LEAN-TO-STEER MECHANISMS WITH LINEAR OR NON-LINEAR STEERING RESPONSES The present steerable wheel assembly incorporates a lean-to-steer mechanism into an inner race of a roller bearing, while a wheel is mounted to an outer race of the roller bearing. A shaft extending from the mechanism is attached to a body, and the mechanism acts to steer the outer race and the wheel about a vertical steering axis when the shaft is tilted about a horizontal axis. The mechanism can be a pivot joint, providing a linear steering response, or can be a lean to-steer mechanism that provides a non-linear response where the steering action is not consistently responsive to tilting over the expected range of tilting. The present non-linear lean to-steer mechanisms can also be incorporated into alternative lean-to-steer devices, and alternative mechanisms can employ tracking structures to coordinate tilting motion of a first moving element with steering motion of a second moving element to provide a non-linear lean to-steer response.