Abstract
In the result of a life cycle assessment (LCA) of motorcycles, CO_2 emissions on the use-stage is about 80% of total one (all stages). It means that a fuel consumption is a large environmental aspect to motorcycles. But customers require acceleration and high speed to motorcycles, so we develop engines to more powerful and responsible than automobiles. For getting better fuel consumption, we have to improve the engine character to fitting for practical use and lighten the body weight (weight reduction).
