You and the revolutionary Polyair Spring

Trip leader Bill Gant recommended, in fact insisted, at a pre-trip get together that Polyair bags were essential for a safer and more comfortable desert crossing.

Initially, I was a “doubting Thomas” and thought I could make a saving of about $400 by not installing these air adjustable bags which fit inside the rear coil springs. But a late decision to follow the experienced advice of Bushman Bill was not regretted. They did, as their advertising claims, improve handling in rough conditions, allowed load levelling with easy inflating, and I am certain they improved vehicle safety in the much less than ideal track conditions in the desert.

The use of additional polyurethane air bags are not a recent innovation, having been developed about forty years ago. What has changed is the more effective marketing and the word of mouth recommendations by users travelling in the outback.

The available literature suggests airbag-supported coil springs help prevent bottoming out and provide extra loading by as much as 500kg. I especially valued their use in avoiding bottoming out on the Simpson’s sand ridges and the protection they afforded the shock absorbers. I hate to think of the discomfort of our trip if we had not had the Polyair bags.

We saw at Birdsville what looked to the novice to be a Rangie overloaded on the roof rack, in the interior and on the extended rear bumper bar which was piled with fuel tanks. This lop-sided RR was about to tackle the desert, presumably without Polyair bag assistance. We saw it later, near Dalhousie, and not surprisingly it had had to shed load to travel comfortably and avoid damage to the vehicle.

A big advantage of the bags is you can easily adjust uneven weight distribution: a boon especially when towing. For normal city use they are recommended to be inflated to 4psi. An excellent gauge, accurate at low pressures, is available from the suppliers for $36.

So Bill’s advice was correct: all RRs on the desert trip had Polyair bags fitted and the promotional material advertising the load levelling, the additional weight carrying capacity, support for springs and shocks, prevention of a lot of the bottoming out ­ a Simpson Desert curse, the reduced vehicle sway, were all evident to our drivers.

The kits can be installed by most handy-people and this of course reduced the cost quoted above. Additional claims are made by the suppliers who quote a 12 months/20,000km warranty. Unquestionably the Polyair bags were helpful in making our Simpson crossing much better than would otherwise have been the case. Our “trippers” recommend them to members making plans which will lead them along challenging 4-wheel driving tracks.

Peter Robinson

1. The air bags were fitted to vehicle number 48074 and pumped up to 30psi. The bags were easily fitted in approximately one hour by unit vehicle mechanics.

2. The unladen vehicle gained stability on curves and corners with much reduced body roll and more positive steering. Travelling any distance was a much more comfortable experience as constant corrections to the steering was eliminated due to the fact that straight line tracking was improved and the vehicle did not continually try to change lanes without the driver moving the steering wheel.

3. The modified vehicle was loaded with 45 twenty litre water jerries with a total weight of 900 kilograms, this was also loaded into a standard 110 Landrover.
The distance between the bumper rubber and the rear axle housing in an unladen standard Landrover is 159mm and an unladen modified Landrover is 163mm.
Fully loaded, the standard 110 is 89mm and the modified 110 is 105mm. The extra height gained and the firmer suspension dramatically increased vehicle stability and handling when driving fully loaded and used in the off-road conditions it is required to be used in.

4. Overall the air bags improved the vehicle’s steering, handling and stability to the extent that I feel that the vehicle is safer and instills a higher level of confidence in the driver, and the sooner the modification is implemented the better as the vehicles will be less prone to accident damage.

J. P. Salter
LtCol
CO 1RAR

A long standing problem has existed with weight distribution of F series ambulances. The right hand side of the unit weighs approximately 300kg heavier than the left. All gases are stored on the right side and added to this fact, the main stretcher is located on that side, plus driver and attendant seats. In the past, to overcome this problem the right hand main leaves were upgraded to 10mm and air shocks were fitted in place of standard heavy duty shocks. This only lasted approximately 20,000km then started to sag, so the process had to be repeated.

We were introduced to Polyair 19th May 1993, when they were fitted to Unit 33 as a test case. We ran pressures of 10psi on the left hand side and 15psi on the right. This levelled the rear and also improved the patient ride.

Reports from ambulance officers show it also improved the handling of the unit, for example, cornering and weaving in and out of traffic. The air bag stopped all excessive roll of modular, which is a major factor in resuscitation procedures undertaken in the back of the unit. On the basis of reports from ambulance officers every ambulance in the St. John fleet Northern Territory was equipped with Polyair.

They have been in situ for approximately six months and we have not experienced one failure - which we fully expected due to adverse conditions such as unmade roads and extremes of temperature.

We are perfectly happy with performance and we recommend to most other ambulance services - as our problem was not isolated, but exists in all states - and Polyair is a quick and economic solution.

Fitting time is approximately one and a half hours and pressure can be adjusted to suit load. They are fitted with standard gas shocks and there is no reason to upgrade main leaves in spring cluster.

The rate of failures is yet to be determined. We have units on road which have done in excess of 20,000km and have not experienced problems as yet.

Dennis Ashley
Fleet Supervisor
St John Ambulance Service