I am not an advocate for towing trailers off road. As explained elsewhere in my write-ups, our situation made the Land Rover Discovery 1 a very practical vehicle for our needs. However, it has just about no packing space and a trailer was therefore a must have for us.
Tow rimes with slow and for good reason. A heavy trailer behind a vehicle changes the handling dynamics drastically and while a trailer should be perfectly stable in a straight line, very little needs to go wrong to make it a real hand full.
I am often stunned by people claiming to have a vehicle that comfortably maintains 140 km/h with the off road trailer behind. Sometimes they even argue that a vehicle with a trailer stops in a shorter distance than a single vehicles. If you wondered, the latter has been proven many times - a vehicle / trailer combination can in fact stop in a shorter distance as a single vehicle but that is just about the only single advantage of towing.
Just keep in mind that a loaded off road trailer with tent, water fuel, food and clothes, easily weighs over a ton. The fact that your towing vehicle may be about double that weight, should not be used to fool yourself that it cannot do much to your vehicle.
Beware! A trailer can swing like you have not imagined is possible in your wildest dreams. If you get to tyre marks in the roads with alternating half moons going left and right then you know who ever was the driver, Supervan or not, had brown undies.
Apologies for being boring again, but very first of all, keep the speed down. With a heavy trailer behind, the maximum recommended towing speed on good tar, is 90 km/h. Yet, you will be surprised how little time you will "loose" instead of trying to tow much faster.
On gravel, it is usually recommended that a single vehicle not travel faster than 80 km/h and with a trailer, you need to be even more careful. There is no reason though not to see it as a golden opportunity to enjoy the surroundings so much more and drop the speed to say 60 km/h. You will soon learn that damaged sections in gravel roads in any case, slows you down to walking pace.
Straight Line Instability
A trailer should be perfectly stable in straight line and there should not be a trace of sideways movement in the mirrors. If it is not, you have trouble that needs to be addressed on the spot.
Usually, instability of trailers in a straight line is due to following:
The trailer runs head up. This is particularly dangerous when you need to brake hard as the trailer will try to lift the rear wheels, making the tail of the vehicle very light. This needs to be rectified with a drop plate and the trailer should be level at worst, but preferably slightly nose down.
There is too little weight on the tow ball. For a 1 ton trailer, the tow ball weight should be about 75 kg. It is important to mention that the pivot of trailer weight distribution, is the axle. In other words, the axle is your reference point when you load your trailer. You can measure the towball weight by putting the nose wheel on a bath room scale. The balance can be altered by moving heavy items like the tent, forwards or backwards in relation to the axle. If any item is exactly above the axle, it will not alter the towball weight. Move it backwards and the towball weight will become less. Move it forward and it becomes heavier. That is why things like tanks with variable loads like water and fuel, should be loaded with the middle above the axle.
The trailer is loaded too heavy on one side. This could be hard to identify, but at least stand behind it and see if it sags more on one side.
Uneven tyre pressures. Take the gauge and measure. This can upset the trailer and is easy to rectify.
Even though a trailer should be perfectly stable in a straight line, it is also just about the only place where it is perfectly stable. This is then where driving technique comes in. Once a trailer gets unstable, there is very little you can do to make it stop, therefore the best way is not to get there.
With a trailer behind, everything you do needs to be slower, more controlled and smoother than with a single vehicle. If you brake, you do it gentle, if you change direction, you do it gentle. Think of it like dancing with a rather fat partner.
Sudden side wind gusts is a common occurrence and have many reasons. There may be a strong wind from the side that is broken when you pass a big truck. There may be no wind and just a sudden unexpected draft. Bridges over rivers for example, are well known to be spots where powerful crosswinds are generated.
A trailer is often excited when one wheel hits a big pothole.
Another important cause for instability is going down hill as insignificant as it may seem. Braking hard going down hill often induce swinging and for some reason, overtaking another vehicle going down hill could induce violent swinging so even though this may look like a golden opportunity to get in front, it is not a great idea.
Similarly, breaking hard in bends - especially shorter bends - could easily cause a jackknife. If you can, only brake in a straight line.
How to Handle Instability
With a mild swing, put the right foot in deep and see if the power can pull the rig straight. Once it is straight, reduce speed, stop and try to find if the cause. If the power does not work almost immediately, reduce it smoothly and let the wind do the braking until you can stop.
But, lets assume you did your best to prevent getting into trouble and eventually the tail wags the dog - the kind of wag that you could swear you read the number plate of the trailer in the mirrors. What then?
As sickening as it may sound, you do absolutely NOTHING! You simply keep all your wits together and keep the steering as close as possible to straight as you can and pray for friction to damp the motion. It is a horrible experience and one that makes you cold down to the feet.
In particular, don't brake. Don't try to counter steer the swing since the whip in the back moves considerably faster than the reaction time of most mortals. And if that all happens in a bend, I really have no advice for you apart from hoping for a miracle.