Trailer tires
How do you check trailer tire pressure correctly?
A passenger car tire is set from the door jamb placard, at a pressure below the sidewall maximum, because the car's own weight is what the placard figure was designed around. An ST trailer tire works nothing like that. It is rated to carry its full published load only when inflated to its maximum cold pressure, printed right on the sidewall, and running it below that figure is the single most common cause of trailer tire failure. A soft ST tire flexes more in the sidewall, generates more heat, and fails at highway speed, usually on whichever corner nobody happened to be watching.
"Cold" has a specific meaning here: before the trailer has moved that day. A tire that has been rolling for even twenty minutes has already heated up and its pressure has risen above true cold, so checking it at a fuel stop and topping it back down to the target number actually under-inflates it. Check every trailer tire before you pull out of the driveway, not during the trip.
Load range sets the pressure, not a placard
Every ST tire is stamped with a load range letter, and each range has a published maximum cold inflation pressure. This comes directly from the tire industry's own load and inflation tables, printed on the sidewall of every trailer tire sold.
A load range E tire, common on heavier tandem axle travel trailers, is rated to 80 psi cold, a figure most car tire gauges cannot even display.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Load range | Ply rating | Maximum cold pressure |
|---|---|---|
| B | 4 ply | 35 psi |
| C | 6 ply | 50 psi |
| D | 8 ply | 65 psi |
| E | 10 ply | 80 psi |
| F | 12 ply | 95 psi |
| G | 14 ply | 110 psi |
Published tire industry load and inflation figures, printed on the sidewall of every tire sold at that load range. Your own tire's sidewall is the authority for your specific tire.
Step by step: checking pressure the right way
- Check before the trailer has moved that day. Cold means before rolling, not after a fuel stop. A tire that has been driven for even a short distance reads higher than its true cold pressure.
- Use a gauge rated well above your target pressure. A gauge that reads to 200 psi such as this digital gauge covers any ST tire on the market. A gauge capped at 60 psi, the kind that ships with most cars, cannot even display an 80 psi reading.
- Check every tire, including the spare. A spare that sits for a year loses pressure through the rubber itself even with no puncture, and it is useless at the roadside if it was never checked.
- Set the pressure to the sidewall maximum. Unless the trailer maker publishes a different figure for your specific tire and rim combination, run the tire's own stamped maximum cold pressure.
- Never bleed pressure down after it rises from heat. A tire that reads above its cold target after miles of driving is behaving normally as it warms up. Releasing air to bring it back to the cold number under-inflates it for the rest of the trip.
- Record the baseline once you set it. Knowing what a fresh cold check reads on your own trailer makes it obvious the next time something looks off, rather than guessing at whether a reading is normal.
A gauge that cannot read high enough is worse than no gauge
Most gauges sold for ordinary cars top out around 60 psi, and a gauge that pegs at its maximum gives no useful information about a tire that actually needs 80. Confirm the gauge's stated range covers your tire's load range before trusting it. A dually-chuck gauge is also worth having if the tow vehicle has dual rear wheels, since the standard chuck cannot reach the inner valve stem at all.
Reaching 80 psi with a hand pump is a long, tiring job across four or six trailer tires. An inflator with an automatic shutoff, such as this battery-powered inflator, sets every tire to the same target without standing over each one watching a gauge.
Frequently asked questions
What does "cold" mean for trailer tire pressure?
Before the trailer has moved that day, not simply at room temperature. A trailer tire that has rolled even a short distance has already generated heat and its pressure has risen above its true cold reading. Check pressure first thing, before pulling out of the driveway or the campsite, rather than at the first fuel stop of the trip.
Why should I not bleed a tire down after it heats up on the road?
Pressure rising while a tire is rolling and warming up is normal behavior, not overinflation. Releasing air to bring a hot tire back to its cold target number leaves it under-inflated once it cools back down, which is the exact condition that causes sidewall flex, heat buildup and failure. Set the pressure cold, then leave it alone for the rest of the trip.
What pressure gauge do I need for trailer tires?
One rated to read at least 100 psi, since load range D and E tires need 65 and 80 psi cold respectively and most gauges made for ordinary cars stop at 60 psi. A dually-specific chuck is also worth owning if the tow vehicle itself has dual rear wheels, since a standard chuck cannot reach the inner valve stem on those wheels at all.
Should I check the spare tire's pressure too?
Yes, every time. A spare that sits unused for months loses pressure gradually through the rubber itself even with no leak or puncture, and a spare that was never checked is effectively useless the moment you actually need it at the roadside. Check it on the same schedule as the mounted tires rather than assuming it holds pressure indefinitely.
How often should I check trailer tire pressure?
Before every trip, cold, without exception, and again if a tire pressure monitoring system flags a sudden change while towing. Trailer tires lose pressure slowly through the rubber even with no damage, and a trailer that sits between trips can have noticeably low pressure by the next time it is hitched, even though nothing visibly changed.
Is a higher pressure than the sidewall maximum ever a good idea?
No. The sidewall maximum is the pressure the tire's load rating was tested at, and running above it does not add capacity, it just increases the risk of a harsh ride and uneven wear from a tire that is effectively over-inflated for its design. Run the sidewall maximum cold unless the trailer manufacturer publishes a different figure specific to your tire and rim combination.
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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.