The FUNN UpDown dropper seat post uses a Twin Tube Cartridge System instead of a traditional IFP (internal floating piston) design. This Twin Tube Cartridge System means the dropper post can mechanically resets itself so as to eliminate unwanted seat post sag! Comes with an ultra-adjustable lever made to mount top or bottom of the bars, where its position can be rotated to achieve the desired angle.

Construction

The UpDown looks similar on the outside, but it uses a different design than many other posts currently on the market. The cartridge has an outer and inner tube which contain compressed air and hydraulic oil. When the actuator is in a closed position, the seatpost is locked out and the hydraulic oil contained in the inner chamber supports the rider's weight.

When the actuator opens and dropper compresses, oil flows from the inner chamber to the outer chamber and compressed air enters the upper part of the inner chamber. At full compression, the piston pushes both hydraulic oil and unwanted air from the inner tube.

When the cartridge rebounds from full compression, compressed air pushes the piston shaft upwards and only the hydraulic oil gets sucked into the inner chamber. This way, the cartridge can effectively reallocate both air and oil back to its proper designated locations in the system. This ability to self-restore and refresh theoretically means lower maintenance and no "bobbing" or "sinking" issues with the dropper.