BMW has redesigned its roadster for 2009, and the change amounts to comprehensive maturation, if not quite the obvious transformation from newborn Z3 to adolescent Z4. The new two-seater retains the name Z4, but it adopts two clumsy new model designations, the sDrive30i and sDrive35i. You'll notice there's no M roadster anymore, and word is that none is forthcoming. Nor will we see a return of the historically slow-selling hatchback coupe variant.
The previous entry-level, 215-hp in-line six is history, and the old car's more powerful 255-hp, 3.0-liter powerplant is now found in the base Z4 sDrive30i. Meanwhile, the twin-turbocharged six that we know and love from the 335i and the 135i puts 300 hp under the hood of the Z4 sDrive35i. We had a chance to sample the latter model, equipped with a seven-speed dual-clutch automatic transmission, a variant of the BMW M3's M DCT gearbox. Appearing in the Z4 for the first time, this transmission is exclusive to the turbocharged car. The base Z4 offers a conventional, six-speed automatic (with shift paddles); both Z4 models come standard with a six-speed manual.
With thirty fewer horses than the old M roadster - which used the 330-hp six from the previous-generation M3 - the sDrive35i can't match that car's frenetic persona. But the twin turbo makes 38 lb-ft more torque, so acceleration isn't far off. The factory-measured 0-to-60-mph time is 5.0 seconds (add 0.1 second for the manual gearbox), versus 4.9 for the old M roadster. The blown six is pretty sweet in its own right, its turbos so seamlessly integrated, its torque band so wide, and its power delivery so linear that a driver might never suspect it is turbocharged.
Pairing it with the new dual-clutch gearbox may help wring out the last tenth of the engine's performance - there's even a launch-control mode - but it's not as involving as a true manual. Strangely, the steering-wheel-mounted shift paddles do not follow the same logic here as they do in the M3, where one paddle upshifts and the other downshifts. Instead, either paddle can shift up (by pushing forward) or down (by pulling back) - the idea being that the Z4 can be shifted with only one hand on the wheel, whereas the more serious M3 pilot is someone who drives with two hands.
Of course, the Z4 driver is also highly likely to simply slap the lever into Drive, in which case the dual-clutch gearbox commendably emulates the smoothness of a conventional, torque-converter automatic, particularly in stop-start-and-reverse maneuvering. Even in D, instant downshifts are still available at the push of a paddle. The transmission eventually will return to Drive; to hold a gear, the lever must be in the manual gate - all of which is pretty standard, and logical, practice.
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