I was hoping that unity 5 could resolve it but looking at their video it seems not:
as you can see the wheel is intersecting the blue mesh because the wheel collider only raycasts down from the center of the wheel.
This is not only a visual problem, but also creates a wrong physics result because the wheel is not pulling up the car at all. The car goes up only because is already moving forward with enough speed. But if you start from zero the car could just get sucked there.
How do you suggest to resolve it? Any trick? Or I have to complete recode the behaviour of the wheel collider with some capsule collider, joints, etc.?