Trailer Tire Load Range & Ply Rating Chart (ST Tires)
For ST (Special Trailer) tires, load range is the single most important spec — it determines how much weight the tire can carry and at what inflation pressure. This chart explains trailer tire load range and ply rating so you stock and sell the right tire.
Load range & ply rating chart
| Load Range | Ply Rating | Relative capacity | Typical use |
|---|---|---|---|
| B | 4-ply | Lightest | Small utility & light trailers |
| C | 6-ply | Light–medium | Utility, boat, small cargo trailers |
| D | 8-ply | Medium–heavy | Cargo, equipment, larger boat trailers |
| E | 10-ply | Heavy | Heavy cargo, car haulers, RVs |
| F | 12-ply | Heaviest | Severe-duty & high-capacity trailers |
“Ply rating” is an industry strength equivalent — modern tires don’t literally use that many plies.
How to use load range correctly
- Match capacity to the loaded trailer. The combined max load of all tires must exceed the fully loaded trailer’s weight (with margin).
- Higher load range = higher max inflation. Each step up allows more cold inflation pressure and carries more weight.
- Inflate ST tires to the sidewall max cold PSI. Unlike passenger tires, trailer tires are designed to run at their stamped max pressure for full capacity.
- Don’t downgrade. Never fit a lower load range than the trailer/axle calls for.
Reading an ST size
Example: ST205/75R14 Load Range C — ST = special trailer, 205 = section width (mm), 75 = aspect ratio, R = radial, 14 = rim diameter (in), Load Range C = 6-ply equivalent. (New to size codes? See our how-to-read-tire-size guide.)
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Frequently asked questions
What does load range mean on a trailer tire?
It indicates the tire’s strength/capacity and max inflation pressure. Higher letters (B→F) carry more weight.
Is load range the same as ply rating?
They correspond: B=4-ply, C=6-ply, D=8-ply, E=10-ply, F=12-ply equivalent.
What PSI should I run in ST trailer tires?
Generally the max cold pressure stamped on the sidewall for that load range, to achieve rated capacity.
Can I use a higher load range than required?
Yes — a higher load range adds capacity and durability, as long as the size fits the wheel and fender.