What is the difference between a single and dual clutch transmission? – Jalopnik

Raise your hand if you answered that the difference between a single and dual clutch transmission is one clutch. Excellent. We’re halfway home.

Single and dual clutch transmissions differ in the way they are designed to select gears, but they basically share the basic principles. Power reaches the drive wheels by transmitting engine torque through a rotating, gear-lined input shaft – linked via clutch to the engine’s flywheel – which meshes with the gears on a corresponding output shaft. The idea is to select gears that work in harmony with the engine as speed increases and decreases, whether there is one or two clutches.

Their paths part from here. Single clutch transmissions, also called SCTs, use one shaft for the input gears and another for the output gears. Only one gear can be selected and engaged at a time, either manually, such as with a clutch pedal and shifter, or electronically. Dual-clutch transmissions – often just DCTs for short – trade a clutch pedal for an extra clutch, one for the odd gears and one for the even gears, and separate those odd and even gears on two axles. The links work electronically. That means that while you’re spinning one clutch in third gear, the other will pre-select the next gear (say, second or fourth) and engage almost immediately. Manual input is optional.

Clutches do the same thing in single and dual clutch designs: they act as power brokers between engine and transmission. When an engine is running, it sends power through the crankshaft to a flywheel, which smoothly transfers power to the clutch, which is connected to the transmission’s input shaft.

A clutch is a set of three components attached together: a clutch disc, which mounts on the transmission input shaft, like a plate on a turntable hub, and grips the front of the flywheel; a pressure plate that holds the clutch disc on the flywheel face; and a diaphragm spring, which ensures that the pressure plate keeps the clutch disc in contact with the flywheel.

In a car with a single-clutch manual transmission, an arm or clutch fork rotates like a small pry bar behind the pressure plate to relieve tension on the diaphragm spring, disengaging the clutch from the flywheel and the motor from the transmission. Depressing the clutch pedal moves that fork.

The unholy grinding sound of a poorly executed manual shifter is the result of poorly timed clutch and flywheel engagement when accelerating (or trying to shift without depressing the clutch) causing the gears to mix together at different speeds. Dual-clutch transmissions avoid that noise by letting electronics do the tap dance.

The roots of the single-clutch transmission date back at least to 1891, with French inventor Louis-René Panhard’s sliding gear system. George Borg of Borg & Beck introduced notable refinements in clutch design in 1910 that reflect modern designs, despite not knowing how to drive. Materials have improved, but the operation of a manual SCT remains the same today.

In a single-clutch automotive transmission, the gear sets are stacked sequentially on the input and output shafts: first, second, third, and so on. You always move this line up and down for as long as it takes to shift from gear to gear as you speed up and slow down.

The input gears are locked in place along the input shaft so that the entire assembly rotates when the clutch is engaged. The output gears rotate freely on the output shaft and do not transmit power until they are locked in place by moving the gear lever through the cartridge. (Selecting reverse cuts in the input/output part with a convenient gear on its own axis, designed to rotate the output shaft in the opposite direction.)

Depressing a clutch pedal effectively cuts off the transmission’s power on that one row of gears, allowing you to cycle through the changes manually – which is how single-clutch transmissions have largely persisted – but there are electronic examples in the SCT family tree. The sequential unit in the 2002 E46 BMW M3 SMG boldly ditched the clutch pedal in favor of a computer-controlled electro-hydraulic system. It was innovative, but some readers felt it ruined a great car.

Dual-clutch transmissions hit showrooms with the 2003 Volkswagen Golf R32, but their DNA dates back to Adolphe Kegresse in 1930s France. Porsche’s modern PDK system evolved from the company’s dual-clutch prototype of the 1960s, which was refined in the 1980s. At the time, Porsche took its new toy racing and won at Monza in 1986, while Audi enjoyed a double-clutch victory in the Semperit Rallye in 1985. In addition to these Volkswagen Group brands, BMW, Chevrolet, Hyundai and Nissan, in collaboration with companies such as Borg Warner, Getrag, Tremec and ZF, have also launched dual-clutch units.

Driving a dual clutch is like having two transmissions that you can precisely control and switch between by pressing a toggle switch. Power is efficiently transferred to the wheels almost continuously. One clutch controls the odd-numbered gear shaft from one to three to five, while the other clutch controls the other’s even-numbered two to four gears – and these shafts can rotate independently. So apart from simply lining up the next gear for input, the other clutch is already turning the next gear and can be engaged electronically within milliseconds by engaging one clutch and disengaging the other.

It’s possible to shift straight into third from sixth gear on an off-ramp – without hellish grinding – because of the way dual clutches can jump between those respective gear shafts. One clutch with one gear on one output shaft cannot achieve this, even with digital supervision.

Dual clutches let you choose your own adventure in manual mode, often with paddle shifters on the steering wheel or a bump of the selector lever on the console. Or all this can be done automatically for you, but double clutches and automatics are different beasts.

Despite having computer brains with an automatic mode, dual-clutch transmissions are not automatics. How automatics change gears is a whole different story, with torque converters and planetary gear sets playing the leading role. General Motors launched the first fully automatic transmission on 1940 Oldsmobiles as an attractive, convenient alternative to do-it-yourself transmissions. While automatics continue to improve and are the mainstream choice these days, manual transmissions remain popular among enthusiasts.

The dual-clutch transmission, with its single-clutch-like heart and automatic brain, aims to offer the best of both worlds: smooth urban comfort on the road, with trackday chops at the ready. The quick on/off shift of the dual clutch can feel abrupt or jerky at low speeds at stoplights, but modern dual clutches have different driving modes that help overcome this feeling. Even for the most ardent clutch pedal disciples – not to mention those of us with a clumsy left knee – quickly switching between dual-clutch gears without having to use a pedal can provide its own special, liberating sensation.

Since BMW dumped its electronically controlled SMG offering in 2010, you’ll have to hit the used market to find a single-clutch transmission that isn’t a manual. Shopping for a 2025 manual car offers some great choices, like the Acura Integra Type S, Honda Civic Si, BMW M2, or the Ford Bronco and Jeep Wrangler if you’re looking for something rugged. For some people, manual shifting offers an instant connection and joy that can’t be replaced, even if the clutch work can be a pain to live with in city and traffic traffic.

Porsche and Audi offer dual-clutch transmissions in their ranges, as does Hyundai, and the Volkswagen Golf GTI is also one. Although there are rumors of a manual C8 Corvette, that car is currently only available with a DCT. As you can probably tell from that list, dual clutches tend toward the performance side of the market.

Car companies may love DCTs, but they also have some compromises for anyone looking for the fully automatic experience. Ridiculously fast shifts and the ability to shift gears with both hands on the wheel make dual-clutch transmissions great for enthusiasts who like to be in control of the action, but also appreciate being able to put things in the automatic from time to time.