The Convertible is remarkably quiet with the top up, nearly as quiet as the coupe. As mentioned, the power rear windscreen can be lowered even when the top is up, though we didn't find it significantly added to air circulation. Conversely, the rear glass can be raised when the top is down to act as a windblocker, but turbulance with the top down was minimal, and raising and lowering the glass didn't seem to make a big difference.

The BMW 6 Series coupe and convertible are comfortable and sporty. Driving these cars is a joy. The BMW 645Ci Coupe ($69,300) and 645Ci Convertible ($76,300) are priced between the Mercedes CLK Coupe ($52,800) and CLK Convertible ($59,850) and the Mercedes SL500 ($88,500). And in terms of wonderfulness, it falls somewhere between the CLK and SL.

They look like no other BMW past or present, but people will instantly recognize the new 6 Series models as BMWs. The coupe and convertible drew lots of attention when we drove them around Beverly Hills and they looked right at home pulling up to the posh Beverly Hills Hotel.

The twin-kidney grille, quad headlamps and other classic cues quickly identify the 6 Series as a BMW. The 6 Series shares some key elements with the new 5 Series sedan, but it was designed from the ground up as a coupe rather than a sedan with two doors lopped off. Indeed, the new 6 Series is a classic BMW coupe: The front and rear overhangs (the distance from the wheels to the bumper) are short. The greenhouse is set back from the hood, observed by the relatively long distance from the trailing edge of the wheel well to the leading edge of the door. The 6 Series cars are shorter in overall length than the 5 Series sedans, yet the 6 Series benefits from a relatively long wheelbase (the distance between the front and rear wheels). In short, you know it handles great just by looking at it.

The turn signals are located above the headlamps allowing the headlamps to be moved farther around the corners to the sides of the car. The grilles take front and center stage with no ledge in front of them. When viewed from overhead, the front corners look rounded giving the 6 Series a shark nose.

In profile, the lines are sculpted but clean. Side marker lights at the trailing edge of the front wheel wells give the impression of attention to detail. The Hofmeister kink, a traditional BMW design feature named after an early designer, shortens and shapes the trailing edge of the rear side window, subtly conveying an impression of a BMW.

From the rear, however, the new 6 Series cannot be identified as readily. The tail lamps and badge label it as a BMW, but the rear looks different from past BMWs. The first time I caught a glimpse of one racing ahead on a winding road, my brain registered ''Chrysler'' before correctly identifying it. The tail lamps wrap around to the sides, so there's no precise point where the rear of the car ends and the side begins. As with the new 7 Series cars, critics don't like the way the rear deck looks somewhat disconnected from the rear fenders. BMW points out that the high deck improves rear grip at high speeds and allows for a big trunk. In any case this is a tidy, attractive car that looks very sporty. It looks best in silver and other lighter colors; the design details blend together on darker cars.

The roofline of the convertible is nearly identical to that of the coupe, and the soft top looks great when it's up. The convertible features a fastback roofline with fins on the trailing edges that frame the vertically mounted glass backlight (rear windshield); the rear glass can be raised or lowered like a side window by pressing a button. A reinforced B-pillar and extensive reinforcements on the lower sides of the convertible's monocoque were added to increase chassis rigidity.

The 6 Series comes standard with adaptive headlamps that aim toward the inside of a corner as the steering wheel is turned. This helps throw light around the bend, reducing shadows and improving visibility for the driver. Sometimes just that extra nanosecond of warning can make for a safer and more enjoyable drive.

The BMW 6 Series is smooth and precise. Always poised, it is easy to drive smoothly and quickly. The ride is taut but not harsh. The engine is silky smooth and tractable for easy going around town or in stop-and-go traffic. Yet you're rewarded with immediate response whenever you press down on the accelerator. This car immediately becomes and extension of the driver, smoothly and flawlessly executing his or her wishes. It's easy to modulate the brakes and throttle and the steering is very precise, all making for a smooth driving experience.

BMW's 4.4-liter V8 delivers 325 horsepower and 330 pound-feet of torque to the coupe and convertible. The 3,781-pound coupe with the manual or SMG can accelerate from 0 to 60 mph is 5.5 seconds, according to BMW. The convertible is heavier and about a half-second slower. The 32-valve V8 benefits from Valvetronic variable valve timing and variable lift; breathing is controlled entirely by the valves. There is no traditional throttle, so that pedal on the right is more accurately called an accelerator pedal. It's a fascinating engine for engineers and car buffs with technological marvels such as its Double VANOS steplessly variable intake manifold. But the bottom line is that there's lots of power throughout the rev range, so the 645Ci responds quickly and precisely in any situation. It's also an efficient powerplant, so energy is not wasted but is instead channeled into fuel-efficient power. The engine sounds great, emitting a guttural roar under hard acceleration through its nicely tuned exhaust system.

As mentioned, three transmissions are available. We recommend choosing the six-speed Steptronic automatic unless you're a serious enthusiast, in which case we recommend the six-speed manual. We did not care for the six-speed sequential manual gearbox, or SMG. The Steptronic automatic is smooth in normal driving and very responsive for spirited driving. In fact, a 645Ci with the automatic is nearly as quick as a well-driven 645Ci with the manual. As with all BMW automatics, it offers a Sport mode setting that moves shift points to higher revs for increased response; the manual Steptronic mode enables the driver to shift manually, imparting some of the sportiness of a manual. We found little need to shift into the manual mode, however, because it always selected the right gear automatically. The manual gearbox is smooth and precise, easy to shift, with easy clutch pedal effort; it's lighter than the six-speed used in the BMW M3. The SMG is the same transmission yet it operates the clutch electronically, eliminating the clutch pedal. Though I like the SMG in the M3, I found the 645Ci's SMG shifted too slowly and took some of the enjoyment out of driving it.

The 645Ci offers a nice balance of ride and handling. Though taut, it doesn't beat up your passenger on rippled highways. The springs and shocks are firmer than on the 545i, but not as firm as those on the 545i sport package, which are quite firm; and the 6 Series cars ride lower than the 5 Series. On a mountain road it's absolutely joyful. Handling is precise, with a superb self-centering feel to the steering. It goes around high-speed turns like it's on rails. It can be driven very hard into tight corners. The suspension is tuned to minimize undesirable behavior when lifting off the gas while cornering, braking hard, or accelerating hard.

Active Roll Stabilization dramatically reduces body roll in cornering. Under hard cornering, the anti-roll bars are twisted by little hydraulic motors, so the 645Ci motors around turns with little leaning. In addition to increasing driver confidence, the system improves handling over bumps, increases cornering capability, and improves steering response.

Drive the 645Ci past the limit of the tires and the Dynamic Stability Control and other active safety systems kick in, allowing the car to motor around the corner without undue drama. The DSC system prevents the car from skidding into understeer or oversteer, making it easier for the driver to maintain control. Simply aim the 645Ci where you want to go and it'll go there. And if it snows, press the DTC button to turn on the traction control system. The brakes are excellent, with big, lightweight discs and calipers, and ABS, electronic brake proportioning and dynamic brake control.

The 6 Series cars come standard with high-performance run-flat tires, aggressive 245/45VR18. The coupes and convertibles we drove were equipped with 19-inch wheels, part of the optional Sport Package, and they rode well. The Sport Package also includes active steering, which improves high-speed stability and makes it easier to steer in parking lots.

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