when i next have a test day i will be having a go at the wool test, tape a lot of 2 inch long bits of wool over the car and drive it a differant speeds with somone taking photos of it.
cheap windtunnel
going to be trying to make the bottom of the car as flat as poss this year with a defuser running from the rear axle line to about 5 inchs behind the rear panel.also going to be making some deep side skirts with a kick up at the rear to try and remove the sharpe jion between the rear 1/4 and the rear wing, might also help in dirrecting air to the rear wing.
main thing to aim at is stopping as much air as you can from going under the car, front and side, and giving it the smoothest route out. heance the rear defuser.
cheers rob