Some back of the envelope math suggests the rotational inertia of your wheels is around 6.5% of your total vehicle's inertia (I made what I felt were some reasonable assumptions about wheel moment of inertia). The wheels themselves are also, surprisingly, just about 6.5% of the total vehicle mass, so you're looking at affecting approximately 13% of the energy need to accelerate and decelerate. Or, in other words, my math supports that taking a pound out of the wheels is like taking two pounds out of the car.
Looks like the total inertial savings is ballpark 1.5% from the entire vehicle. I can only guess at how that would relate to fuel consumption. Maybe 1/3 to half that in mixed driving?
