ST Tires vs LT Tires

01What the letters mean

ST — Special Trailer. Built for trailer axles only, and marked "trailer use only" by retailers for that reason. The construction prioritizes a stiff sidewall and heat resistance under sustained load. ST tires are not rated for a powered or steered axle and should never go on a tow vehicle.

LT — Light Truck. Built for pickups, vans, and body-on-frame SUVs. Heavier construction than a passenger tire, higher load ranges available, and a tread designed to put power down and steer. LT tires are the correct tire for the truck doing the towing.

P — passenger, or a size with no letter at all. The lightest construction of the three. A P-metric tire used in trailer service is derated by 10 percent of its rating, which is a formal industry adjustment, not a rule of thumb — a fact that alone should end most arguments about putting car tires on a trailer.

02The capacity difference is real and it goes the way people do not expect

For the same nominal size, an ST tire carries approximately 10 percent more load than an LT tire and roughly 40 percent more than a P-metric tire. That is the figure published across the trailer industry, and it exists because the rating standards for ST tires assume a trailer application: lower speeds, no traction or steering demands, and an axle that sits near its rated load whenever the trailer is used.

Which means the intuitive assumption — that a big tough truck tire must be stronger than a trailer tire — is backwards at the same size. The LT tire is more capable in more ways; the ST tire carries more weight.

Where LT wins on paper is at the top of the size range. There are LT sizes with capacities no ST tire in a comparable diameter matches, which is why heavy-duty equipment trailers occasionally end up on LT rubber. That is a size argument, not a construction argument.

03Construction: what the sidewall is doing

A trailer tire's sidewall spends its life resisting lateral force. Every crosswind, every lane change, every passing semi, every bit of sway pushes the trailer sideways, and there is no steering input to correct it — the tire's stiffness is the correction. That is why ST tires are built with stiffer, thicker sidewalls than LT tires of the same size, and why an LT tire's more compliant sidewall, which exists to make a truck ride well, is a liability behind one.

An LT tire's sidewall is tuned for a compromise the trailer does not need: ride comfort, steering feel, and impact absorption on a vehicle carrying people. Softer flex means more heat under a trailer's constant load, and heat is the mechanism behind most trailer tire failures.

Tread is the mirror image. LT tread patterns are engineered for traction under power and braking, which a trailer axle does not do. On a trailer, tread pattern matters far less than construction — which is why an aggressive-looking all-terrain LT tire on a trailer looks capable and is doing nothing useful.

04Speed ratings — the 65 mph rule is out of date

The most persistent piece of trailer tire folklore is that every ST tire is limited to 65 mph. That was broadly true for years and is still true for bias-ply and older radial ST tires, which is why the rule refuses to die.

It is not true across the board anymore. Tredit's Trailer King II ST line carries an M speed rating — 81 mph — across every size from ST175/80R13 to ST235/85R16. The Goodyear Endurance carries an N rating, 87 mph, across its entire range. Those are real service descriptions on real tires, not exceptions.

The practical rule: read the service description on the tire you actually own. If it ends in M you have 81 mph, if it ends in N you have 87, and if there is no speed symbol at all you are almost certainly on a 65 mph tire. And in every case the rating is a structural limit rather than a target — a trailer's stability, its brakes and its load are all separate reasons to tow below it.

05When LT on a trailer is a deliberate choice

This is where the blanket "never" gets in the way of an honest answer. Some heavy equipment trailers, flatbeds and goosenecks do run LT tires, and the owners running them are not all confused. The reasons are consistent: at 16 inches the LT market is far deeper than the ST market, LT tires from major manufacturers are widely available with real warranties and fresh date codes at any tire shop, and the higher speed ratings suit a trailer that lives on the interstate.

The trade-offs are equally consistent, and you have to accept all of them. The LT tire carries less than an equivalent ST at the same size, so the capacity math has to be redone rather than assumed — the tire's rating at the pressure you will actually run must meet or exceed what the axle demands, with margin. The softer sidewall means more sway, which matters more on a tall trailer than a low one. And on a travel trailer or camper, where the tall body and the light tongue weight make sway a real handling issue, the case for LT largely evaporates.

Where it is not a judgment call: if your trailer's certification label specifies ST and you are not doing the load math yourself, fit ST. And a passenger tire is not part of this conversation in either direction.

06The mistake in the other direction

Putting ST tires on a tow vehicle is the error nobody talks about, and it is worse than the reverse. ST tires are rated for trailer service only. They have no traction design for a driven axle, they are not built for the cornering and braking loads of a steered vehicle, and retailers mark them trailer-use-only for exactly that reason.

If the truck needs more capacity, the answer is an LT tire in a higher load range — see E-rated tires for what that buys and what it costs you in ride quality. The tow vehicle's requirements live on its door-jamb placard; the trailer's live on its certification label. They are two separate specifications and neither one substitutes for the other.

07Sorting it out in West Georgia

The practical version, for a trailer owner out here: read the certification label on the trailer, buy ST in that size and load range or higher, inflate to the sidewall pressure cold, and replace on age. That covers utility trailers, boat trailers, car haulers and campers, which is nearly everything towed in Carroll, Douglas, Paulding, Haralson and Heard counties.

This directory does not track trailer tires as a separate service, and no shop in it lists them as its own line item — but 73 of the 75 shops listed sell and mount tires, and the common ST sizes are widely available locally. If a shop tries to sell you an LT tire for a trailer that specifies ST, ask them to show you the load rating at your working pressure against your axle rating. A shop that can do that math is worth keeping; one that waves it off is not.

RimsAndTires is a free directory rather than a tire seller. Tell us what you tow and we will match you with a local shop that has the right tire.

ST vs LT tires compared