Race car designers go to extreme measures to make competition vehicles as light as possible. Lighter is faster. It’s simple physics; less horsepower is required to accelerate a light vehicle compared to a heavy one. So on a given amount of horsepower, a lighter race car will be faster than one that weighs even a few pounds more. It also takes less energy to slow the car, providing better braking performance. A lighter car will generally handle better, too, since there is less mass working on the chassis through the corners.
Lighter vehicles are also more environmentally friendly since they require less energy to move from point A to point B. Shaving a few hundred pounds off a car design can yield major improvements in fuel economy. In addition to improved mileage, electric vehicles will see longer range between charges if they can be made lighter.
Trimming pounds off a production car is not as easy as it seems, however. Today’s road worthy vehicles must feature hundreds of pounds of federally mandated safety equipment that wasn’t required or available a few decades ago. Equipment like antilock brake systems, multiple airbags, advanced computer controls, and crash mitigating high-strength body structures all add weight to a vehicle design. Pile on the comfort and convenience equipment that most new car buyers expect in a modern car or light truck and the extra bulk adds up fast.
That’s why vehicle designs like the new BMW i3 and i8 are so intriguing. These models are revolutionary for mass production vehicles, featuring clean sheet designs that found BMW designers throwing traditional materials and production methods out the window, resulting in lightweight electric-drive cars with maximum strength for safety.
For example, the i3’s primary body and chassis structure are composed of two separate units that form what BMW calls the LifeDrive architecture. The primary body structure is the Life module and the Drive module incorporates the powertrain components. The passenger cell module is made from Carbon Fiber Reinforced Plastic, or CFRP. This is the first ever use of CFRP in a mass production vehicle. Carbon Fiber Reinforced Plastic is every bit as strong as steel yet is 50 percent lighter. When you can trim half the weight off something as large as a body structure, you are talking major weight savings.
Aluminum has been used as a lightweight material in the transportation industry for many years. The i3’s rear Drive module that houses the electric drive motor, rear suspension, and optional range extending gasoline engine is made of aluminum. While both are light and strong, Carbon Fiber Reinforced Plastic is even 30 percent lighter than aluminum. Materials throughout the i3 were selected for their weight saving properties and for their sustainability characteristics.
Beneath the flat floor (there is no transmission tunnel) of the i3 is a space-saving 22-kWh lithium-ion battery pack that tips the scales at 450 pounds. Power is delivered by a hybrid synchronous electric motor. The motor produces 170 horsepower with 184 lb-ft torque and can spin up to 11,400 rpm. The compact electric motor offers immediate torque and weighs just 110 pounds. With a curb weight of just 2,700 pounds, the i3 is nimble and great fun to drive. As in racing, automakers strive to save weight because it gives them a competitive edge. Sometimes, less is more.