I felt something strange about rear derailleur.
because, sometime suddenly changed gear when I did not excepted.
So that, I went to a Giant store to check about it.
I thought, a wire or a chain should be extened. becaue I ride more than 2000km already.
After checking my bike, a staff told me a rear derailleur hanger was broken. a little bit bend. then asked me that did I fall down to right side before? Or something hit when I carrin in ( Rinkou)?
Yes, I remember that I felt down right side twice a few month ago. (Tachigoke!!)
A rear derailleur hanger is a very sensitive part. because it protect flame.
This is the rear derailleur hanger. it was broken.
There is a hanger between rear derailleur and flame.