Wheel and tyre maintenance
Those round things that keep your van rolling are often the least thought about yet, perhaps, the most important, component of your van. It’s a good idea to know how to maintain your wheels and tyres and also to know how to read the danger signs of when they are about to fail.
When buying a new van, you should have no problems with your (presumably) new wheels and tyres, but it still is a good idea to check them anyway.
Start off by checking the load rating. To do this, have a look at the sidewalls of each tyre, where you will see a figure expressed in kilograms that denotes the tyre’s load rating. Then check that the sum of the tyres’ individual ratings meets or exceeds the ATM on the caravan plate (or tyre placard). So if, for example, your van has an ATM of 2400kg, each tyre should have a minimum 600kg load rating.
The minimum speed rating should be noted on the caravan plate (usually it is an ‘L’ rating or 120km/h, but check). While the Australian standard for trailers, Vehicle Standards Bulletin 1, says all trailers must have a tyre placard; most vans have this information on the caravan manufacturer’s plate.
TIME TO TORQUE
Check what tightening torque the manufacturer recommends for wheel nuts and, if they’re steel wheels, undo the nuts one at a time, check that there is bare metal and not paint on the mating surface of the wheel (otherwise they will loosen) and then retighten to the specified torque. Now is the time to buy a good torque wrench if you don’t have one.
If you don’t have, or can’t find, the recommended torque figure, 110Nm of torque is generally accepted as an appropriate torque figure for road wheels on vehicles and trailers.
No one pays much attention to valve caps, but they are intended for more than just decoration – a tyre can deflate when grit enters the valve because the cap has gone missing. Check that the caps are finger tight and that the valve stem is sitting centred and straight in its aperture. Opinions will vary but steel valve stems and locking valve caps can increase the likelihood of air leaks. Stick to rubber-cased stems and plastic non-locking caps.
TYRE BIRTHDATE
It is rare for the tyres to be manufactured in the same month as the caravan is – they will be older and, depending on how often the caravan manufacturer restocks tyres, could be several months older.
Look for a four-digit figure such as ‘5108’ stamped into the sidewall within an indented border. The first two digits represent the week of the year the tyre was made and the last two digits the year it was made. So ‘5108’ means the tyre was made in the 51st week of 2008.
Tyres that are about seven years old have reached the end of their service life. Fine cracks in the sidewall are clear evidence that the tyre has perished to the point that it would be unsafe to use. Even if they have plenty of tread left, they should be replaced. Tyres in this state cannot withstand expansion and, as they heat up, they have a high chance of delaminating and blowing out.
Check what cold inflation pressure is recommended on the tyre placard and see that your van’s tyres are on the correct pressure – when cold of course, and not hot just after a run.
A good way of checking that your pressures are correct for your application is the 4psi rule for passenger car tyres, or 5-6psi rule for light truck (LT) tyres. Check tyres cold and then later, straight after a decent highway run of 100km or so and you should see a 4psi increase (5-6psi for LT tyres). If it is less, you have set your cold tyre pressure too high; if it is more, then you have set them too low. Adjust the cold pressures accordingly and check the results when hot again and you should see a tyre pressure difference as per the above. While checking pressures, check the valve has sealed properly and is not leaking. The easiest way to do this is to apply some saliva to the valve and see if it bubbles. If so, you have a leaking valve.
SECOND-HAND VANS
If buying a used van, all the above also applies but treat the wheels and tyres with even more suspicion, as you don’t really know how long they have been on the van or what life they have led.
For steel wheels, see if they have much corrosion on them or appear buckled, or have a bent rim outer. Rust is usually a cosmetic issue, although if the van has been left standing in a salt-air environment for a long period, you still need to check them very closely for structural damage. For aluminium alloy wheels, look for fine cracks, or bent outer rims. If cracked, seek professional advice immediately as this is a dangerous condition. Bent rims, especially steel rims, can be repaired.
Bent alloy rims can sometimes be repaired, although you need to take the wheel to a wheel repair specialist to verify this. Look for the size stamped on the rim and that it matches the rim size requirement on the caravan identification plate.
If they’re new steel wheels and look freshly painted, it is a good idea to see that the mating surface for wheel nuts and hub do not have paint on them. If they do, you may encounter problems fitting the wheels or nuts, or the wheel nuts may come loose, even though they have been torqued up to specification.
HOW’S YOUR SPARE?
Everyone forgets the spare wheel until they really need it. Make sure you have one (usually this is obvious, as they often are mounted externally, but sometimes they are not). If you don’t, go and get one with size, load and speed ratings that match the wheels and tyres already on the van. Don’t get a steel rim spare if you have alloy wheels or vice-versa, as offsets are likely to be different and, unless you are prepared to carry different wheel nuts, you won’t be able to secure the spare wheel safely on the axle.
If your second-hand van has a spare tyre, don’t forget to scrutinise its manufacture date, as chances are it has never been used and will be older than the van.
Some people like to match wheels and tyres between vehicle and van to make it easier if changing a flat tyre, as it can double up the spare wheel count if you have a spare in the vehicle and a spare in the van.
Generally, tandem-axle offroad vans are easier to match rims and tyres with a 4WD tug, because you’ll likely use heavy construction LT tyres with high load ratings for both, and the offroad tyres in popular patterns and sizes are more widely available in remote areas. If going down the path of wheel/tyre matching, you still have to check all wheels and tyres exceed the minimum load ratings and minimum speed ratings for both vehicle and van.
WHAT ABOUT WEIGHT?
Like all crucial load-bearing components in or on your rig, tyres are only designed to operate within certain parameters and, in the case of tyres, they can only carry so much weight and only go so fast before eventually blowing out.
Weight carrying capacity for tyres is expressed as a three-digit load rating and speed rating is expressed with a letter, both stamped on the sidewall of the tyre. So ‘96N’, for example, can be broken down into the load rating (96 equals 710kg) and speed rating (N which equals 140km/h).
When storing your van for extended periods, it’s best to either remove the wheels and store them in a dark place or lift the van so there’s no weight on the tyres. It’s also a good idea to keep the sunlight off the tyres whenever possible, as this will also help to improve their longevity.
The full feature appeared in Caravan World #540 August 2015. Subscribe today for the latest caravan reviews and news every month!