I always noticed some sort of input lag in RBR with my G27, the "vsync" lag. I thought it was inherent to the game itself, since I couldn't find any "Vsync" option anywhere. The problem is in fact situated in the Richard Burns Rally/Plugins/FixUp.ini file. Just change the vSyncActive value to 0, and that's it, no more input lag. Why this option is on by default is beyond me. I thought it was worth sharing, since I found a lot of people complaining about the issue but couldn't find a solution. Hope it helped.