I've looked at the equations for torque, inertia, and angular acceleration, but I still can't figure this out. I was hoping someone could push me in the right direction. This is the question I'm trying to solve: In a situation where an engine propels a required amount of weight, is a reduction in rotating mass really beneficial (in non-constant RPM situations) because any weight savings in rotating mass is added back as static weight. For instance, let's say a 1000 kg vehicle had an engine driving a single disk (solid, uniform density) rear wheel. If a 10 kg weight savings is made to the rear wheel, that 10kg must be added back to the vehicle as static weight so that the vehicle weighs 1000 kg total. I believe that the engine will be able to angularly accelerate the lighter rear wheel faster, but since it's propelling more static weight, will the net advantage be positive, negative, or negligible? Thanks in advance!