An adjustable-height bicycle seat post 
assembly comprises a hollow seat post for supporting a bicycle seat slidably on plastic guides or shims inside a hollow tube. The hollow tube clamps into the frame of a bicycle. A 
mainspring forces the post upward, but a 
locking mechanism interconnects the post with the tube in various fixed positions relative to the tube. The 
locking mechanism includes a housing, which supports a 
plunger for reciprocating movement into and out of engagement with holes on the post. The 
locking mechanism is affixed to the outside of the tube to bear shearing forces on the 
plunger. An endcap on the locking mechanism and a topcap on the tube protect the 
assembly from foreign debris. The locking mechanism may be manipulated remotely using a 
magnetic switch assembly or manually using a mechanical assembly. A lost motion 
coupling is integrated into the locking mechanism and / or 
actuator assembly to enable the remote 
actuator to be moved or deployed while the latch remains trapped under the influence of a dominant 
shear load. The lost motion 
coupling is also effective to allow an operator to deploy the remote 
actuator at any convenient time prior to a desired change in seat height.