is created between the rear surface 104 and the separated air streams 102 and is generally located behind the vehicle 100 the pressure in the lower pressure region 106 is lower than the pressure near the front of the motor vehicle 100 resulting in a net drag force on the vehicle 100 this pressure drag ultimately results in lower fuel efficiency and increased fuel consumption for a motor vehicle 100 the effect of pressure drag is magnified in vehicles that have poor aerodynamic shapes such as suvs vans trucks pick up trucks etc a rear surface 104 that is generally perpendicular to the ground is usually indicative of a poor aerodynamic shape especially when compared to sports cars or other vehicles with relatively tapered rear ends for these vehicles with poor aerodynamic shapes the lower pressure region 106 has a lower pressure closer to a true vacuum than in smaller more aerodynamic vehicles resulting in a larger pressure and force differential u2014 and thus more drag the size of the lower pressure region 106 and its actual pressure i e how close it is to a vacuum depend on many factors besides vehicle 100 shape the lower pressure region 106 will enlarge and the pressure will go down as vehicle 100 speed increases other variables such as air pressure wind speed and direction weather etc will also impact the.