TowingMath

Trailer Tire Load Range Chart

Load ranges B through F, what each one means, and — the part most charts skip — how to work out the per-tire capacity your trailer actually needs.

Load rangePly ratingMax cold pressureTypical use
B 4-ply rated 35 psi Small utility and light boat trailers
C 6-ply rated 50 psi Single-axle utility, small campers
D 8-ply rated 65 psi Tandem utility, mid-size travel trailers
E 10-ply rated 80 psi Large travel trailers, heavy equipment
F 12-ply rated 95 psi Heavy commercial and large fifth wheels

Load range is not a weight. This is the single most common mistake made with this chart. A letter tells you the tire's construction strength and its maximum pressure — it does not tell you how many pounds the tire carries, because capacity depends on the tire's size too. Two load range E tires in different sizes carry different loads. The governing number is the maximum load stamped on the sidewall of the specific tire, at its stated pressure.

Trailer tire sidewall markings A tire sidewall showing the size code beginning with ST, the load range letter, and the maximum load and maximum cold inflation pressure. The maximum load stamped here is the figure that governs capacity, not the load range letter alone. ST225/75R15 LOAD RANGE E Size — "ST" means Special Trailer MAX LOAD 2830 LB AT 80 PSI COLD the number that governs Load range letter NOT a weight Example markings
Where to look. The load range letter narrows your shopping; the MAX LOAD figure stamped on the sidewall is what actually governs capacity.

What capacity do my tires need?

Use GVWR if you want the tires rated for a full load.
Carried by the tow vehicle, so it never sits on trailer tires.
Industry practice is 10-20% headroom. Trailer tires fail from heat and sustained load.
Required capacity per tire —

Enter your numbers above.

Verify before you tow. These figures are a planning aid, not professional or engineering advice. Your real limits are the ones printed on your vehicle's door-jamb placard, your trailer's VIN plate, and your owner's manual - and those override anything calculated here. When numbers are close, weigh the rig and go with the more conservative answer.

The formula

Weight on tires = Loaded trailer weight - Tongue weight

Tires on the ground = Number of axles x 2

Load per tire = Weight on tires / Tires on the ground

Required capacity = Load per tire x (1 + margin)

Then buy a tire whose SIDEWALL maximum load meets or exceeds
that figure. Use the load range letter to narrow the search,
not to make the decision.

Worked example

Tandem-axle travel trailer at its GVWR   7,600 lb
Pin/tongue weight                          -990 lb
                                          --------
Weight carried by the tires               6,610 lb

Tires on the ground: 2 axles x 2         =      4
Load per tire: 6,610 / 4                 =  1,653 lb

With a 15% margin:
  1,653 x 1.15                           =  1,900 lb per tire

So you need tires stamped for at least 1,900 lb each. In common trailer sizes that typically lands in load range D or E territory — but confirm against the actual sidewall, because the same letter spans a wide range of capacities across sizes.

Why trailer tires fail

Almost always heat, and heat comes from three things: underinflation, overloading, and speed. They compound — a tire that is 10% underinflated and 10% overloaded is not 20% worse off, it is running far outside what it was designed to shed.

Two practical consequences. First, set pressure cold, before the trailer has moved; a warm tire reads high and tempts you into bleeding out air you needed. Second, age matters independently of tread. Trailer tires frequently time out before they wear out, because a trailer sits still for months and sidewalls degrade from UV and ozone regardless of mileage. Plenty of blowouts happen on tires with excellent tread and a date code seven years old.

Common questions

What does trailer tire load range mean?

Load range is a letter, B through F, describing how much load the tire's construction can support and the maximum cold inflation pressure it is designed for. B is 4-ply rated at 35 psi, C is 6-ply at 50 psi, D is 8-ply at 65 psi, E is 10-ply at 80 psi, F is 12-ply at 95 psi.

The "ply" figure is historical. A modern radial "10-ply" tire does not contain ten layers - it might have two steel belts and a polyester body ply. The rating means it has the equivalent strength of old ten-ply cotton-cord construction.

How much weight can a load range E tire carry?

There is no single answer, and any chart that gives you one is misleading you. Load capacity depends on the tire's SIZE as well as its load range. An ST205/75R15 load range E and an ST235/85R16 load range E carry very different loads.

The only figure that governs is the maximum load stamped on that specific tire's sidewall, at its stated cold pressure. Use load range to narrow your shopping; use the sidewall to make the decision.

Do I have to run trailer tires at max pressure?

For ST (Special Trailer) tires, generally yes - inflate to the cold pressure stamped on the sidewall. This is the opposite of passenger car practice, where you follow the vehicle placard rather than the tire.

The reason is heat. ST tires only reach their rated capacity at full inflation; underinflated, the sidewall flexes more, builds heat, and heat is what destroys trailer tires. Set pressure cold, before driving - a tire checked warm reads high and tempts you to bleed air out, which is exactly wrong.

Can I put a higher load range tire on my trailer?

Usually yes, and it is a common upgrade - a load range E in place of a D gives more capacity margin and runs cooler at the same load. Confirm the wheel is rated for the higher pressure first, because the wheel has its own limit and it is often the constraint.

What it does not do is raise your trailer's GVWR or its axle GAWR. Those are set by the manufacturer as a system. Better tires remove the tires as your weak link; they do not license you to load heavier.

What does the speed rating on a trailer tire mean?

Most ST tires are rated to 65 mph unless the sidewall says otherwise, and some carry a letter speed symbol allowing 75 or 81 mph. Exceeding the rating builds heat the tire was not designed to shed.

Speed rating and load rating interact: a tire running near its load limit has far less margin for the heat that speed adds. If you tow fast and heavy, you need headroom in both.

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