Originally Posted by jz19
It is rare too see a steel bike with a replaceable derailleur hanger. I have read that replaceable hangers are there to protect the derailleur in case of a crash not the frame. The logic been that it is cheaper to replace the hanger that the rear derailleur. Nowadays at home we have all steel bike that came without them and this does not make me loose any sleep.
Aluminum frames commonly use replaceable hangers because a bent aluminum hanger may crack and eventually break if it is bent and subsequently straightened. Thus the hanger ultimately protects the expensive frame. It is unlikely to provide much protection to the derailleur since the hanger typically bends due to an impact to the derailleur. Steel frames do not use replaceable dropouts because it is a simple and safe procedure to bend the hanger back into alignment. I suspect titanium's properties are more like steel than aluminum in this regard. Perhaps a titanium expert can address this.