Mercedes-Benz makes only minor updates to its CLS-Class four-door luxury-oriented coupes for 2010. A fine-grained premium-leather-wrapped steering wheel now comes as standard equipment, and Mercedes adds HD Digital Radio to the CLS-Class's 510-watt, 12-speaker Harman Kardon digital surround sound audio system, which also includes a 6-CD changer and Sirius satellite radio. Mercedes bills the CLS-Class, introduced in 2005, as the world's first four-door coupe. Drawing design inspiration from the CL-Class coupes, the CLS-Class features a long, low profile, arched sidelines from front to rear, and a pillarless cabin design, resulting in a clean, uninterrupted profile with the windows open or closed. Other design features include clear-lens headlights, wraparound LED taillights, a muscular rear end, and trapezoidal chrome exhaust tips. The CLS-Class consists of the CLS-550 and the CLS63 AMG for 2010. Both trims seat four passengers and deliver a potent combination of high performance and upscale interior, along with an extensive list of standard features. A 5.5-liter, 382-hp V8 engine powers the CLS-550. The V8 generates 75% of its peak torque of 391 lb-ft at just 1,000 rpm, resulting in impressive acceleration and passing performance. The engine links to a seven-speed automatic transmission with the Touch Shift manual-shift feature and pushes the CLS-550 from 0-60 mph in 5.4 seconds. Owners can add steering-wheel-mounted paddle shifters as an option. The rear-wheel-drive CLS550 rides on an Airmatic air suspension system featuring electronically controlled air springs, which adjust automatically to different driving conditions. The air suspension also lowers the car's height at higher speeds to improve aerodynamics and automatically levels the vehicle to compensate for cargo or passenger weight. The Airmatic air suspension works in conjunction with an Adaptive Damping System, which enables drivers to choose from one of four damping modes, or automatically selects a damping profile to provide an optimal ride on all types of road surfaces. The CLS63 AMG sports a hand-built, naturally aspirated 6.3-liter V8 engine, which pumps out 507 hp and 465 lb-ft of torque. The engine links to a seven-speed AMG Speedshift automatic transmission with steering-wheel-mounted fingertip shift paddles. The CLS63 AMG rides on an AMG Sports Suspension based on the Airmatic air suspension system with self-leveling and the Adaptive Drive System, and features a number of components designed by AMG, Mercedes' in-house tuner, including an AMG sports exhaust system and a high-performance braking system, as well as AMG exterior styling. Inside, the CLS-Class comes well-equipped with such standard features as leather upholstery, 10-way power-adjustable front seats with memory, high-gloss laurel wood trim, and four-zone digital climate control. In addition, the CLS-Class trims come equipped with a voice-activated navigation system, which includes an 8-inch color LCD screen, a 40-gigabyte hard drive, Sirius traffic updates, and Zagat restaurant reviews. Other standard features include a four-way power tilt/telescopic steering wheel, the Smart Key remote entry system, and the COMAND Cockpit Management and Data system, which drivers can use to manage the car's audio, climate control, and navigation systems. The CLS63 AMG adds such features as AMG multicontour leather front seats with adjustable side bolsters and alcantara shoulder inserts, an AMG ergonomic sports steering wheel, an AMG instrument cluster, and AMG sports pedals. Options include heated and ventilated seats, the Parktronic parking assist system, and the Distronic adaptive cruise control system, which maintains a pre-set distance behind the vehicle ahead. Electronic stability control, speed-sensitive power-assist steering, and antilock brakes with brake assist come standard on the CLS-Class. The CLS550 4MATIC rides on 18-inch wheels with high-performance tires, while the CLS63 AMG travels on 19-inch light-alloy wheels.