What makes a
good off road trailer?
It can be a
little daunting buying your first camper trailer or perhaps
upgrading to an off road model, not knowing what components make a
good camper trailer or more importantly one that will handle the
tough outback conditions & not let you down. Forums such as the
Australian CamperTrailers Group make an excellent resource to
gain a little knowledge before that big outlay. Although the group
does not push one brand over another, we
hope we can steer prospective owners in the right direction & help
them make an educated decision.
There are a few points to consider
which makes a good off road trailer stand above an on road trailer
design. Setting up a camper trailer to handle the harsh off road
conditions is more involved than just throwing a set of heavy duty
springs under it. Axle, suspension & bearing selection all play a
vital role as well as the chassis they are connected to. On road
trailers are commonly built from lighter RHS (Rolled Hollow Section)
than that of a purpose built off road trailer and are generally
considered too light for such work.
The first question that you should ask yourself is
WHAT WEIGHT LOAD WILL YOU BE CARRYING??? From
there you can work out your suspension requirements, axle weight &
chassis. The chassis is the
foundation of a good off road camper trailer. A full chassis is your
best option for strength. The chassis rails could be built from say
60x60x4 RHS, the cross members 50x50x4 RHS and the A frame from
75x50x4 RHS. Spring hangers have been known to tear clean out of
thin walled RHS in corrugated conditions.
frame. It is a good idea to
position the A frame back to the front spring hangers for maximum
strength and from RHS of a larger vertical dimension than that of
the main chassis, as in the dimensions above. The National Code of
Practice booklet ‘Building a Small Trailer’ which is available from
motor registries, states drawbars must withstand certain forces
applied at the centreline of the intended coupling without
detachment or any distortion or failure which will affect the safe
drawing of the towed trailer:
tension and compression (N) .............................. 1.5 x
9.81 x ATM (kg)
.............................................................. 0.5 x
9.81 x ATM (kg)
and compression for rigid drawbar trailer (N) 0.5 x 9.81 x ATM (kg)
The length of the A
frame can be governed by what you want to carry on it, but keep in
mind not to overload the ball weight. More on this later. In extreme
off road conditions the shorter the A frame the better with a
minimum ball weight of around 10% to 15% of the trailers overall
Leaf, coil or rubber sprung??? Each have their good & bad points,
but having any suspension too stiff is just as bad as having it too
soft. There is no comprise, you must have it right. Either too soft
or too heavy & the suspension over the endless corrugations will
shake everything to pieces inside the trailer as well as the trailer
itself & can cause components to fatigue & break. This either takes
a lot of skill, knowledge & expertise to get right or a longer
process of trial & error. Start by calculating your intended trailer
weight & load & go from there.
Slipper springs are not the right choice for off road work. The
majority of off road camper trailers use eye to eye leaf or
independent coil suspension.
shockies Shock absorbers
play a very important roll as part of the integral suspension of an
off road trailer, especially when traveling on our very rough
corrugated roads up north. Shockies on the suspension for kilometre
after kilometre of corrugations are essential. Shock absorbers help
in the rebound of the springs/coils. Without shockies the spring
will rebound with equal force to that it was depressed resulting if
fatigue of components & eventual failure.
A type of leaf
suspension with small reverse leafs positioned on the top side to
reduce the rebound force of the main leafs are known as rebound leaf
suspension and do a similar job to that of a shock absorber.
axle weight Under estimating
the axle weight could see you with a bent axle. Around 1300kg is a
good starting point for an off road trailer. You will need to
reassess your axle weight to safely carry extra loads like a boat,
outboard, fully loaded box on the A frame with food stuff and fridge
The axle chart at
http://www.campertrailers.org/axles_bearings.htm sets out
recommended axle size to weight carried. You will notice there is a
maximum distance from the chassis to the centreline of the tyre
before load capacity is reduced. These charts have been reproduced
with permission from Vehicle Components.
bearing size The size of the
bearings in relation to load weight is an important issue as well.
