The 5-Series is offered with three different engines--designated by the models 528, 535 and 550. A 230-horsepower, 3.0-liter in-line 6-cylinder engine is standard on 528 models; 535 models get a 300-horsepower, turbocharged 3.0-liter six. A 4.8-liter V-8 engine making 360 horsepower equips the 550. The 528 models are offered with rear-wheel or all-wheel drive, as are the 535 models, while the 550 is only available with rear-wheel drive. Each of the models comes with a standard 6-speed manual transmission. A 6-speed automatic transmission with Steptronic shift command is optional. The M5 model resides at the top of BMW's performance lineup. It's powered by a monster of a V10 engine that makes 500 hp and 383 lb-feet of torque. Power gets to the road via a 7-speed sequential transmission. The M5 utilizes a specially tuned sport suspension and unique cross-drilled disc brakes. M5-specific 19" wheels all around, a special spoiler and air diffuser also distinguish the M5 sedan from the rest of the 5-Series. The most popular 5-Series configuration is four-door sedan, but a 5-door wagon is also available, coming solely in all-wheel-drive 535xi trim. The wagon features the same performance-oriented engineering as the sedan, but also comes with a cargo cover, cargo net, and under-floor storage compartment. The 5-Series models have a roomy interior, with front seats that are excellent for long trips, enough back seat space for adults and, in sedans, a very roomy trunk. The instrument panel looks deceivingly simple, with a streamlined, horizontal design, but there's an underlying complexity in the iDrive controller that's needed to access some functions. Though the standard suspension setup is already quite firm, rear-wheel-drive models can be specified with a Sport Package, which brings a tighter Sport suspension, grippy multi-contour front seats, and upgraded wheels and run-flat performance tires. The package also includes Active Roll Stabilization, a system that simulates much stiffer anti-roll bars with an electronically controlled pump system. Another performance option is Active Steering, which actually helps steer the car back toward a more stable situation when the electronic stability control intervenes. Front side-impact and head-protecting airbags for front and rear outboard occupants are standard. Rear side airbags, a rare safety feature, are optional. Compared to other mid-size sport sedans, the 5-Series is a technology powerhouse. To help increase alertness and safety, BMW has designed a lane departure warning system. A clever night vision system is available, which helps spot and avoid animals in the darkness ahead. BMW's active cruise control is one of the most advanced offered, capable of even stopping and restarting the vehicle in traffic. Other unusual options include a heads-up display, high-definition (HD) radio and a high-beam assist feature.