Towing and Hauling: How to Adjust Tire Pressure for Load

Why heavier loads require higher pressure

A tire's load rating is the maximum load it is rated to carry for a given inflation pressure, as defined in Federal Motor Vehicle Safety Standard No. 139 for new pneumatic radial tires for light vehicles. Higher inflation pressure makes the tire capable of supporting more weight. Conversely, if you add cargo or tow a trailer without raising the pressure, the tire may be asked to carry more than its rated load at that pressure, causing excessive deflection, heat buildup, and possible failure.

When a vehicle is loaded to its gross vehicle weight rating (GVWR), the tires must be inflated high enough to support the load placed on each axle. For vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less, Standard No. 110 requires that the vehicle maximum load on the tire not exceed the maximum load rating marked on the sidewall. Understanding tire load ratings is the first step to setting the right pressure.

The relationship between load and pressure is not linear across the full range. Load tables published by tire makers show the load capacity of a given tire size at each inflation pressure, in increments. For a tire that will carry a heavy load, you move up the table to find the pressure that matches the actual load on that tire.

Find your starting point: the placard and the sidewall

Start with the vehicle manufacturer's recommended cold inflation pressure, which is printed on the vehicle placard (usually on the driver's side door jamb) and in the owner's manual. This is the pressure for the vehicle at its normal, fully loaded condition, assuming the original tire size is installed. Federal regulations define the vehicle placard as a source of the manufacturer's recommended cold tire inflation pressure pursuant to Standard No. 110. For a refresher, see tire inflation pressure basics.

The sidewall of a tire shows its maximum permissible inflation pressure, which is the maximum cold pressure to which the tire may be inflated, as defined in Standard No. 139. For passenger car tires, allowable maximum pressures are typically 32, 36, 40, or 60 psi, or 240, 280, 300, 340, or 350 kPa, per Standard No. 109. Do not confuse the maximum sidewall pressure with the recommended operating pressure.

When you inflate for a heavy load, you are choosing a pressure that sits between the placard recommendation and the sidewall maximum, based on the actual weight on each tire. The placard pressure for a car with P-metric tires is often the same as the pressure needed for maximum load, because these tires are usually sized so that the rated load at the placard pressure covers the vehicle's GVWR. For light trucks with LT-metric tires, the manufacturer may specify a higher pressure for heavy loads, and you should review tire load ranges and ply ratings to understand the differences.

Use the tire's load and inflation table

Every tire size has a load and inflation table published by the tire manufacturer, showing the load each tire can carry at various cold inflation pressures. To use it, you need to know the actual weight on each tire when the vehicle is fully loaded. This means visiting a scale and weighing each axle (or each corner) with the vehicle loaded as it will be when towing.

Once you know the weight on a given tire, find that value (or the next higher amount) in the table for your tire size, then read across to the corresponding pressure. Set all four tires to that pressure. For the tires on the towing vehicle, the rear axle usually carries more weight when a trailer is hitched, so the rear tires may need more pressure than the front. Trailer tires also need to be set to the pressure that matches the load they carry, using the table for that specific trailer tire size. Useful guidance appears in our trailer tire buying guide.

If your vehicle has a gross vehicle weight rating above 10,000 pounds, Standard No. 119 applies to its tires, and Standard No. 120 covers tire selection and rim requirements for those vehicles. These standards set out the same principle: the sum of the maximum load ratings of the tires on each axle must be at least equal to the gross axle weight rating (GAWR). Load and inflation tables exist for LT tires as well, so the process is the same: find the load, read the pressure.

P-metric vs. LT tires: a different approach

Passenger (P-metric) tires are designed for vehicles with a GVWR of 10,000 pounds or less. Standard No. 110 requires that the normal load on any tire not exceed 94 percent of the tire's load rating at the manufacturer's recommended cold inflation pressure. When a P-metric tire is installed on a light truck, its load rating must be reduced by dividing by 1.10 before calculating whether it can support the axle rating, per Standard No. 120 for heavier vehicles and its light-vehicle counterpart. This reduction means a P-metric tire on a truck may need a higher pressure than the same tire on a car to carry the same load.

