Don't forget both the front and back wheels are turning (I don't know if we can see it's twice better, but it is!).
I didn't upload the video with the car driving on the floor but it's quite good.
Ok, I hope you don't mind Denny, but I tried to build something on my own, based on your first work, but with XL motors.
You can see two videos:
I'm sorry but the first video is all upside down, damn iPhone! :D