A Bissell or Bissel truck is a single-axle bogie which pivots towards the centre of a steam locomotive to enable it to negotiate curves more easily. Invented in 1857 by Levi Bissell and usually then known as a pony truck, it is a very simple and common means of designing a carrying wheel.

A bogie is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transport. A bogie may remain normally attached or be quickly detachable. It may include a suspension component within it, or be solid and in turn be suspended ; it may be mounted on a swivel, as traditionally on a railway carriage or locomotive, additionally jointed and sprung, or held in place by other means.