To assess the factors that contribute to head and neck dynamics in motorcycle crash simulation tests. Method: A series of laboratory tests was undertaken using an oblique impact rig. The impact rig included a drop assembly with a Hybrid III head and neck. The head struck the top surface of a horizontally moving striker plate. Head linear and angular acceleration, striker plate force, and upper neck loads were measured. The following test parameters were varied: drop height to a maximum of 1.5 m, horizontal speed to a maximum of 35 km/h, impact orientation/location, and restraint adjustment. Two helmet models were used for the majority of tests. Visor impacts were conducted as were comparisons across 4 helmet models. Descriptive statistics were derived and multiple regression was applied to examine the role of each parameter. The data were compared to unhelmeted tests. Results: The tests confirmed that motorcycle helmets compared to no helmet provide a high level of protection to the head and neck through management of both linear and angular head acceleration and neck loads. In the most severe lateral impacts (drop height 1.5 m and horizontal speed 35 km/h): the mean head injury criterion (HIC15) and mean maximum headform acceleration were respectively 648, 150 g for 4 helmet models; the mean +ay was +9.5 krad/s2 and +ax was +5.1 krad/s2; the upper neck resultant force, -Mx and -My, respectively, were 4947 N, -80 Nm, and 55 Nm. Drop height was a significant predictor of peak linear headform acceleration, HIC15, and striker force. Horizontal speed and impact orientation were significant predictors of peak angular acceleration, in addition to drop height.