What tyres should a boat trailer actually run?

A boat trailer spends its life doing the one thing passenger car tyres are worst at: carrying a concentrated, unsprung load, often sitting for weeks, then being reversed into salt water and dragged across soft sand. The tyre you want for that job has a stiffer carcass and reinforced sidewalls, and it is rated to carry your loaded rig with margin to spare.

In practice that means a light-truck (LT) tyre or a purpose-built trailer tyre, identified by the letters on the sidewall. Australian tyre guides are blunt about it: as Tyroola’s trailer and caravan guide puts it, you should “never fit passenger tyres to your trailer or caravan,” because LT tyres have “a more robust carcass and rigid sidewalls that bear excess weight and boost puncture resistance.” If you are still learning the markings, our guide to reading a tyre sidewall decodes every number and letter.

LT, ST and passenger tyres compared

ST (Special Trailer) tyres are engineered specifically for towed axles and are common overseas; in Australia the LT tyre is the more widely stocked option, and either is a valid choice provided the load rating is right.

Why not just fit passenger tyres?

Passenger tyres are built to flex and grip under a steering, driving, braking wheel. A trailer wheel does none of that — it just carries weight and follows — but it carries that weight in a much less forgiving way. Cooper Tires Australia notes that light-truck tyres are made with heavier-duty construction and higher load-carrying capacity than passenger tyres. Fit a soft passenger tyre and you risk sidewall flex, heat build-up and, in the worst case, a blow-out on the highway with a fully laden trailer behind you. The stakes of getting this wrong are covered in what happens if you fit the wrong load rating tyres.

How do you get the load rating right?

This is the number that matters most. Every tyre carries a load index — a code near the end of the sidewall marking that corresponds to a maximum weight per tyre. The rule of thumb from Australia’s touring community applies just as well to a boat trailer: the combined load rating of your trailer’s tyres must comfortably exceed the trailer’s fully loaded weight (its Aggregate Trailer Mass), with the boat, motor, fuel and gear all aboard.

A worked example from RV Daily’s caravan and 4×4 tyre guide shows the method: for a tandem-axle trailer with a gross trailer mass of 2000 kg, each of the four tyres should carry a load index of at least 90 — which equates to roughly 600 kg per tyre. Do the same sum for your rig: divide loaded weight by the number of tyres, add a safety margin, and choose a load index above that figure. Our tyre load index chart for Australian vehicles turns the code into kilograms, and if the trailer has a compliance placard, treat its figures the way you would a car’s — see what happens if your tyres don’t meet the placard load rating.

These are illustrative starting points, not a substitute for weighing your loaded rig and confirming the exact index against the load chart. Always round up.

What about the soft sand ramp itself?

Here is the part most people get backwards. On a soft, sandy or unsealed boat ramp, the trailer tyres do almost none of the pulling — they are being dragged. The traction that gets your boat up the ramp comes from your tow vehicle’s tyres. So the single biggest thing you can do for a soft ramp is not the trailer tyre at all; it is airing down the tow car.

Dropping the tow vehicle’s pressures lengthens the contact patch and floats it over soft sand instead of digging in. Our correct tyre pressures for sand driving in Australia guide covers the numbers, but as a guide, soft sand often calls for the high-teens in psi, dropped further only with care. Keep steady momentum, avoid wheelspin, and — critically — reinflate to on-road pressures before you drive back onto the bitumen. Where to do that is covered in where to find air after a beach drive. If you launch on actual beaches under a vehicle permit, read best tyres for beach driving on Australian sand permits too, and check the managing authority’s rules for your ramp or beach.

The trailer tyre’s job through all this is simply to survive: to carry the load without overheating and to resist punctures from shell grit and ramp edges. That is exactly what LT construction delivers.

Do boat trailer tyres need special corrosion care?

A boat trailer is the one road trailer that routinely gets dunked in salt water. The tyres themselves shrug off salt, but the wheels, valve stems and wheel bearings do not. Rinse the trailer with fresh water after every salt-water launch, pay attention to the rims and valve area, and keep an eye out for the white oxidation and bead-seat corrosion that causes slow leaks. If your trailer runs alloy rims near the coast, the same principles in coastal salt air and wheel corrosion apply.

Age matters more on a trailer than a car, because trailer tyres often wear out from time and sun long before they wear out from kilometres. Australian touring guidance puts the useful life of a tyre at around five to six years regardless of remaining tread, after which the rubber deteriorates — so check the date code and don’t run a spare or trailer tyre indefinitely just because the tread looks fine. See do tyres expire: shelf life vs road life in Australia.

The boat-trailer tyre checklist

• Fit LT or ST trailer-rated tyres — never passenger tyres.
• Choose a load index that comfortably clears your fully loaded trailer weight, per axle.
• Run the correct road pressure for the load; check it cold before each trip.
• For a soft ramp, air down the tow vehicle, not the trailer, and reinflate afterwards.
• Rinse with fresh water after salt-water launches; watch rims and bearings.
• Carry a correctly rated, in-date spare and replace tyres by age, not just tread.

Bottom line: Match the tyre to the load, not to the ramp. A light-truck or trailer-rated tyre with the right load index will carry your boat safely for years; getting off a soft sand ramp is a tow-vehicle and tyre-pressure problem, solved by airing down the car and reinflating before the highway.

Frequently asked questions

Can I use car tyres on my boat trailer?

You shouldn’t. Passenger tyres lack the reinforced carcass a trailer load needs, and Australian tyre guides advise against fitting passenger tyres to trailers or caravans. Use LT or trailer-rated tyres.

What load rating do boat trailer tyres need?

Enough that the tyres on each axle comfortably exceed the trailer’s fully loaded weight. Divide loaded weight by the number of tyres, add a margin, and pick a load index above that — round up rather than down.

Should I lower the trailer tyre pressure on a soft ramp?

Focus on the tow vehicle instead — that is what provides traction. Lowering trailer pressure does little for grip and risks rolling the tyre off the bead. Keep the trailer tyres at their rated road pressure.

How often should boat trailer tyres be replaced?

By age as much as wear. Tyres are generally considered past their useful life at around five to six years, and a trailer tyre often ages out before it wears out. Check the date code and inspect for cracking.

Do I need snow-flake or all-terrain tread on trailer tyres?

No. A trailer tyre is dragged, not driven, so aggressive tread does little for it. Prioritise load rating and construction over tread pattern.

Sources: Tyroola — Trailer and Caravan Tyres Guide; Cooper Tires Australia — LT vs Passenger Tyres; RV Daily — Essential guide to tyres for 4x4s, caravans and camper trailers. Prices, loads and rules change and vary by rig — confirm with your tyre retailer and the ramp’s managing authority.