center axis A 1  of the bicycle rear sprocket assembly  14 . At least two internal spline teeth of the plurality of internal spline teeth  64  is circumferentially arranged at a second internal pitch angle PA 22  with respect to the rotational center axis A 1 . In this embodiment, the second internal pitch angle PA 22  is different from the first internal pitch angle PA 21 . However, the second internal pitch angle PA 22  can be substantially equal to the first internal pitch angle PA 21 . 
     In this embodiment, the internal spline teeth  64  are circumferentially arranged at the first internal pitch angle PA 21  in the circumferential direction D 1 . Two internal spline teeth of the internal spline teeth  64  is arranged at the second internal pitch angle PA 22  in the circumferential direction D 1 . However, at least two internal spline teeth of the internal spline teeth  64  can be arranged at another internal pitch angle in the circumferential direction D 1 . 
     The first internal pitch angle PA 21  ranges from 10 degrees to 20 degrees. The first internal pitch angle PA 21  ranges from 12 degrees to 15 degrees. The first internal pitch angle PA 21  ranges from 13 degrees to 14 degrees. In this embodiment, the first internal pitch angle PA 21  is 13.3 degrees. However, the first internal pitch angle PA 21  is not limited to this embodiment and the above ranges. 
     The second internal pitch angle PA 22  ranges from 5 degrees to 30 degrees. In this embodiment, the second internal pitch angle PA 22  is 26 degrees. However, the second internal pitch angle PA 22  is not limited to this embodiment and the above range. 
     At least one of the at least ten internal spline teeth  64  has a first spline shape different from a second spline shape of another of the at least ten internal spline teeth  64 . At least one of the at least ten internal spline teeth  64  has a first spline size different from a second spline size of another of the at least ten internal spline teeth  64 . At least one of the at least ten internal spline teeth  64  has a cross-sectional shape different from a cross-sectional shape of another of the at least ten internal spline teeth  64 . As seen in  FIG. 27 , however, the internal spline teeth  64  can have the same shape as each other. The internal spline teeth  64  can have the same size as each other. The internal spline teeth  64  can have the same cross-sectional shape as each other. 
     As seen in  FIG. 28 , the at least one internal spline tooth  64  comprises an internal-spline driving surface  66  and an internal-spline non-driving surface  68 . The at least one internal spline tooth  64  includes a plurality of internal spline teeth  64 . The plurality of internal spline teeth  64  includes a plurality of internal-spline driving surfaces  66  to receive the driving rotational force F 1  from the bicycle hub assembly  12  ( FIG. 6 ) during pedaling. The plurality of internal spline teeth  64  includes a plurality of internal-spline non-driving surfaces  68 . The internal-spline driving surface  66  is contactable with the sprocket support body  28  to transmit the driving rotational force F 1  from the sprocket SP 1  to the sprocket support body  28  during pedaling. The internal-spline driving surface  66  faces in the driving rotational direction D 11 . The internal-spline non-driving surface  68  is provided on a reverse side of the internal-spline driving surface  66  in the circumferential direction D 1 . The internal-spline non-driving surface  68  faces in the reverse rotational direction D 12  not to transmit the driving rotational force F 1  from the sprocket SP 1  to the sprocket support body  28  during pedaling. 
     The at least ten internal spline teeth  64  respectively have circumferential maximum widths MW 2 . The internal spline teeth  64  respectively have circumferential maximum widths MW 2 . The circumferential maximum width MW 2  is defined as a maximum width to receive a thrust force F 3  applied to the internal spline tooth  64 . The circumferential maximum width MW 2  is defined as a straight distance based on the internal-spline driving surface  66 . 
     The internal-spline driving surface  66  includes a radially outermost edge  66 A and a radially innermost edge  66 B. The internal-spline driving surface  66  extends from the radially outermost edge  66 A to the radially innermost edge  66 B. A second reference circle RC 21  is defined on the radially outermost edge  66 A and is centered at the rotational center axis A 1 . The second reference circle RC 21  intersects with the internal-spline non-driving surface  68  at a reference point  68 R. The circumferential maximum width MW 2  extends straight from the radially innermost edge  66 B to the reference point  68 R in the circumferential direction D 1 . 
     The internal-spline non-driving surface  68  includes a radially outermost edge  68 A and a radially innermost edge  68 B. The internal-spline non-driving surface  68  extends from the radially outermost edge  68 A to the radially innermost edge  68 B. The reference point  68 R is provided between the radially outermost edge  68 A and the radially innermost edge  68 B. 
