The tire's circumference is approximately 88 inches. This is the perimeter or distance around the circle. As the bike moves forward one full rotation of the wheel, all of the wheel will touch the ground at some point. The bike will move about 88 inches forward when the wheel does one full rotation.
A good way to visualize this is to imagine cutting the tire so that you can unroll it to lay it out completely flat forming a straight line. This line will be roughly 88 inches long.
