what is the use of a roof rack
A roof bike rack or a roof rack, is a set of bars secured to the roof of a vehicle. It is used to carry bulky items such as luggage, bicycles, canoes, kayaks, skis, or various carriers and containers. There is a long history of the use of roof racks and their designs.
Roof rails are used to carry bulky cargo or sporting equipment overhead that can use special roof mounts which can be fixed on to these rails. They are a modern version of the old 'luggage carrier' except that they are designed to be mounting points rather than carriers.