     A total of the circumferential maximum widths MW 2  is equal to or larger than 40 mm. The total of the circumferential maximum widths MW 2  is equal to or larger than 45 mm. The total of the circumferential maximum widths MW 2  is equal to or larger than 50 mm. In this embodiment, the total of the circumferential maximum widths MW 2  is 50.8 mm. However, the total of the circumferential maximum widths MW 2  is not limited to this embodiment. 
     As seen in  FIG. 29 , the at least one internal spline tooth  64  has an internal-spline major diameter DM 21 . The at least one internal spline tooth  64  has an internal-spline root circle RC 22  having the internal-spline major diameter DM 21 . However, the internal-spline root circle RC 22  can have another diameter different from the internal-spline major diameter DM 21 . The internal-spline major diameter DM 21  equal to or smaller than 30 mm. The internal-spline major diameter DM 21  is equal to or larger than 25 mm. The internal-spline major diameter DM 21  is equal to or larger than 29 mm. In this embodiment, the internal-spline major diameter DM 21  is 29.8 mm. However, the internal-spline major diameter DM 21  is not limited to this embodiment and the above ranges. 
     The at least one internal spline tooth  64  has an internal-spline minor diameter DM 22  equal to or smaller than 28 mm. The internal-spline minor diameter DM 22  is equal to or larger than 25 mm. The internal-spline minor diameter DM 22  is equal to or larger than 27 mm. In this embodiment, the internal-spline minor diameter DM 22  is 27.7 mm. However, the internal-spline minor diameter DM 22  is not limited to this embodiment and the above ranges. 
     As seen in  FIG. 28 , the plurality of internal-spline driving surface  66  includes the radially outermost edge  66 A and the radially innermost edge  66 B. The plurality of internal-spline driving surfaces  66  each includes a radial length RL 21  defined from the radially outermost edge  66 A to the radially innermost edge  66 B. A total of the radial lengths RL 21  of the plurality of internal-spline driving surfaces  66  is equal to or larger than 7 mm. The total of the radial lengths RL 21  is equal to or larger than 10 mm. The total of the radial lengths RL 21  is equal to or larger than 15 mm. In this embodiment, the total of the radial lengths RL 21  is 19.5 mm. However, the total of the radial lengths RL 21  is not limited to this embodiment and the above ranges. 
     The plurality of internal spline tooth  64  has an additional radial length RL 22 . The additional radial lengths RL 22  are respectively defined from the internal-spline root circle RC 22  to radially innermost ends  64 A of the plurality of internal spline teeth  64 . A total of the additional radial lengths RL 22  is equal to or larger than 12 mm. In this embodiment, the total of the additional radial lengths RL 22  is 27.95 mm. However, the total of the additional radial lengths RL 22  is not limited to this embodiment and the above ranges. 
     At least one of the internal spline tooth  64  has an asymmetric shape with respect to a circumferential tooth-tip center line CL 2 . The circumferential tooth-tip center line CL 2  is a line connecting the rotational center axis A 1  and a circumferential center point CP 2  of the radially innermost end  64 A of the internal spline tooth  64 . However, at least one of the internal spline teeth  64  can have a symmetric shape with respect to the circumferential tooth-tip center line CL 2 . The at least one of the internal spline tooth  64  comprises the internal-spline driving surface  66  and the internal-spline non-driving surface  68 . 
     The internal-spline driving surface  66  has a first internal-spline-surface angle AG 21 . The first internal-spline-surface angle AG 21  is defined between the internal-spline driving surface  66  and a first radial line L 21 . The first radial line L 21  extends from the rotational center axis A 1  of the bicycle rear sprocket assembly  14  to the radially outermost edge  66 A of the internal-spline driving surface  66 . The first internal pitch angle PA 21  or the second internal pitch angle PA 22  is defined between the adjacent first radial lines L 21  (see, e.g.,  FIG. 26 ). 
     The internal-spline non-driving surface  68  has a second internal-spline-surface angle AG 22 . The second internal-spline-surface angle AG 22  is defined between the internal-spline non-driving surface  68  and a second radial line L 22 . The second radial line L 22  extends from the rotational center axis A 1  of the bicycle rear sprocket assembly  14  to the radially outermost edge  68 A of the internal-spline non-driving surface  68 . 
     In this embodiment, the second internal-spline-surface angle AG 22  is different from the first internal-spline-surface angle AG 21 . The first internal-spline-surface angle AG 21  is smaller than the second internal-spline-surface angle AG 22 . However, the first internal-spline-surface angle AG 21  can be equal to or larger than the second internal-spline-surface angle AG 22 . 
