well, i suppose wheelies are possible since there is pictures of people doing it.. guess you gotta drive REALLY fast with no downforce in the front and max in the back. i would go try right now but i'm in the middle of an endurance...
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edit: i tried it. with the minola on the seattle circuit.. i used these special settings o get it to lift off:
All ballast in the back.
No downforce in front but full in the back.
NOS on full power.
The rest of the settings don't matter..
Going up the hills in Seattle just simply boost your car with the NOS and up you go!!
You cannot do it off the line like a drag car. You can only do it with aerodynamics or a jump. Also, this is a well-covered topic, so please try searching. Next time, try putting a word like "wheelie" into the advanced search box, and restrict the search to the GT4 forum and thread titles. See how well that works.