When it comes to towing, your tyres do all the heavy lifting — literally. Yet, they’re often the most overlooked part of a trailer setup. Whether you’re pulling a caravan, car transporter, or plant trailer, knowing your tyre ratings, tread depths, and sidewall markings is vital for safety and compliance.
Here’s everything you need to know to keep your trailer rolling right.
Trailer Tyre Condition: Don’t Risk It
By law, both car and trailer tyres must have at least 1.6 mm of tread across the central 75% of the tyre’s width around the entire circumference.
That’s the minimum — but in wet weather, tyres with less than 3 mm of tread start to lose serious grip, especially under braking.
You should also check for:
Deep cuts or bulges – signs the tyre is breaking down internally.
Mismatched types – it’s illegal to mix cross-ply and radial tyres on the same axle.
Correct rating – always ensure your trailer tyres match or exceed the manufacturer’s load and speed specifications.
A blown trailer tyre at 60 mph is nobody’s idea of fun.
Trailer Tyre Sidewall Markings Explained
All those numbers and letters on your tyre sidewall actually tell a full story. Here’s what they mean:
Nominal section width: The tyre’s width from side to side. On radials, it’s in millimetres (e.g. 185). On cross-ply tyres, it’s in inches.
Aspect ratio: The height of the sidewall as a percentage of the tread width.For example, in a 185/70R13, the “70” means the tyre’s height is 70% of its width.
Construction type: “R” = radial, “B” = bias belt, “D” = diagonal.
Rim diameter: The internal diameter of the tyre in inches (e.g. 13).
Load index & speed symbol: Show how much weight the tyre can safely carry and its maximum rated speed (see Brent’s guides on Tyre Load Index, Speed Symbols, and Pressure Ratings).
If your trailer uses retread or remould tyres, they must also be marked with:
“RETREAD” or “REMOULD”, and “BSAU 144” instead of the ECE Type Approval mark.
That ensures they meet British safety standards.
Tyre Ratings: Load, Speed & Pressure
Every trailer tyre is designed to handle a specific load and speed. You’ll find these details right on the sidewall, usually next to the size — for example, 185/70R13 93N.
The load index (93) tells you how much weight each tyre can safely carry.
The speed symbol (N) indicates the top speed the tyre can handle under that load.
Inflation pressure affects both — running underinflated tyres generates heat and can cause blowouts, while overinflation reduces grip and increases wear.
Brent’s handy Speed Symbol Guide and Load Index Chart make it easy to check you’re using the right combination.
Brent’s Tyre Tips
Here’s the short version:
Keep tread above 3 mm for grip, not just legality.
Replace tyres showing cracks, bulges, or perishing — especially if they sit outside for months.
Don’t mix radial and cross-ply types.
Always match or exceed your trailer’s rated load and speed.
Check pressures before every long trip.
Your tyres carry everything — your trailer, your load, and your peace of mind.
Brent’s Take
At Brent, we’ve seen it all — from brand-new tyres with the wrong load rating to old rubber that’s seen more summers than it should.
A well-chosen set of tyres means smoother towing, better fuel efficiency, and fewer roadside dramas. So whether you’re checking your setup or shopping for a road-ready trailer, make sure your tyres are up to scratch.
You’ll find fully compliant trailers, all properly rated and tested, right here on Brent — where safe towing comes as standard.
-Brent