     The first internal-spline-surface angle AG 21  ranges from 0 degree to 10 degrees. The second internal-spline-surface angle AG 22  ranges from 0 degree to 60 degrees. In this embodiment, the first internal-spline-surface angle AG 21  is 5 degrees. The second internal-spline-surface angle AG 22  is 45 degrees. However, the first internal-spline-surface angle AG 21  and the second internal-spline-surface angle AG 22  are not limited to this embodiment and the above ranges. 
     As seen in  FIG. 30 , the internal spline teeth  64  mesh with the external spline teeth  40  to transmit the driving rotational force F 1  from the sprocket SP 1  to the sprocket support body  28 . The internal-spline driving surface  66  is contactable with the external-spline driving surface  48  to transmit the driving rotational force F 1  from the sprocket SP 1  to the sprocket support body  28 . The internal-spline non-driving surface  68  is spaced apart from the external-spline non-driving surface  50  in a state where the internal-spline driving surface  66  is in contact with the external-spline driving surface  48 . 
     As seen in  FIG. 31 , the sprocket SP 2  includes a plurality of internal spline teeth  70 . The sprocket SP 3  includes a plurality of internal spline teeth  72 . The sprocket SP 4  includes a plurality of internal spline teeth  74 . The first ring  59 A includes a plurality of internal spline teeth  76 . As seen in  FIG. 32 , the hub engagement part  60  of the sprocket support  56  includes a plurality of internal spline teeth  78 . The plurality of internal spline teeth  70  has substantially the same structure as that of the plurality of internal spline teeth  64 . The plurality of internal spline teeth  72  has substantially the same structure as that of the plurality of internal spline teeth  64 . The plurality of internal spline teeth  74  has substantially the same structure as that of the plurality of internal spline teeth  64 . The plurality of internal spline teeth  76  has substantially the same structure as that of the plurality of internal spline teeth  64 . The plurality of internal spline teeth  78  has substantially the same structure as that of the plurality of internal spline teeth  64 . Thus, they will not be described in detail here for the sake of brevity. 
     In accordance with a first aspect, a bicycle rear sprocket assembly comprises at least one sprocket. The at least one sprocket includes at least ten internal spline teeth configured to engage with a bicycle hub assembly. 
     With the bicycle rear sprocket assembly according to the first aspect, the at least ten internal spline teeth reduce a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a second aspect, the bicycle rear sprocket assembly according to the first aspect is configured so that a total number of the at least ten internal spline teeth is equal to or larger than 20. 
     With the bicycle rear sprocket assembly according to the second aspect, the at least twenty internal spline teeth further reduce the rotational force applied to each of the at least twenty internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a third aspect, the bicycle rear sprocket assembly according to the second aspect is configured so that the total number of the at least ten internal spline teeth is equal to or larger than 25. 
     With the bicycle rear sprocket assembly according to the third aspect, the at least twenty-five internal spline teeth further reduce the rotational force applied to each of the at least twenty-five internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a fourth aspect, the bicycle rear sprocket assembly according to any one of the first to third aspects is configured so that the at least ten internal spline teeth have a first internal pitch angle and a second internal pitch angle different from the first internal pitch angle. 
     With the bicycle rear sprocket assembly according to the fourth aspect, the difference between the first internal pitch angle and the second internal pitch angle helps the user to correctly mount the bicycle rear sprocket assembly to the bicycle hub assembly, especially concerning a circumferential position of each sprocket of the bicycle rear sprocket assembly. 
     In accordance with a fifth aspect, the bicycle rear sprocket assembly according to any one of the first to fourth aspects is configured so that at least one of the at least ten internal spline teeth has a first spline shape different from a second spline shape of another of the at least ten internal spline teeth. 
     With the bicycle rear sprocket assembly according to the fifth aspect, the difference between the first spline shape and the second spline shape helps the user to correctly mount the bicycle rear sprocket assembly to the bicycle hub assembly, especially concerning a circumferential position of each sprocket of the bicycle rear sprocket assembly. 
     In accordance with a sixth aspect, the bicycle rear sprocket assembly according to any one of the first to fifth aspects is configured so that at least one of the at least ten internal spline teeth has a first size different from a second size of another of the at least ten internal spline teeth. 
     With the bicycle rear sprocket assembly according to the sixth aspect, the difference between the first size and the second size helps the user to correctly mount the bicycle rear sprocket assembly to the sprocket support body, especially concerning a circumferential position of each sprocket of the bicycle rear sprocket assembly. 
     In accordance with a seventh aspect, the bicycle rear sprocket assembly according to any one of the first to sixth aspects is configured so that the at least one sprocket includes a smallest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the smallest sprocket is equal to or smaller than 10. 
