Are two really better than one?
To Clutch or Not to Clutch: A Guide to Dual Clutch Transmissions
Since General Motors introduced the first Hydra-Matic automatic some 70 years ago, the world has been divided between two types of drivers: those who push a clutch pedal and shift, and those who do not. But in a world where fuel economy takes up the majority of the automotive attention span, a third possibility looms: the dual-clutch transmission, or DCT. Learn to love it. Unless you’re just a passenger holding the steering wheel and pointing your two tons of SUV at Point B, DCTs represent the best hope for engaged, entertaining driving and reasonable fuel economy.
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Though the system is typically referred to interchangeably as an automated manual transmission or semi-manual automatic, neither of those descriptors is entirely accurate. There is a clutch, but no clutch pedal; it is an automatic, but it shifts gears internally, via a clutch, like a manual. What’s really happening inside the dual-clutch ’box is that two separate gear shafts (one for odd-numbered gears, one for the evens) are engaging and disengaging via two electro-hydraulically actuated clutches (thus the “dual clutch” designation). Ratios are computer-selected automatically depending on engine and vehicle speed, or manually chosen by the driver via a shift lever or steering-wheel-mounted shift paddles.
The big difference lies in the computerized robotic clutches, which handle all of the duties formerly the responsibility of the manual-transmission clutch operator (or the torque converter in a fluid automatic). This means no more heel-and-toe rev-matching on downshifts to smooth the transition from gear to gear, but also no constant, leg-wearying clutch pedal calisthenics in stop-and-go traffic. “Hooray!” say commuters who want the efficiency of a manual but hate having to push and release a clutch pedal a hundred times in a mile of traffic. “Sacrilege!” moan enthusiast-purists for whom the loss of a clutch pedal represents the elimination of yet another critical touch point in the man-machine interface.
Ferrari 458 Italia
Audi R8 V10 Plus
The DCT was invented before World War II, but the idea sat on the shelf until the mid-1980s when Porsche and Audi began using the technology in race cars. Quickly, car makers with ties to Formula One racing learned from racing applications that computer-controlled DCTs could react quicker and with more precision than even the world’s best race drivers could. Volkswagen produced the first DCT-equipped production car, the 2003 Golf R32, a performance variant of its standard fourth-generation Golf. The car developed a cult following, in part because of its crisp handling and power, but also because its quick-shifting six-speed Direct-Shift Gearbox helped it achieve a 0-60 time of 4.4 seconds.
Since that auspicious start, DCTs have found homes in dozens of models, although initially in cars at the stratospheric end of the price scale. But foregoing the manual transmission in favor of DCT technology in high-end production cars like the Ferrari 458 Italia and California, the Porsche 911 Carrera, the McLaren MP4-12C and Mercedes-Benz SLS AMG took an education campaign and hands-on experience before enthusiasts could accept the change.
In some cases, the transmissions themselves were their own worst enemies. Early versions in some high-powered performance cars with DCTs were awesome for track days, but brutal in their day-to-day operation. Some, like the Smart ForTwo, touted “automated manual” gearboxes but were actually single-clutch versions, which gave the entire genre a bad reputation due to a combination of dull engine and transmission response. Intelligent Smart owners learned to drive their diminutive buggies as though a third pedal was present, releasing the accelerator at the engine’s redline shift point, and allowing the shift to take place and the clutch to engage before mashing the accelerator back to the floor.
There were bright spots. From its World Rally Championship racing experience, Mitsubishi developed the Twin-Clutch Sportronic Shift Transmission (TC-SST), a wickedly precise, highly responsive and adjustable dual-clutch transmission offered in its all-new Lancer Evolution when the 10th generation rally car arrived worldwide in 2008. Professional test drivers remarked that they didn’t even bother with the shift paddles — the transmission was so intuitive it knew when to shift better than they did. As the transmissions evolved, even Porsche and Ferrari owners, who tend to be critical of cars lacking a third pedal and a shift knob, came to grudgingly appreciate the ease of operation, automatic rev-matching throttle blips and speed at which the transmissions could swap cogs. Today, most accept that the gearboxes are here to stay, and that in many cases they represent a drivetrain improvement.
In some cases, the transmissions were their own worst enemies. Early versions in some high-powered performance cars with DCTs were awesome for track days, but brutal in their day-to-day operation.
Though most manufacturers have stayed true to the dual-clutch pattern (two gear splines and two clutches), BMW chose a seven-speed single-clutch version for its mid-2000s M5 super-sedan, while supercar-maker Lamborghini also went with the single-clutch gearbox for its Aventador. The Italian maker said a single-clutch system was quicker shifting and saved weight, despite its more abrupt action. The single-clutch operation of the M5 was brutally efficient under power, but hard to gauge at anything less. Determining when exactly the clutch would engage during low-speed driving — say, pulling into a parking space — could be an exercise in guesswork. Not the best feeling with 500 horsepower at the driver’s disposal. (BMW subsequently changed to a dual-clutch gearbox in the current M5 introduced in 2011.) McLaren, on the other hand, addressed lag in shift response in its seven-speed DCT in the MP4-12C by incorporating a precognitive system that allows the driver to preselect the next gear and prepare it for use, nearly eliminating shift delay or loss of torque.
As with any automotive technology, with time comes the progress, offshoot developments, and lower costs necessary to bring DCTs to a wider range of cars. Today, dual-clutch transmissions can be found in higher-end sports cars as well as some of the market’s least costly options. Chrysler’s Dodge Dart offers a DCT (with a dry clutch vs. a wet or “oiled” clutch, which is required in higher output applications), courtesy of the company’s Fiat owners; Ford fits its Fiesta compact with one; and even Korean automaker Hyundai puts a dual-clutch in its quirky Veloster hatchback. When the 2014 Mercedes-Benz CLA250 sports sedan goes on sale this fall, the only transmission offered will be a seven-speed dual-clutch.
Yes, there’s still a certain amount of resistance from some buyers, mostly those who read “automatic” and think their transmission should operate as smoothly as any torque-converter, fluid-actuated gearbox. But with global fuel economy and emissions requirements top of mind, most automakers are looking to DCTs as the best method to gain efficiency while maintaining performance. The alternatives are single-speed electrics, myriad-speed automatics (we’re up to nine ratios now — how far can it go?), or the rubberband-like response of continuously variable transmissions. Dual-clutches, save us.