I am not a huge fan of the tilt, mostly because of the way it gets used. The only reason to tilt is to add to the impact of the shot, for me tilting so that it just makes the car/bike look like it is going up or down hill is pointless
All of these shots are far to extreme. The last one has potential.
When I am shooting I don't think about whether I am tilting the camera or not, I just try to get whatever I am shooting to sit the best in the frame.
This is an extreme tilt, but the tilt doesn't dominate the shot.
This is about as extreme as I would go with a car.