The driving forces, which run over the chain are not to be underestimated. All the forces have to travel over the derailleur and be carried by the derailleur hanger during shifts with the added frictional forces.
From the derailleur the forces are transmitted to the dropout, the connection node to the seat stay and chain stay on the right side, the so-called rear triangle. Dropouts or even integrated derailleur hangers made of carbon or aluminum are the weak point of the whole frame.
Break off the derailleur hanger, is often not easy to replace, because there is a special derailleur hanger for almost every frame and the model variety seems infinitely large, why? Technical reasons are often secondary to this. Due to the design, a few basic technical variants are inevitable, determined by the distance, the height of the rear derailleur with respect to the rear hub, e.g. between road bike and mountain bike. These differences are dictated by the switch manufacturers for clean gear changes and the frame builders then have to adjust this to the frame via the derailleur hanger. However, this variety of models can not be justified naturally. Ultimately, Taiwan decides how to handle, how it is setup. Here are the most bicycle frames produced worldwide for well-known brands. Neglected a resident producer with a brand manufacturer for a low price for the production, the design of the derailleur hanger is completely subordinated, since there is no international standard for derailleur hangers. For example, at many bicycle manufacturers, the rear derailleur variants change not only from model to model, but also from year to year within a model range.
Nevertheless, with a little research and patience, a new, fitting derailleur hanger is usually found, provided that the dropout itself for attachment of the same is still in tact. Paying attention to the fit and positioning of the threaded screws is mendatory.
To avoid such damage in regular driving, always make sure that the circuit is set up correctly and rejust the circuit in regular intervals. In addition, the chain wear must be checked with a gauge, and if necessary, make a timely chain change. Also, the sprocket package itself wears and replace it in the episode, there is a pinion wear gauge. The same applies at this point, of course, for the rear and front derailleur socket, also here it may come to the exclusion of the same.
In this case, the damage means the end of the frame. The demolition of the derailleur hanger has also demolished the dropout and repair is excluded.
With regard to transport in a bicycle case or carton, the dropouts (including the left) must be specially protected against impact. We recommend to dismantle the derailleur with chain and derailleur hanger from the dropout before packing, to fix padded in the rear triangle. After unpacking so no re-adjustment must be made. At this point the special transport protection of Bopworx should be mentioned.
Everything else is fate, the branch on the ground, which brings the rear derailleur to block, the side lintel, etc., all this forces the derailleur hanger, or even the dropout to the breaking point.
And last but not least when shifting backwards, never accidentally trigger a gear shift when loosening backward cranking. It is clear in itself, but nevertheless can happen accidentally.
However, the above described is only half the truth, in itself any frame could be repaired with such damage again, as long as you can raise a second, identical frame and the same frame size and so swaps the entire rear triangle. Only who can find such a framework and the found spare parts dispenser would most likely be easier to repair.