I've found towing mileage change was very dependent on the vehicle. For example, I had a Dodge Durango which got pretty much 16mpg no matter what, whether driv

I've found towing mileage change was very dependent on the vehicle. For example, I had a Dodge Durango which got pretty much 16mpg no matter what, whether driving empty or towing a car on a flatbed trailer at highway speeds, still 16mpg. Next vehicle was a used manual transmission BMW X5, got 22-24mpg empty on the highway, but just towing an empty flat trailer would drop that to 17mpg, and a car on it would be 16, and the same towing a small U-Hual box trailer, just instantly drop to 16. So, one was highly stable and the other highly variable with different weight/aero loads.