Harley-Davidson recommends the use of their own proprietary brand of oil, which is formulated specifically for their motorcycles. This oil is a synthetic blend that is designed to provide optimal performance and protection for Harley-Davidson engines.
It's important to note that manufacturers may update their recommendations over time, so it's always a good idea to consult the owner's manual or contact an authorized Harley-Davidson dealership for the most up-to-date information regarding the recommended oil for your specific model and year of motorcycle. They can provide you with the accurate and current information based on the latest recommendations from the manufacturer.