Sequential Manual Gearbox (SMG)

Having premiered this system on the M3, BMW is rapidly extending the offering of SMG to other Series; for ’04 it is available in the 5, Z4 and 3 Series as well. In the 3 Series, it is offered on all models except those with all-wheel drive (the “xi” models).

In these three Series, SMG takes a less complex form than in the M3s, whose SMG offers fully 11 shift programs. But the concept is the same: electrohydraulic shifting and electronic controls applied to a 6-speed manual transmission to achieve a choice of driver-controlled or automated shifting, automatic clutch operation, and variable programming for the shifting.

In the 325 models, the SMG option includes the 6-speed transmission instead of the standard 5-speed; in the 330 models it employs the already standard 6-speed. The driver selects the desired operating range (N, R, D, S = Sequential) with a console-mounted selector lever, and can execute manual shifts with that lever or with two “paddles” on the steering wheel. After starting the engine in N, the driver moves the lever to the right; this selects the Sequential mode, in which each tap of the lever or paddle(s) shifts the transmission up or down one gear. Tapping the lever to the right toggles the unit to its Automated mode, in which shifts occur without the driver’s intervention. To revert to Sequential shifting, the driver can either toggle the lever to the right again, simply tap it toward “+”for an upshift or “-“ for a downshift, or actuate a paddle in the same manner.

On the console is a Sport button, which applies either of two effects:

• In Sequential mode, the shifting action is quicker; appropriate to sporty driving.
• In Automated mode, the shifting action is quicker and shifts occur automatically at higher engine speeds.

Though SMG does offer automated shifting, it is not meant as a substitute for a conventional automatic transmission. Just as with a manual transmission, power is interrupted for shifts – though in hard, performance-oriented driving the shifts can be stunningly quick. SMG’s appeal lies in these considerations:

• It is a racing technology, pioneered in Formula One competition and predominant in that sport today.
• Relative to a manual transmission, it entails no performance loss and almost no increase in fuel consumption. In fact, it can match or even exceed the performance achieved by an expert driver.