Originally Posted by drinkcoke3
get a gopro! you wont have to worry about a $5k+ camera on the outside of ur car
If he is going for the type of photos I think he is, like this
(taken by a friend of mine), then he wouldn't be driving down the road with it attached to his car. Shots like that, most of the time, the car is barely crawling, if its even running in the first place. Sometimes the car is pushed if you can keep the pushers out of frame. With the long exposure settings needed, driving the car at anything more than a crawl will cause vibration issues in the shot, ruining the photo. He normally rolls the car just enough so he can easily walk next to the car and camera to fire the shutter.
A long sturdy pole, suction mounts, mount the camera (usually upside-down at the end of the pole), wide angle lens, very slow rolling, long exposure, and mad photoshop skills.
I know most of the steps my friend takes to achieve photos like that, however I won't go into great detail and he doesn't like to tell. He might give you some info though if you'd ask him. Send him a comment on Flickr.