 2011 BMW 135i Cabriolet. Click image to enlarge |
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2011 BMW 1 Series
One might be the loneliest number, but seven surely makes for one sexy party. At least, I’d bet BMW thinks so, as it rolls out a new transmission for 2011, the seven-speed Dual Clutch Transmission (DCT) that now serves as the extra cost option in 1 Series models powered by the company’s turbocharged six-cylinder engine.
In the 2011 BMW line-up, the DCT can be ordered in the Z4 sDrive35i and 35is, as well as the 335is coupe and convertible. Lower-end versions of those cars, as well as all versions of the 3 Series sedan and the 128i, use the six-speed automatic carried over from 2010, while the 5 and 7 Series both use a new eight-speed automatic.
The DCT is the biggest bit of news for BMW’s smallest model, the 1 Series, for 2011. In North America, this little Bimmer is offered as a two-door coupe or convertible with a choice of two engines – a naturally-aspirated 230-hp, 3.0-litre six-cylinder in the 128i and a turbocharged 3.0-litre six making 300 horsepower in the 135i. Note that this motor used to be a twin-turbo but is now a single turbo engine that BMW refers to as a TwinPower turbo setup. Confusing, no?
BMW is understandably keen to show off their new toy, so my 135i Cabrio tester was fitted with the DCT. Like Porsche’s PDK, VW/Audi’s DSG/S-Tronic and Mitsubishi’s TC-SST twin-clutch transmissions, the BMW transmission is most simply described as two separate transmissions, each with its own clutch, one of which is connected to the odd-numbered gears and the other to the evens. When one gear is engaged and driving the car, the next gear is also selected so that when it’s time to shift, one clutch lets go and the second engages, for a smooth and quick transition through the ratios.
  2011 BMW 135i Cabriolet. Click image to enlarge |
The dual-clutch transmissions offered by VW, Mitsu and Porsche are all very good, so the question is: what’s different about the way this one works? Not much, but it is an improvement over BMW’s original dual-clutch transmission, the SMG (Sequential Manual Gearbox) used in the last generation (2006-2010) M5. It was impressive for its time, but this new DCT is much better.
Like its similar counterparts, the DCT can be driven as an automatic transmission, or shifted manually. In full-auto mode, it feels like a conventional auto, shifting smoothly both up and down. Moving the shifter left into the manual gate activates the transmission’s sport mode, which holds gears longer and makes the shifts crisper and quicker. The sport button just behind the shifter allows for the same quicker shifts, but using the regular Drive mode’s more economical shift points. Official fuel consumption numbers for the 135i Cabrio with the DCT are 11.8/7.9 L/100 km; my real-world average in mostly city driving was 12.9 L/100 km.
But never mind economy. I had this car during one of the nicest weeks Ottawa had seen since the warm weather arrived, so I had two objectives: driving with the top down as much as possible, and enjoying what proved to be a terrific drive-train.
Given my choice (and my cash), I prefer a true three-pedal manual transmission, but a gearbox like the DCT is a compromise that I could see myself making. In sport-automatic mode, it makes driving the 135i surprisingly satisfying, given the lack of a clutch pedal, and it’s also a great match for BMW’s twin-turbocharged six-cylinder.
  2011 BMW 135i Cabriolet. Click image to enlarge |
If you want to be able to hear the engine’s gorgeous exhaust note, use the transmission’s sport mode. It holds each gear longer, letting the motor spin faster – to about 3,000 rpm in normal driving – and sing louder. Do this, and you’ll find yourself actually hoping that traffic lights will turn red for you, just so you can accelerate and listen to the car some more.
Leave the transmission in Drive and upshifts come early and often; you’ll find yourself toodling along in seventh gear by the time you reach 60 km/h. That’s nowhere near as much fun, but it does highlight this turbo engine’s terrific torque curve: the 300 lb-ft peak happens at just 1,200 rpm, which means effortless acceleration without the need for a downshift, unless your right foot tells the car you’re in a big hurry.
The manual mode, by the way, works great too. Shifting can be done via the console shifter – pull back for upshifts, push forward to shift down – or steering wheel paddles. The paddles are useful as you never have to take your hands off the wheel, but they rotate with the wheel, so shifting in the middle of a turn is best accomplished with the console lever.
