this is my first attempt at a 3D printable object. It's based on a design (http://www.thingiverse.com/thing:9710#) I saw at my friend's house. It is a single print that has moving parts. This has now been updated to have much better tolerances between the wheel and the wheel-well. Enjoy :D
Note: I've uploaded a new file that should fix the issue that slic3r was having (resulting in only half the car printing) also, smoothed for better wheel rotation. VRRROOOM!
I printed this to be about 4 inches long on the longest side, at that scale the tolerance around the wheels work great! You could probably print it smaller (as long as your printer is well calibrated) or bigger and it would be fine.