CVT

All cars are an exercise in compromise. A major limitation of the internal combustion engine is that it has a fairly narrow rev range where it is efficient in terms of power output for fuel used. Anything outside that band and you start to lose efficiency. This is why electric cars, electric trains and boats are efficient transport. The engine spins at close to it's ideal rev range almost all of the time because they have flexibility built into the drivetrain.

Cars on the other hand, have to vary their speed significantly and often and have a rigid connection between the engine and the tyres on the road. So gears were added. These allow cars to keep their rev range somewhere around their most efficient level but still be able to vary their speed. This applies to both manual and automatic transmissions.

A new kind of transmission has been developed. CVTs (Continuously Variable Transmission) have a theoretically infinite number of gear ratios, allowing the engine to stay in it's most efficient rev range regardless of the road speed. It's a great technology.

You know how lots of automatics now have that 'semi-automatic' mode that allows you to change the gear up or down by moving the transmission selector to the side and moving it forwards or backwards? This always seemed odd to me, because why not get a manual and enjoy the improved efficiency.

So here's the funny part. Yet another example of marketers taking a great engineering idea and weirding it. Nissan has released a car with CVT and they've put in this 'manual' mode. They've taken a masterpiece of engineering that allows an infinite number of transmission ratios and they've deliberately hobbled it by forcing the transmission to stick at certain pre-defined ratios! It's like developing a new, propellent-free rocket, but NASA deciding that the big flames coming out of the space shuttle were more 'dramatic' and putting a rocket engine on the back to produce the flames.