Light truck (LT) tires are designed for use on lightweight trucks and multipurpose passenger vehicles. They have thicker sidewalls, higher ply ratings, and higher maximum inflation pressures than P-metric tires. The load and inflation tables for LT tires are published separately and show higher load capacities at higher pressures. If you regularly tow near your truck's GVWR, an LT tire is the safer choice, because it has more reserve capacity at the pressures specified in its load table. See our best light truck tires for options that handle heavy loads well.

Extra load (XL) and reinforced tires are designed to operate at higher loads and higher inflation pressures than standard tires, as defined in Standard No. 139. If your vehicle came with XL tires, its placard pressure already accounts for the higher load capacity of those tires. When you add a heavy load, use the XL load and inflation table to adjust. Learn more about extra load and XL tires.

TPMS: know what the warning means

Vehicles with a gross vehicle weight rating of 10,000 pounds or less are required to have a tire pressure monitoring system (TPMS), per Standard No. 138. The system must illuminate a warning telltale within 20 minutes after the pressure in one or more tires drops to 25 percent below the manufacturer's recommended cold inflation pressure, or to a level specified in a table in the standard, whichever is higher.

When you increase the pressure for towing, the TPMS threshold moves with it, because the threshold is based on a percentage below the vehicle manufacturer's recommended pressure. This means you may get a TPMS warning if pressure drops from your towing inflation level, even if that level is still above the placard recommendation. That is expected behavior, not a malfunction. If you need a refresher on TPMS, read our guide to tire pressure monitoring systems.

After you unhitch and return the vehicle to unloaded use, reset the tires to the placard pressure. Driving unloaded with towing pressure reduces ride comfort, increases wear in the center of the tread, and can make the tires more susceptible to impact damage. TPMS will not warn you about over-inflation, so this is a manual step you must remember.

When to adjust and when to leave it alone

Check and adjust tire pressure when the tires are cold, meaning the vehicle has not been driven for several hours. Pressure rises as tires heat up from rolling. Setting pressure on hot tires to the cold target will result in under-inflation once the tires cool down. Use a reliable gauge and check all tires, including the spare.

If your towing load is light, under half of the vehicle's rated capacity, the placard pressure may be sufficient. The load tables tell you whether the placard pressure covers the actual load on each tire. If it does, no adjustment is needed. If it does not, increase the pressure in the affected tires to match the load.

Be cautious about exceeding the maximum pressure molded on the sidewall. That number is a limit, not a recommendation. Inflating beyond it can damage the tire and the wheel. If the load table for your tire calls for a pressure above the sidewall maximum, you need a tire with a higher load rating, not more pressure in the current tire. For trucks and SUVs that tow routinely, consider the best all-terrain tires or best mud-terrain tires for added capacity and durability.

What to pick for your towing and hauling needs

Questions

Should I inflate my tires to the maximum pressure printed on the sidewall when towing?

No. The sidewall maximum is a limit, not a target. Use the load and inflation table for your tire size to find the pressure that matches the actual load on each tire. That pressure may be above the placard pressure but should not exceed the sidewall maximum.

How do I find the correct tire pressure for a specific towing load?

Weigh the vehicle with the trailer attached and the load in place. Then consult the load and inflation table published by the tire manufacturer for your exact tire size. Find the weight on each tire and read the corresponding cold inflation pressure.

Do I need to adjust tire pressure for the trailer tires too?

Yes. Trailer tires have their own load and inflation tables, and ST (special trailer) tires are covered by Standard No. 119. Set trailer tire pressure based on the actual loaded weight on each trailer tire, using the table for that tire size.

Will my TPMS warn me if I inflate the tires too much for towing?

No. TPMS is designed to detect under-inflation, not over-inflation. The system warns when pressure falls to 25 percent below the manufacturer's recommended cold inflation pressure, per Standard No. 138. You must manually verify that your towing pressure is correct.

How high can I go above the placard pressure when towing?

Only as high as the load and inflation table for your tire requires to support the actual load. The upper bound is the maximum permissible inflation pressure molded on the sidewall. Do not exceed it for any reason.

Is it safe to run lower pressure in the front tires when towing?

Only if the load tables show that the lower pressure still covers the load on the front axle. Many tow vehicles carry more weight on the rear axle, so the front may need less pressure than the rear. Always use the tables, not guesses.