Trailer Tyre: Load Ratings, Pressure, and When to Replace Them

· Published 15 October 2026

Getting your trailer tyre pressure wrong is a safety issue. Whether you’re hauling machinery, horses, or a skip bin full of rubble, the tyres are the only thing between your load and the road. And unlike your ute’s tyres, trailer tyres are easy to neglect because they rack up far fewer kilometres.

This trailer tyre pressure guide covers everything you need to know about the trailer tyre load rating system, how to calculate the right pressure for your trailer, and when it’s time to replace.

Key Takeaways

Your trailer’s correct tyre pressure depends on the load you’re carrying, not a single fixed number.
The trailer tyre’s load rating (found on the sidewall) indicates the maximum weight it can carry at its maximum pressure.
Always check the pressure cold, and check it monthly.
Replace trailer tyres every five to seven years regardless of tread depth. Rubber degrades with age, not just mileage.
The legal minimum tread depth in Australia is 1.5mm, but safety experts recommend replacing at 3mm.

What Is a Trailer Tyre Load Rating?

The trailer tyre load rating (also called the load index) is a number stamped into the sidewall of every tyre. It indicates the maximum weight that tyre can safely carry at its maximum rated inflation pressure.

You’ll typically see it in the tyre size code. For example, in 205/65 R15 94H, the number 94 is the load index. A load index of 94 corresponds to a maximum load per tyre of 670kg. On a single-axle trailer, those two tyres could carry a maximum combined load of 1,340kg.

Load index numbers generally range from around 60 to 130. That range equates to a maximum per-tyre load of roughly 250kg at the low end, up to 1,900kg at the high end.

The tyre industry recommends you never exceed 90% of the tyre’s load index. So for a 670kg-rated tyre, your real-world ceiling per tyre is around 600kg.

The first step before calculating pressure is to confirm your tyres are rated for your trailer’s Aggregate Trailer Mass (ATM), which is the combined weight of the trailer and its full load. This figure is on your trailer’s compliance plate.

How Trailer Tyre Pressure and Load Rating Work Together

A tyre’s load-carrying capacity only applies at the correct inflation pressure. Drop the pressure, and you drop the capacity.

If your tyre pressure is too low, your trailer tyres won’t be able to carry the weight indicated by the load index. On the other hand, overinflated tyres won’t provide enough grip on the road.

How to Calculate the Right Trailer Tyre Pressure

You don’t need a mechanic for this; you just need three numbers:

Your trailer’s ATM (from the compliance plate)
The tyre’s load rating (from the sidewall)
The tyre’s maximum inflation pressure (also on the sidewall)

Here’s the formula used across the industry:

(Max pressure ÷ load rating) × (ATM ÷ number of tyres) = recommended pressure

For example, using a 205/65 R15 94H tyre with a maximum inflation pressure of 60 PSI, on a trailer with a GTM of 1,800kg: (60 ÷ 670) × (1,800 ÷ 4) = approximately 40–41 PSI.

A few practical notes:

Always check pressure when the tyres are cold before the trailer has moved more than a couple of kilometres.
As a rule of thumb, a hot tyre will read about 4 PSI higher than when cold. If the difference is greater than 4 PSI, your cold pressure was too low. If it’s less, it was too high.
For dual-axle trailers, divide the GTM by four tyres, not two.
Check pressure at least monthly, and always before a long haul or a heavy load.

When to Replace Your Trailer Tyres

This is where trailer owners get caught out. Because trailers do fewer kilometres than passenger vehicles, tread depth rarely triggers a replacement. Age does.

Age

Trailer and caravan tyres should generally be replaced every five years and should never be used beyond seven years. Importantly, a tyre’s age starts from when it was manufactured, not when it was fitted.

Tyres in the five-to-seven-year range are in a critical window and should be professionally inspected, especially before long trips. Tyres between 7 and 10 years old are approaching the end of their safe service life, and replacement should be planned. Tyres over ten years old should be replaced regardless of how new they look.

You can find the manufacture date on the sidewall as part of the DOT code. The last four digits of the DOT code indicate the week and year of manufacture. For example, ‘2023’ means week 20 of 2023.

Tread Depth

The legal minimum tread depth in Australia is 1.5mm across the central three-quarters of the tread. Most tyre safety experts recommend replacing tyres at 3mm of remaining tread rather than waiting for the wear indicators.

You should also watch for signs of uneven wear patterns, which can indicate alignment or inflation problems.

Replace immediately if you see:

Sidewall cracking or bulging
Visible cord or fabric through the tread
A tyre that’s been driven flat, even briefly
Any bulging, which can indicate internal structural damage

Tips for Maintaining Safe Tyre Pressure

Check pressure monthly, and before every trip with a heavy load.
Use a quality pressure gauge; don’t rely solely on the tyre’s appearance.
If your trailer sits stored for extended periods, check the pressure before use. Tyres naturally lose pressure over time.
Tyres stored on stationary trailers can also develop uneven wear due to non-rotation. If your trailer is parked for weeks at a time, consider moving it periodically or using tyre cradles.
UV exposure accelerates tyre degradation. Cover tyres when the trailer is stored outdoors for long periods.

For more on keeping your trailer in good condition year-round, see our maintenance tips for trailers. And if you want to understand another component that affects trailer reliability under load, our guide to the benefits of enclosed bearings is worth reading.

Get the Right Trailer for the Job

Tyre safety starts with a trailer that’s built to handle what you’re hauling. At Coastmac, we stock a broad range of purpose-built trailers for work and recreation, from machinery trailers and tipping trailers to horse floats and more. Every trailer is backed by strong warranties and genuine after-sales support. Browse the full Coastmac range to find the right fit for your needs.