#8759, "RE: will bigger wheels always make you slower, and other ?" In response to In response to 3
Actually, it's the diameter of the tire and the change in the moment of inertia that make the difference. Larger circumference wheels move more of the weight to the outer edge of the wheel/tire combo thus increasing your moment of inertia (effective load the engine sees due to your wheel weight). However, a light 18" wheel could perform the same as a heavier 17" wheel. If the weights are close, the difference will not be great, but it's something to keep in mind if you're really concerned about it.
This is all assuming the outer tire diameter stays the same which can basically be done if you pick the right tire for your wheel.