Aerodynamics is a combination of downforce or lift, and drag that apply on a few points on the car. Drag pushes the car down on its rear tires because it applies above the ground. Rear wings could have 'lift' values but overall the car might have rear downforce.
The RSR 3.0 for example has 3kg downforce at the front and 12.5kg downforce at the rear axle at 200km/h
Some cars have some lift, but you are talking the same ish amount, just a few kg.. Put that into perspective; the cars are usually about 1000kg, so with 10kg downforce at the rear, that is 1% of the car weight. Downforce / lift is a very small part of the handling of the cars.
Now I put the values better into perspective, I didn't know that rfactor actually calculated the effect of aero drag as transmitted to the ground via tires and previously thought it was only used in 2 dimensions. Impressive ...
Thus I thought before that the rear wing lift implemented was actually meant to represent car body lift with more accurancy than what is normally available with the [BODY] section. Using only that body section in the hdv one can't put downforce in one point (f.e. front of the body due to hood and windscreen angle) and lift on another (f.e. rear, representing the final high pressure area above the rear hood and window), so there is a need to use the front and rear wing sections for that (And eventually the diffuser), which complicates things a bit more unless one simplifies and calculates all values to the axis (And take acount yourself of the cantilevering added by the real location of the pressure centre)
Anyway in rFactor i have always found aero grossly exagerated. Maybe it was just a matter of the mods I have seen so far, but small changes seem to have too big effects.
But after getting more used to the car, and as I predicted, I start to like it much more and understand that the behaviour is truly more realistic.
Thanks again for your explanations Niels