The chart on the above page will also give you a recommended bearing
size to load carried. Overloading your trailers wheel bearings may
see them collapse at the most inopportune time leaving you stranded
on the roadside miles from anywhere. It is always a good idea to
carry a spare set of wheel bearings in your spares kit & know how to
With the major structural components taken care of we will look at
other factors which add to make a reliable bulletproof trailer which
handles all conditions.
Painted or galvanized. Painting has its merits. You can weld
additions at a later date and then camouflage it with a simple touch
up. Gravel roads sandblast the trailers underside removing all
traces of paint. You will need to maintain the steel underside &
watch for rust.
stands up to the elements more, especially if you camp on the beach,
however you need to be careful not to break this coating if adding
items at a later date. It is better to bolt on attachments in these
Having the same tyre/wheel combination on your trailer is another
good idea along with a spare for the trailer if you are intending
touring the remoter areas of our great outdoors. With two wheels
interchangeable around the whole rig and a good tyre repair kit you
should be able to get out of most situations.
track If you are going into
the desert or on the beach it is a good idea to set up your trailers
track the same as the tow vehicle. This will reduce extra drag &
reduce fuel consumption.
ball weight A good rule of
thumb is to have around 10% to 15% of the trailers weight on the
towball. This will ensure it has a good forward tracking motion. Tow
ball weight is not only an important aspect to the small & medium
sized vehicle, but the larger vehicles as well. Make sure your
vehicle manufacturers towing specs, as well as your towbar are rated
for which camper you have in mind as this could void your warranty &
insurance if overloaded.
weight distribution Weight
distribution is also of importance as this will also govern the
tracking performance & trailing characteristics of the camper.
Thought must also be given when packing the camper. We usually pack
items one by one & the overall weight is not felt until the camper
is hooked up & towed.
An old mate of
mine used to build box trailers for a living. The theory used to
locate the axle was an old 'rule of thumb measurement' as a rough
guide. The axle offset toward the rear of centre is an inch to the
foot. That is if the trailer is six foot long, then the axle offset
will be six inches off centre toward the rear of the trailer. This
measurement is regardless of A frame length. He said this would
allow the trailer to track well behind your vehicle. Most trailers
he built were of the 'garden box variety' and used to get a load of
sand or gravel & take stuff to the tip.
As you know with camper trailers all sorts of gear of varying
weights are loaded into the camper trailer so careful thought must
be given when packing to give the camper the recommended 10 to 15%
ball weight. Underslung waters tanks can be anything from 60 to 120
litres, jerrys for fuel & water on the front or sides, weighting
around 1kg per litre. The above rule of thumb can be used as a
starting point to located your axle taking into account loaded
toolboxes, battery location, water tanks & fridges etc especially
when forward of the axle.
You can quickly add weight to the drawbar by adding things
like batteries, front mounted fridge boxes & pantries with canned
food, tool boxes, spare wheel & out boards, so a little thought is
needed to loading this area up. A toolbox mounted to the A frame is
a good idea for extra space, but don't forget that everything you
put in the box & therefore onto the drawbar will affect the towball
weight of the trailer & result in the trailer becoming 'unbalanced'.
With an off-road camper trailer it is a good idea to have your hitch
light enough to lift. A situation may arise where you might have to
manhandle it in a recovery or even where you store it, like dragging
it out onto the grass etc.
Canned food is heavy & will quickly add to the weight. Water
& fuel weigh about 1kg per litre & a 10Rx15 tyre & steel wheel
combination weighs 30 kg. Just by adding the 3 jerrys + 60 litre
water tank + spare tyre = 180 kg for starters. Then there's the bbq
plate, camp ovens, spade, axe, recovery gear, batteries, tools &
spares. Before you know it the trailer weighs a tonne plus. And
don't forget the boat & outboard. Are your axle & bearings rated to
carry such a load???
It will only cost you a small fee to have your camper trailer
& ball weight weighed on a public weight bridge. You can find these
in your local area listed in the yellow pages under weighbridges.
National Code of Practice ‘Building a Small Trailer’
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