Note: These settings are likely only useful for the DFGT. Even the G27 seems to like completely different settings if memory serves what MMCK used to run with his G27 compared to my DFGT.
Make a profile just for Grid 2.exe in the Logitech Profiler. Check all settings on except Combined Pedals, and set all levels to 67%. I prefer very quick ratio steering so have the degrees set to 200. Most prefer ~360 degrees.
Then launch through the Profiler and use the Start button A on your wheel when the game asks for it. Bind your buttons, then adjust your in-game wheel settings. Here's my current settings...
Steering Deadzone: 0%
Steering Saturation: 100%
Steering Linearity 2
Throttle Deadzone: 5%
Throttle Saturation: 90%
Brake Deadzone: 5%
Brake Saturation: 100%
Vibration and Feedback: On
Vibration Strength: 50%
Wheel Strength: 40%
Wheel Weight: 60%
Update: As the cars get more powerful it becomes easier to spin out if you apply too much throttle too soon coming out of corners, so I've upped the throttle deadzone and backed off the saturation.
Also backed off the wheel strength as the tracks got faster since it was working me too hard.
Grid 2 playername: Boss 429
TDU2 playername: Medcave, Texican, Boss 429 (current)