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Thirteen years after the launch of the Monroe Gas-Magnum 4x4(r)
shock absorbers, Tenneco Automotive - a world leading manufacturer of
ride control systems - introduces a range of innovative shock
absorbers for off-road vehicles, the Monroe Adventure(TM), designed
to meet the needs of a rapidly growing off road car park.
In studies of the off-road market, Monroe found out that only 10%
of these vehicles are driven off road, while the majority (90%) are
actually driven on road. Suspension therefore, originally designed
with a high rigidity in off road vehicles for absorbing the impact of
rough terrain, would have to provide increased comfort for on road
In designing its new 4x4 shock absorber, Monroe has tried to find
innovative solutions to combine safety and comfort both on and off
road into a single all-purpose shock absorber. The result is the new
Monroe Adventure(tm), a monotube shock absorber which ensures the
driver's safety and comfort on different road surfaces and various
driving conditions, and whose high performance remains unaltered
throughout its entire life.
But why choose a monotube shock absorber? The monotube design
exposes the shock body to maximum airflow, lowering the operating
temperature of the internal components and fluid, thereby extending
the life of the shock absorber. In addition, this particular design
allows for a corresponding larger piston (46 mm in diameter instead
of the 34.9 mm of a twin-tube shock) therefore allowing higher
sensitivity to wheel motions.
Inside the shock absorber, the nitrogen gas (which unlike air,
does not change temperature when compressed) is separated from the
superior grade oil by a specially designed, close tolerance, floating
piston. This provides a constant pressure of 360 psi (20 bars)
against the hydraulic fluid, absolutely eliminating any contact
between gas and oil and the performance loss that is common to
conventional twin-tube shocks, as the emulsion provoked by
overheating creates micro-cavities (the emulsion/cavitation
phenomenon) which prevent the smooth operation of valves.
The total elimination of foaming results in uninterrupted damping
for even the smallest wheel deflections (2 mm): performance which no
other type of shock can match.
The self-adjusting working piston (46 mm in diameter), with
spring-steel valving discs, precisely regulates oil flow for optimum
compression and rebound control. There are no check valves or springs
to wear out.
A high-viscosity superior grade oil guarantees uninterrupted and
optimal damping at different temperatures ranging from -40°C to
+120°C. When driving an off-road vehicle in particularly dry areas,
the shocks temperature can even reach 100°C.
The piston rod, with a diameter of 14 mm (unlike the conventional
models currently available on the market, which have a diameter of 11
mm) is hard-chromed uniformly without intermediate layers, and is the
strongest in the industry. The self-lubricating rod guide and end
seal insures longevity and prevents leakage, as well as corrosion and
The tube wall has a thickness of 2 mm (against the 1.27 mm of
conventional twin-tube models), therefore the damage provoked by
stones or external blows is drastically reduced.
These unique design features function in unison to allow Monroe
Adventure(TM) shocks to operate at peak performance levels for life.
The Monroe Adventure(TM) shock absorbers ensure five innovative
* Better heat dissipation
A shock is an energy converter. Spring energy has to be converted
into thermal energy and the resulting heat has to be dissipated as
quickly as possible.
A shock absorber's effectiveness is directly proportional to its
ability to dissipate heat, since a "hot" shock quickly loses its
In conventional twin-tube shocks, the heat must pass through two
tubes. New Monroe Adventure(TM) monotube design results in a cooler
running, more efficient and durable shock.
* Innovative piston design
The greater piston area - as a result, among other things, of the
larger space available in monotube shocks - provides greater
sensitivity for small piston movements to achieve effective damping
at wheel motions as small as 2mm.
* Lighter weight
The reduced "unsprung mass" allows wheels and tyres to respond
more readily to surface irregularities for improved control.
Additionally, by reducing the unsprung mass, wear and tear on
suspension and steering components is reduced.
* High-pressure gas
The permanent pressure exerted on the oil by the gas ensures
instantaneous response as well as a smoother operation of piston
valves. In addition, the gas pressure eliminates cavitation and
foaming phenomena which could compromise the shock function, in
particular under severe driving conditions.
