[ODE] How to Avoid Walls when using 4 spheres and box for a Car

[kurimail]

Sorry for the long topic name, but that is my question...

When i use 4 spheres for the car and i get near to a wall the car goes up
trying to climb the wall. Is there any way to avoid this?

I know that a possible solution could be to make the box for the car
bigger than it is, but i don't want to use this because then the car
collides with nothing (space between the wall and the real body car).

any help please?

Thanks in advance!