How to obtain wheel diameter
Let's recall that the overall diameter of the wheel includes the rim which is at the center of two sides of the tire sections. This means that the section height that we obtained earlier will be multiplied by 2.
Again a 20 inches rim = 20 × 25.4 = 508 mm.
Therefore, wheel diameter = (114.75 × 2) + (20 × 25.4) = 229.5 + 50.8 = 280.3 mm.
280.3mm is the overall diameter of the wheel.If we are to convert to inches = 280.3/25.4 = 11.04 inches.
These calculation steps are same you should follow if you want to compare the tire diameter of different tires. A larger diameter or tire will give you higher ride height and vice versa.
Note that a larger aspect ratio value does not always translate to a larger diameter tire since it depends on the value of the section width.