Volkswagen BlueMotion is a series of vehicles with additional tweaks designed to increase fuel economy. Depending on the vehicle, some of the tweaks include special engine tuning, low rolling resistance tires, and aerodynamic tweaks to lower drag including lowered suspensions and special spoilers, closed front grill, unique wheels, and even under-body modifications. A start/stop system automatically shuts off the engine when the vehicle is stationary (and in neutral with the clutch released for cars with manual transmissions), and then restarts it automatically when the clutch pedal is depressed (on manual cars) or brake pedal is released (on cars with automatic transmissions). BlueMotion vehicles are engineered to be lighter than their regular counterparts, and some cars get longer gears in the transmission to keep revs down and an alternator configured to do as much charging as possible when the car is decelerating and as little as possible when accelerating. Together all these small tweaks combine to make a surprising difference in vehicle efficiency.