A Continuously Variable Transmission ("CVT") is a power transmission system which can smoothly vary gear ratios between maximum and minimum, rather than only being able to use fixed gear ratios. This can be achieved through a variety of systems; Honda uses a system with two pulleys which change in size and thus change relationship, while Nissan has a system with a pair of toroidal shapes which mesh where they meet. New York subway cars using a CVT were tested long ago; their transmission consisted of a belt which slid back and forth across a pair of inversely related cone shapes. CVTs permit you to run the transmission always within its powerband for peak efficiency.