For most trailers fitted with Special Trailer (ST) tires, tire pressure for trailer tires should be checked cold and set to the inflation pressure shown on the trailer’s tire placard or in its owner’s documentation. If that information is unavailable, the tire sidewall and the tire manufacturer’s load-and-inflation data are the starting points. Do not copy the pressure recommended for the tow vehicle: its tires, axle loads, and handling needs are different. Correct pressure allows each trailer tire to carry its assigned load, limits heat buildup, and helps the trailer track predictably.
A tire’s sidewall contains the information needed to identify what it is designed to do. Along with the tire size, construction, load range, and speed symbol where applicable, it will state a maximum load and the cold inflation pressure associated with that maximum load. For example, wording such as “maximum load … at … psi cold” does not mean that pressure is a generic setting for every vehicle. It means the tire reaches that listed load-carrying capability only at that cold pressure.
This matters especially on trailers because the tires often work close to their capacity. A compact utility trailer may have a modest load most of the time, while a travel trailer, enclosed cargo trailer, equipment trailer, or boat trailer can place substantial and uneven demands on its tires. Underinflation reduces a tire’s load capacity and causes more sidewall flex. Flex produces heat, and excessive heat can damage the tire internally before a driver sees obvious trouble.
The trailer manufacturer’s certification label or placard is the best first reference because it identifies the tire size and recommended cold inflation pressure for the trailer as supplied. It accounts for the trailer’s original axle and tire specification. If replacement tires are the exact specified size and load range, follow that label unless the tire manufacturer gives a more restrictive instruction.
If you have changed tire size, load range, wheels, axles, or the trailer’s intended use, the original placard may no longer reflect the installed equipment. In that case, confirm that the tires and wheels are suitable for the actual axle loads, then use the tire manufacturer’s published inflation guidance. A tire dealer or qualified trailer service professional can help interpret a mismatch, but they cannot make an inadequate tire or wheel safe merely by adding air.
Passenger vehicles and trucks typically use a door-jamb placard showing pressures selected for that vehicle’s ride, steering, braking, axle loads, and tire specification. Those numbers apply to the tow vehicle only. They do not transfer to a trailer, even if the trailer and truck happen to use tires with similar dimensions.
Trailer tires face different forces. They are not steered, often see long periods of storage, and can experience sharp side loading in tight turns. Tandem- and triple-axle trailers also scrub their tires while turning because the axles cannot all follow the same path. A pressure that is acceptable for an unloaded pickup tire may leave a trailer tire below the pressure needed to support its load safely.
| Reference | What it applies to | How to use it | Common mistake |
|---|---|---|---|
| Trailer placard or certification label | The trailer as originally equipped | Use the listed cold pressure for the specified tire size and load range. | Ignoring it because the tow vehicle has a different recommendation. |
| Tire sidewall | The individual tire’s maximum rated load and pressure | Confirm size, load range, and the maximum cold pressure limit. | Reading “maximum” as an automatic target without checking the trailer specification. |
| Tire manufacturer load-and-inflation table | A specific tire model or tire type | Match actual tire load to the manufacturer’s published data where applicable. | Using a chart for a different tire size or construction. |
| Tow vehicle door-jamb label | The truck, SUV, or car | Set the tow vehicle tires separately, according to its label and loading guidance. | Putting the same pressure in trailer tires. |
Many trailers use ST tires, identified by “ST” before the size designation. They are built for trailer service and commonly have a stated maximum cold inflation pressure that corresponds to their rated load. On trailers using the original ST tire specification, the placard often calls for the sidewall-listed cold pressure. That is why owners frequently hear that trailer tires should be inflated to the sidewall number.
That advice needs context. The sidewall number is not simply a “maximum you should never use” in the way some drivers think of a passenger-car tire. With ST trailer tires, it is often the pressure needed to obtain the tire’s rated carrying capacity, and it may match the trailer label exactly. The right instruction still comes from the trailer placard first, followed by the tire manufacturer’s guidance for the actual tire installed.
Some trailers use Light Truck (LT) tires, particularly larger or modified trailers. LT tires have their own load-and-inflation tables, and the correct pressure may depend more directly on actual wheel load. Passenger (P-metric) tires may be fitted to certain light trailers but should not be substituted casually. Their load rating and suitability for trailer use must be confirmed, particularly when replacing ST tires. Matching the visible diameter alone is not enough.
Load range is a strength classification associated with the tire’s construction and maximum inflation capability. It can help distinguish otherwise similar-looking tires, but it does not mean every tire of the same nominal size has the same capacity. Check the complete sidewall marking and the manufacturer’s documentation. A replacement tire must have at least the load capacity required by the trailer, and the wheel must be rated for the pressure and load involved.
Air pressure changes with temperature. A tire that was correctly inflated on a cool morning can show a higher reading after highway travel or in hotter weather. That rise is expected; it is one reason pressure should be set cold rather than adjusted at a fuel stop. A sudden or unusually large increase compared with the other tires, however, can point to an overloaded tire, underinflation before departure, a dragging brake, bearing trouble, or another source of excess heat.
