Things You Need to Know About Tyres
BBC One's The One Show recently ran a tyre-safety feature, during which they visited a caravan site and inspected the tyres on a few vans. They all had thousands of miles of tread left, but at least one was eight years old.
But tread isn’t the major concern with caravan tyres; it’s the sidewalls that are the weakest parts. For this reason, all reputable parties in the caravan industry – including Practical Caravan – recommend that tyres be changed every five years, even if they look to be in perfect condition.
Wheel and tyre types
Although we’ll be referring to single-axle caravans throughout this feature, our comments apply equally to twin-axle models. In the case of British caravans, the vast majority have either 13in or 14in diameter wheels. The 13in size is found on older vans, while the 14in was introduced around the turn of the century. The change to 14in was due, at least in part, to the fact that 13in tyres were not as readily available off the shelf as 14in ones – especially if a blowout occurred while towing on the Continent.
The tyre markings panel below shows the markings on a tyre designed to fit a 13in wheel. Besides the size designation, find the load index, the speed symbol, EU type approval and whether the tyre is a tubeless or tube type (see panel, below).
There is no basic difference between a car tyre and a caravan tyre. Both can be either cross-ply or radial-ply, but it is illegal to mix the two on the same axle.
The load index and speed rating also have a significant bearing. For example, in the case of a car weighing 1000kg, the load on each tyre would be roughly 250kg. But on a single-axle caravan weighing the same, the load on each tyre would be roughly double, or 500kg.
Additionally, to provide a margin of safety, the combined load-carrying capacity of the two tyres on a single-axle should be 10% more than the caravan’s maximum technically permissible laden mass (MTPLM). For a caravan with an MTPLM of 1400kg, divide this by 2 and multiply by 1.1 (that is 10%more): 1400/2 x 1.1 = 770kg.From the load index table (left), you can see the tyre’s load index should be 99. The speed rating figure T indicates a maximum speed for the tyre of 118mph – or just under twice the maximum speed for a caravan on a UK motorway or dual carriageway.
The caravan manufacturer will state the pressure to which the tyre should be inflated and this should be checked before every trip when the tyres are cold. It’s the air inside the tyre that actually carries the van’s weight. Under-inflation makes the tyre less able to carry the load, while over-inflation causes the centre section of the tread to wear more rapidly, thereby reducing the tyre’s usable life.
If the caravan isn’t used for long periods, the tyre pressure should be checked monthly because the oxygen in the air inside the tyres leaches out slowly, even when the caravan is parked on the driveway or in storage. It is also a good idea to cover the tyres when the caravan is parked in order to help prevent damage to the rubber from UV radiation. Although it will not be obvious, UV radiation from the sun can damage the walls by reducing their strength – which means they’re more liable to fail suddenly.
As well as checking the van’s tyre pressures before each trip, use a torque wrench to check the wheel bolts. The correct torque will be found in the caravan owner’s manual. For most caravans on Al-Ko Kober chassis fitted with steel wheels and M12 bolts, the correct torque is 88Nm (65lb.ft), and for those on BPW chassis it is 80-100Nm (59-74lb.ft). The torque required for alloy wheels on Al-Ko chassis is 110Nm (81lb.ft), and for BPW it’s 130Nm (96lb.ft).
If you do have to change a wheel for any reason, stop and recheck the bolt torques after the first 30 minutes of towing.
If in Doubt Let Us Check It Out
Spot the problem
In addition to damage from punctures, damage can be caused by kerb strikes, potholes and a host of other objects lying in the caravan’s path. Added to this is the actual flexing of the sidewalls during towing, which can also have an adverse effect on a tyre’s ability to carry the load. Therefore tyres should be inspected regularly for signs of damage and cracks.
This is particularly important in terms of the inside wall, where damage and cracks are less obvious. Regardless of the amount of tread left on the tyre, if any damage or cracks are found on either the outer or inner walls, the tyre should be changed. It is also a legal requirement that if there is less than 1.6mm tread depth over three-quarters of its width and in a continuous band around the tyre, it should be changed.
If the caravan is left parked for long periods, the wheels should be turned slightly each month to prevent the risk of flats occurring.
