1. Your vehicle
Sets contextual guidance. The physics is the same for every vehicle — what changes is how you weigh it and which warnings matter.
Load-based cold inflation pressure
Tire pressure by weight: read max load and max pressure from the tire sidewall, enter the real weight on one tire — the tool computes the required cold pressure with three published methods side by side.
MAX LOAD 850 kg (1874 lbs) and MAX PRESS 44 PSI (300 kPa). SL tires develop max load at 35–36 psi even when the sidewall allows more — the tool maps this per Daws Table 2 automatically.New tire size pressure correction
Plus-sizing or minus-sizing? The door-placard pressure was tuned for the original size. A bigger tire holds more air, so it carries the same load at lower pressure — this tab recomputes it with the TRA power rule on air-chamber volume.
Exact path — new tire sidewall data (required for P-metric ↔ LT swaps)
Air-chamber scaling assumes the same construction. If you change construction class (e.g. P → LT), enter the new tire's sidewall data and the real per-tire load instead.
Tip: get the per-tire load from the By tire load tab (axle weight ÷ tires), then paste it here with margin set to 0%.
Temperature correction
Pressure changes about 1 psi per 10°F (5.6°C) — the ideal-gas rule of thumb used by every tire maker.
What will my pressure read at a different temperature?
What should I inflate to now to hit my cold target in the morning?
Altitude adjustment
A sealed tire carried between altitudes changes its gauge reading by about 0.5 psi per 1,000 ft of elevation change — the air mass inside does not change.
Tire pressure unit converter
Exact factors: 1 psi = 6.89476 kPa · 1 bar = 100 kPa · 1 kg/cm² = 98.0665 kPa · 1 atm = 101.325 kPa.
Underinflation fuel-cost estimator
U.S. DOE rule of thumb: about 0.2% worse fuel economy per 1 psi under-inflated (average of all tires).
Methodology — where the numbers come from
All load calculations implement the three published methods from J.W. Daws, "Inflation Pressures at Less-Than-Maximum Tire Loads" (Tire Society, 2009), the technical basis of the Wikipedia Cold inflation pressure article and TRA/ETRTO practice. Load L always includes a 10% safety margin by default.
P_ref is the pressure at which the tire develops its maximum load (Daws Table 2): SL → 240 kPa if labeled 240, else 250 kPa harmonized; XL → 280 kPa if labeled 280, else 290 kPa; LT and motorcycle → the sidewall maximum. Validation: Daws' own worked example (P235/75R15, 920 kg @ 240 kPa, 1315 kg GAWR) gives 181 kPa here vs 181 kPa in the paper — and the real vehicle placard reads 180 kPa.
New tire size
Load capacity scales with air-chamber volume V = W·H·(Drim+H). The adjusted pressure follows the TRA power rule: Pnew = POE × (VOE/Vnew)^(1/0.8). Construction changes (P-metric ↔ LT) break the volume assumption — use the sidewall-data path instead.
Temperature & altitude
Ideal gas law at constant volume (P₂/P₁ = T₂/T₁) gives ≈ 0.89 psi per 10°F at 32 psi — the industry "1 psi per 10°F (5.6°C)" rule. Altitude: the US Standard Atmosphere loses ≈ 0.5 psi ambient per 1,000 ft, so a sealed tire's gauge reading shifts by the same amount.
Fuel economy
U.S. DOE / fueleconomy.gov: ≈ 0.2% worse fuel economy per 1 psi of under-inflation. CO₂: 2.31 kg/L gasoline, 2.68 kg/L diesel.
Tire pressure notes by vehicle
🚗 Car
For factory sizes the door placard is already optimal. Recalculate only after changing tire size, or when regularly carrying heavy loads.
🚙 SUV / Crossover
Often different front/rear placard pressures. P-metric tires on SUVs carry a 10% DOT derating — the default 10% margin covers it.
🛻 Light truck / Pickup
Placards may list unloaded vs loaded pressures. Weigh the rear axle fully loaded (towing, hauling) and calculate per axle.
🚐 Van
Payload swings axle weights hugely. Weigh in normal working trim — the heaviest regular loading, not empty.
🚚 Caravan / Trailer
Weigh each axle fully laden (water, luggage, gear). ST trailer tires are normally run at sidewall maximum pressure.
🏕️ Motorhome / RV
Get per-axle weights fully loaded for travel; use the heavier side per tire. Check cold every travel morning — big tires leak down slowly and unnoticed.
🏍️ Motorcycle
Always the manufacturer's spec (manual / swingarm sticker). A few psi transforms handling and braking — check cold before every ride.
Special scenarios
🏖️ Sand / desert
Air down to ~15–20 psi for flotation at low speed. Re-inflate before any pavement — carry a portable compressor.
🪨 Rock crawling
~12–15 psi maximizes the contact patch at walking pace. Debeading risk rises — re-inflate immediately after.
🏁 Track day
Set pressures so hot readings hit the target after a session (typically +4–6 psi over cold). Bleed hot, never add cold to a hot target.
Frequently asked questions
What is cold inflation pressure?
How do I calculate the correct tire pressure for my vehicle's weight?
What tire pressure should I use when I change to a bigger or smaller tire size?
How does temperature affect tire pressure?
Do I need to adjust tire pressure for altitude?
How do I convert kPa to PSI (and bar)?
Can I replace P-metric tires with LT tires at the same pressure?
What tire pressure should a caravan, motorhome or RV use?
What tire pressure should a motorcycle use?
Should I lower tire pressure for off-road or sand driving?
Why does my TPMS warning light come on in cold weather?
Is it better to slightly overinflate or underinflate tires?
How does underinflation affect fuel economy (MPG)?
Where do I find the manufacturer's recommended tire pressure?
How often should I check my tire pressure?
What is the difference between SL, XL and LT tires for inflation?
Riding a bicycle? Our Bike Tire Pressure Calculator sizes road, gravel & MTB pressure by rider weight, tire width, and terrain.