RV tire sizes are determined by the size of the rims, which are usually between 14.5 inches to 19.5 inches in diameter on the larger rigs. Half-inch measurements are typically found on heavy-duty trucks and trailers, which are used as chassis for the larger RVs.
RVs built on minivan or light truck chassis, such as the Class B van conversions, use passenger vehicle tire measurements and have average rim sizes of between 14 inches and 19 inches. RV tires also have higher ply ratings and load range ratings. Ply ratings, which refer to the number of support layers in a tire, can range from 10 to 16 layers. Typical load ranges are from E to H, which determines how much weight each tire can support when properly inflated.