Almost, but the image needs to be sized in powers of two, and you should use a "road surface" to squeeze the air under the car for more accuracy.
Right-Click - Save As or Save Image, then open in paint, and save it as a .bmp (I used png to keep the black/white pixels intact). Upload that .bmp to the simulator.
I used this format (512x128) for my car and can just barely see where the turbulence ends behind the car... you can really see that there's room for a whole car in the wake. Drafting anyone?
