A size-adjustable sport shoe includes a shoe head, a shoe insole, and an adjusting telescopic device including a gear, a shaft gear, first and second gear racks, and handle. The first and second gear racks are located at two lateral sides of an elongated adjustment groove at the shoe head, wherein the upper surface of the second gear rack is lower than the upper surface of the first gear rack. The gear shaft is coupled between the gear and the handle. When the handle is folded perpendicularly to an axis direction of the gear shaft, the gear meshes with the first gear rack to lock up the shoe head at the shoe insole. When the handle is folded to coincide with the axis direction of the gear shaft, the gear meshes with the second gear rack to allow the shoe head to be slid from the shoe insole.

A modular, multi-part roller skate is provided. The multi-part roller skate includes a roller skate body, a front wheel assembly, a rear wheel assembly, a support surface for supporting a footwear of a user, and at least one securing element for securing the footwear to the support surface. The multi-part roller skate is configurable as a modular roller skate with a removable pair of rear wheels, an interchangeable modular roller skate and ice skate, and an interchangeable modular roller skate and cross-country ski/snowshoe. In some embodiments, the multi-part roller skate can also be configured as a length-adjustable skate with a length adjustable skate body that includes separate front and rear foot support structures.