Presentation on brake inertia determination for potential amendment to heavy-duty brake emission protocol. Currently proposed protocol assumes test inertia determined based on UN R90, but comparison with C-factor from vehicle testing showed significant differences in inertia and actual load during dynamometer testing, with front and rear values differing by up to 2.3 times. Proposes retaining UN R90-based approach as default method while adding alternative inertia determination method considering vehicle mass and multi-axle configurations. Analysis of 43 Japanese market vehicle models showed UN R90-based approach can result in brake loads ranging from 0.1 to 5.7 times those of vehicle-based approach.