 All piston style seatposts move in a down and forward motion at the slope the seat tube.Because of the need for these parts to slide up and down, all piston style suspension seatposts suffer from at least a slight rotation around the axis of the post resulting in a seat that can wiggle side to side slightly.Piston style seatposts with springs that are not preloaded or other designs with poor tolerances can also have slight up and down wiggle in the seat in the axis of the post.