It might seem that carmakers are no longer that concerned with gas mileage, considering how America is infatuated with pickup trucks and SUVs and other such obvious gas-guzzlers. Still, carmakers have federal gas mileage standards to meet, hence the birth of hybrid drivetrains, lightweight construction and the use of alternative fuels. The high mileage of the econo-cars is averaged with that of the SUVs and trucks and so a corporate "average" is attained.

Thus anything that gives cars better mileage is under scrutiny, like the CVT (continuously variable transmission). This technology is not new by any means as it was originally introduced in 1886. Honda was the first manufacturer to introduce a CVT in he U.S.A. in their 1996 Civic HX, which gets 35/41 mpg city/highway. CVTs have been used by Nissan in other than U.S.A. markets and their Hyper CVT-M6 unit also has a manual mode with six-speeds. This gives the driver the option to let the transmission shift by itself or shift manually, in the same way as Chrysler's AutoStick.

Typically, a CVT is about 20-percent more fuel efficient than a regular automatic.

Instead of using a combination of gears, clutches, hydraulic fluid and a torque converter, the CVTs use a simple belt and pulley design. The pulleys are cone-shaped and there's a belt that runs between the narrow and wide end of each pulley, creating a variable ratio. For example, in the Honda, as the belt moves between the wide and narrow sections of the pulleys, an equivalent gear ratio of 0.45 to 2.45 is attained.

Because there are no gears changing, a CVT is smoother, but its real advantage is that it allows an engine to stay in its power band without having to shift if a hill or a situation requiring acceleration is encountered.

Sounds great. So why don't all cars use them? The problem is that makers haven't quite figured out how to make these transmissions live with high torque/horsepower engines. Belts and pulleys aren't as strong as gears so the CVTs are limited to small engines.

Even so, about one million CVT-equipped cars are sold yearly-most of them in Japan. And as more car companies refine the design, improvements are in the air and I bet we'll see more and more CVTs in American cars.

[Peter C. Sessler is the author of 25 books on cars, published by Motorbooks International, Tab Books, Smithmark Publishers, and HP Books. Some of his titles include "Ford Pickup Red Book," "Muscle Car Greats," and "Car Collector's Handbook." Publication is pending on his latest book, "Model Car Handbook," to be published by Scale Sports.]