BMW proves the German reputation for over-engineering by making the 2009 BMW Z4 sDrive35i the most complicated roadster ever. Unlike the very simple Mazda MX-5 Miata we reviewed recently, the Z4 sDrive35i is a technical tour de force. The engine sports not one, but two turbochargers. The transmission uses two clutches and a computer to move them. The suspension has different modes. And you could spend a couple of days going through the onscreen menus. But all of that technical wizardry results in extraordinary performance, a track-worthy roadster with few rivals.
The 2009 Z4 represents an update to the model, but BMW didn't make any radical changes to the exterior. The Z4 still has the long nose that bulges up, reaching above the level of the lower edge of the windshield, making it seem like you're piloting a World War II fighter plane. There are some refinements in the sheet metal, lines that break up the formerly smooth expanse of sheet metal down the sides.
BMW has gotten good at building cars with split personalities, reasonable everyday commuters that offer serious thrills on the weekends. BMW achieves this by the clever use of buttons around the cabin labeled Sport. The Z4 sDrive35i takes this idea a step further, not only having its various sport settings, but also using a convertible hard top. That top means security when parked in the city, real protection from the elements, and a little extra sound insulation. But it also gives you the option of wind-in-you-hair motoring on sunny days.
That convertible top does a peculiar little dance when going up or down, folding panels underneath each other and stowing its whole apparatus in the trunk. It's not particularly fast, and trunk space is compromised. The Z4 sDrive35i's LCD, mounted in a flip-up section of the dashboard, also stows itself away when not in use. We were impressed to see not only that LCD in a roadster, but BMW's up-to-date iDrive system, as well. The update to the Z4 extends to the cabin electronics.
As in the BMW 750Li we reviewed earlier, the Z4 sDrive35i's navigation system stores its maps on a hard drive, with enough capacity for rich detail. At 8.8 inches, the LCD is very wide, and presents beautiful 3D maps showing topographical features and the occasional landmark building. A 2D map is also available, but not as nice to look at. There's a reason why BMW uses such a wide screen: you can set it to a split view, using a portion of it as the main screen, and a smaller section as an auxiliary, useful for showing trip, audio, or route guidance information.
The Z4 sDrive35i is the third BMW we've seen with the new iDrive system, and it's still a relief from the old interface. But it's not without its problems, either. For one, it isn't always obvious which way to push the controller to back out of menus. Also, BMW offers a lot of customization options for its cabin tech, and you can drill down through quite a few levels in the settings menu. Digging into the Z4 sDrive35i's system, we made sure the navigation was set to automatically route around traffic problems.
Our Z4 sDrive35i came equipped with the dual-clutch transmission (DCT), which wasn't obvious initially as it has the same weird-looking shifter found in BMWs with automatic transmissions. The DCT, developed for the M3, shifts through seven gears, using two computer-controlled clutches for extremely smooth sequential changes. The DCT has automatic drive and sport modes, and a manual mode, controllable with the shifter or chunky paddles on the steering wheel.
Given the Z4's designation, sDrive35i, it should be obvious what sits under the hood. The Z4 sDrive35i is powered by a twin turbocharged 3-liter inline six-cylinder engine using BMW's Valvetronic system, for variable valve lift, and double-VANOS system, which changes the angle of the valves to enhance performance. The turbos each force air into a set of three cylinders, raising engine output to 306 horsepower at 5,800rpm and 295 pound-feet of torque from a low 1,300 to 5,000rpm.
This complex power train results in some unevenness when driving the car around a city. At low speeds, acceleration becomes difficult to modulate. Applying moderate pressure on the gas pedal might move the car smoothly forward, or deliver a sudden burst of speed. In drive mode, the DCT tended to upshift rapidly, working its way up to fifth gear as we cruised at 30 mph. Fortunately, it was just as quick to downshift when we wanted power, being very responsive to accelerator and brake input.
This Z4 sDrive35i also came with the M suspension package, a button on the console letting us select Normal, Sport, or Sport Plus modes. Normal produces a comfortable ride, which gets noticeably harsher in either of the Sport modes. Taking a couple of quick turns around town, classic BMW handling became evident, the back end letting loose just enough to pivot the car.