I have run into this problems as well.
You issue is that the wheels and the car body must be exactly aligned on the layout.
The wheels are not "moved" to the position they are joint at. They are joint at the distance at which they are set on the layout (try to move the wheels far way from the body and run the layout, then you will see what i mean).
In your case the body and the wheels had some odd positioning. so take out a piece of paper and make sure that the wheels origin point in x,y coordinate is exactly the same as the point you make the joint at on the car body (in your case imagepoint 1(backwheel) and 2(frontwheel)).
Hope i made myself understandable.