CNET Car Tech tries out the 2008 BMW M3 with a double-clutch gearbox.
Wayne CunninghamManaging Editor / Roadshow
Wayne Cunningham reviews cars and writes about automotive technology for CNET's Roadshow. Prior to the automotive beat, he covered spyware, Web building technologies, and computer hardware. He began covering technology and the Web in 1994 as an editor of The Net magazine.
When we tested the 2008 BMW M3 Coupe recently, we were so impressed with it that we gave it an Editors' Choice award. But now we've driven the M3 equipped with BMW's new double-clutch gearbox, and found that perfection could be improved upon. We got our first sense of the brilliance of this gearbox on a public road, where we shifted up through the gears until the indicator in the instrument cluster showed a seven. Yes, seven speeds. One critique we had of the six-speed manual M3 Coupe we reviewed was that its fuel economy was low, sticking around 14.5 mpg during our time with it. Although we didn't extensively test the double-clutch gearbox M3, we noted that, during a day when plenty of automotive journalists were driving it, the trip computer showed 17.2 mpg, comporting with BMW's claim of a significant economy improvement with this transmission. On top of that comes the incredible shifting performance of this gearbox. With a flick of the paddles or a push of the stick, shifts happen effortlessly, perfect for a quick downshift before a corner. This is also the first time we've seen a double-clutch transmission mated to a V-8 engine. Audi only uses its direct-shift gearbox on engines with six cylinders or less, which leads us to speculate that it can't handle higher torque.
A double-clutch gearbox uses two gear shafts, one with odd gears and the other with the even gears. Each shaft gets its own clutch, and while one is engaged, the other is disengaged. When you choose an up or down shift, the engaged clutch lets loose while the other engages the appropriate gear. Because these clutches are computer-controlled, you can also have an automatic program that will shift at specific engine speeds. BMW's Double Clutch Gearbox has 11 programs for fine-tuning its performance, five in automatic mode and six in manual mode. The manual mode programs include launch control, so you can maximize 0 to 60 mph times without wasting tenths with wheel spin.