Considering the financial savings involved in building transmissions with just three shifting parts, you’ll realize why car companies have become very thinking about CVTs lately.
All this may sound complicated, but it isn’t. Theoretically, a CVT is far less complex than a normal automatic transmission. A planetary gear automatic transmission – sold in the tens of millions last year – has a huge selection of finely machined moving parts. It provides wearable friction bands and elaborate digital and hydraulic regulates. A CVT like the one explained above has three basic moving parts: the belt and the two pulleys.
There’s another advantage: The cheapest and highest ratios are also further apart than they would be in a conventional step-gear tranny, giving the transmitting a greater “ratio spread” This implies it is a lot more flexible.
The engine can always run at the optimum speed for power or for fuel economy, whatever the wheel speed, which means no revving up or down with each gear change, and the ideal rpm for the right speed 
all the time.
As a result, rather than five or six ratios, you get thousands of ratios between your lowest (smallest-diameter pulley environment) and highest (largest-diameter pulley setting).
Here’s a good example: When you start from an end, the control Variable Speed Transmission computer de-clamps the input pulley so the belt turns the smallest diameter while the result pulley (which would go to the tires) clamps tighter to make the belt switch its largest diameter. This creates the lowest gear ratio (say, 3.0-to-1) for the quickest acceleration. As speed builds, the computer varies the pulley diameters, as conditions dictate, for the best balance of fuel economy and power.