Direct sunlight can also make one side of a parked trailer read higher than the shaded side. For a consistent check, park on level ground, avoid checking immediately after moving the trailer, and use the same gauge. If you must add air during a trip because a tire is visibly low, inspect for a puncture, leaking valve stem, damaged wheel, or other cause as soon as it is safe to do so.
Altitude, seasonal temperature shifts, and long storage periods can affect readings as well. A trailer stored through colder weather may need attention before its first trip. Pressure loss is not always dramatic enough to notice by sight, particularly on stiff trailer sidewalls, so a visual check alone is not sufficient.
Correct inflation supports the tire’s load capacity, but it does not solve an improperly loaded trailer. Too much weight behind the axle can reduce tongue weight and make the trailer prone to sway. Too much weight concentrated at the front can overload the hitch, rear axle of the tow vehicle, or trailer tires. A side-to-side imbalance can overload one tire or one side of an axle even when the total trailer weight appears acceptable.
Before a trip, load heavy items low and close to the trailer axle area while maintaining the tongue-weight range specified by the trailer and hitch manufacturers. Secure the load so it cannot move. Then consider the real weight carried by each trailer axle, including cargo, water, equipment, and accessories permanently attached to the trailer.
Uneven wear does not diagnose pressure by itself. Underinflation can contribute to shoulder wear, while overinflation may contribute to more center wear, but alignment, bent components, axle problems, worn suspension parts, and load distribution can produce similar patterns. Treat abnormal wear as a reason to inspect the whole trailer system rather than adding or removing air at random.
| Mistake | Why it creates risk | Better action |
|---|---|---|
| Using the tow vehicle’s tire pressure | The number does not reflect the trailer tire’s load requirement. | Follow the trailer placard and the installed tire’s guidance. |
| Inflating by appearance | Trailer sidewalls can look normal when pressure is too low. | Use a gauge before every trip. |
| Bleeding air from hot tires | The warm reading includes normal operating pressure increase. | Set pressure only when cold unless addressing an emergency underinflation issue. |
| Ignoring the spare | A flat spare turns a manageable roadside stop into a recovery problem. | Inspect and inflate the spare during the same pre-trip check. |
| Adding pressure to cure overloading | Inflation cannot raise a tire, wheel, axle, or trailer’s rated capacity beyond its limits. | Reduce the load or use equipment correctly rated for it. |
| Mixing unmatched tires on an axle | Different sizes, constructions, or capacities can share load unevenly. | Use matched tires meeting the required specifications. |
For many trailers equipped with the original ST tires, the manufacturer’s placard calls for the same cold pressure shown on the tire sidewall, because that pressure supports the tire’s rated load. Do not assume this without checking the trailer label, tire type, and wheel limits. If the installed tires differ from the original specification, use the tire manufacturer’s applicable load-and-inflation guidance.
Do not reduce pressure simply because the trailer appears lightly loaded. Many trailer manufacturers specify one cold pressure for the installed tires, and trailer tires can experience demanding forces even on a relatively light trip. If a lower-pressure approach is permitted for your particular LT or other tire type, it should come from the tire manufacturer’s load-and-inflation data and actual measured loads, not guesswork.
Check it before every towing trip and before setting out after the trailer has been stored. On longer trips, inspect the tires at fuel or rest stops, but make cold-pressure adjustments only after the tires have cooled. A tire-pressure monitoring system can provide an added warning, but it does not replace a hands-on pre-trip inspection.
One hot tire may be underinflated, overloaded, damaged, or subject to abnormal scrubbing from alignment or suspension issues. Heat can also come from a dragging brake or a failing wheel bearing, so compare the tire, wheel, and hub carefully without touching potentially hot parts. Stop towing and arrange inspection if there is smoke, a burning smell, rapid pressure loss, or a significant temperature difference.
No. The tire’s maximum cold inflation pressure and maximum load are limits, not targets to exceed. The wheel, valve stem, axle, suspension, and trailer structure also have separate ratings. If the trailer is overloaded, remove cargo or use a trailer and tire combination designed for the load.
Start by identifying the trailer’s original tire specification through its owner’s documentation or manufacturer support, if available. Until you can verify it, inspect the installed tire sidewalls for size, load range, maximum load, and maximum cold pressure, and do not assume the tow vehicle’s settings apply. A qualified trailer technician can help assess whether the tires, wheels, and axles are properly matched.
The safest routine is simple: check tire pressure for trailer tires cold, follow the trailer’s specified inflation guidance, verify that the sidewall and wheel ratings support the required load, and inspect the tires before every departure. Keep the tow vehicle and trailer pressure requirements separate. Proper inflation is one part of safe towing, alongside sound tires, balanced loading, secure cargo, working brakes, and equipment that remains within its ratings.