Tyre Pressure Calculator

Use this tyre pressure calculator to find a safe cold starting pressure for your caravan or trailer tyres before you tow.

Enter your trailer’s loaded weight (ATM), tow-ball weight, the number of tyres on the ground, and your tyre’s max load and max pressure from the sidewall. The calculator works out the load each tyre actually carries and gives you a recommended cold pressure — running under-inflated builds up heat and is a leading cause of trailer tyre failure, while over-inflation reduces grip and wears the centre of the tread.

You’ll also get the industry-standard load/pressure figure alongside a slightly more conservative recommendation, plus a built-in 4 PSI rule check so you can confirm your pressures out on the road.

Weight kg lbs
1 Caravan / Trailer
Aggregate Trailer Mass — weighed loaded, ideally hitched off
Weight on the tow ball (~8–15% of ATM is typical)
Exclude spares.
2 Tyre Ratings (from sidewall)
Sidewall rating, e.g. “Max Load 670kg”
Sidewall rating, e.g. “Max Pressure 60 PSI”

Disclaimer

These calculations are theoretical, starting-point estimates for educational purposes, based on the industry TRA load/pressure curve. The correct pressure for your setup depends on your specific tyres, axle configuration, load distribution and travel conditions.

Real-world factors such as driving style, road conditions, ambient temperature and tyre age/condition are not fully accounted for. Always verify against your trailer’s tyre placard and the tyre manufacturer’s load/inflation tables, and consult a professional if you’re unsure. Never exceed the maximum pressure rating on your tyre sidewall.

Smarter Towing accepts no liability for decisions made based on this calculator.

Tow Tyre Pressure Calculator FAQs

What pressure does this calculator give me?

A cold starting pressure – the pressure to set before you tow, while the tyres are cold (parked a few hours or first thing in the morning). Pressure rises naturally once you’re driving; that’s expected and is what the 4 PSI rule check confirms.

Why do you ask for ATM and tow-ball weight, not just one weight?

Only the weight sitting on the trailer’s own tyres matters for pressure. That’s your loaded weight (ATM) minus the tow-ball weight the car carries. We subtract it for you, so the figure is based on the true axle load.

What's the difference between the "TRA standard" and "Conservative" figures?

Tire and Rim Association (TRA) standard is the technical minimum from the industry load/pressure curve. The Conservative figure uses a simpler linear method that runs a little higher for extra margin – we recommend it as your cold starting point, especially for lightly loaded vans where the raw minimum can be impractically low.

I don't know my tyre's max load — can I still use it?

Yes. Use the load index dropdown under the Max Load field. Pick the number on your sidewall (e.g. 94) and it fills in the max load  for you.

Where do I find max load and max pressure?

On the tyre sidewall, usually in smaller text – e.g. “Max Load 670kg, Max Pressure 60 PSI”. Max load can also be read from the load index number.

What is the 4 PSI rule?

A no-maths way to confirm your cold pressure is right. Set the tyres cold, drive 30–60 minutes, then check them hot.
 
A correctly inflated tyre gains about 4 PSI. More than 4 = too low (add air); less than 4 = too high (let some out). Light-truck (LT) tyres often rise closer to 6 PSI.

Can I go by the pressure on my caravan's placard instead?

The placard figure assumes the van is loaded to its maximum. If you tow lighter than that, a load-based figure like this calculator’s is often more accurate. Always cross-check both, and never exceed the sidewall maximum.

Should I run tyres at their maximum load rating?

No. Industry advice is to stay under about 90% of the tyre’s rated load. If the calculator flags an overload, you’re too close to or over the limit.

Does this work for US tyres too?

Yes. The load/pressure method and the load-index table are international standards. Enter weights in kg or lbs using the toggle; pressures are shown in PSI (with kPa alongside).

US trailers: should I just run the max pressure on the sidewall?

Many US Special Trailer (ST) tyres are designed to run at their maximum cold sidewall pressure, because they only reach their full load rating at that pressure. This calculator gives a load-matched figure instead, which suits lighter loads and matches Australian practice. If you’re running ST tyres rated at 80 PSI or less, or you’re near your trailer’s max weight, it’s common and safe in the US to set the max sidewall PSI cold. Never go below the pressure your load actually needs.

What's a "Load Range" letter (B, C, D, E)?

It’s the US way of describing tyre strength, and each letter ties to a max pressure – commonly C = 50 PSI, D = 65 PSI, E = 80 PSI. The max load and max pressure printed on the sidewall are what this calculator needs; the Load Range letter is just shorthand for that pressure ceiling.

What does "cold" actually mean?

The tyre hasn’t been driven more than about a mile, or has sat parked for at least 2–3 hours. Check first thing in the morning, out of direct sun, before you set off. Don’t pre-compensate for the day getting hotter – set the cold figure and let the 4 PSI rule confirm it.

Where's the pressure info on a US trailer?

Two places: the trailer’s certification/placard label (often on the front left of the tongue or frame), which lists the factory tyre size and recommended cold PSI; and the tyre sidewall, e.g. “Max Load 2,830 lbs at 80 PSI Cold”. Also never exceed your wheel/rim rating.

Do ST tyres have a speed limit?

Most US Special Trailer (ST) tyres are speed-limited to around 65 mph, and many makers recommend towing at 60 mph or less, regardless of pressure. Correct pressure helps, but it doesn’t raise the speed rating.

Other Useful Resources

Android Auto User Manual
Apple CarPlay User Manual
Installation Manual
Tyre age calculator
Towing Capacity calculator

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