In recent years, the concept of social networking combined with the Internet of Vehicles has brought to the definition of the Social IoV (SIoV) paradigm, i.e., a social network where every vehicle is capable of establishing social relationships in an autonomous way with other vehicles or road infrastructure equipment. In SIoV, social networking is applied to vehicular networks according to how social ties are built upon, i.e., either among vehicles or humans. This creates a twofold nature of SIoV i.e., both based on human social relationships, and as an instance of the Social Internet of Things (SIoT). This twofold nature of SIoV is not in contrast with itself, but allows to distinguish different applications and use-cases. This paper analyzes the SIoT-based social relations in a vehicular network scenario for establishing a Social Internet of Vehicles and providing insights on this growing research area.