A wheelie thread!!! dang, it's been awhile since i seen one of these in GT2!
Anyways, i'm being silly. here's a couple threads to get you started.
https://www.gtplanet.net/forum/showthread.php?t=5933&highlight=wheelie
https://www.gtplanet.net/forum/showthread.php?t=78758&highlight=wheelie
I've personally never done one, but here's some text in the GT3 forum that gives you the settings. Apparently it works for GT2 too.
Here is how to set the car up to reach speeds in excess of 860mph.
1. Have a car with OVER 1000 HP. Like the Escudo, GT-one race car, or R390 GT1 Race car.
2. Equip the highest stage turbine kit or NA tune possible.
3. Decrease spring rate to the smallest possible value for both front and rear.
4. Decrease ride height to the smallest possible value for both front and rear.
5. Set the gear ratio's auto setting to the highest level possible.
5. Set the gear ratio's final gear to about 3.000
6. Decrease the front downforce to the smallest possible value.
7. Increase the rear downforce to the largest possible value.
8. Set ASM to level 0.
9. Set TCS to level 0