How it works
Part of the trailer’s weight rides on the tow vehicle through the tongue (or kingpin). The rest is shared by the trailer tires:
Load on trailer tires = loaded trailer − tongue weight
Load per tire = load on trailer tires ÷ (axles × tires per axle)
Minimum tire rating = load per tire × (1 + margin)
If your tire’s sidewall rating meets the minimum, the result is OK. If it carries the load but without the full margin, it is shown as at the limit. If the load per tire is above the rating, the tires are overloaded.
Worked example
A tandem-axle travel trailer weighs 7,000 lb loaded with 900 lb of tongue weight. The tires are rated 2,150 lb each.
- Load on tires: 7,000 − 900 = 6,100 lb
- Per tire: 6,100 ÷ 4 = 1,525 lb
- Minimum rating with 15% margin: 1,525 × 1.15 = 1,754 lb
- 2,150 lb tires leave a 41% reserve: OK.
Minimum tire rating chart
Per-tire rating needed with a 15% margin, assuming 10% tongue weight and single tires on each axle.
| Loaded trailer | Single axle (2 tires) | Tandem axle (4 tires) |
|---|---|---|
| 3,000 lb | 1,552 lb | 776 lb |
| 4,000 lb | 2,070 lb | 1,035 lb |
| 5,000 lb | 2,588 lb | 1,294 lb |
| 6,000 lb | 3,105 lb | 1,552 lb |
| 7,000 lb | 3,622 lb | 1,811 lb |
| 8,000 lb | 4,140 lb | 2,070 lb |
| 10,000 lb | 5,175 lb | 2,588 lb |
| 12,000 lb | 6,210 lb | 3,105 lb |
| 14,000 lb | 7,245 lb | 3,622 lb |
Tips for trailer tire safety
- Inflate to the sidewall pressure when the tires are cold. Most ST tires need their maximum pressure to carry their rated load.
- Check the trailer’s VIN label. It lists the original tire size and cold pressure for the trailer’s GVWR.
- Watch the age. Trailer tires often age out before they wear out. The DOT date code shows the week and year of manufacture.
- Dual tires carry less each. Dual-fitment ratings are lower than single ratings; use the dual figure from the sidewall.
- Weigh each side. Slide-outs, kitchens and batteries often put more weight on one side.
Need the loaded weight first? Use the RV water and propane calculator or theboat trailer weight calculator.
Common mistakes
- Dividing the full trailer weight by the tires. That overstates the load slightly; subtract tongue weight first. (The calculator does.)
- Using the dry weight. Tires carry the loaded trailer, water and gear included.
- Running zero margin. Uneven loading and heat can overload a tire that looked “just enough” on paper.
- Ignoring pressure. A tire at 50 psi cannot carry the load printed for 80 psi.