Royal Enfield recommends using 15W50 or 20W50 viscosity grade engine oil for their motorcycles, depending on the specific model and operating conditions. It's important to consult the owner's manual or contact a Royal Enfield authorized service center to confirm the recommended oil grade for your particular motorcycle. Different models or specific requirements may have variations in the recommended oil grade.
Additionally, when choosing an engine oil, it's crucial to consider the quality and specifications of the oil. Look for oils that meet the necessary industry standards, such as API (American Petroleum Institute) or JASO (Japanese Automotive Standards Organization) ratings. It's often advisable to use oils specifically designed for motorcycles, as they typically contain additives that enhance performance and protect the engine under high-stress conditions.
Ultimately, for the most accurate and up-to-date information, it's best to refer to the Royal Enfield owner's manual or consult with an authorized service center for the recommended engine oil for your Royal Enfield motorcycle.