Geometric modelling of Coronal Mass Ejections (CMEs) is a widely used; tool for assessing their kinematic evolution. Furthermore, techniques; based on geometric modelling, such as ELEvoHI, are being developed into; forecast tools for space weather prediction. These models assume that; solar wind structure does not affect the evolution of the CME, which is; an unquantified source of uncertainty.; We use a large number of Cone CME simulations with the HUXt solar wind; model to quantify the scale of uncertainty introduced into geometric; modelling and the ELEvoHI CME arrival times by solar wind structure. We; produce a database of simulations, representing an average, a fast, and; an extreme CME scenario, each independently propagating through 100; different ambient solar wind environments. Synthetic heliospheric imager; observations of these simulations are then used with a range of; geometric models to estimate the CME kinematics. The errors of geometric; modelling depend on the location of the observer, but do not seem to; depend on the CME scenario. In general, geometric models are biased; towards predicting CME apex distances that are larger than the true; value. For these CME scenarios, geometric modelling errors are minimised; for an observer in the L5 region. Furthermore, geometric modelling; errors increase with the level of solar wind structure in the path of; the CME. The ELEvoHI arrival time errors are minimised for an observer; in the L5 region, with mean absolute arrival time errors of 8.2±1.2h,; 8.3±1.0h, and 5.8±0.9h for the average, fast, and extreme CME scenarios
