During each test, the lubricant was added to the test chamber and the system was heated with the ball and disc rotating but not in contact. Once the desired lubricant temperature (T = 60-120 °C) was reached, a short running-in procedure was carried out at conditions of U = 0.1 m s -1 , SRR = 50 %, and W = 100 N load for 1 minute. The short running-in stage neither resulted in any measurable change in surface roughness of the specimens nor was it essential for subsequent tribofilm formation; however, it did improve the repeatability of the tribofilm formation tests, possibly by removing any adsorbed contaminants on the test specimens by rubbing. The contact was then unloaded and U increased to 0.75 m s -1 with SRR = 2 %. The target load (W = 600-1500 N) was then applied and an extended test carried out under full-film EHL conditions.