Warning: my rear derailleur hanger was bent 4mm and I chased the wrong fix for two weeks
Last month my shifting went sloppy on my Tuesday ride through Forest Park and I blamed the cable, so I swapped it and re-indexed three times with zero luck. A guy at the shop on Vandeventer put a hanger gauge on it and showed me the bend was 4mm off, which no amount of barrel adjusting was gonna fix. I straightened it with an adjustable wrench in about two minutes and the shifting snapped back to normal right away. Now I'm kicking myself for buying a $40 cable set I didn't need. How often do you all check the hanger before touching the cable tension?