The Mercedes CLS550 is generally a joy to drive. Its 382-horsepower V8 delivers a wad of acceleration-producing torque at any speed. Its computer-managed air suspension scoffs at whatever the road serves up, delivering that classic Mercedes balance of ride comfort and predictable handling. This car is rock steady and inspires confidence at speeds that could earn you a nice set of handcuffs, courtesy of the highway patrol.
The CLS is loaded with technologies, but they can be a double-edge sword. Two drive-by-wire systems, the throttle/accelerator and brake controls, work to different effect. Both use sensors and servo motors in place of cables, virtually eliminating mechanical parts. The electronic throttle control is fantastic. It delivers instant engine response and integrates with the transmission and cruise-control system for smooth shifts and seamless operation, and it can actually improve fuel economy.
The drive-by-wire brakes, on the other hand, are not so satisfying. They will stop the CLS right now, and repeatedly, with no noticeable degradation in performance. Yet the engineers haven't quite figured out how to make these brakes more pleasing to the senses. The electronic brakes lack the steady pedal feel of the best mechanical systems. It's more difficult to modulate the pedal consistently, and smooth stops befitting a car of such grace can be a challenge.
Electronics aside, the CLS63 AMG stops like a sports car, and goes with almost as much enthusiasm as a race car. Its 6.2-liter V8 is a welcome improvement. Previously powered by AMG's supercharged 5.5-liter V8, this car with was fast. With the new 6.2-liter V8, it's blindingly quick but it's also super smooth. With 507 horsepower, the naturally aspirated 6.2-liter V8 delivers slightly more power than the supercharged engine it replaces. The 6.2-liter engine gets racing-style features such as dry sump lubrication, which ensures proper oiling under extreme g-forces.
This is the first AMG engine matched with the Mercedes seven-speed automatic transmission. Called, the AMG Speedshift 7G-Tronic, it pairs with the 6.2-liter V8 to form one of the most impressive powertrain combinations from Mercedes in years. Throttle response is instantaneous, automatic downshifts nearly so. The manual control electronics, which allow a driver to shift the transmission like a manual using either the shift lever or paddles on the steering wheel, are excellent. Speedshift allows the driver to hold a gear right at the 6.2 V8's 7200-rpm redline, where it's much silkier than the previous supercharged engine. There's a nice burbly exhaust tone at part throttle, and something more like a rebel yell when you floor it.
In the CLS63, the air suspension is tuned with a bias toward the handling side of the equation, or more firmly than some owners might like. It's also fitted with larger, Z-rated tires. In our view, it's not uncomfortable, and the payoff in improved response is worth it. Most Mercedes-Benz cars will go along for the ride when pushed, behaving predictably. The CLS63 AMG likes to be pushed. Think of it as a more willing participant in a spirited drive. SCCA Trans-Am champion Tommy Kendall gave took us on a couple of laps around the fast 2.5-mile Willow Springs International Raceway and quickly showed that that CLS63 worked at the limit of its tires very well at high speeds. Kendall had little trouble changing direction with a quick lift of the throttle while sliding the CLS63 through the turns.