     With the bicycle rear sprocket assembly according to the seventh aspect, it is possible to widen a gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with an eighth aspect, the bicycle rear sprocket assembly according to any one of the first to seventh aspects is configured so that the at least one sprocket includes a largest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 46. 
     With the bicycle rear sprocket assembly according to the eighth aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a low gear side. 
     In accordance with a ninth aspect, the bicycle rear sprocket assembly according to the eighth aspect is configured so that the total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 50. 
     With the bicycle rear sprocket assembly according to the ninth aspect, it is possible to further widen the gear range of the bicycle rear sprocket assembly. 
     In accordance with a tenth aspect, a bicycle rear sprocket assembly comprises at least one sprocket. The at least one sprocket includes a plurality of internal spline teeth configured to engage with a bicycle hub assembly. At least two internal spline teeth of the plurality of internal spline teeth are circumferentially arranged at a first internal pitch angle with respect to a rotational center axis of the bicycle rear sprocket assembly. The first internal pitch angle ranges from 10 degrees to 20 degrees. 
     With the bicycle rear sprocket assembly according to the tenth aspect, the first internal pitch angle reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with an eleventh aspect, the bicycle rear sprocket assembly according to the tenth aspect is configured so that the first internal pitch angle ranges from 12 degrees to 15 degrees. 
     With the bicycle rear sprocket assembly according to the eleventh aspect, the first internal pitch angle further reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a twelfth aspect, the bicycle rear sprocket assembly according to the eleventh aspect is configured so that the first internal pitch angle ranges from 13 degrees to 14 degrees. 
     With the bicycle rear sprocket assembly according to the twelfth aspect, the first internal pitch angle further reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a thirteenth aspect, the bicycle rear sprocket assembly according to any one of the tenth to twelfth aspects is configured so that at least two internal spline teeth of the plurality of internal spline teeth are circumferentially arranged at a second internal pitch angle with respect to the rotational center axis. The second internal pitch angle is different from the first internal pitch angle. 
     With the bicycle rear sprocket assembly according to the thirteenth aspect, the difference between the first internal pitch angle and the second internal pitch angle helps the user to correctly mount the bicycle rear sprocket assembly to the bicycle hub assembly, especially concerning a circumferential position of each sprocket of the bicycle rear sprocket assembly. 
     In accordance with a fourteenth aspect, the bicycle rear sprocket assembly according to any one of the tenth to thirteenth aspects is configured so that the at least one sprocket includes a smallest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the smallest sprocket is equal to or smaller than 10. 
     With the bicycle rear sprocket assembly according to the fourteenth aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a fifteenth aspect, the bicycle rear sprocket assembly according to any one of the tenth to fourteenth aspects is configured so that the at least one sprocket includes a largest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 46. 
     With the bicycle rear sprocket assembly according to the fifteenth aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a low gear side. 
     In accordance with a sixteenth aspect, the bicycle rear sprocket assembly according to the fifteenth aspect is configured so that the total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 50. 
     With the bicycle rear sprocket assembly according to the sixteenth aspect, it is possible to further widen the gear range of the bicycle rear sprocket assembly. 
     In accordance with a seventeenth aspect, a bicycle rear sprocket assembly comprises at least one sprocket. The at least one sprocket includes at least one internal spline tooth configured to engage with a bicycle hub assembly. The at least one internal spline tooth has an internal-spline major diameter equal to or smaller than 30 mm. 
     With the bicycle rear sprocket assembly according to the seventeenth aspect, it is possible to manufacture a bicycle rear sprocket with a total tooth number that is equal to or smaller than 10. Therefore, it is possible to widen a gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with an eighteenth aspect, the bicycle rear sprocket assembly according to the seventeenth aspect is configured so that the internal-spline major diameter is equal to or larger than 25 mm. 
     With the bicycle rear sprocket assembly according to the eighteenth aspect, it is possible to ensure strength of the at least one sprocket with widening the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a nineteenth aspect, the bicycle rear sprocket assembly according to the eighteenth aspect is configured so that the internal-spline major diameter is equal to or larger than 29 mm. 
     With the bicycle rear sprocket assembly according to the nineteenth aspect, it is possible to further ensure strength of the at least one sprocket with widening the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a twentieth aspect, the bicycle rear sprocket assembly according to any one of the seventeenth to nineteenth aspects is configured so that the at least one internal spline tooth has an internal-spline minor diameter equal to or smaller than 28 mm. 
     With the bicycle rear sprocket assembly according to the twentieth aspect, the internal-spline minor diameter can increase a radial length of a driving surface of the at least one internal spline tooth. This improves strength of the at least one sprocket. 
