While operating in an overexpanded condition, rocket nozzles exhibit dynamic off-axis loads caused by asymmetric internal flow separation. It has been demonstrated that topologies, which only display free shock separation, produce side-load magnitudes lower than those that can transition to restricted shock separation. It is therefore suggested that geometries such as truncated ideal contour nozzles could be used on launchers with large-area-ratio designs providing improved vacuum performance. Part of the challenge of designing nozzles to operate in the overexpanded regime is characterizing and quantifying associated side loads. This paper presents the methodology and results of an analytical model that simulates side loads induced by free shock separation. The pressure distribution within a separated rocket nozzle is produced using free interaction theory, and a spring-damper analogy is used to model shock fluctuations in response to external pressure disturbances. Good agreement has been found between simulated side loads and experimentally measured forces on four conical and one truncated ideal contour nozzle.