Sunday, April 20, 2008

The Latest Trend in Microcars Positions the Engine as Backseat Driver

by John Voelcker

Half a century ago, the BMC Mini defined the modern econobox: a small front-mounted engine in a front-wheel-drive car that was easy to handle and compact yet spacious. This vehicle design has since become a mainstay of the auto industry, the preferred way to propel more than 2,000 pounds of commuting fury forward. But now the smallest cars — the Smart Fortwo, Mitsubishi's Japanese-market i, and India's forthcoming Tata Nano — are all shifting gears. Their engines are migrating to the back.
But these engines aren't cantilevered behind the rear wheels as in the original Beetle — with its consequent unpredictable handling. The new configuration, called rear-mid-engine, places the motor under the rear seat and over the rear axle. The result: spacious interiors, improved safety, and better road manners.
Because the power plant sits under the rear passenger, more of the car's volume can be used for people and stuff. The 11-foot-long Mitsubishi i boasts the longest wheelbase in its class — 8 feet, 4 inches — making for an especially roomy cabin. And there's the reason Formula One race cars — along with most Ferraris and Lamborghinis — mount their high-revving monsters in the middle. It puts all that weight between the axles and closer to the car's center of gravity, so there's less danger of spinning out of control if the tires lose their grip. Plus, in very small cars, a front-mounted engine can end up in your lap after a crash; it doesn't deform to absorb impact. Move it to the back, though, and the front crumple zone can be deeper and crush more gradually.
The rear-mid layout also reduces production costs: If the rear wheels do the driving, you eliminate the complexity and expense of transferring the engine's power to axles that are spinning and steering. It takes the philosophy of front-wheel drive and simplifies it to its essence.

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