* More safety
All these characteristics ensure safer driving conditions both on
road and off road, as well as higher comfort.
"The tyre to road contact is increased under any driving
condition, both on road and off road" says Jean-Pierre Dolait, Vice
President of Tenneco Automotive Europe's Aftermarket Sales and
Marketing division. "In the case of an emergency stop, the braking
distance is strongly reduced. A safer journey is also guaranteed
under diverse weather conditions such as rain, wind, snow and ice.
The new Monroe Adventure(TM) shocks - concludes Dolait - indeed allow
for better vehicle control on the road as well as in extreme
"The new shock absorbers designed for off-road use - underline
Tenneco engineers - protect all the fundamental components of the
vehicle, tyres included, against early and hazardous wearing."
Monroe Adventure(TM) does not need manual adjustment to compensate
for wear or for varying road surfaces. The shock responds
instantaneously to the speed of suspension movement to provide the
exact damping characteristics required for maximum control, safety
and performance. But, how has been possible to achieve all this?
A piston fixed to the car body by the piston rod slides into oil
filled cylinder that moves together with the wheel. During that
movement calibrated openings in the piston allow the oil to pass
between the upper and lower chamber of the cylinder, so damping the
oscillation of the spring. The monotube shock absorber contains at
one end a small quantity of an inert gas (nitrogen) under high
pressure (20 to 25 bars). A floating piston separates this gas from
During the compression stroke, the rod changes the volume
available for the oil, which compresses the nitrogen. During the
rebound stroke, the rod moves out again, and the gas pushes the
floating piston back to its original place.
The force generated by the damper during its rebound or
compression stroke must be variable in function of the vehicle speed
and of the road surface. The reaction forces must be able to control
the car body movements on motorway at high speed as well as the fast
movement on a bad road at low speed and still providing the best
compromise between comfort and road holding.
The Monroe Adventure(TM) shocks have 3 stage valves to provide the
ideal damping under all circumstances. The first stage corresponds to
the low piston speeds (motorways), the 2nd stage to the medium speeds
(standard or dirt roads) and the 3rd stage to the high speeds
The monotube valving functions as follows:
1st stage (low piston speed): When for instance the shock absorber
is slowly extended, the piston and the rod move upwards and force oil
to flow from the upper chamber to the lower chamber through the
piston valve. It flows successively through the holes in the piston
and through the constant orifices (bleeds) shaped in the discs at the
bottom of the piston. Due to the very small size of the bleeds, the
flow resistance of the oil increases rapidly with the piston speed.
2nd stage (medium piston speed): When the piston speed increases,
the pressure is high enough to lift the discs The damping
characteristic is now linear.
3rd stage (high piston speed): When the piston moves very quickly
into the cylinder, it is necessary for the damping force to increase
rapidly as well to prevent topping. So, at that moment the discs are
completely open and their limited opening now form a restriction that
builds up a higher resistance for the oil flow.
The permanent pressure exerted on the oil by the gas guarantees an
instantaneous response as well as quieter operation of the piston
Monroe has always invested a large part of its resources in
offering the best coverage in the industry.
Hard work of research, market analysis and new vehicles
identification are the key for Monroe to offer 96% coverage for 4x4
Generally speaking, shock substitution frequency depends on the
use of the vehicle and the conditions of the road surface. On
average, shock absorbers should be replaced every 50,000 kms, and
checked every 20,000 kms. Drivers are recommended to replace all the
shocks fitted on the same axle at the same time, similarly to brake
disks and tyres, because for increased safety, the shock absorbers on
the same axle must ensure identical performance.
Tenneco Automotive headquartered in Lake Forest, USA is the
world's largest producer of ride control and emission control
products under the Monroe(R) and Walker(R) brand names. With 23,000
employees and a turnover of USD 3.5 billion, the company has over 100
facilities in 22 countries in North and South America, Europe,
Africa, Australia and the Far East.
ots Originaltext: Tenneco Automotive Europe
Tenneco Automotive Europe
Tel. +322 706 9147
Fax +322 706 9199