Pros: Above-average fuel economy; simple, efficient power delivery; you'll never feel a shift.
Cons: Takes some getting used to; can cause engine to drone during hard acceleration.
Summary: If you're shopping for a car and you see the term "CVT," it stands for "continuously variable transmission."
Alright, so what does that mean?
Let's start with the basics. A CVT is a lesser-known alternative to conventional automatic transmissions. You operate it just like a regular one -- slide the shift lever from "P" to "D" and off you go -- but after that, well, it gets a little complicated.
Ordinary automatics have a certain number of gears that are referred to as "speeds," hence "6-speed automatic," for instance. The reason is that each gear is only good for a certain vehicle speed, so if you want to keep accelerating, the transmission has to shift up through the gears -- first 1, then 2 and so forth.
But a continuously variable transmission technically doesn't have gears at all; rather, it's like having one magical gear that's variable across all driving situations. That's why you don't feel shifts from one gear to the next like in a normal car. All you'll notice is changes in engine speed, or RPM: higher for acceleration, lower for cruising.
Here's where it gets really weird. The CVT orders up the most efficient engine speed for each situation and keeps it constant even if the vehicle is accelerating rapidly. In a passing scenario, for example, the CVT knows the optimal engine speed is pretty high (typically around 5,000 RPM on the tachometer), so it zings you up there as soon as you floor the gas. But as you pile on vehicle speed (50 miles per hour, 55 mph, 60 mph), the engine speed remains exactly the same! There's no "running through the gears" like with a regular automatic, no rising crescendo as the passing gear nears its limit. Instead, you hear a steady hum -- or, less charitably, a dull drone -- while the engine works efficiently at that sustained high speed.
It's definitely a different way of putting power to the pavement, but it's also an increasingly popular one. Nissan has used CVTs across its lineup for years, and stalwarts such as Honda and Subaru have followed suit.
What it means to you: CVTs tend to squeeze out some extra miles per gallon, especially in urban driving. That could tip the scales if you're comparing, say, the CVT-equipped 2013 Nissan Altima (27 mpg city/38 mpg hwy) to the 2013 Hyundai Sonata (24 mpg city/35 mpg hwy). But the real question is whether you like the way that CVTs respond to your right foot -- a question only a thorough test drive can answer.