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The ultimate driving machine in a two-door GT
Introduction
The BMW 6 Series delivers stellar performance, brilliant handling, and that arrow-like stability that marks this marque. The 6 Series is a true grand touring car, unique in the BMW line-up. And it comes in coupe and convertible styles.
The 645Ci coupe and 645Ci convertible are essentially hard top and soft top versions of the same car. Bristling with the latest in technology, they are based on the superb new 5 Series chassis but are not simply two-door versions of the sedans. The 6 Series cars are modern GTs, or Gran Turismo cars. They offer greater luxury and comfort than the Z4 sports car, yet with higher performance, more agile handling, and sportier styling than the 5 Series sports sedans.
The 645Ci Coupe and 645Ci Convertible each qualify as an ultimate driving machine, yet either can be driven all day in perfect comfort. 
Driving Impressions
The BMW 645Ci 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 an 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. The 3,781-pound coupe with the manual or SMG can accelerate from 0 to 60 mph in 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. (Technically, there is no throttle, so the pedal on the right is more accurately called an accelerator.) It's a fascinating engine for engineers and car buffs with technological marvels such as its Double VANOS steplessly variable intake- and exhaust-valve timing. 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 engine, 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.
Of the three transmissions available, we recommend the six-speed automatic unless you're a serious enthusiast, in which case we recommend the six-speed manual. The 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 Steptronic manual 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 in automatic mode. 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 . In short, the six-speed manual is an excellent choice. The sequential manual gearbox, or SMG, is the same transmission as the manual, but 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; it lacks the degree of adjustability of the M3. I did not care for the SMG.
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. The 6 Series cars ride lower than the 5 Series. A 645Ci is absolutely joyful on a winding road, as we discovered on some mountain roads near Santa Barbara. 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 braking hard, accelerating hard, or lifting off the gas while cornering.
Active Roll Stabilization dramatically reduces body roll in cornering. As the car turns corners, the anti-roll bars are twisted by little hydraulic motors, so the 645Ci leans very little, even in hard cornering. 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 corners without undue drama. The DSC 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, assuming the laws of physics allow it. If it snows, press the DTC button to turn on the Dynamic 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 aggressive 245/45VR18 high-performance run-flat tires. 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. Some drivers don't like BMW's active steering; I'm not one of them. |
