When blurring the backplate, remember to match the angle of the blur to the direction of the camera/car. Also, break your backplate into visual planes and apply a lesser amount of the same blur to each section with the far distance getting just a little blur. This is a very quick example using a still I found and very basic blur of the wheels.If you want to go crazy, you can use a gradient to change the blur as the distance increases. Subtle, but adds to the realism.