D: means drag (air resistance).
L: means lift,which in negative value is downforce.
Also what you're showing in screen is at 7° wing angle on both ends,while the mod has option to set 0-20° to front and 0-30° to rear "wing",eventually increasing downforce faaaaaaaaaar beyond the values you set on default set (my mentioned ~1300kg at 250km/h). To make it correct,you should remove ability to adjust wings as I personally don't see anything adjustable on the car. If there really is such thing as adjustability of the downforce,it can be only like 3° at each end with rather minor effect. What nowhere is written is downforce distribution - one can only suck out of finger which part provides how much downforce as only value known (also claimed by manufacturer,which not always is real) is the total downforce. Additionally we have unsettable variable in LFS - ride height strongly affects strength of undertray,unfortunatelly we have to live with that until it gets updated.
PS. I'm no engineer either,just a simple handyman with passion for this racing simulator.