Thanks Eric. I actually did not forget. I radial-blurred it & then removed it.
I wanted the contours of the wheel to show. I concede, for true motion it should be blurred. But in this case,
I did not want it to take away the neat metallic contours of the wheels.
You forgot to blur the wheels. Otherwise, nice motion blur.
I did a similar effect here: http://www.pbase.com/image/27492191 In addition to blurring the background and wheels, I added a very subtle "airstream" streaking behind the car. I was toying with the idea of creating a "Matrix bullet trail" effect, which would be neat, but decided against it.
