BMW 6 Driving Impressions II

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.