2004 BMW 645Ci Convertible Road Test

Whether tooling about town or tackling mountain passes, BMW's new flagship

Somehow BMW has managed to fabricate a drivetrain that functions so smoothly it feels capable of compensating for a driver's unflattering shifting skills. (Photo: Rob Rothwell, Canadian Auto Press)

convertible never has to reach too deeply into the well to stay out front of the pack. Power output is delivered in a smooth, progressive manner by a mill that eagerly spins to redline, while exhibiting delightful polish and refinement. BMW engineers have ensured that the engine is free of any and all unpleasant vibrations and thrashiness. The smooth torque generated in my tester was funneled through a six-speed manual gearbox before making its way to the rear wheels. Somehow BMW has managed to fabricate a drivetrain that functions so smoothly it feels capable of compensating for a driver's unflattering shifting skills. Driveline slap and clunk is non-existent, which certainly imparts a sense of quality, especially when trudging along in stop-and-go traffic. Although the stick in the 645Ci is a little taller and its throws a little longer than in some competing brands I have sampled, it actuates with deft precision. Each of the 6-forward gears notches smoothly in and out of place without resisting or feeling vague. Once a cog has been inserted, the clutch takes-up very easily and smoothly as the pedal nears the end of its outward travel. If a manual is not to your liking, BMW includes two more relaxing alternatives. The first is a Steptronic automatic offering six forward gears and manual actuation. The second is a variation of the brand's 6-speed SMG, or sequential manual transmission, the same type as used in the hot M3, albeit watered down somewhat.

BMW equips the midsize convertible with Active Steering and Active Roll Stabilization. (Photo: Rob Rothwell, Canadian Auto Press)

The 645Ci is also not technology-starved when it comes to handling enhancing driver's aids. BMW equips the midsize convertible with Active Steering and Active Roll Stabilization. The Active Steering technology (also termed Dynamic Driving Control) won the Automobile Journalists Association of Canada award for Best New Technology in 2004. I sampled this system in the 545i previously and was quite impressed with its ability to improve the vehicle's agility and nimbleness at low speeds, as well as stability at high speeds. The same holds true for its effectiveness in the 645Ci. Essentially the technology inserts a planetary gear into the steering column, which either increases the amount of steering input or decreases it, depending on the vehicle's speed. The advantages include go-kart quick steering when maneuvering through parking lots or around tight bends, and decreased steering sensitivity when highway cruising. The latter technology mentioned Active Roll Stabilization (also termed Dynamic Drive), which uses electronically controlled actuators integrated into the roll bars to apply opposing forces on the front and rear axles during cornering. This sophisticated suspension technology keeps the car pan-flat during aggressive maneuvers. It also mitigates the need to control body-roll through the use of human-punishing spring-rates.