Youre trying to get the wheels to look like they're spinning, like this:
I heard a good rule of thumb a while back to match the shutter speed to what how fast you think the car is moving. 50mph would be 1/50, etc. I don't think I'd go too much faster than 1/150, or slower than 1/50. Just make sure you have enough daylight. But just keep in mind, the slower the car, the more blurry everything's gonna be. Shouldn't have too much of a problem with that on a racetrack but driving down a street will be more difficult.
Oh, and tracking: moving your camera with the car. Practice this skill when you're at racetracks.