So, I have been thinking about this idea for a long time. I have heard that if you travel behind a semi-truck, then you drive within a pocket of stagnant air behind the truck and will end up using less gas because of this... My question is, if I attached a large piece of plywood in front of my car to a long metal bar mounted to my car, with the plywood being perpendicular to the ground and parallel to the front of my car, then would I be able to use less gas on my trip? I really really need to save money on gas.. I have attached a schematic image depicting the situation. Tell me if I will use less gas on my trip.