Everything you need to know about tyres for your tow vehicle, caravan and camper-trailer
By Philip Lord
Article from RV DAILY Magazine
Tyres might not be sexy, but they are vital for touring safely and reliably. It’s a cliché, but tyres are the only contact between your vehicle/trailer and the road. So, knowing as much about them as possible is vital.
There are three types of tyre pattern used on 4WDs — Highway Terrain (H/T), All-Terrain (A/T) and Mud-Terrain (M/T) tyres and three types of tyre construction Passenger, Commercial and Light Truck. Caravans tend to come with Commercial tyres, A/Ts or M/Ts.
Tyre types explained
Let’s look at the benefits of each tyre type. Highway Terrain tyres are relatively quiet and smooth and typically last longer than other tyre types. They have a high-speed rating and relatively light sidewall construction. These tyres, with a tread pattern like a ‘car’ tyre, often provide the best on-road traction. Highway Terrain tyres are fitted to most new 4WD wagons and some 4WD utes too and are marked as Mud and Snow (M+S) tyres, which relates to their tread pattern being slightly more open than a regular passenger rated tyre. If you restrict yourself to on-road driving and towing, then H/T tyres will do the job fine.
What exactly defines an A/T tyre depends on how the tyre manufacturer has designed it. Some A/Ts will offer a tread pattern and carcass construction similar to a H/T tyre, while others will have a more aggressive (read: blocky) tread and stronger construction closer to an M/T. Often the A/T tyre will be marked as ‘M+S’ which means it has a more open tread pattern than a standard passenger tyre.
Mud Terrain tyres (the heaviest, strongest construction and a blocky, deep tread pattern) have low-speed rating and a high-load rating. Their tread pattern is designed for biting through mud, and they offer good grip in other off-road situations such as climbing rock steps.
Of the tyre construction types, Passenger-rated tyres are the least puncture-resistant but are lightest, often cheapest to buy and have the highest speed rating. Some H/T tyres are P-rated (with a ‘P’ prefix on their tyre size, such as P225/75R16).
Light Truck (LT) tyres have a stronger carcass so that they can meet the load requirements of light trucks, but how puncture-resistant they are can vary. Light Truck tyres are available in A/T, Commercial and M/T tread patterns.
LT Commercial-rated tyres are intended, as the name suggests, for commercial vehicle applications where the vehicle’s high load-carrying requirements necessitate a heavier construction tyre. They usually have a simple on-road, or sometimes a more open Mud and Snow tread pattern and don’t have a high-speed rating. Their heavier construction allows a higher load rating and also gives them better puncture-resistance than passenger tyres. They can be identified by a ‘C’ suffix in their tyre size, for example, 185R14C.
“If you’re going to be slipping and sliding on a muddy track, a good A/T tyre is going to do as good a job of keeping the van straight as an M/T in most situations”
The Best Compromise
An all-terrain tyre in LT construction is the best compromise for your tow vehicle for both on-road driving and towing off-road. While A/T tyres typically have a lower speed-rating than an H/T tyre — often between T and H, this is still beyond the highest speed you can legally tow at (see speed-rating chart), they have a higher load rating and more open, aggressive tread pattern for better off-road performance. A/Ts will have a more puncture-resistant, more robust construction too. Check the tyre specs online or on the tyre sidewall — eight- or 10-ply ratings are best for protection against stone damage and sidewall staking
If you’re going to be slipping and sliding on a muddy track, a good A/T tyre is going to do as good a job of keeping the van straight as an M/T in most situations. If you’ve got the trailer trying to jack-knife on soapy mud, then you’d have to ask yourself why you’re dragging it through there in the first place.
Many on-road caravans are fitted with Commercial-rated tyres, and they are the best compromise for such a van in terms of having sufficient load rating, cost, and offer an improvement in puncture resistance over P-rated tyres.
Mud Terrain tyres on a caravan are overkill for most tourers. They often cost more than other tyre types, their added rolling resistance will add to towing fuel consumption, they offer less grip on the road — especially in the wet — and there is little if any off-road grip advantage in having M/Ts instead of A/Ts on a caravan as they are not driven wheels.
When touring in remote areas, it is useful to have a vehicle and van fitted with matching wheels and tyres. If you get several punctures or damaged tyres or wheels, you have more than one spare to go around to suit either vehicle or van. This set-up requires a trailer to be fitted with the same stud pattern, offset and tyres with the same rolling radius as the tow vehicle.
