Understanding Caravan Tyres

Car tyres vs caravan tyres
There is a myth that caravan tyres are very different from car tyres but fundamentally there is no difference between the two. Having said that, the role of the two tyres is somewhat different and this leads to differences in the way they are specified. In a typical front wheel drive family saloon the front wheels do all the driving, all the steering and most of the braking. They also carry most of the weight. The rear wheels by contrast have a much easier life.

A caravan’s tyres would have a relatively easy life too, apart from one thing – load. Most caravans have just two wheels so the weight on them can be much higher than in a car. This means that the load rating of caravan tyres is often significantly higher than for a similar size tyre fitted to a car.

To cope with these higher loads caravan tyres tend to have more reinforcement (in the form of plies) than car tyres. However the fact that they do not have to drive, steer or brake heavily does mean that caravan tyres can be run nearer to their load limit than would be permissible for a car. This point is lost on a number of tyre fitters and explains why they sometimes condemn the rating of original equipment tyres and advise fitting uprated ones.

Of course there’s nothing wrong in fitting uprated tyres, provided they are the same size, but it should be remembered that tyres are a fundamental part of a vehicle’s suspension system and that fitting uprated tyres may result in a harsher ride. This point is particularly relevant for tandem axle caravans where the load rating tends to be much lower than for single axle types because there are four wheels to share the load instead of two. I have known cases where owners have fitted tyres of a significantly higher load rating than the originals.

The importance of correct inflation
For a tyre to function properly at its maximum rating it must be correctly inflated. Significant under-inflation can cause excessive flexing of the sidewalls. This can lead to overheating and premature failure. Over-inflation will give a harsh ride and can induce stresses beyond those the tyre is designed for, and this too can lead to premature failure. Also, both under and over-inflation can lead to uneven tyre wear.

So, how do make sure your tyres are inflated to the right pressure? The first thing is to check what the pressures should be. Swift publishes this information in the caravan’s service booklet (the one the dealer stamps at service time). If your model is not listed (e.g. because it’s dealer special) ask your dealer or, in case of difficulty, ring Swift’s Customer Care dept.

Next make sure you have a decent pressure gauge with a scale or readout that is easy to see. Finally make sure that the tyres are cool, as a warm tyre will give a false reading.

Caravan Storage
When caravans are left standing for prolonged periods it is easy to overlook tyre pressure checks and flat spots can develop. The higher load rating of caravan tyres means they tend to have more plies than passenger car tyres and this makes them more susceptible to flat spotting if left in the one place for a long time. So, if you intend to store your caravan for more than a few weeks, it is best to remove the wheels and put them in a cool dry place away from direct sunlight. If you put the caravan onto axle stands (as opposed to metal ‘winter wheels’) this will allow the caravan’s suspension to rest thereby helping to protect its rubber innards from permanent distortion.

However before removing the caravan’s wheels check with your insurance company. Some insist that a wheel clamp is fitted at all times and others may take the view that removing the wheels could make the caravan difficult to move in the event of an emergency such as a fire. If you decide not to remove the wheels then try to turn them a quarter turn each month to prevent flat spots from developing.

Tyre markings
Tyres are classified according to their width, sidewall profile (height to width ratio), construction type, the size of rim to which they can be fitted, their load rating and speed rating. This information is given in a code on the tyre wall and looks something like this:

195/70 R 14 99T

Here 195 is the tyre width in millimetres, 70 the height to width ratio, R is the construction type (in this case radial, by far the most common), 14 is the rim diameter in inches, 99 is the load rating index and equates to 775 Kilos or 1705 lbs, and T is the speed rating and equates to a maximum speed of 118mph. Never replace a caravan tyre with one of a lower load rating than the original specified by Swift. The following table lists some of the more popular ratings.

Load Index	KG		Load index	KG
75	387		93	650
77	412		95	690
79	437		97	730
81	462		99	775
83	487		101	825
85	515		103	875
87	545		105	925
89	580		107	975
91	615		109	1030

The speed rating of a tyre is not normally an issue with caravan tyres as, even on the continent, caravans tend to be towed below 70mph for stability reasons. However, on French motorways it is permissible to tow at speeds up to 81mph (130km/h) so it is important to ensure that the tyres are suitably rated. In practice this should only be an issue with older caravans.

