The EPA COMBINED number is the tow number.
The towing penalty is 40%. 1969 tow vehicle or 2019 tow vehicle.
Some extra rolling resistance in towing, but it’s the AERO penalty that matters.
The tests must be the same with the single exception of the trailer.
1). TV loaded for camping. Passenger weight simulated.
2). Same speed solo as towing. 100% use of cruise control
3). Speed not to exceed 60-mph. Roundtrip of 200-miles to same fuel pump. Stop ar first auto-shutoff
Do the tests. If you’re above 40% penalty time to investigate. Alignment, brake drag hitch rigging, etc.
A truly aero TT will come in at under 40% fuel burn penalty. Careful attention to details can get it closer to 30%.
Mines at 36% currently. Work yet to come.
The absolute number doesn’t mean much. The AVERAGE MPG is the thing.
But first, FIND OUT HOW HIGH IT CAN BE.