Bicycle with rear suspension

1. A rear wheel suspension system for a bicycle having a frame with at least a bottom bracket, a seat tube, a top tube and a down tube, the suspension system comprising:

upper and lower pivots adapted to be fixed to said frame at two spaced apart points thereon, said lower pivot being disposed proximate said bottom bracket;

a swing-arm having a forward end pivotally connected directly to said frame by said lower pivot such that said swing-arm pivots about a fixed point at said lower pivot, said swing-arm having a wheel mounting bracket at a rear end thereof for receiving a rear wheel axis;

a first link member having an upper end pivotally connected to said upper pivot and a displaceable lower end pivotable about said upper pivot;

an intermediate lower link member having a forward end pivotally connected to said first link member and a rearward end pivotally connected to said swing-arm;

said first link member rotating in a direction opposite to the rotation of said swing-arm as said suspension system compresses; and

a shock absorber having a first end pivotally connected to said first link member and a second end adapted for connection with said frame.

2. The rear wheel suspension system as defined in claim 1 , wherein said forward end of said intermediate lower link member is pivotally connected to said first link member at a point on said first link member between said upper and lower ends thereof.

3. The rear wheel suspension system as defined in claim 1 , wherein said first and second ends of said shock absorber are disposed on opposed sides of a longitudinal central axis of said seat tube at least when said suspension system is in an uncompressed position.

4. The rear wheel suspension system as defined in claim 1 , wherein said upper pivot is proximate said seat tube.

5. The rear wheel suspension system as defined in claim 1 , wherein said upper pivot is disposed rearward of a first reference axis extending between said bottom bracket and an intersection between said seat tube and said top tube.

6. The rear wheel suspension system as defined in claim 5 , wherein the upper pivot is located rearward of a second reference axis extending through the lower pivot and a center of the bottom bracket.

7. A bicycle frame set comprising:

a main frame including at least a seat tube, a top tube, a head tube, and a down tube having a bottom bracket affixed thereto; and

a rear wheel suspension system pivotally attached to said main frame at two spaced apart locations, said rear wheel suspension system comprising:

a swing-arm having a forward end pivotally connected directly to said main frame by a lower pivot point located proximate said bottom bracket, said swing-arm having a wheel mounting member at a rear end thereof for receiving a rear wheel axle, said swing-arm pivoting relative to said main frame such that the rear wheel axle pivots about the lower pivot point with a constant radius of rotation;

a first link member having an upper end pivotally connected to said main frame at a link pivot point, said first link member having a displaceable lower end pivotable about said link pivot point;

an intermediate lower link member having a first end pivotally connected to said first link member and a second end pivotally connected to said swing-arm;

said first link member rotating in a direction opposite to the rotation of said swing-arm as said suspension system compresses; and

a shock absorber having a first and pivotally connected to said first link member and a second end pivotally connected with said main frame.

8. The bicycle frame set as defined in claim 7 , wherein said first end of said lower link member is pivotally connected to said first link member at a point on the first link member between said upper and lower ends thereof.

9. The bicycle frame set as defined in claim 7 , wherein said seat tube is discontinuous and has a lower remote end, an opening being defined below said lower end and aligned with said longitudinal central axis of said seat tube.

10. The bicycle frame set as defined in claim 9 , wherein said shock absorber extends through said opening.

11. The bicycle frame set as defined in claim 10 , wherein at least one structural support member links said seat tube and said down tube, said structural support member being laterally offset from said opening.

12. The bicycle frame set as defined in claim 7 , wherein said shock absorber is connected to said down tube of said main frame.

13. The bicycle frame set as defined in claim 12 , wherein said down tube has a length L defined between said bottom bracket and an intersection of said down tube and at least one of said top tube and said head tube, and wherein said shock absorber is connected to said down tube a distance less than 0.5 L from said bottom bracket.

14. The bicycle frame set as defined in claim 7 , wherein said shock absorber includes first and second ends, said first and second ends being disposed on opposed sides of a longitudinal central axis of said seat tube.

15. The bicycle frame set as defined in claim 7 , wherein the link pivot point between the first link member and the main frame is disposed proximate said seat tube.

16. The bicycle frame set as defined in claim 15 , wherein the link pivot point is located at least rearward of a first reference axis extending through said bottom bracket and an intersection of said seat tube and said top tube.

17. The bicycle frame set as defined in claim 16 , wherein said link pivot point is located rearward of a second reference axis extending through said lower pivot point and a center of said bottom bracket.

18. A bicycle frame set comprising:

a main frame including at least a seat tube, a top tube, a head tube, and a down tube having a bottom bracket affixed thereto, said seat tube being discontinuous and having a lower remote end, an opening being defined below said lower end and aligned with a longitudinal central axis of said seat tube; and

a rear wheel suspension system pivotally attached to said main frame at two spaced apart locations, said rear wheel suspension system comprising:

a swing-arm having a forward end pivotally connected directly to said main frame by a lower pivot point located proximate said bottom bracket, said swing-arm having a wheel mounting member at a rear end thereof for receiving a rear wheel axle, said swing-arm pivoting relative to said main frame such that the rear wheel axle pivots about the lower pivot point with a constant radius of rotation;

a first link member having an upper end pivotally connected to said main frame at a link pivot point, said first link member having a displaceable lower end pivotable about said link pivot point;

an intermediate lower link member having a first end pivotally connected to said first link member and a second end pivotally connected to said swing-arm; and

a shock absorber having a first end pivotally connected to said first link member and a second end pivotally connected with said main frame, said shock absorber extends through said opening defined below the lower remote end of the discontinuous seat tube.

19. The bicycle frame set as defined in claim 18 , wherein said first link member rotates in a direction opposite to the rotation of said swing-arm as said suspension system compresses.

20. The bicycle frame set as defined in claim 18 , wherein said first end of said lower link member is pivotally connected to said first link member at a point on the first link member between said upper and lower ends thereof.