Harley-Davidson recommends that you use H-D oil, because it is formulated for their air cooled motors and the constant mesh transmissions used in your bike. It is also recommended to use H-D oil to keep from having potential warranty concerns. Harley-Davidson will, on occasion, request service records when reviewing warranty claims. There are other oils that are designed for air cooled motors that perform quite well. It is best to ensure that the oil you choose to use, meets or exceeds Harley-Davidson's specifications