     In accordance with a twenty-first aspect, the bicycle rear sprocket assembly according to any one of the seventeenth to twentieth aspects is configured so that the internal-spline minor diameter is equal to or larger than 25 mm. 
     With the bicycle rear sprocket assembly according to the twenty-first aspect, it is possible to ensure strength of the at least one sprocket with widening the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a twenty-second aspect, the bicycle rear sprocket assembly according to the twenty-first aspect is configured so that the internal-spline minor diameter is equal to or larger than 27 mm. 
     With the bicycle rear sprocket assembly according to the twenty-second aspect, it is possible to certainly ensure strength of the at least one sprocket with widening the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a twenty-third aspect, the bicycle rear sprocket assembly according to any one of the seventeenth to twenty-second aspects is configured so that the at least one internal spline tooth includes a plurality of internal spline teeth including a plurality of internal-spline driving surfaces to receive a driving rotational force from the bicycle hub assembly during pedaling. The plurality of internal-spline driving surfaces each includes a radially outermost edge, a radially innermost edge, and a radial length defined from the radially outermost edge to the radially innermost edge. A total of the radial lengths of the plurality of internal-spline driving surfaces is equal to or larger than 7 mm. 
     With the bicycle rear sprocket assembly according to the twenty-third aspect, it is possible to increase the radial lengths of the plurality of internal-spline driving surface. This improves strength of the at least one sprocket. 
     In accordance with a twenty-fourth aspect, the bicycle rear sprocket assembly according to the twenty-third aspect is configured so that the total of the radial lengths is equal to or larger than 10 mm. 
     With the bicycle rear sprocket assembly according to the twenty-fourth aspect, it is possible to further increase the radial lengths of the plurality of internal-spline driving surface. This improves strength of the at least one sprocket. 
     In accordance with a twenty-fifth aspect, the bicycle rear sprocket assembly according to the twenty-third aspect is configured so that the total of the radial lengths is equal to or larger than 15 mm. 
     With the bicycle rear sprocket assembly according to the twenty-fifth aspect, it is possible to further increase the radial lengths of the plurality of internal-spline driving surface. This further improves strength of the at least one sprocket. 
     In accordance with a twenty-sixth aspect, the bicycle rear sprocket assembly according to any one of the seventeenth to twenty-fifth aspects is configured so that the at least one sprocket includes a smallest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the smallest sprocket is equal to or smaller than 10. 
     With the bicycle rear sprocket assembly according to the twenty-sixth aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a twenty-seventh aspect, the bicycle rear sprocket assembly according to any one of the seventeenth to twenty-sixth aspects is configured so that the at least one sprocket includes a largest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 46. 
     With the bicycle rear sprocket assembly according to the twenty-seventh aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a low gear side. 
     In accordance with a twenty-eighth aspect, the bicycle rear sprocket assembly according to the twenty-seventh aspect is configured so that the total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 50. 
     With the bicycle rear sprocket assembly according to the twenty-eighth aspect, it is possible to further widen the gear range of the bicycle rear sprocket assembly. 
     In accordance with a twenty-ninth aspect, a bicycle rear sprocket assembly comprises at least one sprocket. The at least one sprocket includes at least one internal spline teeth configured to engage with a bicycle hub assembly. The at least one internal spline tooth comprises an internal-spline driving surface and an internal-spline non-driving surface. The internal-spline driving surface has a first internal-spline-surface angle defined between the internal-spline driving surface and a first radial line extending from a rotational center axis of the bicycle rear sprocket assembly to a radially outermost edge of the internal-spline driving surface. The internal-spline non-driving surface has a second internal-spline-surface angle defined between the internal-spline non-driving surface and a second radial line extending from the rotational center axis of the bicycle rear sprocket assembly to a radially outermost edge of the internal-spline non-driving surface. The second internal-spline-surface angle is different from the first internal-spline-surface angle. 
     With the bicycle rear sprocket assembly according to the twenty-ninth aspect, it is possible to save a weight of the at least one sprocket with ensuring strength of the at least one internal spline teeth of the at least one sprocket. 
     In accordance with a thirtieth aspect, the bicycle rear sprocket assembly according to the twenty-ninth aspect is configured so that the first internal-spline-surface angle is smaller than the second internal-spline-surface angle. 
     With the bicycle rear sprocket assembly according to the thirtieth aspect, it is possible to effectively save the weight of the at least one sprocket with ensuring strength of the at least one internal spline teeth of the at least one sprocket. 
