Bicycle suspension system

1. A suspension system comprising:

a front frame connected to a front wheel;

a shock absorber pivotally connected to the front frame and having a preset pressure, wherein the shock absorber is adjustable to set the preset pressure;

a rear frame connected to a rear wheel supported by a ground contact point, and structurally configured to maintain an instantaneous center point of movement of the rear frame relative to the front frame within an angle range of about 45°±15° relative to the ground contact point when the rear frame moves relative to the front frame;

a drive unit having a crankshaft mounted directly to the front frame;

wherein the front and rear frames are arranged to guide a virtual pivot point, which represents a rotating center of a center point of the rear wheel when the rear wheel moves upwardly relative to the front frame, to move from a first position, which is located rearward of a center of the crankshaft, to a second position that is rearwardly spaced away from the first position when the rear wheel moves away from a ground surface.

2. The suspension system of claim 1 , wherein the instantaneous center point of movement comprises a center point of rotation of the rear frame relative to the front frame, and the front and rear frames are connected together at a plurality of rotation axes that define the instantaneous center point of rotation.

3. The suspension system of claim 1 , wherein the front and rear frames are connected together at a first rotation axis, a second rotation axis, a third rotation axis, and a fourth rotation axis, and the instantaneous center point of movement of the rear frame relative to the front frame is substantially aligned with an intersection point between a first line, which extends through the first rotation axis and the second rotation axis, and a second line, which extends through the third rotation axis and the fourth rotation axis.

4. The suspension system of claim 3 , wherein the first rotation axis and the second rotation axis connect a lower connecting bar of the rear frame to the front frame.

5. The suspension system of claim 3 , wherein the third rotation axis and the fourth rotation axis connect an upper connecting bar of the rear frame to the front frame.

6. The suspension system of claim 1 , further comprising a chainwheel of the drive unit, and wherein the rear frame is configured to substantially align movement of the virtual pivot point relative to a line extending between the center point of the rear wheel and a tangent point of the chainwheel.

7. A rear suspension system for a bicycle having a frame supported by a front wheel comprising:

a shock absorber connected to the front frame; and

a rear frame supported by a rear wheel and connected to the front frame of the bicycle at a plurality of pivot points arranged to maintain a pivot of the rear frame relative to the front frame within an angle range of about 45°±15° with respect to a ground surface, where the angle range has a vertex at a rear wheel ground contact point;

a drive unit having a crankshaft mounted directly to the front frame;

wherein the front and rear frames are arranged to guide a virtual pivot point, which represents a rotating center of a center point of the rear wheel when the rear wheel moves upwardly relative to the front frame, to move from a first position, which is located rearward of a center of the crankshaft of the drive unit, to a second position that is rearwardly spaced away from the first position when the rear wheel moves away from a ground surface.

8. The rear suspension system of claim 7 , wherein the rear frame includes a lower connecting bar and an upper connecting bar, and the plurality of pivot points include first and second pivot points between the lower connecting bar and the front frame, and third and fourth pivot points between the upper connecting bar and the front frame.

9. The rear suspension system of claim 7 , wherein the shock absorber is provided with a preset pressure.

10. The rear suspension system of claim 7 , further comprising:

a chainwheel assembly having at least one sprocket mounted on the front frame, the chainwheel assembly having a virtual intermediate circle concentric to the at least one sprocket, the virtual intermediate circle located at an intermediate position of the at least one sprocket, and having an average diameter substantially equal to a diameter of the at least one sprocket; and

wherein the rear frame is configured to guide a movement of the virtual pivot point along a path substantially aligned with a tangent line extending between a center point of the rear wheel and a tangent point on the virtual intermediate circle.

11. The rear suspension assembly of claim 10 , wherein the chainwheel assembly includes three sprockets, and the virtual intermediate circle is substantially coincident with an outer circumference of the intermediate sprocket.

12. The rear suspension assembly of claim 10 , wherein the chainwheel assembly includes two sprockets, and the virtual intermediate circle is substantially coincident with an intermediate circle between the two sprockets.

13. The bicycle assembly according to claim 10 , wherein the chainwheel assembly includes a sprocket, the virtual intermediate circle is substantially coincident with an outer circumference of the sprocket.