This is a “pure sounds” video of the new Audi R18 E-Tron Hybrid LMP1 Race Car doing some testing. This car is the same as their diesel race cars but with the addition of an electric motor that drives the front axle making this a “through the road hybrid.” What that means is the electric drive train is not directly connected to the diesel engine. The electric motor provides regenerative braking and then uses that energy to drive the front wheels on acceleration. Energy storage is handled by a carbon fiber 30cm diameter, 20cm tall flywheel that spins up to 45,000 rpm in a vacuum. Batteries are too heavy and don’t charge/discharge quickly enough for road racing regenerative braking duties. The alternatives for energy storage are flywheels like on this car and the Porsche 911 GT3 RS Hybrid and Ultra-Capacitors like the ones found on Toyota’s new Le Mans car.