     In accordance with a thirty-first aspect, the bicycle rear sprocket assembly according to the twenty-ninth or thirtieth aspect is configured so that the first internal-spline-surface angle ranges from 0 degree to 10 degrees. 
     With the bicycle rear sprocket assembly according to the thirty-first aspect, the first internal-spline-surface angle ensures strength of the internal-spline driving surface. 
     In accordance with a thirty-second aspect, the bicycle rear sprocket assembly according to any one of the twenty-ninth to thirty-first aspects is configured so that the second internal-spline-surface angle ranges from 0 degree to 60 degrees. 
     With the bicycle rear sprocket assembly according to the thirty-second aspect, the second internal-spline-surface angle saves a weight of the at least one sprocket. 
     In accordance with a thirty-third aspect, the bicycle rear sprocket assembly according to any one of the twenty-ninth to thirty-second aspects is configured so that the at least one sprocket includes a smallest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the smallest sprocket is equal to or smaller than 10. 
     With the bicycle rear sprocket assembly according to the thirty-third aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a top gear side. 
     In accordance with a thirty-fourth aspect, the bicycle rear sprocket assembly according to any one of the twenty-ninth to thirty-third aspects is configured so that the at least one sprocket includes a largest sprocket including at least one sprocket tooth. A total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 46. 
     With the bicycle rear sprocket assembly according to the thirty-fourth aspect, it is possible to widen the gear range of the bicycle rear sprocket assembly on a low gear side. 
     In accordance with a thirty-fifth aspect, the bicycle rear sprocket assembly according to the thirty-fourth aspect is configured so that the total number of the at least one sprocket tooth of the largest sprocket is equal to or larger than 50. 
     With the bicycle rear sprocket assembly according to the thirty-fifth aspect, it is possible to further widen the gear range of the bicycle rear sprocket assembly. 
     In accordance with a thirty-sixth aspect, a bicycle drive train comprises the bicycle rear sprocket assembly according to any one of the first to ninth aspects and a bicycle hub assembly. The bicycle hub assembly comprises a sprocket support body including at least ten external spline teeth configured to engage with the bicycle rear sprocket assembly. Each of the at least ten external spline teeth has an external-spline driving surface and an external-spline non-driving surface. 
     With the bicycle drive train according to the thirty-sixth aspect, the at least ten internal spline teeth reduce a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. Further, the at least ten external spline teeth reduce a rotational force applied to each of the at least ten external spline teeth in comparison with a sprocket support body including nine or less external spline teeth. This improves durability of the sprocket support body and/or improves a degree of freedom of choosing a material of the sprocket support body without reducing durability of the sprocket support body. 
     In accordance with a thirty-seventh aspect, a bicycle drive train comprises the bicycle rear sprocket assembly according to any one of the tenth to sixteenth aspects and a bicycle hub assembly. The bicycle hub assembly comprises a sprocket support body including a plurality of external spline teeth configured to engage with the bicycle rear sprocket assembly. At least two external spline teeth of the plurality of external spline teeth are circumferentially arranged at a first external pitch angle with respect to a rotational center axis of the bicycle hub assembly. The first external pitch angle ranges from 10 degrees to 20 degrees. 
     With the bicycle drive train according to the thirty-seventh aspect, the first internal pitch angle reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. Further, the at least ten external spline teeth reduce a rotational force applied to each of the at least ten external spline teeth in comparison with a sprocket support body including nine or less external spline teeth. This improves durability of the sprocket support body and/or improves a degree of freedom of choosing a material of the sprocket support body without reducing durability of the sprocket support body. 
     In accordance with a thirty-eighth aspect, a bicycle drive train comprises the bicycle rear sprocket assembly according to any one of the seventeenth to twenty-eighth aspects and a bicycle hub assembly. The bicycle hub assembly comprises a sprocket support body including at least one external spline tooth configured to engage with the bicycle rear sprocket assembly. The at least one external spline tooth has an external-spline major diameter equal to or smaller than 30 mm. 
     With the bicycle drive train according to the thirty-eighth aspect, it is possible to manufacture a bicycle rear sprocket with a total tooth number that is equal to or smaller than 10. Therefore, it is possible to widen a gear range of the bicycle drive train. 
