Towing Tire Pressure Calculator: Right PSI for Every Axle You're Running
Your door placard was written for an empty truck. The moment you hitch a trailer, the rear axle load changes, the tyre pressure requirement changes, and the sidewall number you trusted all summer is no longer the right one. This calculator works out the exact cold inflation pressure for each axle on both the tow vehicle and the trailer, corrects for temperature, and tells you what chronic under-inflation is actually costing in fuel and tyre life.
Towing tire pressure calculator
Tyre Setup
Pressure Results
Ready when you are
Fill in your axle weights, tyre ratings and current pressure, then tap Calculate Pressures. Each axle gets its own recommended cold inflation, a temperature correction, and a verdict on your current setting.
Per-axle breakdown
Annual cost of under-inflation
Standards this calculation uses
- Load-inflation tables:
ETRTO,ISO 4000-1 - US tyre pressure standards:
FMVSS 139,TIA (Tyre Industry Association) - Trailer tyre guidance:
RVIA,RMA ST tyre standards - Temperature correction: 1 PSI per 10°F (0.07 bar per 5.5°C)
- Fuel penalty reference: US Department of Energy tyre efficiency data
Why most tyre pressure advice for towing is quietly wrong
The number on your door placard is a masterpiece of average-case engineering. It was calculated for the factory tyre size, a nominal load distribution, and a specific temperature. Change any one of those and the correct pressure changes with it. Hitch a caravan, horsebox or boat trailer and all three can shift at once: the rear axle weight jumps, the front lightens, and the trailer tyres that spent all winter in the dark are now expected to manage the whole job at exactly the same PSI they were pumped to last spring.
Tyre engineers do not guess at pressure. They use load-inflation tables that map every combination of load and tyre specification to a recommended cold pressure. This calculator uses that same logic for each axle separately, then applies the temperature correction that most garage-forecourt advice completely ignores, because the rule that tyre pressure drops about 1 PSI per 10 degrees Fahrenheit is not a folk tale, it is physics, and it matters on a cold morning at a campsite or a winter boat ramp.
Per-axle, not per-vehicle
Each axle carries a different load. The front of a towing vehicle often needs less than the placard. The rear needs more.
Trailer tyres separately
ST trailer tyres often need to run at or near their sidewall maximum. They are not the same as passenger or LT fitments.
Temperature corrected
Cold morning, warm afternoon, winter boat ramp, summer desert: the number you set changes depending on when you measure.
Cost of getting it wrong
Under-inflation burns extra fuel and destroys tyre carcasses. This calculator quantifies both so the repair bill becomes motivating.
How to use the towing tyre pressure calculator
You need three things before you start: the loaded axle weights (from a weighbridge, or estimated from the vehicle spec and tongue weight), the tyre sidewall readings for max load and max PSI, and a cold tyre to measure against. Then walk through the steps.
Pick vehicle
Brand and model fill common tyre specs. Set the country for the right units.
Enter axle weights
Loaded front, rear and trailer axle weights. Weighbridge is best, placard estimates work.
Set tyre ratings
Max load per tyre and max pressure from the sidewall, plus load range.
Enter temperature
Ambient air temperature when you measure. Reference is usually 20°C.
Read results
Correct cold pressure per axle, temperature delta, and the cost of chronic under-inflation.
Vehicles built into the preset picker
Select your brand and model to pre-fill a typical tyre size, load range and maximum pressure for that vehicle class. These are the trucks and SUVs people actually use for towing worldwide. Always confirm the preset against your door placard, which knows your exact trim.
Sorting out the towing side before you even get to pressure? Pair this with the towing capacity solver to confirm you are not already overloading the axles, or the Ford-specific towing guide if you are running an F-Series and want the rated numbers for your build.
Our methodology: what the formula actually does
A tyre pressure calculator that will not explain its maths is just guessing. Here is what this one does, in plain language.
