Mountain bikes may use a "dropper" seatpost which allows the seat to remotely drop out of the way for easy maneuvering, and one with a remote allows you to control this from your handleabar. It is important to not use an road bike seatpost on a mountain bike as they are not designed to handle the increased stress of the sport. Seatposts also have a setback. A zero setback will locate the seat directly over the top of the seatpost and is more conducive to a forward position, whereas a 25mm setback will be located 25mm rearward.
