Abstract
A mathematical model for the prediction of the constant speed straight line stability and modal properties of pivot framed tricycles, as functions of forward speed, is developed. The tricycle is treated as consisting of three rigid bodies joined to each other as a chain at the frame pivot and steering axes, and freedoms to move laterally, to yaw, to roll, and to steer are allowed. The rider is taken to be a (rigid) part of the centre frame of the tricycle.