Hunting behaviour differences of three piece bogies compared to primary suspension bogies with reference to profiles and track gauge

Wheel and rail profiles are know to change the resulting effective conicity over the first 3 mm of lateral travel. This is largely believed to be the most significant parameter in the lateral stability of all bogie types. The lateral instability motion of the three piece bogie is shown to vary greatly from a rigid frame viscous damped bogie such as modern passenger bogies. The three piece bogie is shown to have a critical lateral instability speed response to the maximum rolling radius difference (i.e. at flange contact). Because of the rolling radius change the influence of rail gauge on critical lateral instability speeds of a three piece bogie has been shown to be opposite to the rail gauge effects on rigid frame primary suspension bogies.