Originally Posted by Rob M

Smaller wheels would equal less angular moment of inertia. The weight and diameter of the wheels make them harder to spin. The NA Crossfire cannot launch very effectively because of the large wheels; it doesn't have any resulting wheel spin and bogs down since rpms aren't high enough to be where they need to be on torque curve for best acceleration. Even if the diameter of your tires on the 18" wheels is the same as the 19" you would improve the launch because the wheel mass would be less, and the mass would be closer to the axis of rotation. I don't know if the 3.8% speedo difference results in any issues with ABS or TC.