XTRONIC CVT

CVT is a “stepless” transmission system. As opposed to MT (Manual Transmission) or AT (Automatic Transmission), CVT can automatically select the most suitable transmission gear ratio without any steps. Vehicles with CVT can run on the most efficient (i.e. with the best fuel combustion) engine rotation for regular velocity. The technology realizes seamless performance without shift changes when accelerating and decelerating.
It also expands the low-to-high gear ratio range, with transmission gear ratio control matching the way you drive, and delivering both excellent fuel economy and acceleration performance.

CVT adjusts the width of two pulleys and changes the arc radius of the steel belt running between them in order to control the transmission gear ratio.

In the illustration above, the arc radius of the belt for the engine shaft pulley gets narrower. This is ideal for driving at slow speeds, when gears on MT or AT vehicles are lower (for example, first or second gear).
On the other hand, when in high gear, the belt on the drive pulley gets wider. This is suitable for high-speeds when the gear is high, such as in fifth or sixth.
The steel belt is serving here to bridge the two pulleys and change the diameter.
If the gear ratio at low gear is lowered even more, acceleration improves. This is the same as how starting in first gear has more power than starting in second. As well as when moving off, vehicle response improves at lower speed.