Trailer tires should be inflated to the maximum cold pressure molded on the tire's sidewall — not to a number from a vehicle door sticker. Unlike passenger tires, ST trailer tires only deliver their full rated load capacity at that maximum cold inflation. Running below it lets the sidewalls flex and build heat, which is why underinflation is the leading cause of trailer tire blowouts. Check pressure cold, before every tow.
Why Trailer Tires Follow the Sidewall, Not a Door Placard
Passenger cars and trucks use a pressure chosen by the automaker for that specific vehicle. It balances ride comfort, handling, and tire wear, and it is posted on a placard in the driver's door jamb — usually well below the maximum printed on the tire itself.
Trailers work differently. There is no automaker placard tuning pressure for comfort, and an ST (Special Trailer) tire's load rating is tied directly to its inflation: the tire carries the maximum load molded on its sidewall only when inflated to the maximum cold pressure molded right next to it. Drop below that pressure and the tire's real-world capacity drops with it, even though the load range letter stays the same. Our guide to trailer tire load ranges covers how the letter, the load figure, and the pressure figure work together.
One nuance worth knowing: a few tire manufacturers publish load-and-inflation tables that permit reduced pressure for a documented lighter load. Unless your tire maker explicitly provides one, the safe default for a trailer is the sidewall maximum. Your trailer's certification label on the frame also lists the cold pressure for the original tire size — if your current tires match that original spec, the label and the sidewall should agree.
What "Cold Inflation Pressure" Actually Means
"Cold" does not mean cold weather. It means the tire is at ambient temperature: the trailer has been parked for several hours, out of direct sunlight, and has not been towed yet that day. That is the condition the molded sidewall pressure refers to.
Pressure climbs as a tire warms up on the road — that is normal and accounted for in the tire's design. It also moves with the weather: a tire set on a warm afternoon will read lower on a cold morning. The practical habit is simple: gauge-check every tire, including the spare, before the day's first tow.
Underinflation: The Main Cause of Trailer Tire Blowouts
A tire below its cold spec flexes more with every rotation. Flex generates heat, heat breaks down the rubber and the internal plies, and the end result is tread separation or a blowout — most often at highway speed with a load on board.
Trailers are especially exposed to this failure chain:
- No feedback. You can feel a soft tire through a car's steering. A soft trailer tire is nearly invisible from the tow vehicle until it fails.
- Looks are misleading. A trailer tire can be far below spec before the sidewall visibly bulges.
- Heavy, constant loads. Trailer tires often run at or near rated capacity, so any missing pressure cuts into a margin that is already thin.
- Long stretches at speed. Highway towing gives heat time to accumulate.
One more caution: a tire that has been towed while significantly underinflated can be damaged internally even if it holds air again afterward. If that has happened to one of yours, read our guide on when to replace trailer tires before trusting it with another loaded trip.
Trailer vs. Passenger Car: Two Different Pressure Systems
| Question | Passenger car tire | ST trailer tire |
|---|---|---|
| Where the correct pressure is listed | Door-jamb placard set by the automaker | Molded on the tire sidewall |
| Is the sidewall maximum the target? | No — it is an upper limit; the placard is normally lower | Yes — the maximum cold pressure is the operating pressure |
| What the number is optimized for | Ride comfort, handling, even wear | Full rated load capacity and heat control |
| Adjust for a lighter load? | Some placards list separate loaded values | Only if the tire maker publishes a load-inflation table; otherwise run the sidewall max |
| Typical result of running low | Uneven wear, poor fuel economy | Heat buildup, tread separation, blowout |
| Driver feedback when low | Felt through the steering wheel | Little to none until failure |
How Often to Check Trailer Tire Pressure
- Before every tow. Gauge-check cold, every tire, every trip. Slow air loss between trips is normal, not proof the tire is fine or faulty either way — the gauge is the only reliable answer.
- During long trips. At fuel and rest stops, look the tires over and feel for one hub or sidewall running much hotter than the others. Save gauge corrections for the next cold morning unless a tire is obviously low.
- Monthly in storage. Parked tires lose pressure slowly, and trailers can sit for months. This applies to the spare too — see our trailer spare tire guide.
- When the season changes. Falling temperatures pull pressure down; recheck after the first cold snap.
A quality metal-body gauge is worth owning, and an aftermarket trailer TPMS (tire pressure monitoring system) is a reasonable upgrade for frequent towers, because it covers the trailer's biggest blind spot: no feedback from the driver's seat.
FAQ
Should I lower the pressure when my trailer is empty?
The standard practice for ST tires is to run the maximum cold pressure molded on the sidewall at all times, loaded or empty. The ride may be firmer without cargo, but full pressure keeps heat down and the trailer tracking predictably. If your tire manufacturer publishes a load-inflation table you may follow it; without one, stay at the sidewall figure.
My tires read higher after towing — should I let air out?
No. Pressure rising with heat is normal, and the molded maximum is a cold specification. Bleeding a warm tire down to the sidewall number leaves it underinflated once it cools, which recreates the exact condition that causes blowouts.
Where do I find the right pressure for my trailer tires?
It is molded on the sidewall of the tire itself, next to the maximum load figure. Your trailer's certification label on the frame lists the pressure for the original tire size as well. If the rest of the sidewall markings are unfamiliar, our trailer tire size guide walks through each one.
And when a pressure check tells you a tire's time is up, Cheap2Go Tires carries a full range of trailer tires with free shipping from our Orlando, FL warehouse — call (407) 821-7008 if you want help confirming the size and load range before you order.