Some of the youtube videos for Shift 2 drag describe the tuning used, but the wheel spin is mostly an issue with which car you use. I used the Lamborghini LP640 (this is an extra content car, I got it in Limited Edition), and based on youtube videos, the LP640 is the best car for the 1/4 mile drag run (other cars are probably better for the 1 mile run due to higher top speed, despite the wheel spin). With the LP640, wheel spin is not that bad in 1st gear, and you can go full throttle once it shifts into 2nd gear. Other cars will spin the tires up to 4th or 5th gear. Looking at youtube videos, it seems the main tuning used for the LP640 is gearing, and possibly maximum downforce (24/24). I'm able to do low 8 second runs with just downforce tuning. The faster youtube videos show around 7.5 second runs with gearing adjustments, which I never tried, as you only need to beat 10.50 for the career milestone.
I also have the impression that the drag mode is inconsistent, as sometimes you can start earlier than normal without getting disqualified (red light).
