Moved By Bikes Surfboard Racks are designed to be the best racks you can buy. Because they mount right to your frame, they are super stable, even with longboards, but your short board will fit in there just fine too. The rear mount is to your seatpost OR your rear rack, your choice, no special rack required.
Weight: about 5 lbs depending on your specific configuration.
Board size: The Surfboard/Longboard Rack is good for boards up to about 12 feet in length. The bigger limitation is board weight. You should have no issues with boards up to 20 lbs, boards up to 25 lbs can work too if more diligence is taken during installation and with the right combination or bike/rider. The Shortboard Specific Rack is recommended for boards up to about 7 feet in length. The tubes are pre-bent with clearance for boards up to about 3.5 inches in thickness, if you board is thicker than that the bars can be bent open a bit to make more room