Yes, it is legal to ride a motorcycle on Lombard Street in San Francisco. Lombard Street is a public road, and motorcycles are allowed to use it like any other vehicle. However, it's important to note that Lombard Street is famous for its steep, winding section with eight hairpin turns, often referred to as the "crookedest street in the world." This section of Lombard Street is a popular tourist attraction, and traffic can be heavy, particularly during peak times. Therefore, it's advisable to exercise caution and adhere to the posted speed limits and traffic regulations while riding on Lombard Street. Additionally, be mindful of pedestrians and other vehicles in the area.