BMW Z4 sDrive35is
BMW first presented dual clutch transmission in a production car in the high-performance M3 coupé in 2008. The seven-speed transmission for this 420 hp, V8-engined, rear-drive model is sourced from Getrag and has gained copious praise from enthusiastic drivers for its responsiveness, ease of use, and smoothness. Particular praise has gone to the six different manual settings and five automatic programs that give the driver the choice of anything from silky, seamless, comfort-oriented, automatic motoring to the forceful, sharp-edged, full-throttle upshifts and race-style downchanges that the aggressive, sports-minded driver revels in. The beauty of the M3’s M-DCT system is that it caters to everything in-between, too. With a touch on the rocker switch the driver can turn up, or reduce, the sensitivity of the transmission as he or she desires.
After the introduction of the $55,000 M3, BMW said it would roll out an essentially similar DCT system on selected other models on the 3 series range. The DCT case was given a further boost with the re-styled Z4 launched in 2009, when it became the standard transmission on the most powerful version, the twin-turbo three liter. Now comes the latest update in the Z4 story, a further upgraded version tagged sDrive35is, with its engine boosted to 340 hp and an overboost facility taking peak torque from 450 to 500 Nm for limited periods.
In each of these cases, however, the transmission loses its "M-DCT" tag and is labeled "Sport Automatic," becoming slightly less sophisticated in the process. In the Z4, for instance, there are only three gearbox/chassis settings – normal, sport, and sport plus.
The Z4, which saw production shift from Spartanburg in North Carolina to Germany with the advent of the new model, still presents the same tempting, low-slung, two-seater roadster allure as the previous model. Now, however, the creature comforts are more obvious – there is a large, pop-up display screen in the center of the dashboard and the finish is more luxurious. Especially attractive is the milled aluminum finish on the center console surface and the strip running the width of the dash, housing the main switches and HVAC controls.
Controls for the DCT transmission are presented just like those for a conventional automatic, with one important exception. The center shift lever is conventional, with P, R, N, and D in the main plane and Sport, plus sequential manual operation, in a plane to the left, accessed by pushing the lever sideways from D. Park can be quickly selected by touching the button at the top of the lever. The exception is in the arrangement of the steering wheel gearshift paddles. These have identical functions left and right, a thumb-push on the portion just visible above the steering wheel spoke triggering a downshift, and a pull on the portion on the forward side of the wheel giving an upshift. It’s an arrangement that continues to provoke criticism on some Porsche models. Indeed, Porsche now offers the option of a sports steering wheel with the standard system of pull paddles, up on the right and down on the left.
In practice, this paddle system proves to be just about the only irritation – albeit a major one – in driving the new Z4. The driver sits snugly enclosed in the cockpit, well back in the chassis behind the long hood. The three-liter straight six, fueled by twin turbochargers and BMW’s piezo High Precision Injection, has great energy, even from low rpm. The overriding impression is of power and urgency, as 340 hp goes a long way in a car weighing little more than 1,500 kg.
Yet, from a cold start the DCT transmission does not always behave perfectly. On several occasions, in auto mode the system allowed the engine revs to build surprisingly high before the first clutch engaged itself. Even then, progress was not immediately of the smooth standard expected of a BMW. That glitch aside, however, the Sport Automatic incarnation of the seven-speed DCT is easy, appealing and, as shown by the official statistics, a proven fuel saver, too.
Left to its own devices and using a gentle throttle, the DCT will shift up early to higher ratios, yet drop smoothly down a gear with a squeeze on the pedal for an increase in acceleration. Higher-speed kickdowns are easy, too. All in all, it works very well as a full automatic, and the Sport setting – as on most good DCTs – serves to speed up its responses, as well as those of the chassis and steering. The mode switch is very conveniently located on the driver’s side of the transmission tunnel, where it can be reached without looking.
Sport Plus brings an altogether more exciting feeling, accompanied by a warning that some of the chassis dynamic stability systems are being relaxed – though this is nowhere near as intense as on the even more powerful M3. Revs are now held much longer in each gear before upshifts, there is better engine braking into turns, and the car feels tense and alert with all of its substantial horsepower at the ready. Yet, in contrast to some competitors, particularly Porsche with the Boxster, the Z4 is not track- focused and remains easy to drive in town, even in Sport Plus mode.
It is when it comes to using the steering wheel paddles for manual gear selection that the Z4 becomes less instinctive and more confusing to drive. The double-function paddles demand a thumb-push forward to shift down and a pull back with the finger on the blade behind the wheel to change up. This is the exact opposite of the Porsche arrangement, though at least it mimics the layout of the Z4’s central lever. All this is a shame, as it takes surprisingly long to set aside one’s normal instincts, reprogram the mind for this BMW, and begin to exploit and enjoy the car’s gutsy performance.
It is all the more surprising in view of the fact that other BMWs, including the M3 coupé, the most recent 3 series coupé and convertible with DCT, and also the current generation of planetary automatic models such as the 5 series, all have what BMW describes as the unidirectional system – conventional, single-action paddles with a pull on the right for an upshift and on the left to change down a gear. BMW did concede to DCTfacts.com that this was an anomaly that was unlikely to be corrected until the model’s mid-life facelift.
If this Z4 is the only DCT or automatic-equipped car you drive, you are sure to appreciate its quick steering, its absorbent, adaptive-suspension ride, and wonderfully incisive, straight-six powertrain. But if you regularly swap between vehicles, especially automatics, stay clear of the Z4’s reverse-logic steering wheel paddles – they create confusion and the DCT is good enough without them.
| BMW Z4 sDrive35is | |
|---|---|
| Engine | 3.0 liter straight six, 24-valve |
| Fueling | Twin turbochargers, high precision injection |
| Max Power | 340 hp @ 5,900 rev/min |
| Peak Torque | 450 Nm at 1,400-4,500 Nm, with overboost to 500 Nm |
| Transmission | Seven-Speed Sport Automatic DCT, supplied by Getrag |
| Maximum Speed | 250 km/h (electronically limited) |
| 0-100 km/h Acceleration | 4.8 sec |
| Fuel Consumption | 9.0 lit/100 km (26.1 US mpg) |
| CO2 Emissions | 210 g/km |
| Price (U.S.) | $61,000 |
Story Filed: 7/7/2010
By Tony Lewin, managing editor DCTfacts.com