Buying new tyres
When buying new tyres you get what you pay for. Based on the tyre designation, load index and speed symbol, the tyre dealer should be able to offer a choice of makes, with prices varying from cheap to very expensive. Our advice would be to avoid the very cheap. Interestingly, as the years have gone by, caravan manufacturers have increasingly gone for more expensive tyres, perhaps as a result of their experiences with the cheaper ones.
It is also important to make sure that the date code on the tyre is not more than a year or two old. Avoid buying any tyre with a date code more than five years old, if only because the rubber will have deteriorated to some degree, even while the tyre has been in storage.
Retreads and partly worn tyres
It is perfectly legal to buy and fit retreaded tyres instead of new ones, but do bear in mind the comments above if you choose to do so. In particular, check that the load index is correct for the MTPLM of the caravan, and that the tyres are inflated to the correct pressure.
We do not recommend buying partly worn tyres because it is impossible to know the precise conditions under which they have been used.
Caravan manufactures do not have the wheels on their new caravans balanced, and it is a moot point whether or not balancing is worthwhile since the suspension on the caravan – unlike that on any tow vehicle – is very basic. However, when having tyres replaced, the dealer usually offers to balance the wheels and in our opinion the slight increase in cost is worthwhile since balancing will do no harm and might even improve the stability of the outfit.
The spare wheel often gets forgotten until the caravan has a puncture. When this happens it’s likely that the spare will be found to be under-inflated or even flat. So it pays to check it regularly – we suggest once a month. Most spare wheels now fit under the floor, where they pick up all the dirt and grime from the road. Because of this, as well as checking the pressure, the spare should be cleaned so that it is always ready for use.
Tyron safety bands
Tyron safety bands are bands that fit into the wheel to prevent the tyre bead dropping into the well when a puncture occurs. Tests have shown them to be very effective at improving the stability and steering of the outfit in the event of a puncture or blowout on the road.
Not all tyre companies have the facilities to fit the bands or to remove tyres from wheels fitted with them. This obviously can cause problems especially if a blowout occurs while towing. For this reason it’s not a bad idea to carry a Tyron portable fitting machine .
If the caravan is laid up for long periods, in addition to checking the tyre pressure and visually examining the tyres for cracks and any signs of degradation, be sure to turn the wheels occasionally to prevent the risk of flats developing.
Alternatively, some caravanners replace the wheels with stands called winter wheels. Before doing so, you must check with your caravan insurer because some policies void cover if winter wheels are used while the van is in storage. Companies argue that winter wheels will prevent the van from being moved in an emergency. Ironically, they can deter caravan thieves.
Changing a wheel
If a blowout takes place, then we recommend the following procedure. Park the tow vehicle, choose reverse gear – or ‘park’ if it has auto transmission – and switch off the engine. Apply the caravan handbrake fully but do not unhitch the outfit. Wind the steadies down and remove the spare wheel in readiness. Loosen the wheel bolts slightly.
Next, jack up the caravan and wind down the steadies further if necessary. Undo the wheel bolts and remove the wheel. Fit the spare and tighten the wheel bolts. Lower the jack.
Use a torque wrench to tighten the wheel bolts to the correct torque. After driving for 30 minutes, stop and check the wheel bolt torques.
If the blowout occurs on a motorway or any other dangerous stretch of road, get all the passengers out of the vehicle and behind the barrier, then call for assistance. Do not attempt to change the wheel yourself; it is simply too dangerous.
Two types of sealant are available from high street motorist stores: one seals punctures and the other is injected after a puncture to seal it and inflate the tyre. Both are injected through the tyre valve, but the former remains in liquid form until a puncture occurs. However, in the event of a blowout, the hole is often too large for either type of product to make a difference.
Tyre manufacturers don’t like liquid puncture sealants, mainly because of the possibility that the puncture will occur without the driver realising it. Additionally, it can make for a messy business when the tyre company tries to replace the tyre. On the other hand, a sealant that seals and inflates the tyre following a puncture may well enable the outfit to be driven to safety.
At the end of the day, the only thing standing between your caravan and the ground are its tyres. Look after them. Don’t hesitate to change them if the sidewalls show signs of cracking or bulges, or if they are damaged in any way. Also replace them after five years of use, even if the treads still have many thousands of miles left in them. Keeping them could be a false economy – with dangerous results.