P285 65 R18 on this tire size what does the 18 refer to? sidewall height tread depth wheel size Maximum tire pressure

The "R" in the tire size P285/65/R18 refers to radial construction, which is a common type of tire construction where the tire's cord plies radiate outward in a radial direction from the center of the tire. The "18" in the tire size P285/65/R18 refers to the wheel size, which is the diameter of the wheel that the tire is designed to fit. In this case, the tire is designed to fit a wheel with a diameter of 18 inches.