Load-inflation table
The core formula is: recommended PSI = max PSI multiplied by the ratio of actual load per tyre to maximum rated load per tyre. This scales linearly within the tyre's rated range, which mirrors the ETRTO table relationship for LT and ST tyres. Capped at max PSI. Never rounded below 5 PSI less than half the maximum.
Temperature correction
Added delta to the raw recommended: 1 PSI per 10°F temperature difference, or 0.07 bar per 5.5°C. If you are checking tyres at 0°C when the reference was 20°C, the correction adds 2.5 PSI to compensate for the colder, lower-pressure reading.
ST trailer tyre rule
ST tyres rated at 85 PSI or less are handled with a higher minimum floor. Following RMA and RVIA guidance, these tyres achieve their load rating at maximum cold inflation, so we recommend running at or near the sidewall maximum rather than just the load-scaled value.
ETRTO and ISO 4000-1
The load index table and pressure ranges follow the European Tyre and Rim Technical Organisation standard and ISO 4000-1. These are the same references the tyre makers use when they print the sidewall numbers, so the tool speaks the same language.
Under-inflation cost model
Based on the US Department of Energy estimate of 0.2 to 0.4% fuel economy loss per PSI below the recommended level per tyre. Averaged at 0.3% per PSI, multiplied by total PSI deficit, annual distance and fuel price. Tyre wear accelerator adds a fractional replacement cost for carcass fatigue.
FMVSS 139
The US Federal Motor Vehicle Safety Standard for light vehicle tyres. Confirms the pressure labelling requirements and helps calibrate where the sidewall maximum and the recommended operating range sit relative to each other.
Load range and ply rating quick reference
This is the reference table the calculator uses internally. Find your load range letter on the tyre sidewall, and the table tells you the ply-rating equivalent and typical maximum cold inflation pressure. Always verify against your specific tyre's sidewall, which is the actual legal rating.
| Load range | Ply rating equiv. | Typical max PSI | Typical max kPa | Common use |
|---|---|---|---|---|
| P/SL (Standard Load) | 4-ply | 35 to 36 | 241 to 248 | Passenger cars, light SUVs |
| P/XL (Extra Load) | 4-ply (reinforced) | 41 to 42 | 283 to 290 | Heavier passenger loads |
| C | 6-ply | 50 | 345 | Light trailers, small LT vehicles |
| D | 8-ply | 65 | 448 | Medium trailers, light commercial |
| E | 10-ply | 80 | 551 | 3/4 ton and 1-ton pickups, heavy trailers |
| F | 12-ply | 95 | 655 | Heavy duty, larger RV, commercial |
| G | 14-ply | 110 | 758 | Very heavy commercial and specialist |
| H | 16-ply | 120 to 125 | 827 to 862 | Heavy trucks, large commercial |
Note: these are typical reference values from industry standards. Your specific tyre may differ. The sidewall is always the legal maximum. Two tyres of the same size but different load ranges carry different loads at the same pressure, which is why the load range field in the calculator matters.
Towing rules and tyre standards differ by country
Pressure units and tyre labelling systems vary: PSI in North America, kPa across Australia and New Zealand, bar across much of Europe. The legal requirements for trailer tyres, weigh-in obligations and towing speed limits differ too. The country guides below carry all of that local detail, each with its own dedicated towing calculator.
USA towing limits and tyre rules
FMCSA thresholds, state-specific trailer brake rules and a per-state cost per mile, all in one place.
truck tyre pressure towing · ST tyre PSI · GAWR tyre load 🇨🇦Canadian towing weights and winter tyre advice
Provincial brake thresholds, cold-weather tyre pressure notes, and cost per km across all 13 provinces.
tyre pressure winter towing Canada · kPa trailer tyres · provincial brake law 🇦🇺Australian tow ball mass, GVM and tyre limits
The four-limit GCM check with kPa-based tyre guidance and state-by-state recovery cost per km.
tyre pressure in kPa Australia · caravan tyre PSI · GVM tyre load 🇬🇧UK towing licence and tyre pressure guide
MAM checks, the 1997 licence rules, and correct tyre pressure for caravans and horsebox setups.
caravan tyre pressure UK · towing mirrors · noseweight and tyre loadNot sure whether your tyres can legally handle the trailer at all? Start with the complete towing calculator toolkit, which links every tool on the site. Then come back here once you know the axle weights to set the pressures. If the bill for under-inflation surprised you, the towing cost estimator shows what a blowout recovery or roadside call-out actually adds to the trip.
