[apgrok1]

I would have to disagree with Doax. What the VG's do is to disrupt the streamlines going over the vehichle. Streamlines don't like sharp corners and will only bend at about 10-12 degrees. The VG's disrupt the streamlines and create a layer of turbulance next to the vehicle. There are other streamlines that still travel around the vehicle, but they are pushed farther from the surface by the turbulance layer. This prevents the streamlines from hitting sharp corners and allows it to bend easier.