I though you used radial blur on the background You need to put more radial blur on the wheels if you want it to look something else than gaussian blur (no shit).
I really like the 2nd one! But the first one, you kinda motion blurred the edges of the car aswell :P I'm not sure how you stop that though, been trying to not do that on my picture for an hour :S
What I do is seperate the car and the background in a separate layer, and then remove the car from the background (use the Clone Stamp tool, or Content Aware fill or whatever) and then blur the background so the car is not blurred. Don't know if there are easier/other ways, but that's just how I do it.
Keeping the camera in the same place, take two screenshots. One with the car and one without. Place the two images one on top of the other (one with the car on top) and then cut the car out. Apply motion blur to the bottom layer and you shouldn't get the blurred edges on the car.
I'll have to try that, thanks for the tip. I used the pen tool to make a selection right on the edges of the car, but it still did it. That sounds like it'll work perfectly.