Drag, alongside rolling resistance, is the key factor determining the dynamics of a vehicle and its fuel economy. The higher the drag, the more power is needed to accelerate the vehicle to a certain speed and maintain it. Drag is created by the displacement of air around the vehicle and the frictional impact of that air on the surface of the vehicle. It counteracts the direction of motion of a vehicle, and is dependent on the vehicle's speed, its front face area, the drag coefficient (cd), and the density of the air. The formula for calculating drag is: Drag = vehicle speed squared x front face area x cd x 1/2 air density. The typically aerodynamic Volkswagen body style, allied to narrow shut lines, reduces air swirl, helping produce low levels of drag and so delivering lower consumption and greater fuel economy. The key influencing factor, though, is the vehicle's speed, as a doubling of speed quadruples the drag.