Trailers Design

During the years I have received a great deal of conflicting feedback from many trailer manufacturers over what I have written. Nevertheless I must report it as I see it. These are my opinions and are based on what I have heard through the bush telegraph about trailers; what makes them good, and what breaks when they break. My own experience of trailers amounts to towing large yachts, horse boxes and traveling with people who dote on their trailers. I do not own an off-road trailer and have no desire to. I would rather drive a bigger vehicle or carry less.

Suspension and chassis
The type of suspension is critical to the success of an off-road trailer. Trailers tend to bounce around a great deal so it must be built to withstand severe punishment. Suspension types range from torsion bar to leaf spring. Rubber torsion bar suspension is not an option, no matter how “heavy-duty” the axles is claimed to be. They all eventually fail in off-road use.
Leaf springs fitted with shock absorbers are the strongest and appear to work the best. Check where the springs mount onto the chassis – this is where breakage occurs and it must be reinforced. The chassis should be a rigid steel frame, steel tube or heavy channeling, extending all the way to the rear spring shackles. Springs mounted directly onto a stiffened load box are rarely strong enough. Breakages also occur at the joint between the A-frame and the load box and this should be reinforced.
Axle breakages often occur not because the axle is not strong enough but because the mounts aren’t. Should the mount slip or break the axles shifts and the wheels no longer run true. This
creates a build up of heat in the bearing which eventually ceases. When this occurs the hub shaft snaps from the overload. The failure is due to inadequate strength in the mount and not the axle’s
ability to carry a load.
Shock absorbers need to be fitted to leaf spring-sprung trailers. I recommend their use for two reasons; shock absorbers reduce bounce and reduce shock loads to the axle. Vertical wheel travel is of little importance in trailer design but the ability of the axle to absorb shock and not bounce is.

Tow hitch
The tow hitch is a critical component and badly designed ones break! The trailer’s tow hitch must be attached with high-tensile steel bolts. Mild steel bolts are not strong enough. Check your trailer’s bolts and change them if they are mild steel. Light-duty tow hitches welded onto the chassis draw-bar, which is the cheap way to build them, are not strong enough and many have failed in the bush.

Wheels and tyres
To improve stability on bush tracks the wheel track should closely match that of the towing vehicle’s. To avoid having to carry spares specifically for the trailer and to allow its wheels and tires to be interchangeable with the vehicle’s, they need to have interchangeable wheel rims with identical tire diameters. However, trailers with wheels that have a larger diameter than the vehicle’s will pull better through sand. If you can carry a spare specifically for your trailer, fit over-sized wheels and tires on the trailer. These tires can then be deflated to pressures below that of the vehicle and the trailer will cause far less drag.

Rust protection
Most trailers are stored outdoors and therefore are prone to rapid decay by corrosion and a trailer cover is a good idea. A stainless steel body is only necessary if you intend to use your trailer extensively on the beach. Galvanized mild steel is an excellent alternative and is almost as good, easier to repair and cheaper. For use inland, sealer-protected mild steel is fine if the trailer is stored under cover. Trailer components that seem to deteriorate first are attachments such as hinges and clamps. These should be stainless steel and attached with stainless bolts. When looking at the many South African off-road trailers, most manufacturers have placed rust prevention high on their priority list.

Stability at speed
Stability depends more on weight distribution in the trailer and in the towing vehicle than on trailer design. There is no simple way of testing a trailer’s stability at high speed other than to tow it yourself. Weight distribution is critical to stability. If you have deflated trailer tires to assist progress through sand, this will cause instability when you get back on the road. Remember to re-inflate your trailer tires.

Length
The distance from the tow ball to the trailer axle will determine ease of use. The shorter the distance the better it will handle off-road but the penalty comes with reversing and on-road stability. The longer the tow ball to trailer axle distance the easier it will tow in all conditions other than severe off road.

