Needed a derailleur on a build. Pulled a Shimano RD A550 from the parts box.
Seems to be working fine but then I noticed an extra screw on the back of it.
Some digging around, I found the instructions.
Seems the screw controls the “return force” of the RD and I should use a stronger return force if I’m riding in “poor conditions.”
I’m only ever going to ride friction, and I’m never going to ride those monstrosities called bifters, so why does return force matter?
Shimano data sheet follows.