Set tire pressure for a heavy load or towing by starting with the cold pressure on your vehicle’s tire placard and owner’s manual. Use the higher “loaded” or towing value if your vehicle lists one. Do not raise pressure on a guess, and never go above the maximum pressure molded on the tire sidewall.
Key Points Before You Load Up
- The placard lists the manufacturer’s recommended cold pressure for the original tires. The owner’s manual may add figures for full load or trailer towing.
- Check pressure cold: the vehicle has been parked for at least 3 hours, or driven less than one mile at moderate speed.
- Never release air from tires that are hot from driving. Pressure rising above the cold value is normal.
- The trailer has its own tires and its own correct pressure. Tow-vehicle numbers do not apply to it.
- Staying within weight ratings matters more than any pressure adjustment. Pressure cannot make an overloaded tire safe.
Find the Right Numbers
NHTSA notes that tire placards are permanent labels found on the door edge, doorpost, glove-box door or inside the trunk lid. They give both the recommended tire pressure and the vehicle’s load limits. Read both before you load.
| Source | What it tells you | Notes |
|---|---|---|
| Tire placard on the tow vehicle | Recommended cold pressure and load limit | Front and rear values can differ |
| Owner’s manual | Load and towing instructions, sometimes separate pressures | Check the towing section and the tire section |
| Tire sidewall | Maximum pressure and maximum load for that tire | A limit, not a target |
| Trailer placard or tire maker’s chart | Correct pressure for trailer tires | Match it to your exact tire size and load |
The U.S. Tire Manufacturers Association states that the pressure on the sidewall is the maximum allowed in the tire, irrespective of the vehicle, and tells drivers to follow the vehicle manufacturer’s recommendations instead. It also directs readers to the owner’s manual for load recommendations and special instructions such as trailer towing. Its Tire Care and Safety Guide (PDF) covers these basics.
Step-by-Step: Set Tire Pressure Before Towing or Hauling
- Weigh what you can. If you are carrying near the limit, take the loaded vehicle to a public scale and compare the result to the ratings on the door-jamb label.
- Measure cold pressure on all tires with a quality gauge, including the spare.
- Look up the target. Use the placard value, or the loaded or towing value from the manual if it gives one.
- Inflate front and rear separately if the values differ, and keep both tires on an axle at the same pressure.
- Set the trailer tires to the trailer placard, or to the tire maker’s guidance for your exact tire and load.
- Recheck at the first safe stop and again at the start of each day of a long trip, preferably before you drive.
Weight, Axle Loads and Tongue Weight
NHTSA’s tire safety checklist reminds drivers that some of the weight of a loaded trailer is transferred to the towing vehicle. That extra weight lands mostly on the rear axle, so a tow vehicle can be over its rear axle rating even when the total weight looks acceptable.
The terms on the door-jamb label and in the manual:
- GVWR is the maximum loaded weight of the vehicle.
- GAWR is the maximum weight each axle can carry, front and rear.
- Tire load rating is the maximum each tire can carry at its rated pressure, shown on the sidewall.
If a public scale shows you are over any of these ratings, reduce the load first. Changing pressure does not raise a rating.
Using a Tire Maker’s Load and Inflation Chart
Tire makers publish load and inflation tables that show how much weight a tire of a given size and type can carry at each pressure. They are most useful when you have changed tire size, run light-truck tires, or carry heavy loads regularly. To use one, weigh each axle, divide by two to estimate the load per tire (use the heavier end if the sides differ), and find the lowest cold pressure in the chart that supports that load. Then compare the result with the placard. If the two disagree, ask the tire maker or a tire shop before choosing.
Trailer Tires
Trailer tires are marked differently from passenger tires. Many are labeled ST (special trailer) and, as a rule, are sized and rated for trailer duty. Their correct pressure depends on the tire, the load and the trailer maker’s recommendation.
- Use the placard on the trailer if it lists a cold pressure for your tire size.
- If it does not, or you have changed tires, use the tire manufacturer’s recommendation for your exact tire and your load.
- Some trailer tires are rated to carry their maximum load at the pressure molded on the sidewall, so the sidewall number can be the correct cold pressure for them. Confirm this with the tire maker or the trailer placard instead of assuming.
- Trailer tires can sit for months. Check pressure, age and sidewall cracking before each trip.
How Temperature and Time Change Pressure
The U.S. Tire Manufacturers Association says passenger and light truck tires may lose 1 to 2 psi per month under normal conditions, and that pressure falls by roughly 1 to 2 psi for every 10°F drop in temperature. So a tire set in a warm garage can read noticeably low on a cold morning at the start of a trip.
Highway driving heats the tires and raises pressure above the cold value. That is normal. Never bleed air out of hot tires to reach the cold number, because the tires will be underinflated once they cool. If a hot tire reads far above the cold value (for example, much more than a few PSI), stop and check for dragging brakes, overload or a failing bearing.
Monitoring Pressure on the Road
- A tire pressure monitoring system (TPMS) warns only when a tire is well below the recommended pressure. It does not replace a gauge.
- If the warning light comes on, stop in a safe place and check the tire with a gauge.
- Many tow vehicles cannot read the trailer’s tires. A separate trailer TPMS or a gauge check at each stop is the only way to know.
- Feel the hubs and tires at fuel stops, and watch for a trailer tire that looks lower than its partner.
Towing Safety Checklist
- Cold pressures set on the tow vehicle, trailer and spares
- Load within GVWR, axle ratings and tire load ratings
- Lug nuts tight, and checked again after the first miles if wheels were removed
- Hitch, ball, pin and safety chains secured; lights and brakes working
- Load balanced and secured so it does not shift
NHTSA’s tire safety checklist (PDF) summarizes the regular checks: pressure at least monthly including the spare, inspection for cracks and foreign objects, valve caps in place, and a pressure check before long trips.
Frequently Asked Questions
Should I increase tire pressure for a heavy load?
Only if the placard or owner’s manual lists a higher loaded or towing pressure, or a tire maker’s load table calls for it based on your measured weights. If neither applies, use the normal placard pressure.
Should I use the maximum PSI on the sidewall when towing?
Not by default on the tow vehicle. The sidewall number is the most the tire can hold, and the vehicle maker may call for less. Trailer tires are different, because some are rated to carry their full load at the sidewall pressure. Follow the trailer placard and the tire maker.
What does “cold” mean for tire pressure?
The vehicle has been parked for at least 3 hours or driven less than one mile at moderate speed.
What PSI should cargo trailer tires have?
Use the trailer placard if it lists a cold pressure for your tire size. If it does not, use the tire manufacturer’s recommendation for your exact tire and load.
Can I fix underinflation on the road by letting air out later?
No. Adding air is the fix for a low tire. Letting air out only applies to a tire that is over the cold value when it is cold, never when it is hot from driving.