Over-run brakes
Many off-road trailer manufacturers omit over-run brakes or offer them as an option. This is because in very heavy dust conditions brake drums tend to fill up with sand which wears out the shoes. This only occurs in excessive dust conditions. If the wheels are as large as the vehicle’s, which they should be, the same dust problems occur to the vehicle brakes as well. If dust does become a problem simply remove the shoes from the drums and lock the brakes open at the tow arm, an hour’s job for both wheels. As for me, I would rather take the safe route and the unlikely risk of troublesome brakes than drive at 120kph with a ton of unbraked load behind me.
Another argument against the fitting of brakes is that when driving over uneven terrain the brakes engage and disengage as the trailer bumps around. All over-run brake systems are fitted with a locking device on the tow arm. This is a hinged piece of steel that wraps around the arm to prevent the brakes from activating when reversing. This must be engaged when driving over uneven ground where speeds are low and over-run brakes are no longer required.

Trailer manufacturers may place a weight restriction plate stating 750-kgs on a trailer capable of carrying a ton or more, because with a stated payload of over 750 kilograms the trailer must, by law, be equipped with a braking system. The choice is yours; are you prepared to take a risk and tow such a large mass without a braking system? Under normal driving conditions you may not realize the risk, but do an emergency stop and it could mean the difference between stopping clean or rolling your vehicle.

Jockey wheel
This wheel supports the nose of the trailer when standing alone. Because off-road trailers are often left parked on uneven ground, the longer the jockey wheel the better. It must be able to be removed completely and stored on the trailer when driving off-road. If it is simply raised, it is vulnerable to damage off-road.

Trailer-top racks and tents
A tent on a trailer is a excellent, practical idea because the tent need not be taken down when going on a game drive. The trouble is that unless the trailer has side access doors you are unable to get to the trailer’s contents once the tent is erected. A tent does raise the trailer’s center of gravity and those with raised tent platforms tend to be a bit top-heavy.

Auxiliary equipment
A vast range of equipment can be specified when ordering a trailer
as most manufacturers build to order. Articles fitted range from
built-in water tanks with camp showers, dual battery systems linked to the vehicle, fridge/freezer units and simpler items like Jerry can and gas tank racks.
In Chapter-8, I discuss in detail why it is a bad idea to locate a freezer in a trailer and why it’s even a worse idea to fit a battery in a trailer. Briefly, the long cables and trailer connector cannot take the current and the system works at very low efficiency. Freezers and batteries must remain in the vehicle. However, a series of power points and a fluorescent light fitted inside the lid and connected to the vehicle electrics is very handy.
Consider that the more you fit into your trailer, the heavier it will become and the more difficult it will be to handle in the bush.

Storage systems
Weight distribution in a trailer is very important. Some trailer designs have all the Jerry can brackets and water tanks fitted behind the axle which can cause low trailer hitch to total weight ratio. This in turn can cause instability, especially when climbing steep hills, where the trailer lifts the rear of the towing vehicle. I have seen a Pajero battling to get up Sani Pass, which is normally effortless for a 4×4, because its traction was seriously compromised by the badly packed trailer behind it. Consider carefully where the optional extras you choose for your trailer are fitted. Nose-cones storage boxes and boxes on the mudguards are very handy and must be dust-proof and lockable. Jerry can mounts on a trailer must be low down to keep center-of-gravity low. Trailers are ideal for carrying spare fuel.
If your vehicle carries its spare wheel on the tailgate make sure that it can be swung free with the trailer hitched on. Spare wheels carried here can make hitching awkward and any boxes, clamps or other attachments above the tow arm can make matters worse. Another reason for limiting attachments on the towing arm is that anything that could obstruct the wheel carrier from being opened can also hit the spare wheel when driving through a dip, when the trailer lifts and the vehicle drops. The option of removing the spare wheel carrier and placing it on the trailer is an alternative, but remember that the vehicle needs to carry a spare when the trailer is left at ‘base camp’.

Practicality
When judging if a trailer is suitable, open and close all of the boxes and the lid. Pretend you are at your camping site and you need to find something in the trailer. Many trailers are fitted with a tailgate – a very useful feature as you can pack traveling items such as the day’s lunch or a tool box at the back which can be easily accessed when traveling. Other features include cubby holes, exterior boxes or interior compartments, some of which are cleverly designed and some impractical for reasons such as a narrow aperture which become frustrating when packing and unpacking. Some trailers fitted with tailgates require that the roof be opened in order to open the tailgate. That is bad enough but some go even further in poor design – to open the tailgate the lid must first be opened. But in order to support the open lid the tailgate must be closed. Draw your own conclusions!