Originally Posted by
TiHabanero
"They are somewhat designed to fail the idea is those break and save your nice derailleur and your frame."
Yes, they are designed to fail in the event of a maladjusted derailleur or a crash. What I am seeing is the hangers become weak over time under normal use and require realignment and eventually replacement after the hanger has been realigned a few times. Some designs are more susceptible to this than others.
The hanger only becomes weak over time because you are realigning it. You can probably get away with trying to bend a replaceable derailer hanger
once. Any more than that is questionable. Even that once is somewhat questionable.
I have a few bikes with replaceable hangers that have over 10,000 miles on them. I have never had to adjust the hanger at all, much less periodically. I’ve also never replaced one of my own. As a long time volunteer at a co-op where we see just how badly bicycles can be treated, I’ve only had to replace a few (out of close to 15,000 bikes I’ve worked on) and most of those were obviously damaged.