     In accordance with a thirty-ninth aspect, a bicycle drive train comprises the bicycle rear sprocket assembly according to any one of the twenty-ninth to thirty-fifth aspects and a bicycle hub assembly. The bicycle hub assembly comprises a sprocket support body including at least nine external spline teeth configured to engage with the bicycle rear sprocket assembly. At least one of the at least nine external spline teeth has an asymmetric shape with respect to a circumferential tooth-tip center line. The at least one of the at least nine external spline teeth comprises an external-spline driving surface and an external-spline non-driving surface. The external-spline driving surface has a first external-spline-surface angle defined between the external-spline driving surface and a first radial line extending from a rotational center axis of the bicycle hub assembly to a radially outermost edge of the external-spline driving surface. The external-spline non-driving surface has a second external-spline-surface angle defined between the external-spline non-driving surface and a second radial line extending from the rotational center axis of the bicycle hub assembly to a radially outermost edge of the external-spline non-driving surface. The second external-spline-surface angle is different from the first external-spline-surface angle. 
     With the bicycle drive train according to the thirty-ninth aspect, it is possible to save a weight of the bicycle drive train with ensuring strength of the bicycle drive train. 
     In accordance with a fortieth aspect, the bicycle rear sprocket assembly according to any one of the first to ninth aspects is configured so that the at least ten internal spline teeth have an internal-spline major diameter equal to or larger than 25 mm. 
     With the bicycle rear sprocket assembly according to the fortieth aspect, it is possible to ensure strength of the at least one sprocket. 
     In accordance with a forty-first aspect, the bicycle rear sprocket assembly according to the fortieth aspect is configured so that the internal-spline major diameter is equal to or larger than 29 mm. 
     With the bicycle rear sprocket assembly according to the forty-first aspect, it is possible to further ensure strength of the at least one sprocket. 
     In accordance with a forty-second aspect, the bicycle rear sprocket assembly according to any one of the first to ninth, fortieth, and forty-first aspects is configured so that the at least ten internal spline teeth have an internal-spline minor diameter equal to or larger than 25 mm. 
     With the bicycle rear sprocket assembly according to the forty-second aspect, it is possible to ensure strength of the at least one sprocket. 
     In accordance with a forty-third aspect, the bicycle rear sprocket assembly according to the forty-second aspect is configured so that the internal-spline minor diameter is equal to or larger than 27 mm. 
     With the bicycle rear sprocket assembly according to the forty-third aspect, it is possible to certainly ensure strength of the at least one sprocket. 
     In accordance with a forty-fourth aspect, the bicycle rear sprocket assembly according to any one of the first to ninth and fortieth to forty-third aspects is configured so that the at least ten internal spline teeth include a plurality of internal-spline driving surfaces to receive a driving rotational force from the bicycle hub assembly during pedaling. The plurality of internal-spline driving surfaces each includes a radially outermost edge, a radially innermost edge, and a radial length defined from the radially outermost edge to the radially innermost edge. A total of the radial lengths of the plurality of internal-spline driving surfaces is equal to or larger than 7 mm. 
     With the bicycle rear sprocket assembly according to the forty-fourth aspect, it is possible to increase the radial lengths of the plurality of internal-spline driving surface. This improves strength of the at least one sprocket. 
     In accordance with a forty-fifth aspect, the bicycle rear sprocket assembly according to the forty-fourth aspect is configured so that the total of the radial lengths is equal to or larger than 10 mm. 
     With the bicycle rear sprocket assembly according to the forty-fifth aspect, it is possible to further increase the radial lengths of the plurality of internal-spline driving surface. This improves strength of the at least one sprocket. 
     In accordance with a forty-sixth aspect, the bicycle rear sprocket assembly according to the forty-fourth aspect is configured so that the total of the radial lengths is equal to or larger than 15 mm. 
     With the bicycle rear sprocket assembly according to the forty-sixth aspect, it is possible to further increase the radial lengths of the plurality of internal-spline driving surface. This further improves strength of the at least one sprocket. 
     In accordance with a forty-seventh aspect, the bicycle rear sprocket assembly according to any one of the first to ninth and fortieth to forty-sixth aspects is configured so that at least two internal spline teeth of the at least ten internal spline teeth are circumferentially arranged at a first internal pitch angle with respect to a rotational center axis of the bicycle rear sprocket assembly. The first internal pitch angle ranges from 10 degrees to 20 degrees. 
     With the bicycle drive train according to the forty-seventh aspect, the first internal pitch angle reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. Further, the at least ten external spline teeth reduce a rotational force applied to each of the at least ten external spline teeth in comparison with a sprocket support body including nine or less external spline teeth. This improves durability of the sprocket support body and/or improves a degree of freedom of choosing a material of the sprocket support body without reducing durability of the sprocket support body. 
     In accordance with a forty-eighth aspect, the bicycle rear sprocket assembly according to the forty-seventh aspect is configured so that the first internal pitch angle ranges from 12 degrees to 15 degrees. 
