In order to reduce CO2 emission, motorcycle has so far improved the fuel economy by improving brake thermal efficiency of engine, optimizing driving condition, and reducing running resistance. For improving brake thermal efficiency of engine, the main methods are improving combustion efficiency i.e., improving combustion and mechanical efficiency i.e., reducing friction. Specifically, they are enhancement of in-cylinder flow, fuel injection system, offset cylinder, roller rocker arm, coating molybdenum disulfide onto the piston skirt, and etc. For optimizing driving condition, they are down speeding of engine, idling stop system. And for reducing running resistance, it is low fuel consumption tires. Moreover, In order to reduce the friction of motorcycle engine furthermore, various methods were innovated; modifying the striation finish on piston skirt, adding the needle bearing to the rocker arm shaft, press-fitting the bush into the small end of connecting rod, low viscosity oil for motorcycle, and variable cooling system for scooter engine. By innovating these friction reduction methods, the fuel economy was improved compared with each base model.