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How Dual-Clutch Transmissions Took Over the Sports Car World

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In ten short years, automated manuals went from a joke to world-beaters. The dual-clutch gearbox is how it happened.

DSG diagram DSG diagram

For most of automotive history, an automatic transmission was a deal-breaker for “real” enthusiasts. Automatic transmissions were sluggish, they overheated during hard driving, and lost copious amounts of power compared to their three-pedal brethren. Attempts at high-performance automatics were janky, with abrupt shifting and terrible low-speed performance. 

In 2003, all that changed. Volkswagen launched the R32 Golf, a high-performance all-wheel-drive VR6-powered hot hatch. It was an instant classic. Most importantly, the R32’s transmission changed the automotive landscape forever. 

It’s Automatic, Systematic, Hydra-matic

Before 2003, most automatic transmissions were hydraulically actuated. In these “traditional” automatics, there is no friction plate, or clutch, between the engine’s output shaft and the input of the gearbox, as there is in a manual transmission. Instead, there’s a fluid-filled disc known as a torque converter to couple engine and transmission speeds. 

Accelerating the engine spins a hydraulic pump in the transmission, and centrifugal force pushes fluid to the outside edge of the torque converter. There, the fluid passes through fins on a turbine, which spins, transferring power to the transmission. Another finned disc, known as the stator, redirects the fluid to the center of the housing to be re-pumped through the turbine. Behind the torque converter, a planetary gearset controlled by hydraulic pressure and speed handles the job of shifting. 

Variations on this design have been around in the mass market since the early 1940s, with the introduction of the GM Hydra-Matic. For pleasure cruising, it was the top choice for decades. For sports-car drivers, however, it didn’t cut it; There’s a pause between  the initial application of throttle power to feeling the car move, as it takes a moment for hydraulic pressure in the transmission to build. High-pressure, high-speed hydraulic systems generate lots of friction and heat, both enemies of high performance. 

Hydraulic automatics are also generally inefficient. This lost efficiency is especially noticeable in older automatics, which transferred just 85% of the engine’s power to the road, compared to 97% for a manual transmission. It’s easy to see why autos earned the “slushbox” moniker. Additionally, the complexity of a hydraulic automatic’s planetary gear sets meant that most automatic transmissions had fewer gears than contemporary manual transmissions. This further compounded powerband woes. 

Granny Shifting

By the late 1990s, more-advanced “automated manual” transmissions became available in consumer cars to bridge the gap between traditional three-pedal manuals and “slushboxes”. The most notable of these was perhaps the Ferrari F355’s “F1 Edition” gearbox, which marked the first time now-ubiquitous paddle shifters were seen in a Ferrari

The F355 used a Magneti Marelli Selespeed system, which was a true six-speed manual transmission under the skin, clutch and all. The Selespeed gearbox used hydraulic actuators on each gear, as well as electronic clutch hydraulics, to shift between the gears the same way a human would. BMW released a similar system the same year called the SMG.

Both companies’ gearboxes suffered from the same flaws: while they operated well at the limit—the Selespeed was nearly twice as fast as a human driver at shifting once over 7,000 RPM—they suffered from atrocious low-speed performance. Both systems were terrible at rolling away from a stop, with lots of lurching and juddering; Low-speed gear changes felt glacial, and civility around town paled against a comparable traditional hydraulic automatic. This kept automated manuals from gaining popularity.

Double-Clutching (Like You Should)

In 2003, Volkswagen released the R32 Golf. The R32 offered its own take on the automated manual, which VW called the Direktschaltgetriebe, or Direct-Shift Gearbox. That transmission—more easily known by its acronym, DSG—was substantially more advanced than adding solenoids to a standard manual transmission.

The DSG instead splits apart the transmission into two gear sets (usually odd and even + reverse) on two nested driveshafts, with one spinning inside the other. The engine flywheel spins a housing that contains two clutches. Each clutch grips one of the driveshafts. When the car starts in first gear, the shifting mechanism locks first gear into place and the clutch on the inner driveshaft (blue in the above diagram) engages. 

The DSG then prepares for the next shift by locking second gear into place on the outer driveshaft (green). When the upshift paddle is tapped, the outer driveshaft clutch disengages, and the inner driveshaft clutch clamps into place. Because shifting uses two clutches and two entirely separate driveshafts, it’s much easier for a computer to seamlessly transfer power from one to the next, as it’s synchronized speeds between the gears as closely as possible in advance of the gear change. 

When downshifting, the transmission releases its gear and the clutch grabs the opposite input shaft. The transmission computer coordinates with the engine ECU for a throttle blip to bring the newly selected driveshaft up to speed, and then the shifting mechanism locks in the gear change. 

The first wave of VW DSGs were wet-clutch, but within a generation, they moved to a simpler and more-reliable dry clutch. In exchange for a slight increase in weight (about 50 pounds), DSGs cut shift times by a factor of ten, from a human’s 500-millisecond shift to under 50 milliseconds for the DSG’s computer. It eliminated the chance of missing a gear and blowing up an engine as well, which is why dual-clutch gearboxes are a popular choice in race cars and expensive daily drivers. 

R-Thirty-Twin-Clutches

To see how the DSG works in practice, I drove one of the first cars sold in America with the gearbox: a 2008 MK5 Golf R32. (Although the 2003 MK4 Golf R32 was the first production car with a DSG, that gearbox was an option solely in Germany; the MK5 was America’s first go at the new transmission.) I’ve driven a lot of old cars with automated manuals, and in-era reviews don’t lie: they’re awful.

But the Golf R32? Genuinely excellent. It wasn’t quite as refined as a brand-new GTI or Golf R’s DSG, but it was close. Upshifts, especially under medium-to-heavy load, actually offered gear-grabbing violence that felt reminiscent of a manual; Downshifts came rapidly and incredibly smoothly, without upsetting the car’s balance mid-corner. In around-town, low-speed driving, when I let the transmission choose a gear for me, it felt remarkably like a traditional hydraulic automatic: smooth. Competence at every speed is how the R32 redefined hot hatch dynamics, and why a majority of Golf Rs sold today are equipped with the DSG, rather than a traditional six-speed.

Within a decade of the R32’s debut, the dual-clutch had been virtually perfected, and the manual transmission was on the ropes. Ferrari’s paddle-shifters went from a curiosity to mandatory equipment in just 15 years; Today, 60% of Porsche 911s are sold with dual-clutch gearboxes. The speed at which DSGs took over the sports-car world is stunning, considering how most automotive technologies take decades to perfect. Although there will always be a place for three pedals, make no mistake: the DSG has more than proven its performance superiority.

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