The minor axis of the ellipse does not always remain perfectly vertical, however. Take this simple drawing of a pickup truck - how should the ellipses representing its tires be oriented in perspective?
This looks wrong:
Orienting the ellipses vertically looks better, but still not right:
As suggested before, if you imagine the ellipses (or the circles they represent) as the ends of cylinders, the answer becomes clear - the minor axes of the ellipses point toward the left vanishing point.
No other perspective lines define the orientation of these ellipses - only the center line, which aligns with the ellipse's minor axes matters in terms of orienting the ellipse:
And if we place more ellipses within these, say, to add wheel covers, they align on these same center lines: