Air is free – Tyre safety not an over-inflated issue

Heavy-duty Mud Terrain (M/T) tyres fitted to a larger type rig.

Thomas Cook

An often-overlooked safety measure before hitting the road is checking tyre pressure, in both your car and caravan. A road trip in Australia will provide the opportunity or even necessity to traverse an array of surfaces, from bitumen through to mud and perhaps even snow. When you think about it, tyres are the only part of your vehicle in direct contact with the ground. Your vehicle needs correct surface contact to adequately steer, accelerate and brake.

Despite experts differing slightly when it comes to the exact numbers with tyre inflation, they certainly all agree that having the correct tyres fitted and inflated to the correct pressure is crucial. The Caravan Council of Australia warns that wrong tyres or the right tyres inflated to the wrong pressures can lead to swaying and roll-overs

A good place to start is with the purchase of your own tyre pressure gauge. This way you can manage the tyre pressure yourself at any stage of your trip. Increasing and decreasing tyre pressure accordingly is paramount to the safety of those in and around your vehicle. It’s also essential to have a quick deflator and a powerful pump/air compressor because despite the time and effort, you will need to deflate and inflate depending on your terrain.

It is recommended that any change in tyre type or size first involves consultation with the tyre or caravan manufacturer. It’s important that tyres of the correct specification be fitted, with the same construction of tyres on all wheels, along with tyre pressure across an axle being equal. Pressures should be checked and adjusted prior to any journey when the tyres are cold. Reducing pressures on warm tyres could result in them being too low once cooled down. Tyres not inflated to the correct pressure also wear out more quickly.

Different terrains

Sand

Sand can vary rapidly in patches and heat is quickly built up with constant resistance to tyres. The idea when driving across sand is to glide across the surface, and a tyre inflated to road pressure will quickly sink in soft sand. Deflating the tyre increases the surface area of the tyre and will help to prevent the wheels from spinning and your vehicle becoming bogged. When hitting sand, some experts suggest you can lower the tyre pressure to 10 pound-force per square inch (psi), but a minimum of 16psi is recommended to be safe. Only decrease lower (anything lower than 5psi could result in the rim spinning around the tyre) to move out when bogged, immediately increasing pressure again once clear.

Mud

Variables such as slope steepness, mud-type and the surface underneath mud play a factor and you might not even have to lower pressure. Watery mud with a solid base allows for higher pressure but thick mud with a deep base that’s loose requires lower pressure. It’s crucial to maintain momentum and traction but remain in control to avoid vehicle and environmental damage.

When driving on other off-road surfaces, the general idea is the same. Low tyre pressure will assist with traction and prevention of damage to the tyre and vehicle. The increased traction will make it harder for the wheels to spin. The lower pressure allows for the tyre to form around logs, rocks and holes. It also helps with the prevention of punctures from sharper objects. Reducing the inflation pressure reduces that tyre’s loading capacity, and with any terrain, higher pressure is required when carrying heavy loads.

A general guide to tyre pressure:

*This is intended strictly as a guide only

Sealed roads:

Pressure 36 to 40psi
Speed range 90 to 110kph

Good unsealed roads:

Pressure 30 to 34psi
Speed range 70 to 90kph

Rough unsealed roads:

Pressure 26psi
Speed range 50 to 70kph

Rough track – mud, rocks, creek crossings:

Pressure 20 to 23psi
Speed range 10 to 50kph

Soft sand:

Pressure 16psi (10 to 14psi if in strife)
Speed range 20 to 30kph

A reduction of 4-5psi is generally noticeable to the naked eye, which coincidentally is the psi difference recommended for the front (lower) to the back (higher) of your vehicle when towing a caravan due to the heavier loading at the rear. Be wary of any 4WD vehicle placards recommending anything below 30psi on bitumen roads. You may notice this with some older vehicles but the supposed added smoothness to your ride can be dangerous and will most definitely result in disappointing tyre life.

