My flatbed has aerodynamic of open shoe box, so I am happy when it makes 12 mpg driven at 65 mph.
Lately I bought lowboy trailer, who is 20' long plus tongue and weights about 5000 lb.
I might never get solid confirmation on the mpg, since not likely I will run the tank of fuel while towing empty trailer, but I drove over 200 miles on the set yesterday and only 1/2 of tank of fuel. That would indicate potentially more than 12 mpg.
Now on the plus side I tow the trailer at average 61 mph what should bring some fuel savings, but can't believe that the slightly lower speed can compensate for towing 5000 lb on 6 wheels.
I suspect that the flat trailer with dovetail improve the aerodynamics way up what makes the real difference.
Anybody has similar experience?

 

There are a lot of variables to consider such as driving differences (slight as they may be), tire pressures and sizes, brakes, etc. If you have a warped axle, hanging brake, under inflated trailer tire, etc., then that would definitely explain the less mileage in the other trailer. Incidentally, the aerodynamics should not be as much of a variable as the weight and condition of the trailers, even on an enclosed but especially on a floater.

 

Are you saying that you got better mileage towing your trailer than you did before towing anything?

If so, yes, I think the aerodynamics could make a difference. In NASCAR it's called "drafting".

 

I know when I tow flatbeds, even over 10K I can get better mpgs. Best I can with 5th wheels seems to be just over 10.2 mpg.

 

That's right. I know drafting makes the difference, but if pulling 5000 lb flatbed trailer can lower total moving resistance, maybe I should consider making lighter flatbed trailer and tow it behind my flatbed truck all the time?