28' 5th wheel enclosed car carrier. 5600#'s empty, 9-10k loaded. Weight of car doesn't noticeably affect mileage. Wind and fuel quality make all the difference in numbers. Low of 9. 5, high of 16. 5 (high was loaded in the mountains, low was empty trailer pushing high wind in NE). Have about 15k miles towing, solid 12-14 avg. See sig for truck specs. I run speed limit +or-, 75-80 out west, 55-60 in the east.