Because on a scale of 1-10 for simulation, Forza is "Let's artificially widen Karussel" and Gran Turismo is "Face the harsh reality of never getting your course maker".
If you want to fix Veyron, technique is more important than the tune.
Really, the Veyron is underrated though. It's definitely not as much of a boat as people realize. They just think they can use all 1200HP in the corner, and that's utterly stupid. Takes as much throttle control as a Viper.
Quick and dirty, I raised my ride height disparity in F/R to Max/Min, and the Spring Rates 2 or 3 clicks higher than normal for that weight, with an ultra stiff rear, and high front extension. I also had minimal rear camber, with aggressive front camber and toe. Didn't have much front toe, kept that around -10, but rear is about -40.
LSD was about 1/3 of my rear, IT and ACC were high, braking very low.
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Another point on technique, as others have mentioned before, if you try to turn while the big wing is out, bad things happen.