Frequently asked questions
What tyre pressure should I use when towing a caravan?
Higher than you would use empty. Your tow vehicle's rear axle carries the tongue or hitch weight on top of its normal load, so the rear tyres need more pressure than the door placard specifies for the unladen vehicle. The front tyres may need slightly less because tongue weight shifts load rearward. Your caravan or trailer tyres should be set to match the actual load they carry, which for ST tyres rated at 85 PSI or less usually means running at or near the maximum pressure on the sidewall.
Why does cold tyre pressure matter so much?
Because the target number is a cold target. Tyre pressure rises 4 to 6 PSI once you have driven even a few miles, because the air inside heats up and expands. If you measure a warm tyre and then adjust down to the placard figure, you are actually setting it 4 to 6 PSI too low when it cools. Always check and adjust cold: parked for at least three hours, driven less than a couple of miles. The temperature correction in this calculator helps you account for very cold ambient conditions, which can push the reading even lower than expected.
Is the sidewall PSI number the recommended pressure?
For LT and P-metric vehicle tyres, no. The sidewall maximum is exactly that: the most you may put in the tyre, not the everyday recommendation. Inflating to the sidewall maximum on a lightly loaded front axle gives you a harsh, fidgety ride and uneven tread wear in the centre. The correct pressure for vehicle tyres is the load-scaled figure from the manufacturer's table, which this calculator approximates per axle.
For ST trailer tyres, the situation is different. Because the rated load is achieved at maximum cold inflation, running at or near the sidewall maximum is often correct, especially on tandem-axle trailers where interply shear is a real failure mode.
How does a weight distribution hitch affect the required pressure?
A weight distribution hitch (WDH) uses levelling bars to push some of the tongue weight back onto the front axle, which partly restores the front axle load toward its unladen value. This typically reduces the rear axle pressure requirement slightly and increases the front axle requirement slightly. The effect varies by hitch type and setup. The most accurate way to account for it is to weigh the loaded axles after the WDH is correctly set, then use those measured values in the calculator.
What is the difference between PSI, kPa and bar?
They all measure the same pressure, just in different units. One PSI equals 6.895 kPa and about 0.0689 bar. North American tyres, gauges and door placards typically use PSI. Australian and New Zealand vehicles and gauges typically use kPa. European vehicles and many markets use bar. The toggle at the top of the calculator converts all inputs and outputs so you can work in whatever your gauge and door label actually show.
How much does under-inflation actually cost per year?
Based on US Department of Energy data, roughly 0.2 to 0.4 percent in fuel economy per PSI below the correct pressure. A truck running its four towing tyres 8 PSI low each uses about 10 percent more fuel than it should. On 15,000 km of annual towing at a reasonable fuel price, that can easily add up to several hundred dollars a year before you count the accelerated tyre wear that chronic under-inflation causes. Fill in the annual distance and fuel price fields to see your own number.
Can I use this for any country and tyre type?
Yes. The physics of load-inflation is the same whether the tyre is marked in PSI or kPa. Pick your country to set the temperature unit, weight unit and fuel price currency, then toggle the pressure unit to match your gauge. The tyre data fields are unit-neutral once converted. The only caveat is that very heavy truck tyres use different load tables, and the calculator is calibrated for light and medium duty, which covers virtually all recreational towing and the vast majority of commercial towing by private drivers.