     With the bicycle rear sprocket assembly according to the forty-eighth aspect, the first internal pitch angle further reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a forty-ninth aspect, the bicycle rear sprocket assembly according to the forty-seventh aspect is configured so that the first internal pitch angle ranges from 13 degrees to 14 degrees. 
     With the bicycle rear sprocket assembly according to the forty-ninth aspect, the first internal pitch angle further reduces a rotational force applied to each of the at least ten internal spline teeth in comparison with a sprocket including nine or less internal spline teeth. This further improves durability of the at least one sprocket and/or improves a degree of freedom of choosing a material of the at least one sprocket without reducing durability of the at least one sprocket. 
     In accordance with a fiftieth aspect, the bicycle rear sprocket assembly according to the forty-seventh aspect is configured so that at least two internal spline teeth of the at least ten internal spline teeth are circumferentially arranged at a second internal pitch angle with respect to the rotational center axis. The second internal pitch angle is different from the first internal pitch angle. 
     With the bicycle rear sprocket assembly according to the fiftieth aspect, the difference between the first internal pitch angle and the second internal pitch angle helps the user to correctly mount the bicycle rear sprocket assembly to the bicycle hub assembly, especially concerning a circumferential position of each sprocket of the bicycle rear sprocket assembly. 
     In accordance with a fifty-first aspect, the bicycle rear sprocket assembly according to the any one of first to ninth and fortieth to fiftieth aspects is configured so that the at least ten internal spline teeth comprise an internal-spline driving surface and an internal-spline non-driving surface. The internal-spline driving surface has a first internal-spline-surface angle defined between the internal-spline driving surface and a first radial line extending from a rotational center axis of the bicycle rear sprocket assembly to a radially outermost edge of the internal-spline driving surface. The internal-spline non-driving surface has a second internal-spline-surface angle defined between the internal-spline non-driving surface and a second radial line extending from the rotational center axis of the bicycle rear sprocket assembly to a radially outermost edge of the internal-spline non-driving surface. The second internal-spline-surface angle is different from the first internal-spline-surface angle. 
     With the bicycle rear sprocket assembly according to the fifty-first aspect, it is possible to save a weight of the at least one sprocket with ensuring strength of the at least one internal spline teeth of the at least one sprocket. 
     In accordance with a fifty-second aspect, the bicycle rear sprocket assembly according to the fifty-first aspect is configured so that the first internal-spline-surface angle is smaller than the second internal-spline-surface angle. 
     With the bicycle rear sprocket assembly according to the fifty-second aspect, it is possible to effectively save the weight of the at least one sprocket with ensuring strength of the at least one internal spline teeth of the at least one sprocket. 
     In accordance with a fifty-third aspect, the bicycle rear sprocket assembly according to the fifty-first aspect is configured so that the first internal-spline-surface angle ranges from 0 degree to 10 degrees. 
     With the bicycle rear sprocket assembly according to the fifty-third aspect, the first internal-spline-surface angle ensures strength of the internal-spline driving surface. 
     In accordance with a fifty-fourth aspect, the bicycle rear sprocket assembly according to the fifty-first aspect is configured so that the second internal-spline-surface angle ranges from 0 degree to 60 degrees. 
     With the bicycle rear sprocket assembly according to the fifty-fourth aspect, the second internal-spline-surface angle saves a weight of the at least one sprocket. 
     In accordance with a fifty-fifth aspect, the bicycle rear sprocket assembly according to any one of the first to ninth and fortieth to fifty-fourth aspects further comprises a sprocket support to which the at least one sprocket is attached. 
     In accordance with a fifty-sixth aspect, the bicycle rear sprocket assembly according to the fifty-fifth aspect is configured so that the sprocket support is made of a non-metallic material including a resin material. 
     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. This concept also applies to words of similar meaning, for example, the terms “have,” “include” and their derivatives. 
     The terms “member,” “section,” “portion,” “part,” “element,” “body” and “structure” when used in the singular can have the dual meaning of a single part or a plurality of parts. 
     The ordinal numbers such as “first” and “second” recited in the present application are merely identifiers, but do not have any other meanings, for example, a particular order and the like. Moreover, for example, the term “first element” itself does not imply an existence of “second element,” and the term “second element” itself does not imply an existence of “first element.” 
     The term “pair of,” as used herein, can encompass the configuration in which the pair of elements have different shapes or structures from each other in addition to the configuration in which the pair of elements have the same shapes or structures as each other. 
     The terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. 
     Finally, terms of degree such as “substantially,” “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. All of numerical values described in the present application can be construed as including the terms such as “substantially,” “about” and “approximately.” 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.