Derailleurs, front and rear, are the way they are because the shifts to larger cogs or chainrings generally take more force than dropping to a smaller one. So we pull the lever to the bigger cog or chainring, and let the weak spring drop it the other way.

Index shifting brought lifter cog design that decreases the force necessary to shift to larger cogs, making Rapidrise practical.


But a better question is why, in the age of dedicated index-only brifters and one to three click shift maximums, are we putting problematic springs in derailleurs at all?