How it works
Range to empty = fuel × mpg (or fuel ÷ L/100 km × 100)
Distance between stops = range × (1 − reserve %)
Fuel stops = trip distance ÷ distance between stops, rounded up, minus one
The result is compared with the longest stretch on your route without a fuel station you can use with a trailer. It is OK below 90% of your usable range, at the limit up to 100%, and exceeds beyond that.
Worked example
26-gallon tank, 10 mpg towing, 25% reserve, a 600-mile trip with a 150-mile stretch without stations.
- Range to empty: 26 × 10 = 260 mi
- Between stops: 260 × 0.75 = 195 mi
- Fuel stops: 600 ÷ 195 = 3.1 → 3 stops; the 150-mile stretch uses 77% of the usable range: OK.
Miles between fuel stops (25% reserve)
| Tank | 8 mpg | 10 mpg | 12 mpg | 14 mpg |
|---|---|---|---|---|
| 20 gal | 120 mi | 150 mi | 180 mi | 210 mi |
| 26 gal | 156 mi | 195 mi | 234 mi | 273 mi |
| 36 gal | 216 mi | 270 mi | 324 mi | 378 mi |
| 48 gal | 288 mi | 360 mi | 432 mi | 504 mi |
Range shrinks with speed and wind
Fuel economy while towing swings a lot with conditions. A strong headwind or a few mph of extra speed can cost 10–20% of range, because air drag rises with the square of speed (see the trailer drag calculator). Mountain climbs use far more fuel going up than they save coming down. On unfamiliar or remote routes, refill whenever a good station comes up rather than counting on the next one.
With your distance between stops, plan the whole day with the travel time calculator, and work out the cost with the towing fuel cost calculator.
Common mistakes
- Using solo mpg. Towing economy is often 30–50% lower.
- Counting the whole tank. Some of the tank is unusable, and gauges are not linear.
- Ignoring station access. Not every pump fits a long trailer; plan truck-friendly stops.
- Mixing US and UK gallons. Imperial mode uses US gallons (3.785 L).