Urban mobility is a complex socio-technical system. An important part is the behaviour of mobility users, which is in this study defined as being driven by mobility opportunities and perceptions of mobility. This case study in the Tarwewijk in Rotterdam explores what influences those opportunities and perceptions, with a specific focus on income and ethnicity. From mobility data and street interviews followed that income is most important to car ownership, while ethnicity is an important determinant of bike ownership. Other important factors for mobility behaviour include the travel time, the distance to important destinations like schools and shops, and the perception of ease of travel. Combining the diversity of driving factors with three pathways towards sustainable mobility leads to the conclusion that effective sustainable mobility policy is aimed at disrupting the car mobility system, designing a more walkable city and targeting groups based on their specific perception of mobility.