This is basically a demo to the real GT5 thus the Prologue. Once you beat classes C, B, and A you got a unlocked stage called the S where you can do a "quick tune". This "quick tune is hidden kinda until you go to the screen prior to starting the race and that's where it appears. You can increase/decrease HP and weight and adjust gear ratios, change tires but that's pretty much it. It's not anywhere close to the tuning ability of GT4 but the graphics are awesome. Online is great feature too, but there are kinks.