The automatic gearbox is controlled electronically. The gears are shifted up or down automatically according to preset gearshift programmes.
When you drive at moderate speeds the gearbox will select the most economical shift programme. It will then change up early and delay the downshifts to give better fuel economy.
If you drive at higher speeds with heavy acceleration, if you open the throttle quickly, or if you use the kick-down or the car's maximum speed, the gearbox will automatically select the more "sporty" shift programmes.
The S tronic is a dual-clutch gearbox. Torque is transmitted via two independent clutches. They replace the torque converter found on conventional automatic gearboxes and allow for smooth, uninterrupted acceleration of the vehicle.