Any way to change wheel collider raycast direction?

Or any other suggestion for my case?

The robot transform to tank, the pivot direction change as shown.

 

There's no way to change the WheelCollider raycast direction. It's vertically down with respect to the rigidbody it belongs to by design.

The only workaround would be attaching the wheel to a rigidbody, then attaching that rigidbody to the vehicle's rigidbody with a joint. You could then rotate the wheel's rigidbody freely using the joint.