I've got one, not used it for tracks but I can say that if mounted on the door it may pick up more vibration noise when you come to play back the video.
You can mount it on the front wing, I've found this a lot better and if you do it low close to the door it will give you a nice shot of the wheel.
Also if anyone didn't know, GoPro gives you some white rubber thing you can fit in between the gaps on the belt buckle style clips to reduce vibration.
Its also rated to 150mph if I remember correctly.