Most tow vehicles come with factory standard
suspension and that suspension may need to be
upgraded to take the weight of your caravan, 5th
wheeler, travel trailer or camper trailer.
Suspension upgrades are also required with the
installation of long range fuel tanks given the
weight of the extra fuel.
The vehicle suspension comprises springs, shock
absorbers as well as linkages such as wishbones,
control arms and rods that connect the vehicle to
its wheels. Torsion bars, commonly found holding up
independent front suspension, are straight round
bars held to the frame of the vehicle at one end and
the lower wishbone at the other use the twisting
properties along the bar as a spring force. All
these components are designed to allow the wheels to
go up and down and maintain their road contact
angles.
Springs
Springs are the devices that absorb shocks and the
spring rebound is controlled by shock absorbers
(often referred to as ‘dampers’). Most springs
today are powder coated to assist resist corrosion
as well as for aesthetics.
Leaf springs
comprise several layers of metal leaves
which are bound together so they operate as
a unit. The number of design variables is
quite large with variations in leaf width
and thickness. You can obtain a ‘two stage’
leaf pack with a smooth ride on the primary
stage when the vehicle is unladen and when
laden additional support is provided with
the secondary stage employed.
Coil springs
are the most common type of suspension and
they expand and compress to absorb the
motion of the wheels. Constant and variable
rate coils are available. Variable rate
coil springs provide a reasonable balance
between load carrying capacity and ride
quality. They provide a variable rate of
resistance to help reduce side sway, sagging
and unequal weight distribution in your
vehicle and provide a more comfortable ride
than leaf springs.
Given a tow vehicle will do more laden trips you
would fit springs with a higher rate to the rear.
The coils can vary both in length and the number of
spirals. The ‘spring rate’ will determine how firm
or soft your ride is. The ‘spring rate’ is measured
in newtons per millimetre (N/mm) with 10 newtons
being about 1 kilogram this being the units of load
per units of distance so springs with a higher rate
will not compress as much as the standard springs.
When selecting quality suspension coils you will see
terms such as:-
‘Shot peened’ – which is a process of work hardening
and pre-stressing a material to create a harder and
more durable material and
‘Scragging for Quality Control’ - which is where the
coil spring is compressed beyond its yield point to
set up residual stresses thereby increasing the
elastic limit of the spring.
Most shock absorbers(discussed in more detail below) are
speed sensitive and laden touring tow vehicles
driven on corrugated roads will benefit from heavy
duty or multiple shock absorbers. Heavy duty or
multiple shock absorbers help reduce shock fade
which occurs with the heating of the shock’s oil
beyond a reasonable temperature by rapid compression
and rebound of the suspension.
By raising the suspension the transfer case is
raised relative to the differentials and that then
increases the prop shaft angle and increases the
work demanded from the universal joints each end.
Once the rear suspension has been upgraded the front
torsion bars can be wound up to match the suspension
height to make the vehicle look even. However,
winding up the torsion bars will then restrict the
amount of drop your front wheels may have.
Toyota
Landcruiser 100 series have independent front
suspension (IFS) and adjusting the height of the
vehicle will put more stress or load on the front
torsion bar mounts. Accessories such as bull bars,
extra batteries and compressors added to the front
of the vehicle will add extra weight and
subsequently extra load to the torsion bars and
their mounts. A specific problem to the LC 100 is
cracking of the lower suspension A-arm and this is
caused by the suspension bottoming out and hitting
the bumpstop hard. Fitting of a brace between the
torque arm and the control arm is recommended.
Braces are available from Pedders and ARB.
Another solution, used by ATS Geelong, is to
put the lift in but lower the front
differential by about 25 mm by using a new
bracket. By doing this it reduces the angle
the CV joints need to work at thereby
reducing the chance of breakage.
A wheel alignment should be done to complete
this exercise.
