How Much Does Towing Affect Gas Mileage?
Expect to lose somewhere between a third and a half of your unloaded mileage. What decides where you land is mostly the shape of the trailer, not its weight.
Rough expectations
| What you are towing | Typical mpg penalty | Why |
|---|---|---|
| Small low utility trailer | 10–20% | Sits in the tow vehicle's wake; little extra frontal area |
| Boat on a trailer | 15–30% | Heavy but low and reasonably slippery |
| Enclosed cargo trailer | 30–45% | Tall flat front pushing a lot of air |
| Travel trailer | 35–50% | Tall, boxy, and usually the worst case |
| Fifth wheel | 35–50% | Very large frontal area, partly offset by sitting closer to the truck |
Ranges, not predictions. Your terrain, speed, headwind and how the rig is loaded move these substantially. Treat them as a planning starting point and measure your own.
Why shape beats weight at speed
Two forces consume fuel: rolling resistance, which scales roughly with weight, and aerodynamic drag, which scales with frontal area and with the square of speed.
That squared term is the whole story. At 30 mph, weight dominates and drag is minor. At 70 mph, drag has grown by a factor of roughly five relative to 30 mph, and it becomes the main thing your engine is fighting. A travel trailer is essentially a barn door being dragged through the air, which is why a 6,000 lb camper often costs more fuel than a 9,000 lb boat.
Which is why slowing down works so well
Drag is proportional to speed squared.
70 mph -> 60 mph: (60/70)^2 = 0.73
roughly 27% less aerodynamic drag
60 mph -> 55 mph: (55/60)^2 = 0.84
roughly 16% less That is the single largest lever available to you, it costs nothing, and it also reduces tire and transmission heat — which is what actually destroys trailer tires.
Estimating the fuel cost of a trip
Gallons = Trip miles / Towing mpg Cost = Gallons x Price per gallon Example: 600-mile trip, 11 mpg towing, $3.60/gal 600 / 11 = 54.5 gallons 54.5 x $3.60 = $196 Same trip not towing, at 20 mpg: 600 / 20 = 30 gallons x $3.60 = $108 The trailer costs about $88 in fuel each way.
What actually helps
- Slow down. The biggest single lever, for the reason above. 65 rather than 75 is often 1–2 mpg.
- Correct tire pressure, both vehicles. Underinflated tires add rolling resistance and heat. Trailer tires generally run at the cold pressure on the sidewall.
- Load the trailer properly. Correct tongue weight keeps the rig tracking straight instead of constantly correcting, and every correction costs energy. See tongue weight.
- Do not carry water you do not need. Water is 8.34 lb per gallon. A 40-gallon tank is 334 lb hauled up every hill for no reason if there is a tap at the campsite.
- Reduce frontal area where you can. Remove roof boxes and bike racks that stick into clean air.
What does not help much: tuners and programmers, "fuel saver" devices, and tailgate-up-versus-down arguments. The fuel is going into aerodynamic drag, and none of those meaningfully change how much air you are pushing.
Common questions
How much does towing reduce gas mileage?
Commonly somewhere between a third and a half, and a large travel trailer at highway speed can approach halving it. A truck returning 20 mpg unloaded might see 11-13 mpg pulling a mid-size travel trailer.
The range is wide because the dominant factor is frontal area, not weight, and trailers vary enormously in shape. Anyone quoting a single universal percentage is guessing.
Does trailer weight or trailer shape matter more?
Shape, at highway speed. Aerodynamic drag rises with the square of speed, so above roughly 50 mph pushing air is the main cost, and a tall boxy travel trailer is a wall.
Weight dominates in stop-start driving and on climbs, where you are accelerating mass and lifting it. A heavy low boat trailer often costs less fuel on the interstate than a lighter, taller camper.
Does slowing down actually help?
More than anything else available to you. Because drag scales with the square of speed, dropping from 70 to 60 mph cuts aerodynamic drag by roughly a quarter.
Many people see 1-2 mpg from that change alone. It is free, it requires no equipment, and it also reduces heat in tires and transmission — which matters independently of fuel.
Will a tuner or programmer improve towing mileage?
Rarely enough to matter, and the marketing overstates it. Modern engines are already well optimised, and the fuel is going into aerodynamic drag, which no engine tune addresses.
Speed, tire pressure and how the trailer is loaded are where the real gains are, and all three are free.
Related tools
Sources
- US Department of Energy - Fuel economy: driving more efficiently - aerodynamic drag rises rapidly with speed; hauling cargo reduces fuel economy
- US EPA - Fuel economy testing and factors affecting mpg - load and aerodynamics as primary real-world fuel economy factors
- USGS Water Science School - water density - one US gallon of fresh water is approximately 8.34 lb