Car CG and WheelHit.forwardSlip questions

Hello all, here goes my first post. I'm messing around with wheel colliders and Cars, and have two questions:

1st: I draw a cube (dark blue) in the Car CG position (it has two box colliders) and it looks like the CG is outside the car boundaries:

I use the following code:

cgCubeRear.position = rigidbody.centerOfMass;

2nd: Using the WheelHit.forwardSlip the max value I can get for any wheel is 0.4 as seen in the image. Is the forward slip controlled by what? The only correlation I can see is that the WheelColliders have a 0.4 radius:

Thanks in advance!