A roof rack allows you to carry larger cargo than would fit within your vehicle. Ask two questions when deciding which type of roof rack is best for your rig. What kind of cargo is being transported? What kind of roof does your rig have? The two materials most common for roof rack cross bars from 4WD are aluminum and steel. The steel is typically galvanized and then rust protected with plastic coating. Aluminum cross bars cost a bit more because they weigh less and they make less noise during transport. Depending on the type of roof your rig has, rack feet and adapter kits may be required. Depending on the cargo being transported (skis or bicycles for example), rack accessories may be required.