ASK ARB – air
bag compatibility

G’day,

As a newbie, I would like to know more about ARB’s winch rated bull bars.

I’m looking to install an ARB bar on my Prado and would like to know how your bar complies with the air bag requirements of modern 4WDs. I have noticed that on late model Prados, bull bars, both yours and other makes, seem to move about a lot. I assume it has something to do with the mounting requirements for air bags or crumple-zones? Also, if this is the case, and they’re not as securely mounted as on non-air bag 4WDs, would there not be an issue using a Hi-Lift jack on it? I’m sure other readers would like to know the differences between current design bars and those of pre-air bag days.

Thank you.

Regards,
Barry

Dear Barry,

Thanks very much for your excellent question.

This is a concern expressed often by owners of the Prado and other model vehicles which exhibit similar tendencies.

The phenomenon you are observing is actually not related to the air bag compatibility requirements at all. Air bag compatability testing and development requires that we carefully examine the structural elements attached to the front of the chassis of these vehicles. The air bag triggering system is designed to work in harmony with the frontal crush characteristics of a vehicle. These frontal crush characteristics include the design of the bumper assembly, its mounting system, and other components of the vehicle.

On 4×4 vehicles with independent ladder chassis, the manufacturers often also add ‘sacrificial crush sections’ to the front of the chassis members to ensure that minor impacts (such as hitting a kangaroo) are not read by air bag sensors as major impacts, prematurely deploying the air bag(s).

Such premature triggering of the air bag is potentially quite dangerous, and may in fact cause a more severe accident or an injury that would otherwise have not occurred. Likewise, an air bag deploying later than intended by the
manufacturer could also be dangerous.

It is with these dangers in mind, that ARB’s engineers approach the subject of fitting bull bars to such vehicles, with the concern being that fitting a rigid structure, not behaving the same as the original frontal characteristics of the vehicle, may change the deployment timing of the air bag.

From early on, ARB took a very careful approach to the subject and initiated some in-depth research on several fronts to ensure that any product that our company produced for these vehicles was not only up to the expectations of our customers in terms of the traditional protection ARB bar owners have come to expect, but also that such bars would be truly legal and appropriate for the vehicle.

Monash University’s Department of Engineering was contracted by ARB on this project for some years, and their expertise and testing facilities have been used to evaluate, test and approve ARB bars for air bag vehicles.

The essential design criteria ARB uses to ensure compatibility, is to evaluate the standard vehicle’s frontal crush characteristics, and where necessary to duplicate these characteristics as part of the design of the bar and its mounting system. This results in a design which when correctly installed, ensures that there is no change made to the way the vehicle behaves in a collision, and hence there is no change made to the way the air bags deploy.

That is not to say that ARB has developed useless bars that do not offer the vehicle any protection. ARB air bag compatible bull bars do provide significant protection for the vehicle whilst also offering functional winching capability on winch mount versions.

Several different engineered methods of mounting the bar and providing the required collision performance characteristics are available to our designers. This results in products which are unique according to the vehicle model and often feature quite different structural features to fulfil their air bag compatibility requirement.

The engineers analyse many factors at the initial design stage including the vehicle’s structural elements in relation to crash performance, the overall requirements for protection of the vehicle, consideration of pedestrian safety, the need for vehicle recovery points including winch mounting systems, and the overall aesthetic appeal of the product. Naturally we are also looking for a cost effective, value for money solution as well.

This involves the development and testing of several prototypes before the design is approved. This is time consuming, but the patience of our customers is rewarded with a product that is the very best of its type.

For your peace of mind, each of our bull bars and nudge bars for SRS air bag equipped vehicles is fitted with a sticker which reads in part as follows:

“This product and its mounting system has been designed, tested and manufactured by ARB to ensure its fitment to a vehicle fitted with SRS air bags does not affect the vehicle’s compliance to ADR69.”

Now, getting back to your original question. All late model Toyota independent style front end equipped 4×4 wagons that utilise separate chassis’ employ very large and supple body-to-chassis mounts. In operation, their
sophisticated chassis’ flex a lot to provide the smooth, quiet ride with low vibration and harshness. When we bolt our bar to this chassis we simply are allowing the hitherto unseen movement to be seen as the bar moves with the chassis. This flex is nothing to be alarmed about, as, like the flex in an aircraft wing, it is normal and safe.

You will note that a correctly installed ARB bar on the vehicle will have a clearance space between the bumper section and the vehicle’s original bodywork. This is essential space to allow the bar to move without impacting other components.

Most modern ARB bars are also equipped with Hi-Lift jack points and you may rest assured that these are fully engineered and tested for yours and your vehicle’s safety.

Greg Milton
(National Product & Services Manager)