Urban sustainability transitions are journeys of transformative socio-technical change to set course for an envisioned future city. These journeys start out in the minds of change agents as vague conceptual images inspired by far-flung ideals, which are then further substantiated and articulated as ‘urban imaginaries’ – shared understandings of what constitutes a desirable future city. The conceptual contribution of this paper lies in demonstrating the power of the urban imaginaries notion to studying the process of envisioning in the context of sustainability transitions. By following a number of prolific Thai cycling campaigners through the streets of several cities in Thailand – focusing on the urban imaginaries they articulate – this paper shows how urban sustainability transitions are envisioned from the bike saddle, how these imaginaries are mobilised to empower cycling and how a seemingly disparate set of urban development pathways converge around technological artefacts and material infrastructure.