I've been playing with a G27, the default settings are pretty crappy. If you're on a console you could try messing with the settings in-game, but on the PC it's better to use the default game settings and adjust the game-specific settings in Logitech Profiler. See my post above for that. If you search around you can find some suggestions for wheel settings on the consoles.
I've been playing with the difficulty on Professional, after tuning the car I managed to qualify first for the first event with a time in the 1:28s (nearly ran the car out of gas in the last round of qualifying), but I haven't been able to get a decent finish yet, I think I'll have to play through the career twice to get up to Legend level.