The Z4 is now offered in three different models: the Z4 sDrive30i, which comes with a 255-horsepower, 3.0-liter in-line 6-cylinder engine; the Z4 sDrive35i, powered by a 300-hp, 3.0-liter turbocharged six; and the new-for-2011 sDrive35is, which gets a new 320-hp turbo six. Each of these powertrains delivers satisfying performance with the standard 6-speed manual transmission--including a linkage that's still among the best in the business--but the 7-speed dual-clutch (DCT) gearbox in the sDrive35i is a significant step above the 6-speed automatic that's offered in the base model. The DCT shifts very quickly, matches revs for downshifts, and does a great job not interrupting the flow of power. It actually enables slightly quicker acceleration than the manual transmission. Acceleration from zero to 60 mph happens in just 5.0 seconds with the DCT, while top speed with the available Sport Package is 150 mph. Both 6-cylinder engines in the Z4 come with variable valve control and develop plenty of torque at low revs; but the turbocharged engine in the sDrive35i is surprisingly strong. An M Sport Package, available on either model, brings an Adaptive M Suspension that enables the best of both worlds, with improved ride quality plus tight body control when you need it. All Z4 models come with Driving Dynamics Control, which lets you choose between Normal, Sport, or Sport+ modes--each dialing in different settings for the stability control system, throttle response, transmission behavior, and even steering. In Z4s equipped with the Adaptive M suspension, it controls firmness, too. The Z4 doesn't make the safety sacrifices that many soft-top roadsters do; it has a stiff passenger cell and a full roster of airbags, including head and thorax bags that deploy from the seat backrests. Comfort isn't usually something you expect in a roadster, but the Z4 has plenty of it. The 2-seater comes with firm, supportive seats and has a surprising amount of legroom. The available leather is treated with sub-reflective technology that helps keep the interior cool on a hot day. Wind buffeting is good enough at highway speeds to still maintain a conversation with the top down, and with the top up it's nearly as quiet inside as a true coupe. The 2-piece top, made of aluminum, opens or closes in just about 20 seconds. Trunk space becomes a bit smaller with the top down, but with it up the trunk has space for two golf bags, according to BMW. The latest fourth-generation iDrive interface makes its debut in the Z4 for 2011. It includes a vibrant new 8.8-inch wide-screen display, plus new menu structure, including helpful symbols, and the iDrive controller is now flanked with hot buttons for several common functions. Programmable buttons for radio stations, telephone numbers, or even navigation destinations are now included. The navigation system now includes an 80-gigabyte hard drive, with 12 gigs of music storage. For those who want a little more performance, a Sport Package brings high-performance run-flat tires and other extras. Also new for this year is the Z4 sDrive35is, which gets a stronger, 320-hp version of the turbo six, plus the DCT gearbox, Adaptive M suspension, special wheels and trim and other BMW M upgrades.