Indian Two-Wheeler Industry is the largest in the world with the annual growth rate more than 10 percent year after year. More than 60% of gasoline production in India is consumed by two wheeler segment. Ever rising fuel demand and global concern on climate change have focused to develop energy efficient and eco-friendly vehicles. Several techniques such as engine design, efficient transmission and use of better quality of fuels and lubricants are applied world over to improve the efficiency of the vehicles. Low viscosity engine lubricant is one of the approaches which can be easily applied for better fuel economy. The lubricant requirement of motorcycles differs from that of passenger cars. The motorcycle engine oil is subject to both engine as well as wet clutch transmission system which operate under severe conditions. The severity of the engine oil with respect to different viscosity grade and their impact on motorcycle performances and the engine components are studied on two motorcycles. The motorcycles initially tested with high viscosity engine oil and later switch over to low viscosity engine oil with new engine power pack. The motorcycles were tested for initial performance followed by mileage accumulation of 10,000 km on chassis dynamometer as per OEM recommended drain interval and completed the trial after assessing final performance. Inspection and merit rating of critical engine components were carried out for assessing viscosity effects on engine components.