Bicycle rear sprocket assembly

1. A bicycle rear sprocket assembly configured to be mounted to a sprocket support body of a bicycle rear hub assembly, the bicycle rear sprocket assembly comprising:

a plurality of bicycle sprockets comprising:

a first sprocket including:

a first opening having a first minimum diameter that is smaller than a minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

a second sprocket including:

a second opening having a second minimum diameter that is equal to or larger than the minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

at least ten internal spline teeth configured to engage with the sprocket support body of the bicycle rear hub assembly, the at least ten internal spline teeth including a plurality of internal-spline driving surfaces to transmit a driving rotational force between the sprocket support body of the bicycle rear hub assembly and the bicycle rear sprocket assembly,

the plurality of internal-spline driving surfaces each including:

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 being equal to or larger than 7 mm,

the plurality of internal-spline driving surface each having 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 the radially outermost edge of the internal-spline driving surface, and

the first internal-spline-surface angle ranging from 0 degree to 6 degrees.

2. The bicycle rear sprocket assembly according to claim 1 , wherein

the at least ten internal spline teeth includes a plurality of internal-spline non-driving surfaces each having 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, and

the second internal-spline-surface angle ranges from 0 degree to 6 degrees.

3. The bicycle rear sprocket assembly according to claim 2 , wherein

the first internal-spline-surface angle is equal to the second internal-spline-surface angle.

4. The bicycle rear hub assembly according to claim 1 , wherein

at least one of the at least ten internal spline teeth of the second sprocket is circumferentially symmetric with respect to a reference line extending from a rotational center axis of the bicycle rear sprocket assembly to a circumferential center point of a radially outermost end of the at least one of the at least ten internal spline teeth in a radial direction with respect to the rotational center axis.

5. The bicycle rear hub assembly according to claim 1 , wherein

the second sprocket is adjacent to the first sprocket without another sprocket between the first sprocket and the second sprocket in an axial direction with respect to a rotational center axis of the bicycle rear sprocket assembly.

6. The bicycle rear sprocket assembly according to claim 1 , wherein

the first sprocket includes:

a first inward facing side; and

a first outward facing side opposite to the first inward facing side in an axial direction with respect to a rotational center axis of the bicycle rear sprocket assembly, and

the first sprocket includes a first torque-transmitting structure provided to the first inward facing side to directly or indirectly transmit a pedaling torque to the sprocket support body.

7. The bicycle rear sprocket assembly according to claim 6 , wherein

the first torque-transmitting structure includes at least ten first torque-transmitting teeth.

8. The bicycle rear sprocket assembly according to claim 1 , wherein

a total number of the at least ten internal spline teeth of the second sprocket is equal to or larger than 20.

9. The bicycle rear sprocket assembly according to claim 1 , wherein

the at least ten internal spline teeth of the second sprocket have an internal-spline major diameter; and

the internal-spline major diameter of the second sprocket is equal to or larger than 29 mm and equal to or smaller than 33 mm.

10. The bicycle rear sprocket assembly according to claim 1 , wherein

the at least ten internal spline teeth of the second sprocket have an internal-spline minor diameter; and

the internal-spline minor diameter of the second sprocket is equal to or larger than 28 mm and equal to or smaller than 31 mm.

11. The bicycle rear sprocket assembly according to claim 1 , wherein

the plurality of bicycle sprockets comprises a plurality of the first sprockets, the plurality of first sprockets each including the first opening.

12. The bicycle rear sprocket assembly according to claim 1 , wherein

the total of the radial lengths of the plurality of internal-spline driving surfaces is equal to or larger than 10 mm.

13. The bicycle rear sprocket assembly according to claim 1 , wherein

the total of the radial lengths of the plurality of internal-spline driving surfaces ranges from 11 mm to 14 mm.

14. The bicycle rear sprocket assembly according to claim 1 , wherein

a total number of the at least ten internal spline teeth of the second sprocket ranges from 22 to 24.

15. A bicycle rear sprocket assembly configured to be mounted to a sprocket support body of a bicycle rear hub assembly, the bicycle rear sprocket assembly comprising:

a plurality of bicycle sprockets comprising:

a first sprocket including:

a first opening having a first minimum diameter that is smaller than a minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

a second sprocket including:

a second opening having a second minimum diameter that is equal to or larger than the minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

at least ten internal spline teeth configured to engage with the sprocket support body of the bicycle rear hub assembly, the at least ten internal spline teeth including a plurality of internal-spline driving surfaces to transmit a driving rotational force between the sprocket support body of the bicycle rear hub assembly and the bicycle rear sprocket assembly,

the plurality of internal-spline driving surfaces each including:

a radially outermost edge,

a radially innermost edge, and

a radial length defined from the radially outermost edge to the radially innermost edge, and

a total of the radial lengths of the plurality of internal-spline driving surfaces being equal to or larger than 7 mm, wherein

the at least ten internal spline teeth of the second sprocket have a first internal pitch angle and a second internal pitch angle different from the first internal pitch angle.

