The wheel size is the diameter of the wheel, in inches, not counting the tire. Modern tires in North America have several other measurements associated with their size. A tire designated as a "225/70R14" denotes a tire with the following dimensions: width of tread: 225 mm; ratio of tire height to width: 70 percent; rim diameter: 14". Therefore a 185/70R14 has the same rim diameter and aspect ratio, but a smaller overall diameter and narrower tread face than the 225/70R14.