CARAVAN TYRES GUIDE

KEY TYRE TERMS FOR CARAVANS

The modern tyre seems to last forever, and it's easy for owners to fall into the trap of not paying much attention to them. The first time many people consider doing something about tyres is when they fail a rego inspection for lack of tread.

TYRE CONSTRUCTION

The modern radial caravan tyre has layers of steel fabric running around the inner circumference under the tread. These steel “belts” ensure less tread movement when braking or accelerating and the flexible sidewalls allow even tread contact during cornering.

Tyres are either Passenger (P) or Light Truck (LT), also known in Europe as Commercial (C). Only use LT or C tyres on most caravans because P tyres do not have an adequate load rating for the job.

LT tyres are made with casing cords consisting of parallel fabric and steel cords, so they have stiffer sidewalls than passenger tyres and improved load capacity.They are also better at resisting punctures. LT tyres have a much lower speed rating than P tyres, but should have a rating higher than the legal towing speed of 110km/h anyway.

RATINGS AND PLIES

Most caravan tyres are six or eight-ply rated, but this is based on the outdated cotton ply rating, which is rarely used today except for 4WD tyres to denote how rugged they might be offroad. A tyre’s load index (e.g., the number “111” in a size such as 185/75R14 111T) is the current method of denoting a tyre’s load capacity and strength.

When buying a set of new caravan tyres, you should look to replace the tyres with the correct size (check the caravan trailer plate or tyre placard, usually fitted in the front boot). The most important rating on the tyre that you need to verify is the load-rating index.

When shopping for tyres for an offroad caravan, as when shopping for 4WD tyres, it is worth checking how many sidewall and tread plies are in the tyre. This information is often marked on the sidewall on LT tyres (see above), or in the specifications supplied by the manufacturer. Four plies in the tread area and two in the sidewalls suggest it will be a reasonably rugged touring tyre. Eight or 10-ply ratings are best for resisting stone damage and sidewall staking when driving offroad.

Tread depth varies, too, so even though less tread depth usually equals less squirm under load (cornering or braking, for example) and less noise, a deeper tread can give a better ride, be more resistant to tread area punctures and suggests that the tyre has a strong carcass.

TYRE LIFE CYCLE

Caravans usually have bursts of activity with long layover periods, so they often do fewer kilometres than the typical car. While the tyre tread might have plenty of life left, the tyre carcass will have aged and possibly perished as a result. The danger here is that it could delaminate or blow out if you continue to use it.

Check the date stamp on the tyre’s sidewall to see how old the tyre is. You will find this located on the sidewall close to the rim in an area that will look stamped into the rubber of the tyre. This date will be expressed as a week and year date – for example, “3303” means the tyre was made in the 33rd week of 2003.

Tyre companies don’t often stipulate a use-by date for their tyres, but other sources in the tyre industry agree that if the tyres have been in service for more than six years and/or have evidence of cracked rubber, they are much more at risk of failure.

Always check the spare tyre, too, to see that it has not aged beyond the above time frame, has plenty of tread left, is a matching size to the other tyres and that it is able to maintain tyre pressure.

TYRE MAINTENANCE

Rodney Moffitt, Toyo Tyre & Rubber’s technical department manager, says that rotating tyres on a tandem-axle van every 10,000km is a good idea to even out wear. Tyres on the front axle will typically wear more than the rear as they typically carry a slightly higher load.

HOW TO STORE TYRES

Rodney also says that when you store your caravan for extended periods (more than a month) there are two potential problems. The first is flat-spotting, which is when tyres are sitting with low pressures and the tyre ‘settles’ into an out-of-round shape with a flat spot where the tyre is in contact with the ground. When you use the van again, even with the tyre pumped up, it will still have this flat spot.

If you put the axles up on blocks so the weight is off the tyres, it’ll avoid flat-spotting. If you can’t do this, at least pump up the tyres to the maximum pressure allowed on the sidewall. Check them periodically, as tyres do lose air, and if they are allowed to go flat, they will suffer flat-spotting. Good-quality valve caps with a rubber seal help reduce this gradual air-pressure loss but aren’t a guarantee.

The second storage problem is ozone damage to the tyre, which quickens the deterioration of the tyre’s rubber (with cracking sidewalls). Store the caravan in a covered space to stop ozone damage, and if you must store it outside, place a cover over the tyres. Use a material that can’t be sun-affected, like a sheet of MDF board.

CHECKING TYRES

Tyres require a minimum of 3mm tread depth to be roadworthy, but obviously you shouldn’t go on the big trip with only this amount of tread left because they won’t stay roadworthy for long.

When travelling, tyres should not need a lot of maintenance but your van’s tyres should be checked as often as your vehicle’s tyres – preferably a couple times a day but at least once a day. Better still, if you can make tyre checks part of your routine when taking a break on the road, you will reduce your chances of having a tyre problem later on.

Check carefully for cuts in the tyre, or any foreign objects such as nails, sticks or glass that may have pierced the carcass. Also, if you find anything more significant than mild chipping (which you should then keep a close eye on), replace the tyre as soon as possible to avoid the problem developing into air pressure loss, and then get the offending tyre repaired.

Feel how hot the tyre sidewall is with the back of your hand – get used to how hot it feels as part of your checks. If the sidewall is too hot to rest your hand on it, there’s likely a problem. The ‘best’ problem could be that you’re driving too hard, but it could also be due to overloading, under-inflation or a sticking brake or faulty bearing.

If you're in any doubt about how to do these checks, ask your tyre retailer for practical advice on what to look for and how to recognise tyre problems.

TYRE PRESSURE

Always start with the manufacturer’s recommendation for tyre inflation pressure. After setting the pressures with tyres cold, check them again about 50-100km down the highway. You should see a pressure rise of about 5-6psi for LT tyres.

An excessive rise (more than 6psi) means you need to increase the pressure, as you have started with too little air pressure in your tyre. If you don’t pump it up, you will eventually get tyre delamination (the tyre starts to fall apart), which is irreversible damage. The tyre will eventually blow out, and probably not give you much warning. If you get less than a 6psi pressure increase, chances are you have over-inflated the tyre, so you need to deflate slightly. Never increase or deflate the tyre more than a few psi – and never inflate over the maximum inflation pressure stated on the sidewall.

FINAL THOUGHT

Buying and maintaining tyres on a caravan is not difficult, but does require a little effort and time. You should aim to have tyres that are load-compliant, not old, have adequate tread and correct tyre pressures, and are stored properly when not used. Do this and you won't have any ‘tyresome’ surprises when out on tour.