Most of the cars I didn't tune. For the LP640, I set downforce to max, 24 / 24, I don't know if I made any other changes. I'm on the PC version, so I don't know how the console version is. To be honest, I prefer Shift 1 because it was better for analog controllers like joystick. Also Shift 2 has no online chat feature, even when in a lobby waiting for a race, so the experience is not much different than playing in offline mode as there's no way to communicate with other players, unless you use a third party voice based communication system like VOIP, which in turn depends on what percentage of other online players are using it. Shift 2 was never that popular for online racing, probably because of these issues. Shift 1 was popular for online when it was new, but virtually no one plays it online anymore.
I don't know if your controller is analog or digital. Some gamepad like controllers have joysticks, but they are not fully analog, with only a few discreet positions for the joysticks, maybe just 5 different positions (like -2/2, -1/2, 0/2, +1/2, +2/2) which wouldn't work very well with most racing games.