Sizing up the options
You can increase overall tyre diameter by up to 25mm legally, which gives improved ground clearance and often increased tyre options. Check out: tiresize.com to see what you can increase tyre size to legally.
The writing on the wall
Tyre sidewalls contain a lot of useful information about the tyre size, speed rating, load rating and even how it should be balanced.
Join the dots
Wondering what the red and yellow dots mean on your brand-new set of tyres? When tyres are made they are not perfectly balanced nor perfectly round. The red dot on the tyre sidewall marks the point where the tyre is the lightest on its radius, and therefore the tyre fitter should align this mark with the wheel’s tyre valve — which is the heaviest part of the wheel. When the tyre is fitted this way, it will need fewer weights to balance it.
The yellow dot marks the tyre’s high point — and this mark should be aligned with an indent on the wheel, which marks its low point (because wheels are not made perfectly round either).
Reading between the lines
Tyre manufacturers say that tyres only have a useful life of between five and six years before the rubber deteriorates and become dangerous. That means the risk of a total tyre failure — a blow-out — increases exponentially as the tyre reaches five years old, regardless of the amount of tread remaining. To find out how old your tyres are (or how long your new set of tyres have been lying around) look for a four-digit code on the tyre sidewall corresponding to the week and the year it was made. For example, a 4718 code means the tyre was made in the 47th week of 2018.
Like many components on your vehicle and van, tyres are designed to take a maximum weight, and legally their load rating must meet or exceed the Gross Vehicle Mass of the vehicle or Gross Trailer Mass of the van. When replacing tyres (or if you’ve just bought a used tow vehicle or van) check the ratings are correct. For example, if your tandem-axle van has a GTM of 2000kg, each of the four tyres should have a minimum index number of 90 (equating to 600kg load rating for each tyre).
Roll them around
Tyre rotation is essential to even out tread wear, especially for the tow vehicle, which will make the tyre set last longer and should be performed every 10,000km. You want to rotate tyres, so they wear evenly, and you’re not left with tyres that have tread remaining but are too old to use (see above). Provided the tyres are all the same size with the same load rating, the spare is fitted to the right (driver’s side) rear and the (passenger side) left front becomes the spare. The right rear goes to the right front, which goes to the left rear. The left rear moves to the left front.
When touring on outback dirt roads, drop tyre pressures to around 25psi. The less-stiff, more flexible tyre carcass will reduce the chance of tyre punctures. While you shouldn’t tow at more than 80km/h on dirt anyway (due to the reduced grip and because of the damage you can do shaking gear around in your van) this is especially relevant when you’ve dropped tyre pressures as heat build-up in the tyres will risk a tyre blow out. Remember to re-inflate tyres to recommended pressures before returning to sealed roads.
How to read a sidewall
Three types of size description are used on 4X4 tyres, for example:
265 = section width in millimetres;
65 = sidewall aspect ratio, as a percentage;
R = tyre construction, in this case radial;
17 = rim diameter, in inches;
100 = load rating (in this case 800kg); and
T = speed rating (in this case, 190km/h).
9.50 = width in inches;
R = tyre construction, in this case radial;
16 = rim diameter, in inches; and
LT = light truck construction,
32 = diameter of tyre mounted on rim, in inches;
11.50 = section width, in inches;
R = tyre construction, in this case radial;
15 = rim diameter, in inches; and
LT = light truck construction.
Read the placard
A tyre placard is a plate or sticker that by law must be fitted to vehicles and caravans with the tyre sizes designed for the vehicle and the minimum speed and load ratings for those tyres. These are considered the legally correct specification tyres for your vehicle. You can usually find the tyre placard stuck on somewhere like a door jamb or aperture, fuel filler flap or glovebox lid on your vehicle and the compliance plate for your van, usually fitted to either the boot, door entry area or A-frame.
Top tyre tips
1. Before leaving home or camp always check that both vehicle and van tyre pressures are at recommended levels.
2. Check tyre treads and sidewalls for damage or uneven wear regularly.
3. Brush the back of your hand over each tyre when pulled up after a highway run; if tyres are excessively hot it indicates that you may be running too-low tyre pressures (or there’s a brake or bearing issue).