Air Suspension Code

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Introduction
Over the past 20 years suspension design changes, more durable components and
operational needs have evolved to where the industry today has largely taken up air
suspension, often considered to be “road friendly suspension”.
Reasons for this large scale uptake in Australia vary, but include:
1. Various comparative testing by road agencies has shown air suspensions to be the most
road friendly, hence the now common reference to “road friendly suspensions”. Some
mechanical suspensions have now been tested and found to meet the road friendly
performance criteria.
2. Manufacturers have built a greater degree of durability, with longer warranties,
extending vehicle component life, giving improved resale values.
3. Reduced vibration and shock loading giving better cargo ride through superior load
springing and the lower natural frequencies of air suspension systems.
4. Improved driver comfort, and road holding, loaded or empty.
5. Improved braking, as a non-reactive system, no axle-hop, assisting the operation of load
proportioning valves in certain cases.
6. The biggest incentive in Australia to use air suspensions has been the prospect of higher
mass limits.


Code Purpose
This code recommends practices and procedures that will help the vehicle owner, maintenance staff
and drivers to better understand the operation and maintenance of air suspensions.
The Australian Road Transport Suppliers Association (ARTSA) membership includes not only major
heavy vehicle suppliers but many major component manufacturers and suppliers to the Australian
heavy vehicle market. ARTSA sees this code as a positive step to improving wider understanding
among all levels of road transport industry personnel.
This code has been prepared with input from various ARTSA members, the Australian Trucking
Association (ATA), and other contributors.

Suspension Certification
The Department of Transport and Regional Services, Vehicles Safety Standards Branch manage
a certification process that identifies “Road Friendly Suspensions – Performance and Component
Requirements”.
These requirements apply to all new suspension systems put into service after January 2000, with
a “Road-Friendly” suspension classification as set out in performance standards developed by the
National Road Transport Commission. (See glossary.)
Road-Friendly Certificate Numbers (RFCN) are issued, identifying the original equipment supplier with
an RFCN, after the submitted suspension passes the required test. The supplier identifies the approved
suspension with a label or plate in accordance with that supplier’s component traceability procedure.


Principles of an Air Suspension
The first “air-spring” patent was issued to John Lewis of New Haven Connecticut in 1847. The history
of air suspension shows the first early development on production passenger cars in 1914. Further
development progressed during the early 1950’s with the GM Greyhound buses and GM parlor car
passenger rail carriages. After early difficulties, air suspension has finally gained wide acceptance
on trucks and trailers.
A heavy vehicle suspension system’s basic design function is to attach the axles to the frame of the
vehicle and to equalize or distribute vehicle weight in specific ratios between axles. Vehicle weight
distribution becomes extremely important during brake applications, cornering and whilst negotiating
uneven surfaces.