A 255/80R14 tire is 30.1 inches (764 mm) tall and 10.0 inches wide. The sidewall is 80% of the width, 8.0 inches, on a 14-inch wheel, and the tire turns about 671 times per mile.
In flotation terms that is about 30.1x10.0R14. People often call it a 30-inch tire.