It seems that every few years the vehicle manufacturers add more gears. Simply put, more gears mean less rpm drop between shifts - and that allows the driver to keep the engine within its optimum power range as the vehicle's speed changes.

Five-speed transmissions were the hot performance setup in the 1980s and 1990s, then came six speeds in such vehicles as the Acura Legend, Acura NSX, Mitsubishi 3000 GT, Toyota Supra Turbo, Porsche 911, and BMW 540i, M3 and 6-Series. They say 7-speed manual transmissions are coming next.

The state-of-the-art production 6-speed transmission is probably BMW's "Sequential Manual Gear box" (SMG). The SMG tranny, which is about a $1,425 option on BMW 6-Series, M3 and Z4 models, doesn't have a manual shifter in the classic sense because gear changes are handled electrohydraulically. There's also no clutch pedal. The driver chooses an automatic or manual shift mode and the computer handles the rest. The manual mode allows the driver to shift gears at will, either by tipping the shift lever on the center console, or by pressing shift paddles on the steering wheel (similar to Formula 1 race cars). The computer controls the throttle open and operation of the clutch to flawlessly change gears - and faster than any human could make the maneuver. We're talking 80-millisecond shifts at full throttle! The computer is programmed to shift more a...