A front suspension fork includes an adjustable device connected to at least one inner tube of the legs of the front fork and the adjustable device includes a rotatable cap which is fixed to a threaded rod which is moved up and down by rotating the cap. A pneumatic cylinder is connected to the lower end of the threaded rod and a connection part is connected to the lower end of the pneumatic cylinder and the connection part can be moved in the inner tube. The travel of the inner tube can be adjusted by adjusting the position of the threaded rod relative to the pneumatic cylinder.