S tronic is Audi’s version of Volkswagen's direct shift gearbox (DSG) technology that combines the benefits of a manual transmission with the ease-of-use and uninterrupted performance found in an automatic. The S-tronic can be operated manually or automatically, depending on driver preference. The automatic mode is accompanied by settings that allow for standard or and more aggressive sport operation. Audi's S tronic transmissions provide increased performance through lightning-fast shifts, as well as improved fuel economy over conventional gearboxes. For its compact models such as the TT and A3, Audi plans to use its six-speed S tronic gearbox and compact version of the new seven-speed S tronic. With an introduction on the A5, Audi will use the larger version of the seven-speed S tronic on vehicles with transversely mounted engines and the need for high amounts of torque. This six- and bigger seven-speed S tronic gearbox will be able to accommodate up to 258 lb-ft of torque, while the smaller seven-speed can only handle up to 158 lb-ft of torque.
The S tronic utilizes a unique double clutch system. One clutch engages odd-numbered gears, and the other even-numbered gears. When a gear change is made, the engaged clutch releases and the second clutch is engaged almost simultaneously. This changeover happens so fast Audi claims gear changes take place in a fraction of a second.
The practical upshot of this is that there is no lag between gearshifts as experienced with a traditional single-clutch system. The transmission is capable of shifting without interrupting power for a smooth, seamless, and most importantly fast shift without major loss to forward momentum. The Audi S-tronic is considered by many to be one of the best transmissions on the market and a truly innovative feature that sets Audi apart from the competitors.