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. Next Page