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Purpose-built electric cars trump manufacturer-converted models

Consumer Reports News: May 09, 2012 11:08 AM

There are two kinds of electric cars at this year's electric vehicle symposium, fondly known as EVS26: Purpose-built electric cars, and those that have been built from standard gasoline cars. The difference could not be more stark.

Cars that have been built from gasoline models are full of compromises. Often the battery takes up much of the trunk space, as is the case with the Ford Focus electric. Or, as in the case of the Chevrolet Volt, it may even take up passenger space. (The Volt is based on the conventional Chevrolet Cruze.) Its inverted "T"-shaped battery runs through an extra-large tunnel in the car between the rear seats, eliminating the space for a center passenger, and limiting the car as a four-seater. The top of the "T" sits underneath the rear seats, but it still sticks out far enough to compromise foot access into the rear seats.

Ford-Focus-EV-flat-cargo.jpgPurpose-built electric cars are much more space efficient, because they don't try to cram the battery into spaces that weren't designed for heavy powertrain components. Instead, most purpose-built electric cars use flat-format cells sandwiched under the whole floor of the car. This is the case with the Nissan Leaf, as well as several upcoming models at the public ride-and-drive session outside the Los Angeles Convention Center this week: the BYD e6 and the Tesla Model S.

Even the Mercedes-Benz B-Class fuel-cell, which is not strictly a battery-powered electric, as it runs on an electricity-producing fuel cell, houses most of its heavy drivetrain components in the floor. And it's very roomy and nice to drive.

Either way, flattening the drivetrain components under the floor also gives designers flexibility to maximize the shape for other uses. The sleek Tesla Model S has impressive space efficiency, with a flat interior floor that's wide open in front and gives generous legroom in the rear. It has a spacious hatchback big enough for a rear-facing third-row seat, and a trunk up front where the engine would go.

Of course, there are exceptions: For example, while the Coda electric sedan is based on a 2000-model-year Mitsubishi Lancer, the company found a way to sandwich most of the batteries under the floor.

Putting the batteries under the floor has dynamic advantages, as well. Since batteries are heavy, they lower the center of gravity and spread it out, aiding handling, braking, and even the ride. Carrying that much weight around in the trunk can't do much for handling.

We'll be looking for more purpose-built electric cars in the future. The primary reasons to base an electric on a gasoline platform is to save money and race to market--both fair business objectives. That approach may not guarantee an inferior EV driving experience, however. In fact two of the ones we've found most enjoyable to drive, the BMW Active E and the Focus Electric are converted. However, packaging the batteries is often a challenge, typically resulting in compromised cargo space as in these two models. From a consumer's standpoint, the conversion approach does not label the car as an obvious EV (as the uniquely styled Toyota Prius is clearly a hybrid and the Nissan Leaf is clearly electric), which for some potential buyers may impact its appeal, for better or worse.

See our guide to fuel economy and guide to alternative fuels.

Toyota introduces electric RAV4 SUV, starting at $49,800
Mercedes-Benz B-Class fuel-cell-powered car shows progress
Behind the wheel of the improved Coda electric car
We drive the first Chinese car expected in the U.S., the electric BYD e6
Do electric cars even need special chargers?

Updated: 5/20/12

Eric Evarts

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