The derailleur hanger, or dropout, forms the link between derailleur and bicycle frame. It protects the rear derailleur from damage in the event of a fall or fall over. The derailleur hanger bends or breaks on the ground at the moment of impact and sacrifices itself for the frame. A derailleur is cheaper and easier to replace. Usually only screws are necessary for the assembly, because the quick release of the rear wheel ensures additional stability and fixation on the frame. However, there are also bicycle frames without the possibility to attach a derailleur hanger. In this case, it is attached directly to the frame, which can lead to damage of the frame and the shifting in the event of a fall. Bicycles with hub gears do not need derailleur hangers.
