In developing motorcycle regulations, the increment of inertia weight to be set on the dynamometer was picked as 10kg. To provide data to support the choice of inertia increment, the effect of inertia on emissions and fuel economy needed to be quantitatively defined. Since road load horsepower setting is based on inertia increment, its effect on emissions and fuel economy required evaluation. A test program involving measuring emissions and fuel economy at various inertia and road load horsepower settings was conducted. Also evaluated was the magnitude of variations in the actual distance covered while driving the UDDS, and determine the effects on emissions and fuel economy.