Diameter is a 2 dimensional measurement, defined as the distance of a straight line reaching from edge to edge of a circle that passes through the center point of the circle. So the thickness of the wheel doesn't change the diameter.
Uh, yeah, I know what diameter is.
But it would seem to me that if you stretch
a tire on a wider wheel, the profile drops. And if the profile is in affect less, then so would the diameter. For instance, let's say you take the standard tire, 195/55/16, which is installed on a wheel that is 7" wide. If you put that same tire, on a 9" wide wheel, you have to stretch the tire, thus the profile is no longer 55mm and would be less. The same goes if you put it on a narrower tire, thus "bulging" the tire, and making the profile higher.
Is this not so?
Edit: This stemmed from Art's comment, when he said "The only thing is that the chart and calculator don't consider stretch."