The efficiency of converting a unit of fuel to rotation of the driving wheels includes many points of friction loss and heat loss through the exhaust or cooling system. Friction inside the engine happens along the cylinder walls, crankshaft rod bearings and main bearings, camshaft bearings, drive chains or gears, plus other miscellaneous and minor bearing surfaces. An electric motor has internal friction only at the main axle bearings. Friction outside the motor/engine includes loads from the generator / alternator, power steering pump, A/C compressor, transmission, transfer case (if four-wheel-drive), differential(s) and universal joints, plus rolling resistance of the pneumatic tires.