BMW's 6-Series models include a 360-horsepower, 4.8L V8 engine with variable valve timing and variable intake lifts and a dual exhaust system. The engine is matched to two possible transmissions: a 6-speed manual transmission or a 6-speed sport automatic transmission with steering wheel paddles. The convertible model has a thick, well-insulated soft top with an electrically retractable glass window; overall its coefficient of drag is almost as good as the coupe's, which should result in low wind noise. It includes additional body reinforcements and an Automatic Rollover Protection System. The 650i includes many features geared toward enthusiastic driving, without giving up comfort when it's appreciated. The Dynamic Driving Control system is standard, with which the driver can change the behavior of a number of controls, including the throttle, transmission and steering feel. Active Roll Stabilization, which aids in flat cornering, is also standard and vehicle speed-sensitive steering is also standard. An Active Steering system, which varies the steering ratio according to speed and other conditions, is optional. Big 4-wheel disc anti-lock brakes are standard, along with 18-inch run-flat tires. An optional Sport Package brings 19-inch wheels with performance tires in staggered sizes, front to back, for improved performance. There are also some innovative lighting features; xenon adaptive headlamps swivel slightly to the side to help illuminate into corners, and adaptive brake lights shine brighter during hard braking. To remove three things from the list of driver worries, there are new options for high beam assist and a lane departure warning system, and the adaptive cruise control now features a "stop and go" function. Inside, the 6-Series is a 2+2, meaning that the back seat only has enough space for small children. For front passengers, the experience is high-tech and luxurious. All 6-ers includes BMW's iDrive system, which combines controls for communication, audio, climate control and navigation into a menu system accessed through a haptic controller mounted on the center console. A Pearl leather option, with different stitching and Nasca leather trim, offers a more supple feel relative to the standard Dakota leather. The 6-Series models come very well equipped as luxury cars, but especially notable standard equipment includes power seats with adjustable lumbar support, leather upholstery, a power moonroof (on coupes), and a dual-zone climate control with odor filtration and humidity control. The standard sound system includes eight speakers and two subwoofers. At the top of the range is the high-performance M6 model, with a 500-horsepower, 5.0L V10 engine and 7-speed sequential manual gearbox (SMG). BMW claims a 0-60 time of only 4.5 seconds, though the major magazines have clocked it even faster. The M6 is available in both coupe and convertible variants, and loaded with equipment to make it track-ready, such as a G-sensitive lubrication system, a variable differential lock, a specially designed suspension, a performance-calibrated version of the DSC stability system, an Electronic Damping Control (EDC) system that allows customizable settings and a twin-chamber exhaust system that allows two different sound characteristics.