Speed Symbol	Max speed mph	Max speed km/h
L	75	120
M	81	130
N	87	140
P	93	150
Q	99	160
R	106	170
S	112	180
T	118	190
H	130	210
V	149	240
W	168	270
Y	186	300
ZR*	over 149	over 240

*ZR will gradually replace W and Y. In the interim tyres may carry both markings e.g. 195/50ZR 15 82W and 195/50ZR 82Y

Puncture sealants
These fall into two categories – pre and post puncture. The first type is designed to be used at the roadside to for a temporary repair and the second to live permanently inside the tyre ready to seal a puncture should one occur.

If you suffer a puncture whilst travelling then the roadside repair variety may well be the quickest way to get you to a garage. Beware though that many caravan tyre punctures result in too much damage for these products to work. Beware also that some tyre fitters may refuse to repair a tyre that has been filled with sealant. This is because the sealant can be difficult to remove to enable inspection and possible repair. 

Pre-puncture sealants may seem very attractive but the British Rubber Manufacturers Association (BRMA) specifically recommends against such products and the existing British Standard for tyre repair states that sealants cannot be considered to be a permanent repair under the terms of that standard. Another concern is the possibility of running round on a damaged tyre without realising it.

Tyre safety bands (e.g. Tyron bands)
These are designed to help keep the tyre on the rim following a puncture. They work by filling the well on the rim that is needed for the removal and replacement of tyres. If you have safety bands fitted do remember to keep the special Allen key to hand together with the (multilingual) instructions that advise tyre fitters how to remove and replace the bands when changing a tyre. Failure to observe these could result in tyre damage.

Inspection requirements
Like all tyres, caravan tyres should be inspected regularly for signs of damage or wear. Pay particular attention to the sidewalls as these are the weakest part of the tyre. Use a mirror to aid inspection of the side of the tyre facing the chassis. Any bulges indicate serious trouble and require the tyre to be replaced without delay.

Deterioration with age
There is clear evidence to suggest that older tyres have an increased likelihood of failure due to exposure to the environment. As a tyre ages its rubber becomes more brittle and the bonding of any steel reinforcing to the rubber can be weakened by moisture. (This moisture could even be in the air used to inflate the tyre.)

The Caravan Club recommends that caravan tyres should ideally be replaced when 5 years old but should never be used beyond 7 years old. They go on to recommend that tyres that need a high inflation pressure (say 50 psi or more) should be inspected for signs of deterioration from 3 years old and should never be used beyond 5 years. These recommendations form sound advice and are borne out by the experiences of our members, especially those who frequent the Continent during the hot summer months.

Also any minute cracking or crazing of the rubber in the tread grooves or sidewall (see below) is a sure sign that the rubber is deteriorating and the tyre should be replaced.

Tread & sidewall cracking due to environmental exposure to oxygen, heat and sunlight

This is all very well I hear you say - but how do I tell the age of a tyre if I’m not sure? The answer is to look for the DOT code that is stamped on the sidewall of all tyres. This gives information about where the tyre was produced and when. The last part of the code gives the date of manufacture. Since early 2000 this has consisted of four digits (against three previously). The first two digits indicate the calendar week of production, the next two the year. So, if a tyre is marked DOT T7E9 AM 2402 the last four digits mean it was produced in week 24 of 2002.

If your caravan's tyres are more than 5 years old this could be all they're fit for!

Legal requirements on tread depth
A caravan tyre is much more likely to need replacing through damage or age rather than tread wear. However, for the record, the UK requirement is a minimum of 1.6mm in a continuous band across the central three-quarters of the tread width, throughout the whole of the circumference. Some European countries are a bit tougher than this so, to be on the safe side, the BRMA suggests that the 1.6mm depth requirement be applied across the whole width of the tyre and not just the central three quarters.

Wheel Balancing
There is no need to balance a caravan’s tyres since any imbalance is unlikely to have a detrimental effect on towing performance or to be felt in the towcar. Despite this, I like to get mine balanced to ensure that the caravan has a smooth a ride as possible.

Conclusions
Punctures are inconvenient but blowouts can be very nasty indeed. Even if you manage to come to a safe stop the chances are that the caravan will be damaged in some way. I have known cases where extensive damage has resulted, rendering the caravan unusable and holidays wrecked. If you have any doubts about the condition of your caravan’s tyres get them replaced. You can’t put a price on safety