At first glance, tire sizes can be confusing. They are coded, may be in British or metric units, use a few important numbers... For example, 33 inches and 285 mm represent completely different sizes https://automobible.com/33-inch-vs-285-mm/. This article will use this example to explain how to figure it all out. "33 inches" in the tire code is the outside diameter; it is also 838.2 mm. 285mm is the tread width; in a 285/75 R16 tire, the sidewall height is 75% of that width.