It’s been nearly two years since BMW’s Vision EfficientDynamics concept debuted at the 2009 Frankfurt show, and the car has now officially re-emerged one step closer to production as the BMW i8 concept. As you can see, little has changed in the styling department. In fact, other than a new wheel design, the only other notable change we’ve spotted concerns the doors, which seem to have claimed some territory along their bottoms and thereby reduced the size of the blue body-side accent. Interestingly, the car didn’t show that change when BMW paraded it around for spy photographers this past March, but we like it.
As with the i3 city car concept that debuted at the same time (you can read about it in full here), the story of the i8 begins with its LifeDrive architecture. BMW says that its experiences in creating the Mini E and 1-series-based BMW ActiveE showed that adapting cars engineered for internal-combustion power to electric propulsion results in a lot of excess weight and compromises in packaging. As a result, both the i8 and i3 are built using two purpose-built modules: one to house passengers, dubbed “Life,” and one for propulsion and suspension components, called “Drive.” Combine them, and you have a car—and marketing-friendly “LifeDrive” branding.
While the i3 and i8 share the LifeDrive architectural philosophy, the cars differ in execution. That’s because the i3 is fully electric, while this i8 is a plug-in hybrid, so its Drive component is actually split in two, with an electric motor at the front axle and a gas engine at the rear. Unlike the i3, which situates its batteries below the passenger compartment, the i8’s lithium-ion cells are actually part of the Life module, stacked through a central tunnel that might house a transmission and driveshaft in a conventional car. Arranging them this way allowed BMW’s engineers to achieve yet another claim of perfect 50/50 weight distribution, thereby preserving peace in the city of Munich. As in the i3, the i8’s Drive components are largely crafted of aluminum, while the Life module uses a carbon-fiber-reinforced plastic monocoque. Using so much lightweight material essentially cancels out the added weight of the heavy electric drive components, thereby allowing the car to weigh less than 3300 pounds, according to BMW. The rigidity imparted by the carbon fiber also allows for long, dramatic doors that ease access to the two small rear seats, and is a boon to crashworthiness, too.
While most other so-called “through-the-road” hybrids (meaning the propulsion systems each drive their own axle) are based on existing front-drive vehicles—meaning they add electric power to the rear wheels—BMW had the luxury of starting from scratch. Because most braking energy gathers at the front of the vehicle, the i8 has its electric motor up front for the sake of recapturing energy. The i8 uses a modified version of the i3's electric motor, with a peak output of 168 hp and 184 lb-ft of torque. It’s fed juice, of course, by those lithium-ions, which take about two hours to charge and return 20 miles of all-electric driving.
Thanks to: Car and Driver