This is doable the way I mentioned with a showroom stock car with only an oil change. No need to adjust aero, gearing, or purchase softer tires. All I did was trace the yellow line near the apron with my left tires. No fuss, no muss.
Paused before crossing the line:
1. Purchase an oil change.
2. If you have a DFGT, turn off the ASM with your dial thingamabob. If you have any other wheel or use the DS3, do this (from 0010111 at GameSpot forums):
I haven't seen this talked about yet on this board, and I bet there are a lot of people unaware of this function if you haven't read the manual in depth or explored the controller configuration menu.
The RA Menu allows you to tune some aspects of your car while you're actually on the track. You can adjust Traction Control, Stability Management, Anti-lock braking, 4WD distribution, and Brake Bias; and best of all you can change your adjustments throughout the race. Unlike the quick-tune menu that has to be unlocked, the RA Menu can be accessed at any time.
First, you've got to set your controller up for RA Access. I reccommend assigning the R3 button to "(RA function) Show Menu" and then assigining up and down on the control pad to "(RA function) Select+/-." Then all that's left is to assign left and right on the control pad to "(RA function) Adjust -/+"
(TIP: When all buttons are assigned, the symbols should read +, -, -, + from top to bottom or you'll have the adjustments backwards)
Now it's as simple as pressing R3 during a race to bring up your new RA Menu, and then using the control pad to quickly and easily make adjustments during a race. Enjoy.