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TRAILER TYRES – THE FORGOTTEN LINK

The RV Daily Practical guide to modern towing: Part 5

Any car enthusiast forum will have lots of discussion on tyres, but that never extends to the trailer

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Nobody cares very much about trailer tyres, which is fine until you need to stop in a hurry, handle trailer sway, or a tyre bursts apart as you cruise down the freeway. It’s then that you realise the tyre is the sole link between the trailer and the road, and therefore the difference between a crash and a scare. So maybe we should give our trailer tyres a bit more love and thought than, well, never.

The basics of choosing a tyre for your trailer are the same as your car. The simplest and quickest way to replace the tyres is to ensure they are the same specification as the current tyre, and that means meeting three criteria.

Size: For example, 265/70/R17 (width, sidewall height, rim diameter)

Load rating: For example, 121/118 (two ratings, first one for two tyres on an axle, second for four tyres on an axle like you find on trucks. The 121 rating means a load of 1450kg)

Speed rating: For example, Q (this translates to a maximum speed of 160km/h)

You can find these specifications embossed on the side of the existing tyres, so simply find a tyre that matches those three ratings, or exceeds speed and load, and that will be a good start. There are numerous charts available on the web listing all the speed and load ratings. But of course, that’s not all.

The assumption made above is that the tyres already fitted to the trailer are in fact correct for the trailer, but given the lack of care taken with trailer tyres, that may not be the case. What you need to do is check the trailer placard, which will have the minimum requirements for load and speed rating, then fit tyres that match or exceed those.

The exact size of the tyre isn’t critical for trailers, unlike cars, so you can change the width and diameter a bit, but bear in mind that doing so may cause problems. For example, a shorter tyre will reduce ground clearance, a taller tyre may rub against bodywork under suspension compression, change the drawbar height and so on.

Once you have the basic tyre specifications sorted it’s time to look at construction and tread pattern. Construction is how strongly the tyre is made, and there’s two basic types: P for Passenger, and the stronger LT or Light Truck construction. For road-going use P is fine, but for off-road or dirt use choose LT. Some trailers may require LT tyres merely to handle the weight, or C-rated commercial light truck tyres.

The tread pattern will vary from a shallow, road-oriented tread to a deep, chunky off-road tread called a mud tyre. Now, you do see a lot of ‘off-road’ caravans fitted with mud tyres, often twin-axle units weighing around 3000kg. Frankly, a mud tyre on those big trailers is a waste of time and money and I believe it’s mostly done for show. You are not going to tow such a big trailer anywhere other than a dirt road, so your tyre choice should be optimised for bitumen with some dirt, and that means an all-terrain tyre at best. A mud tyre will be noisy, expensive, wear out quickly and won’t grip the bitumen as well as a road tread, particularly in the wet. Just don’t bother, albeit with one exception, and that would be to tyre match.

For smaller trailers like campers it is a good idea to match the tow car’s tyres and wheels to that of the trailer, so you can swap between them as needed. For example, if you run mud-terrain tyres on a 4WD, that would mean having exactly the same spec on the trailer. It should be stressed that this is ideal but not critical, given the puncture resistance of modern tyres. And generally, the smaller and lighter the trailer, the more likely it will be that you can tow it seriously off-road.

Another tyre selection consideration is the type of pattern: bi-directional or uni-directional. A uni-directional tyre is designed to operate forwards only, not backwards, and you see them on high-performance cars. The disadvantage is the performance in reverse, which isn’t a problem for trailers … but it does mean that you need two spare tyres as you can’t swap wheels left and right. It’s best not to use uni-directionals on recreational trailers for that reason.

Now we need to come to the single biggest issue with trailer tyres, and that is age. Tyres of any description should be replaced either when worn, or when too old, whichever comes first. In the case of car tyres the replacement trigger is almost always wear, so the concept of an aged tyre is never really considered. On the other hand, most trailers do far fewer kilometres than cars; sitting around for a while, towed to a campsite and then left, so it’s easy for a tyre to get to maybe seven or eight years old and have only covered a few thousand kilometres, leaving it looking new … when in reality, it’s deadly. Don’t neglect the spare either, as an old spare tyre isn’t really a spare at all, but merely a child’s swing seat mounted on a trailer.  

The problem is that like any rubber-based product, tyres degrade over time. They lose their natural oils and with it their pliability, becoming hard and unyielding. That means a lack of grip, and a weaker carcass, the result being potential loss of control, and even tyre failure. So what you have to do is make sure all your trailer tyres are no more than five years old, as a general rule. If you own a trailer, go outside now and check the tyre age before you forget (see the photo caption for instructions).  

To prolong the useful life of your tyres, you need to care for them. For example, when you’re not using the trailer, store it somewhere where it is cool, dry, and not exposed to sunlight. Also rotate the tyres; swap them from side to side and back to front. This is because every tyre on a trailer wears slightly differently, even those on a single-axle trailer, and a tyre becomes useless when it is worn. By rotating the tyres you even out the wear and prolong life.

Air inflation pressure is also critical for tyre life and safety. Every tyre will lose air over time, and an under-inflated car tyre is more easily noticed than an under-inflated trailer tyre, but the results are the same – poor handling, reduced grip, and a potentially overheated tyre leading to an explosive failure down the road … literally.  

The right inflation pressure for the trailer will vary for the same reasons as the tow car – the amount of weight on the tyre, speed of travel, and the terrain.  The heavier the load, the greater the tyre pressure, and the rougher the terrain, the less the tyre pressure and the slower the speed. Given the huge variety of trailers on the market it is hard to give specific advice, but if you work on a pressure rise of 2-3psi from cold to hot (after 30 minutes of driving) then that should be in the ballpark. Sometimes the tyre pressure in the trailer will be greater than that in the tow car, for example with a heavy trailer and light tow car … other times it will be the reverse, for example a heavy, modified 4WD towing a relatively light camper-trailer.

The bottom line is that tyres are easy to forget and year after year you ignore them, but then there’s that one time when you really need them to work for you and that’s when neglect will bite you, and hard.   

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