16. The bicycle rear sprocket assembly according to claim 15 , wherein

the first internal pitch angle ranges from 13 degrees to 17 degrees.

17. The bicycle rear sprocket assembly according to claim 15 , wherein

the second internal pitch angle ranges from 28 degrees to 32 degrees.

18. The bicycle rear sprocket assembly according to claim 15 , wherein

the first internal pitch angle is half of the second internal pitch angle.

19. A bicycle rear sprocket assembly configured to be mounted to a sprocket support body of a bicycle rear hub assembly, the bicycle rear sprocket assembly comprising:

a plurality of bicycle sprockets comprising:

a first sprocket including:

a first opening having a first minimum diameter that is smaller than a minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

a second sprocket including:

a second opening having a second minimum diameter that is equal to or larger than the minimum outer diameter of the sprocket support body of the bicycle rear hub assembly; and

at least ten internal spline teeth configured to engage with the sprocket support body of the bicycle rear hub assembly, the at least ten internal spline teeth including a plurality of internal-spline driving surfaces to transmit a driving rotational force between the sprocket support body of the bicycle rear hub assembly and the bicycle rear sprocket assembly,

the plurality of internal-spline driving surfaces each including:

a radially outermost edge,

a radially innermost edge, and

a radial length defined from the radially outermost edge to the radially innermost edge, and

a total of the radial lengths of the plurality of internal-spline driving surfaces being equal to or larger than 7 mm, wherein

a total tooth number of the first sprocket is equal to or smaller than 10.

20. A bicycle rear sprocket assembly comprising:

at least one sprocket including at least ten internal spline teeth configured to engage with a sprocket support body of a bicycle rear hub assembly, the at least ten internal spline teeth including a plurality of internal-spline driving surfaces to transmit a driving rotational force from the at least one sprocket to the sprocket support body of the bicycle rear hub assembly and a plurality of internal-spline non-driving surfaces provided on a reverse side of the internal-spline driving surface in a circumferential direction with respect to a rotational center axis of the bicycle rear sprocket assembly;

the plurality of internal-spline driving surfaces each including:

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 being equal to or larger than 7 mm;

the plurality of internal-spline driving surface each having 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 the radially outermost edge of the internal-spline driving surface, the first internal-spline-surface angle ranging from 0 degree to 6 degrees; and

the plurality of internal-spline non-driving surfaces each having 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 ranging from 0 degree to 6 degrees.

21. The bicycle rear sprocket assembly according to claim 20 , wherein

the first internal-spline-surface angle is equal to the second internal-spline-surface angle.

22. The bicycle rear hub assembly according to claim 20 , wherein

at least one of the at least ten internal spline teeth of the at least one sprocket is circumferentially symmetric with respect to a reference line extending from the rotational center axis to a circumferential center point of a radially outermost end of the at least one of the at least ten internal spline teeth in a radial direction with respect to the rotational center axis.

23. The bicycle rear sprocket assembly according to claim 20 , wherein

the at least ten internal spline teeth of the at least one sprocket have a first internal pitch angle and a second internal pitch angle different from the first internal pitch angle.

24. The bicycle rear sprocket assembly according to claim 23 , wherein

the first internal pitch angle ranges from 13 degrees to 17 degrees.

25. The bicycle rear sprocket assembly according to claim 23 , wherein

the second internal pitch angle ranges from 28 degrees to 32 degrees.

26. The bicycle rear sprocket assembly according to claim 23 , wherein

the first internal pitch angle is half of the second internal pitch angle.

27. The bicycle rear sprocket assembly according to claim 20 , wherein

the at least ten internal spline teeth of the at least one sprocket have an internal-spline major diameter; and

the internal-spline major diameter of the at least one sprocket is equal to or larger than 29 mm and equal to or smaller than 33 mm.

28. The bicycle rear sprocket assembly according to claim 20 , wherein

the at least ten internal spline teeth of the at least one sprocket have an internal-spline minor diameter; and

the internal-spline minor diameter of the at least one sprocket is equal to or larger than 28 mm and equal to or smaller than 31 mm.

29. The bicycle rear sprocket assembly according to claim 20 , wherein

the total of the radial lengths of the plurality of internal-spline driving surfaces is equal to or larger than 10 mm.

30. The bicycle rear sprocket assembly according to claim 20 , wherein

the total of the radial lengths of the plurality of internal-spline driving surfaces ranges from 11 mm to 14 mm.

31. The bicycle rear sprocket assembly according to claim 20 , wherein

a total number of the at least ten internal spline teeth of the at least one sprocket is equal to or larger than 20.

32. The bicycle rear sprocket assembly according to claim 20 , wherein

a total number of the at least ten internal spline teeth of the at least one sprocket ranges from 22 to 24.