Trailer tires
What cold pressure should a trailer tire actually run?
An ST trailer tire carries its full rated load only at its maximum cold inflation pressure, printed on the sidewall next to the load range letter. This is the opposite of a passenger car tire, where the door jamb placard sets a running pressure below the sidewall maximum. On a trailer there is no lower placard number: you run the sidewall maximum, cold, every time, unless the trailer maker publishes something different for that specific tire.
"Cold" means measured before the trailer has moved on a given day, not after even a short drive to a fuel stop, because a tire's pressure rises as it warms from rolling. Running an ST tire soft is the most common cause of trailer tire failure: the sidewall flexes more than it is built for, heats, and separates, usually at highway speed on the one corner nobody is watching.
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What is the maximum cold pressure for each load range?
A Load Range E tire, the common upgrade for heavier travel trailers, runs at 80 psi cold, and nothing on the trailer benefits from running it lower.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Load range | Maximum cold inflation |
|---|---|
| Load Range B | 35 psi |
| Load Range C | 50 psi |
| Load Range D | 65 psi |
| Load Range E | 80 psi |
| Load Range F | 95 psi |
| Load Range G | 110 psi |
This is the published maximum cold pressure for each load range, the same figure covered on the trailer tire load range chart. Read your own tire's sidewall to confirm; a trailer maker can publish a different figure for a specific tire.
Why does a trailer tire run at the maximum instead of a lower placard number?
A passenger car's placard pressure, found on the driver's door jamb, is deliberately set below the tire's sidewall maximum, because a car tire's rated load at that lower pressure is already more than the vehicle's corner weight requires. An ST trailer tire is engineered differently: its full rated load capacity, the number used on the trailer tire load index chart, is only achieved at the maximum cold pressure printed on the sidewall. Running it below that maximum reduces the load it can safely carry, even though the tire still looks properly inflated.
What gauge and inflator actually reach 80 psi?
Most automotive gauges and shop compressors top out around 60 psi, which cannot even display a Load Range E tire's correct pressure, let alone Load Range F or G.
The JACO ElitePro Digital reads to 200 psi, well above the highest published load range on this chart.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Tool | Pressure range | Covers up to |
|---|---|---|
| JACO ElitePro, mechanical | 100 psi | Load Range E (80 psi) |
| AstroAI Heavy Duty Digital | 230 psi | Load Range G (110 psi) |
| JACO ElitePro Digital | 200 psi | Load Range G (110 psi) |
| DEWALT 20V MAX Tire Inflator | Inflates and shuts off at a set target | Any load range, set the target to the sidewall maximum |
A gauge that reads only to 60 psi cannot verify a Load Range D, E, F or G tire at all, and a gauge that reads high but is never checked against a known reference can be wrong in either direction. Check a gauge periodically against another gauge you trust.
Does a tire pressure monitor replace checking cold pressure by hand?
No. A monitor such as the Tymate TM7 reports pressure continuously while towing, which catches a slow leak or a puncture long before it becomes a blowout, and that is a real safety improvement a hand gauge cannot provide while the rig is moving. It does not replace setting the correct cold pressure before the trip: a monitor calibrated against an already-soft tire simply confirms that the tire is staying at the wrong pressure rather than catching the problem.
See best trailer tire pressure monitoring systems for the options at different sensor counts.
How do you check trailer tire pressure correctly?
- Check first thing, before the trailer moves. Pressure has to be read cold. A short drive to a gas station is enough to read several psi high.
- Read the load range off the sidewall. Find the load range letter and confirm the maximum cold psi against the chart above.
- Inflate to that maximum, not a lower guess. Unlike a car tire there is no lower placard number to aim for; the maximum is the target.
- Use a gauge rated well above the target pressure. A 60 psi automotive gauge cannot even display a correctly inflated Load Range E tire.
- Check every tire, including the spare. A spare that has slowly leaked for a year is not a spare. Trailer tires lose roughly 1 to 2 psi a month even with no puncture, which is normal seepage through the rubber, not a leak to chase.
Frequently asked questions
What pressure should I run in my trailer tires?
Run the maximum cold pressure printed on the tire's own sidewall, which is set by its load range: 35 psi for Load Range B up to 110 psi for Load Range G. Unlike a car tire, there is no lower recommended pressure to target; the tire only carries its full rated load at that maximum figure.
Why is trailer tire pressure different from car tire pressure?
A car's placard pressure is set below the tire's sidewall maximum because the vehicle does not need the tire's full rated load capacity at that corner. An ST trailer tire is built the opposite way: its full rated capacity only exists at the maximum cold pressure on the sidewall, so trailers run that maximum rather than a lower number.
What does cold pressure actually mean?
Cold means measured before the trailer has traveled that day, including before a short drive to a fuel stop. Rolling friction warms the air inside a tire and raises its pressure, so a reading taken after even a few miles will read higher than the tire's true resting pressure and can lead to under inflation once it cools.
Can I use a regular car tire gauge on my trailer tires?
Only if it reads high enough. Most automotive gauges top out around 60 psi, which cannot display the correct pressure for anything above Load Range C. Use a gauge rated to at least 100 psi, and higher for Load Range F or G tires.
How often should I check trailer tire pressure?
Check cold pressure before every trip, and again if the trailer sits for more than a few weeks between trips, since ST tires lose roughly 1 to 2 psi a month through normal seepage even with no puncture. A tire pressure monitoring system adds continuous checking while towing, but it does not replace the pre-trip cold check.
Does a tire pressure monitor replace checking pressure by hand?
No. A monitor is excellent at catching a slow leak or blowout risk while the trailer is moving, but it reports whatever pressure is already in the tire. Setting the correct cold pressure before the trip still has to happen by hand with a gauge rated for the tire's load range.
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Researched, not professional advice. This page is compiled from published standards, manufacturer towing guides and product specifications, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are towing convention rather than published standards, and they are labelled that way wherever they appear. Nothing here overrides your own ratings. Work your payload sum before your tow rating, because payload is the limit that actually binds on most half ton trucks and nearly every SUV. Load a conventional trailer to 10 to 15 percent tongue weight and a fifth wheel to 15 to 25 percent pin weight, and never lighter: a tail heavy trailer is what starts sway. Weigh the rig loaded rather than trusting a brochure dry weight. A weight distribution hitch and a set of air bags both restore ride height and control, and neither one raises a single rating. Trailer brakes are required by state law above a threshold that varies by state, and a breakaway battery that has quietly gone flat is the normal condition of most trailers on the road.