This type of transmission system uses metal belt or rubber running over pulleys so that to change their effective diameters, unlike the manual transmission that uses gears as it means of producing various vehicle speeds at different engine speed.
In this transmission, one pulley will add to its effective diameter, while the other will reduces its effective diameter by exactly the same amount. This operation is to keep the belt tension at best condition. This action is exactly analogous to the effect produced when gears of different diameters are engaged.

How Continuously Variable Transmission (CVT) Works

Microprocessor-controlled sensors quantify load diversity and by adjusting both pulleys, the optimum operating speed for the engine can be maintained without any input from the driver.
One pulley is driven by the engine and the other is connected to the drive shaft, an infinite number of ratios can be produced. This enables it to always run at the most efficient speed, regardless of the load placed on it.