Advantages and Disadvantages of twin-clutch/DSG transmission
Most twin-clutch transmissions have a manual mode which allows manual shifting via the shift lever or paddles mounted on the steering wheel. When driven in manual mode, the clutch is still operated automatically, but the driver controls which gears are selected and when. The transmission will follow the driver’s commands unless the selected gear would over-rev the engine (i.e. commanding first gear while driving 80 MPH).
Advantages of the twin-clutch/DSG transmission
The primary advantage of the twin-clutch/DSG is that it provides the same driving characteristics of a manual transmission (i.e. quicker throttle response and no drop in engine speed when the driver lifts off the accelerator) with the convenience of an automatic. However, the ability to perform near-instantaneous gearshifts gives the twin-clutch advantages over both manuals and SMTs. Volkswagen’s DSG takes about 8 milliseconds to upshift. Compare that to the SMT in the Ferrari Enzo, which takes 150 ms to upshift. Instant gear shifts mean faster acceleration: According to Audi, the A3 runs 0-60 in 6.9 seconds with a 6-speed manual and 6.7 seconds with the 6-speed DSG.
Disadvantages of the twin-clutch transmission
The main limitation of the twin-clutch/DSG is the same as all geared transmissions: Because there are a fixed number of gears, and the transmission cannot always keep the engine at its best speed for maximum power or maximum fuel economy. Because of this, twin-clutch transmissions generally cannot extract as much power or fuel economy from an engine as a continuously-variable automatic transmissions (CVTs). But because twin-clutch transmissions provide a more familiar driving experience than CVTs, most drivers prefer them. And while the twin-clutch provides superior performance compared to a manual, some drivers prefer the interaction that a manual clutch pedal and gearshift provide.