The way tuning works in the game is kind of like the tuning in GT5 Prologue but more simplified. For a regular race you can change spring height, rate, damper, toe, and camber. No tuning options for transmission. You can adjust HP and Weight by up to 10%, but you cannot do this in Time Trial mode or Race mode, only in Drift mode.
I am very pleased with the game. The physics are very impressive as are the graphics. The best part of it for me is the track selection. There are no license tests like in the previous games, but there are 102 challenges (btw Christian, I have 41 Gold now, busted).
Car selection is great, JGTC 300 and 500 cars are back, LM spec race cars, Formula 1 Cars, Trucks are back along with classic American muscle, I just bought a Honda Odyssey, and if you pre-ordered the game you got a special car to start out (I got a Black Veyron).
I am also at S on 12 tracks so HA! again Christian.