The
replacement front bracket lowers the front
diff by 25mm
Shock absorbers
Shock absorbers control the spring
rebound or bounce so it is important
the shock absorber is the right
length and has enough ‘travel’ in
compression and rebound to provide
the dampening effect. A piston
moves inside a gas or oil filled
cylinder and the hydraulic fluid is
forced through tiny holes in the
piston head as it compresses and
rebounds.
Some shock absorber brand names are
Old Man Emu, Monroe, Bilstein and
Rancho shock absorbers.
Bushes
All suspension arms that pivot, as the wheels move
up and down, run on rubber, polyurethane or nylon
bushes. These bushes assist to insulate the body of
the vehicle from harsh vibrations. As they wear
vibration starts to creep in and the suspension arms
are no longer in the ideal position to hold the
wheels due to the extra movement of the worn
bushes. As a result, handling performance suffers
and tyre wear increases.
Polyurethane bushes are generally stiffer and last
longer than the rubber bushes and work very well
when lubricated.
Air Bags or Air Springs
Pneumatic airbags can be used as a way to carry
loads such as caravans, 5th wheelers and
trailers without having to fit stiff springs. Air
springs are preferred by some as they are adjustable
by inflating or deflating the air bag. Air
suspension kits are available to assist coil or leaf
suspensions. Air bags can be mounted inside
existing open coil spring suspension and accessories
are available to inflate and deflate the bags from
the comfort of the inside cab of your vehicle.
Some brand names for air springs are Firestone
Coil-Rite, Air Bag Man and Polyair Springs.
Firestone Ride-Rite kits are available for leaf
suspension.
Polyair bags have a low air pressure requirement and
can be filled with air from a hand pump or service
station air hose. The manufacturer states they are
made from
highly durable space age urethane material and when
properly inflated will provide years and years of
trouble free service.
Steering Stabilisers
Steering
stabilisers are basically a shock absorber for the
vehicle’s steering system specifically designed to
operate horizontally. Although some 4WD vehicles
have factory fitted steering stabilisers aftermarket
kits are recommended if your vehicle is fitted with
over-sized tyres or a winch. Fitted to live-axel
4WDs steering stabilisers dampen jolts and wheel
shimmying on rough roads or hard impact like
potholes and help stop the steering wheel jolting
out of your hands.
Adjustable
Panhard rods can also be fitted to stop side to side
axle movement. A Panhard rod attaches to the axle
on one side of the vehicle and the frame on the
other side and may be fitted to the front and rear
of a vehicle.
Suspension upgrades should be completed by a
professional. Suspension kits are available from
ARB, TJM, Opposite Lock and other 4WD specialists.
Popular modifications to improve ground clearance
for 4WDs including raising the suspension can have
other implications and if an engineer’s certificate
become necessary very few insurance companies will
provide cover for your vehicle.
For further details do a Google Search
at the top of this page.
Toyota
Landcruiser 100 series have independent front
suspension (IFS) and adjusting the height of the
vehicle will put more stress or load on the front
torsion bar mounts. Accessories such as bull bars,
extra batteries and compressors added to the front
of the vehicle will add extra weight and
subsequently extra load to the torsion bars and
their mounts. A specific problem to the LC 100 is
cracking of the lower suspension A-arm and this is
caused by the suspension bottoming out and hitting
the bumpstop hard. Fitting of a brace between the
torque arm and the control arm is recommended.
Braces are available from Pedders and ARB.
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Steering
stabilisers are basically a shock absorber for the
vehicle’s steering system specifically designed to
operate horizontally. Although some 4WD vehicles
have factory fitted steering stabilisers aftermarket
kits are recommended if your vehicle is fitted with
over-sized tyres or a winch. Fitted to live-axel
4WDs steering stabilisers dampen jolts and wheel
shimmying on rough roads or hard impact like
potholes and help stop the steering wheel jolting
out of your hands. 
Adjustable
Panhard rods can also be fitted to stop side to side
axle movement. A Panhard rod attaches to the axle
on one side of the vehicle and the frame on the
other side and may be fitted to the front and rear
of a vehicle.