The T2 Pro X 2 Bike Add-On uses a 2-inch hitch receiver to allow for a total capacity of four bikes when used with the Thule T2 Pro XT hitch rack. It's ideal for carbon frames, mountain, downhill, and fat bikes since it fits 20 to 29-inch wheels and up to five tires without adapters, and it secures bikes quickly without frame contact. We like this add-on for traveling with friends or transporting family bikes to trailheads or across the states.