The BMW Z4 is clearly aimed at those who enjoy driving. The retractable hardtop and added features have nudged it a bit closer to grand touring car than sports car. The inline six-cylinder engines rev smoothly to redline.
The shift lever on models equipped with the automatic transmission and the DCT is a bit tricky to figure out and takes a while to get used to. Neutral is the default position and Park is a pushbutton; push the lever forward for Reverse and backward for Drive.
The new four-cylinder engine on our sDrive28i was snappy and able. We noticed the extra torque when passing slow-moving trailers on a two-lane highway, although we did find ourselves wishing for the extra power of the higher-end models when making passes through hilly terrain. The 8-speed manual transmission gave us the gear we needed, and when in Sport mode, didn't give us any unwanted upshifts. But, given the choice, we'd prefer the manual gearbox.
The more powerful sDrive35i gets to 60 mph a tad quicker than the sDrive28i, with plenty of power for street and track alike. It will wind to 7000 rpm but there's really no point with that abundance of torque, and while it's a superb engine it doesn't offer the delightful rev-happy feel the sDrive28i does. EPA numbers for the sDrive35i are 18/25 mpg with the manual transmission and 17/24 mpg with the DCT. We managed almost 24 mpg in a manual-transmission model over some amusing roads and 38 mpg at 72 mph on an 80-mile leg from 4,000 feet elevation down to 700.
The sDrive35is model has a more powerful version of the twin-turbo engine. Turbo boost increases from the sDrive35i's 8.7 psi to 11.6 psi in the sDrive35is. Those changes increase horsepower to 335 and up torque to 332 pound-feet. An overboost mode allows for 14.6 pounds of boost for up to seven seconds. The overboost feature adds another 37 pound-feet of torque for a total of 369 lb.-ft. Aggressive exhaust tuning gives the sDrive35is a great burble. The extra boost cuts 0.3 off the 0-60 mph time, which is an impressive 4.7 seconds. It comes only with the DCT. Fuel economy is the same as in the sDrive35i at 17/24 mpg.
The 6-speed manual transmissions for the sDrive28i and sDrive35i offer soft, progressive clutch take-up for smooth starts whether crawling in traffic or weekend autocrossing. Shift action is light, short and semi-notchy, rather like there's a rubber-edged metal gate hiding under the shift boot. Shifts are quick, clean, and error-free.
BMW's 7-speed DCT dual-clutch automated manual transmission comes standard in the sDrive35is and is optional for the sDrive35i. Also used in the M3, this transmission has clutches, but there is no clutch pedal. Put it in Drive and step on the gas. Around town you will feel like it has a momentary delay between when you press the accelerator from a stop and when the car starts moving.
The DCT can shift faster than a manual transmission, emitting brief burps from the exhaust pipes as it rips through the gears. It's also smart, dropping gears automatically (rev-matching the downshifts) when you brake hard for a corner, but it will shy away from gear changes mid-corner so it doesn't upset the balance of the car. There is a launch control mode for ultimate acceleration, but make sure to read the owner's manual cautions before you take the steps and disappear in a wisp of tire haze.
Brake performance and feel is good across the range. We had no brake issues during a day at the track in the sDrive35is. Nor did we experience fade when tossing the sDrive28i from corner to corner in near-100-degree weather. Since they have more power and weight, the turbocharged sDrive35i and sDrive35is get substantially larger brakes, and that may be a deciding factor for drivers intending to take their Z4 to track events. These models also have wider rear wheels and tires to cope with the added weight and power.
For the ultimate performance, though, the sDrive35is is the clear choice. It delivers performance levels exceeded by only the most powerful, and expensive supercars. We had the opportunity to drive it on a racetrack and there it felt right at home, hunkering down through corners, accelerating willingly, braking with power, and staying flat and balanced. For those hoping for a Z4 M, this is as close as it gets.
We found the Z4 rides commendably well, even on the standard run-flat tires (no spare) and optional Sport Package. Credit the rigid structure, BMW's magical suspension tuning, and the technology involved in the Driving Dynamics Control, which adjusts steering feel, throttle response, and the limits of the stability control system. A sport package adds electronic control of the shocks with Normal, Sport, and Sport-Plus settings. The Normal mode is the most relaxed, and it's the choice for the highway or around-town cruising. Sport and Sport-Plus sharpen the responses and firm up the ride. These modes are meant for more spirited driving. Choose the mode that fits your preferences, mood and situation.
Steering is electromechanical but you'd never tell by how well it communicates what the front tires are doing. Unlike many sports cars, in which it seems that heavy steering was a design requirement, the Z4 steering is light around town, weights up nicely with cornering force and reminds us somewhat of the Honda S2000. The sDrive35is model is a bit quicker and sportier. It can't match the surgical detail of the Porsche Boxster, but nothing at this price, short of a Lotus, does.
With a low center of gravity and near-perfect weight distribution with occupants, the Z4's handling is exemplary. You'd need something considerably lighter, more stiffly sprung, and equipped with fatter or stickier tires to make notably faster progress. The Z4 is not only nicely balanced and goes where you point it, it does so with little drama and it's relatively easy to find where its limits are.
Every Z4 model is fun to drive in its own way. And while the hard top does offer added sound insulation over a traditional soft top, it was still noisy. Both road, tire and wind noise penetrated the cabin at highway speeds. But to some extent that's to be expected in this type of little car.
Putting the top down doesn't change the Z4's behavior thanks to its lightweight aluminum panels. We found that the inside mirror and only the inside mirror vibrated a bit on poor road surfaces, a sign that body rigidity characteristics don't change much top up or top down.
Among the competitors, the Mercedes-Benz SLK also offers a folding hardtop, while the Audi TT and Porsche Boxster use folding cloth tops. The latter are perhaps not as quiet and sealed as a hardtop, but trunk space doesn't suffer as much when motoring top-down. The Audi TTS has the foul-weather bonus of all-wheel drive and a nicely finished cabin, but not the same balance and precision finesse as the Z4. The Mercedes offers many similar amenities but is less a driver's car and more a small version of the SL luxury convertible. The Boxster has better driving precision, with power comparable to the sDrive35i and the driver's engagement of the sDrive28i, but the BMW isn't as painful on the wallet.