Among the heaviest parts of a car or truck are those that compose its "heart" — the engine. Items in the engine bay, such as the engine block, pistons, crankshaft and various accessories are made of high-strength, heat-resistant metals. They have to be, in order to withstand the tremendous stresses and temperatures created by the force of thousands of controlled explosions per minute that take place beneath the hood.
The trade-off for that durability is that traditional engines are extremely heavy — several hundred pounds in the case of a typical passenger automobile.
Once running, the engine has to transfer its rotational energy from the engine compartment to the wheels on at least two of the four corners of the car. To do this requires a transmission, drive axles and more parts that add weight and inefficiency.
Electric motors placed directly at the hub of an individual wheel eliminate the need for many of those bulky and maintenance-prone parts on a conventional car. These motors are then controlled by a computer that directs them to spin the wheels as needed. Michelin and car company Venturi made a big splash with this technology in 2010, showing off Michelin's Active Wheel System on the swoopy-looking Venturi Volage concept. Not only did it contain electric motors in the wheels, but also a powerful electric braking system and active suspension (also inside the wheel hub)!
In addition to the design of the parts themselves, it's quite important what they're made of. Head on over to the next page to read about the smart materials that are making car parts lighter.