It is important to know the laden weight of your caravan, which can easily be achieved through a weighbridge. Your empty vehicle or caravan’s weight is known as tare weight. Subtracting your tare weight from your laden weight determines the weight of your load. A simple maths equation to identify individual tyre loads is to divide the laden weight by the number of tyres on your caravan. As a general tip, allow around 15 per cent margin for safety with all weight measurements. Remember that caravan tyres wear a lot quicker than car tyres due to the loadings they are subjected to. Consult your tyre specialist should you think wear is premature or uneven but it is usually attributed to under-inflation and/or overloading.

Driving across sand will require the lowest PSI but it’s important to remain heedful.
Your tyres and vehicle must be compatible to battle various terrains.
Lower your PSI when driving on unsealed roads and across dirt.
Going off-road is a common occurrence when traversing the great Australian outdoors.
Heavy-duty Mud Terrain (M/T) tyres fitted to a larger type rig.

A properly inflated tyre will wear evenly over the whole tread, whereas an under inflated tyre will show more wear on the outside than the inside and an over inflated tyre will show the wear in the centre of the tread. Do not exceed maximum pressure, which manufacturers stamp on the tyre’s sidewall. To help with this scenario, you first need to decipher the code on the tyre wall.

Sidewall markings on Australian tyres may feature the manufacturer’s logo/brand name, the size, series, rim size, load and speed rating/symbol, a serial number (which is the manufacture date), whether it’s radial, tubeless or tubed, country of origin, mould and factory code numbers.

A tyre sidewall could read P205/65 R16 95 V for instance:
P = type of vehicle the tyre was made for (P = Passenger in this case)
205 = section width of the tyre in mm
65 = sidewall height as a percentage of section width
R = radial ply construction (most common tyre construction)
16 = diameter of wheel rim in inches
95 = load index (the maximum load capacity of each tyre in kg ‑ in this instance is 95, which equates to 690kg)
V = speed rating (maximum speed tyre can carry its rated load). V equates to 240kmh

The load rating/index and speed limit go hand in hand, so in this example the tyres can handle 240kmh with 690kg of load per tyre. Caravans are generally fitted with light truck tyres (LT) but some are passenger rated (P). Other markings will include M and S for mud and snow tyres (check with relevant authorities regarding snow tyres and chains as rules vary according to your area). Speak to your tyre specialist for further information.

kpa-to-psi
A good quality tyre gauge and air compressor will give you an accurate reading and makes inflating and deflating tyres quick and easy.
speed-symbol

Your caravan’s compliance plate will confirm the tyres fitted are compliant and their recommended (cold tyre) pressure. Be sure to load your caravan evenly and that it’s within the total load capacity specified by the manufacturer. An unevenly loaded caravan will be off balance and put undue pressure on the tyres and wheels. Loading too much on either side will cause excessive wearing to tyres on the weighted side. Over-loading on the front and rear of a caravan can actually cause tipping. Try towing your caravan at highway speeds for up to an hour then re-checking the pressure in each tyre. If there’s a 5psi-6psi rise in pressure, your cold inflation pressure is perfect. Any less and cold pressures are too high and any more, cold pressures were set too low. Reduce caravan tyre pressure to match your vehicle’s and remember to drastically reduce your speed when tyre pressure has been reduced – go low, go slow.

General tyre maintenance means you should rotate regularly (every 10,000 kilometres), ensure they are installed correctly and are aligned, balanced and maintained at the correct pressure. When it comes to your spare tyres (yes, carry more than one and it’s a real bonus if interchangeable across car and caravan), make sure they are rated by the tyre manufacturer for the appropriate use, the tyre construction is the same on each axle and if retreaded, they are marked to Australian standards. Complacency with checking caravan tyres is common when compared to that of the towing vehicle but it shouldn’t be. Safety rests with you. Again, please consult the vehicle manufacturer or your local tyre specialist if you’re ever in doubt.

Having the right tyres inflated to the right pressure will help preserve everything underneath your caravan.

In Australia, ‘M&S – mud and snow tyres are a common compromise that can also be driven on gravel roads at higher speeds and temperatures.

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