Adjustable seatpost

1. A seat post assembly for a bicycle, the seat post assembly comprising:

a first tube having a first distal end;

a second tube having a second distal end, the first tube and second tube movable relative to one another to establish a distance between the first distal end and the second distal end along a tube axis;

a first pressure chamber having a loaded pressure proportional to a load applied along the tube axis;

a second pressure chamber having a second pressure not proportional to the load;

a flow path connecting the first pressure chamber and the second pressure chamber; and

a valve having an isolator disposed along the flow path and configured to move between a closed position closing the flow path and an open position opening the flow path between the first pressure chamber and the second pressure chamber,

wherein the isolator is configured to nullify any resultant force produced by the loaded pressure of the first pressure chamber acting on the isolator.

2. A seat post assembly of claim 1 , wherein the isolator moves between the closed position and the open position along an isolation axis.

3. A seat post assembly of claim 1 , wherein the second pressure is a preset pressure and wherein an isolation force produced by the preset pressure in the second pressure chamber acts on a distal end of the isolator.

4. A seat post assembly of claim 3 , wherein the isolator, in the closed position, is biased against a valve seat by the isolation force produced by the preset pressure in the second pressure chamber acting on the isolator.

5. A seat post assembly of claim 1 , wherein the isolator, in the closed position, is biased against a valve seat by an isolation force produced by a preset pressure in the second pressure chamber acting on a portion the isolator.

6. A seat post assembly of claim 1 , wherein a loaded force that is produced by the loaded pressure in the first pressure chamber acts on an intermediate portion of the isolator.

7. A seat post assembly of claim 6 , wherein the intermediate portion of the isolator includes opposing surface areas in a direction along an axis of the isolator.

8. A seat post assembly of claim 1 , wherein a loaded force that is produced by the loaded pressure in the first pressure chamber and that acts on the isolator is balanced along an isolation axis.

9. A seat post assembly of claim 8 , wherein the loaded force is balanced through opposing surface areas on the isolator along the isolation axis.

10. A seat post assembly of claim 1 , wherein an actuation axis of the isolator is non-parallel to the tube axis.

11. A seat post assembly of claim 10 , wherein the actuation axis is perpendicular to the tube axis.

12. A seat post assembly of claim 1 , wherein an actuation force required to actuate the valve under a larger load that is applied to the second distal end of the second tube is less than the actuation force required to actuate the valve under a smaller load that is applied to the second distal end of the second tube.

13. A seat post assembly of claim 1 , wherein, in the closed position, the isolator is biased closed by a fluid closing force acting on the isolator and produced by the second pressure, the fluid closing force being greater than a fluid opening force acting on the isolator and produced by the loaded pressure, whereby the distance between the first and second distal ends is maintained, and

wherein, in the open position, the isolator is opened against the fluid closing force by a combination of the fluid opening force and an actuation force that acts on the isolator whereby fluid can be exchanged between the first and second pressure chambers via the flow path and whereby the distance between the first and second distal ends can be adjusted.

14. A seat post assembly of claim 1 , wherein the first tube has an inner diameter and the second tube has an outer diameter that is smaller than the inner diameter so that the second tube is telescopically slidable along the tube axis to extend and retract the second tube relative to the first tube to adjust the distance between the second distal end and the first distal end.

15. A seat post assembly of claim 1 , further comprising:

a first fluid reservoir including the first pressure chamber, the second chamber, and the flow path.

16. A seat post assembly of claim 1 , wherein the isolator is configured having opposing surfaces such that a fluid opening force acting on one surface of the opposing surfaces is balanced by a fluid closing force acting on another surface of the opposing surfaces that opposes the one surface, the fluid opening and closing forces acting along an axis of the isolator.

17. A seat post for a bicycle, the seat post comprising:

a first tube having a first distal end;

a second tube having a second distal end, the first tube and second tube movable relative to one another along a tube axis to establish a height of an attachment portion of a seat post head for attaching a bicycle seat, the attachment portion carried on the second distal end; and

a battery pack including a battery and a battery housing, the battery housing configured for removable attachment of the battery pack to the attachment portion and configured to provide power to operate a height adjustment system of the seat post.

18. A seat post of claim 17 , the height adjustment system comprising:

a valve operable between an open position and a closed position, respectively, to selectively permit and prevent adjustment of the height of the attachment portion.

19. A seat post of claim 18 , further comprising:

a wireless actuator positioned remote from the valve and the battery pack, the wireless actuator actuable to selectively operate the valve.

20. A seat post of claim 17 , wherein the height adjustment system includes a bleed orifice that selectively opens to a fluid pressure chamber.

21. A seat post of claim 17 , wherein the height adjustment system comprises:

a motor operably coupled with the battery pack and disposed at a first radial distance from a tube axis of the seat post, the first radial distance being greater than a second radial distance from the tube axis to an outer wall of the second tube of the seat post.

22. A seat post of claim 17 , wherein the height adjustment system further comprises:

an isolator disposed along a flow path and configured to move between a closed state closing the flow path and an open state opening the flow path between a loaded pressure chamber and a preset pressure chamber; and

a driver having an eccentric bearing surface configured to contact a distal end of the isolator to actuate a valve including the isolator.

23. A seat post of claim 22 , where the driver includes a bearing attached to the eccentric bearing surface, the bearing having an inner race in contact with the eccentric bearing surface and an outer race that contacts the isolator.

24. A seat post of claim 23 , wherein the bearing is a ball bearing.

25. A seat post of claim 17 , wherein the height adjustment system comprises:

a wireless actuator positioned remote from the battery pack;

a motor; and

a printed circuit board configured to operate the motor in response to signals received from the wireless actuator.

26. A seat post of claim 25 , wherein the motor is positioned at the second distal end of the second tube.

27. A seat post of claim 26 , wherein the motor is carried on or in the attachment portion.