Originally Posted by Nightshade

Yes that is exactly what a rig is. Hanging $1000+ in camera gear is not something to take risks with which is why the secrecy to it all.

You could do it the way you describe and I myself have hung out of cars doing 70+ down the freeway dragging the shutter, but results are incnsistent at best and many times shooting feature vehicles you have a limited amount of time with the car, so getting results by pure chance is something you don't have the option of doing.