maintain distance between two objects

hi evryone,
i am trying to develop a simple car game, and to do that i have to maintain the distance between the two wheels.
for the collision detection i have used coreyoneil class, which i think is excellent. i cant get the distances to go smoothly. and basically i am finding it hard to get the physics to work. if anyone has an idea what i should do, or has a good example it would be greatly appreaciated.

i have attached the swf and fla for you to see.

thanks.