Car transmissions go hi-tech

NEW YORK (CNNMoney.com) -- Do you know how many gears your car's transmission has? If you're like most people, you'll probably guess "four." And you'll probably be right.

But, with gas getting more expensive and engineering getting more advanced, that number is rising.

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We're also seeing some cars with "continuously variable" transmissions that, instead of having set "gears" change gear ratios in a smooth, linear fashion.

If you prefer to handle shifting gears yourself, you can have it all, more or less, with automatic transmissions that let you take over.

This is important stuff: We're all aware of how a car's engine - its size, its power, its fuel consumption - can effect your car's performance.

The transmission can have just as big an effect on performance as the engine.

Gallery: Hi-tech shifting

From a practical standpoint, there's not much to recommend a manual transmission anymore. Automatic transmissions have become so advanced and efficient that the fuel economy benefit is, at best, negligible. In terms of driving in snow, electronic traction control is easier. Some Porsche sports cars are actually just a bit faster, going from zero to sixty miles per hour, with the company's advanced automatic transmissions than with a stick.

But for sheer fun and total control, nothing beats a stick. The fleet-footed driver can precisely control every aspect of the transmission's activity. Upshifts, downshifts, engine speed, it's all up to you.

Driving a stickshift car is a rapidly vanishing skill, however. One benefit to that is that fewer people can steal (or ask to borrow) your car. The downside is that, other than in sports cars, having a manual transmission can significantly reduce a car's resale value. There are simply fewer people who could buy it.

Basically, more gears equals more performance, smoother gear shifts and better fuel economy. That's why car companies keep packing more gears into their automatic transmissions.

Even relatively cheap cars like the Ford (Charts)'s midsized Fusion sedan are getting six-speed automatics. General Motors' (Charts) new large SUV's have six-speed automatics as well.

While six-speed transmissions currently account for less than five percent of transmissions built in North America, that's expected to increase to 40 percent by 2012, according to a report by auto industry forecaster CSM Automotive.

Newer cars and SUVs from DaimlerChrysler (Charts)'s Mercedes-Benz, such as the S-class sedan and R-class crossover SUV, use that company's seven-speed transmission.

Soon, Toyota (Charts) will begin selling the Lexus LS460 luxury sedan, with its eight-speed transmission.

Paradoxically, adding gears can reduce complexity and weight in a transmission, said Casey Selecman, manager of North American Powertrain Forecasts for CSM.

Because of clever engineering, a modern six-speed transmission actually uses fewer parts than a four speed, he said.

The more gears a car has, the better it can stay within its most efficient speed range even as the car itself keeps going faster. With fewer gears, the engine would have to rev higher before shifting to the next gear.

The most efficient transmission, at least theoretically, would have an infinite number of gears. That's the idea behind continuously variable transmissions like the one used in the Nissan Versa and Dodge Caliber. (Although the cars are entirely unrelated, both use the same transmission.)

These sorts of transmissions can feel peculiar to drivers because the speed of the engine can remain constant while the car accelerates. Instead of the usual "vrroom... vrrrrroom..." that you hear as most cars get up to speed, in a car with a CVT you get "Vrrrrrrrrrrrrrrrr......"

Even though the CVT is maximizing the engine's efficiency, it can sound as if the engine is straining. Engineers designing the Nissan Versa and Dodge Caliber took different approaches to minimizing that effect, making the transmission feel more "natural."

While they are more efficient, CVT's are also technically complex and there's a limit to how much power they can handle. That's why you won't find them on cars with big V-8 engines. They are used in a lot of hybrid vehicles.

Many cars today have manually shiftable automatics. These allow the driver - either by tapping paddles or switches on the steering wheel or wiggling the gear selector stalk - to choose when the transmission shifts up or down a gear.

It's actually a simple and inexpensive feature for a car company to offer. There's nothing mechanically different about the transmission. The only thing required is the addition of some sort of input mechanism - the steering wheel paddles, for example - and a tweak to the transmission's computer programming.

For that reason, it's a feature that's often seen on vehicles, like the Hyundai Tucson SUV, that otherwise don't seem tailored for performance-oriented drivers.

"The large majority of people never or very rarely use it," said Selecman.

The control still isn't as complete as you have with a manual transmission. For example, since there's no clutch pedal, you can't control when the engine is engaged or disengaged from actually driving the wheels.

Depending on the car's computer programming, manually shiftable autoomatic transmissions can vary greatly in their behavior. Some shift gears immediately when the driver flicks a button. In other cars there's a moment of delay. Some cars will shift gears, whether you request it or not, if you let the engine rev too high. Others leave that to you.

To see some examples of cars with these and other advanced transmission options, see our gallery.

Gallery: Hi-tech shifting

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