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Trailer Design & Technology
The main parts of a trailer, especially off-road trailers, are the structure and suspension design. Manufacturers have their own opinions about chassis design and choosing suspension design – some with prejudiced opinions on a particular design regardless of its actual real-world application. In fact, different chassis and suspension designs and types have their own advantages and disadvantages, otherwise the ones with disadvantages would fade out.
Buyers should be aware when coming across some prejudiced opinions only in favour of particular type of suspension or chassis design, because most likely they are leading you to what they can offer.
Chassis:
There are several key factors in chassis design and production. They are type and form of materials, size, wall thickness, layout of chassis, and the relationship between the drawbar and chassis. The optimal configuration is a balance between strength and weight.
Type/Form of material
Nowadays, manufacturers tend to use only RHS for making chassis rather than angle. The strength is determined by the area of cross section of the material, as well as its thickness.
Size/Wall thickness
Do you know that for a pallet racking beam of 2.4m long with two-tonne capacity, the wall thickness of the beam is 2mm or below. To increase the capacity of the pallet racking beam, all we need to do is enlarge the cross-section area (size) rather than increasing the wall thickness.
The reason is simple – enlarging the cross-section area makes the beam stronger without adding too much weight, and is also very cost effective. Over-engineering might ensure the strength, but it also creates unnecessary increases in weight, wasting petrol to tow and reducing the carrying capacity of the trailer. Ideally, materials shall be chosen to fit a purpose with sufficient surplus for unexpected conditions.
Layout/Relationship between drawbar and chassis
The layout of the beams on the chassis frame has an impact on the strength. A rule of thumb is to let the load be evenly spread through the whole chassis rather than concentrating on certain spots.
Quite often, you will see manufacturers mention about welding the drawbar to reach the spring hangers. This is true for heavy-duty trailers, especially those with heavy carrying on the drawbar.
There are two supporting spots (upward force) on the chassis – the spring holding spots and the tow coupling. There are also two load spots (downward force), and those are the area between the tow coupling and the spring hangers, and the rear section behind rear spring holding points.
The rear section can be easily neglected unless the user intends to concentrate excessive weight (in tonnes) on just that small section to travel off-road. The front loading area is much bigger than the rear section and too costly to neglect. For off-road use, we suggest using a triple drawbar to share the loads. Also, drawbar RHS shall reach the front spring hanger, and with the middle bar passing the front hanger, ideally reaching the axle axis.
Suspension
There are several major types of suspension systems on trailers, such as leaf spring, independent suspension with coil springs, rubber airbag or combination leaf spring etc. We cannot say one is better than the other is. All of these have their advantages and disadvantages on different applications and road conditions.
In most cases, a beam axle will be used with leaf springs. The problem with beam axle is stability when travelling off-road. No need to be an engineer, you can imagine how the trailer will behave when one side of the wheel hits a rock while travelling. It will bounce. Because it is a beam axle, when one side bounces up, the trailer might tilt over if the load centre of the trailer passes the load centre of the wheel. To avoid this, the user should drive slowly and carefully on uneven roads.
Independent suspension allows wheels on each side to act against the impact individually without affecting each other. Thus, in many cases, independent suspension is ideal for off-road (uneven road condition such as dirt tracks). It allows the user to move much faster off-road than a beam axle trailer.
Beam axle with leaf spring suspension is common on most of the camper trailers, simply because it is cheaper to build. The shortfall is that the beam axle reduces the underbody clearance that is vital for off-road towing.
Coil spring independent suspension can conquer lot of difficult off-road conditions with its independent handling of road surfaces. Replacing a coil spring is easy and inexpensive. A jack is the only tool needed to replace a coil spring. The cost for a coil spring is less than half of an off-road leaf spring with similar capacity. It also weighs about 20% of that of an off-road leaf spring with similar capacity, making it easy to carry a couple of spares while travelling.
We tend to use the old way – field-testing the trailer to find out the best configuration of materials rather than sitting in the office playing around with 'high-tech simulations', simply because it is realistic and reliable. Please check our photo gallery from time to time to see more action photos.
Materials
Currently, all our off-road models use DuraGal tubes and Zincaneal sheet to manufacture. The following photos show two pieces of metal sheet left outdoor side by side for one week after exposure to rainy days. The left (white colour) one is Zincaneal sheet, the right one (rusty) is Blackform sheet.
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Blackform metal sheet becomes very rusty after one week's exposure to rainy weather, while Zincaneal sheet has no observable change. Imagine if a trailer is built without using Zincaneal sheet – any stone chips on the trailer will become rusty very easily. The rusty area will keep enlarging, while a trailer built with Zincaneal will have much better rust resistance. This greatly reduces the rust problem and thus increases the lifespan of the trailer. The only weak spot on a trailer built with galvanised material is the welding spots, which could form rust if paint is chipped off.
Now, not just our off-road models will be built with galvanised material, but all our camper trailers will be built this way. |
Gap sealing
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