Is it meant to be adjustable down to -2%? If so, where do you use it I usually do that with the WTCR cars as they are FWD, but I never saw this option at a GTR3 car Greetings
I believe that even at -2 degrees, the wing is streamed in such a way that it still generates downforce. It surely does not produce any lift at the back as the minus would suggest. But interesting nonetheless, maybe you can check the change of the ride hight in the second monitor app. It should decrease from static to going fast in any case I think.
Good question. Yes it is intended, the adjustment ranges in game are all matched to what's available on the real cars. So the common train of thought is that if a wing is showing a negative angle, it must be making positive lift (or negative downforce, although aerodynamicists actually refer to downforce as negative lift..) right? Well, no. A wing generates lift due to it's shape, forcing air to take a longer journey on it's underside, which creates negative pressure and 'draws' the wing down into the void created. You can see that happening below: It's commonly confused with how a spoiler works, which basically vectors air pressure to create downward force. As long as it's working within it's operating window, for a wing to generate lift it needs to be completely inverted, as if it was fitted to an aircraft. A wing's operating window is the angle it can work effectively in an airflow. Above or below a certain angle (which can be for example +-20 degrees) the wing will stall. What that means is the wing is simply acting as an obstacle for the air flow and will generate a lot of drag with very little positive effect. What I'm getting at is that you would have to set the Z4 rear wing at something silly like -20 degrees to see any actual positive lift from it.
I think the first cars in RaceRoom that came up with negative wing angles were the TCRs. In the beginning I also wondered what this might be about until I took a closer look at the TCRs during my visit to Oschersleben last year. There I saw this: If you look closely, you can see that the front part of the wing is higher than the rear end. And I think this is what translates to negative wing angles in RaceRoom. Due to the characteristics of a wing shape this still generates downforce as explained by @Alex Hodgkinson. This Opel has a different setting compared to the Audi above:
The most prominent example of it I've seen is in this picture of an Aston Martin Nimrod at Le Mans in 1983/4
Found an example of a rear wing where an angle of -8 is given for the point of zero lift. Just an example as that all depends on the exact profile of a wing. But I thought I'd add it here. Source: http://www.formula1-dictionary.net/angle_of_attack.html