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POST ON Aug 16, 2017
One of a number of products lines we are proud to sell at 4WD1.com is Airbag Man airbags. We've been dealing with these guys for many years now, and everything about their product and people is first-class.
Why airbags? No matter how you think about it, and despite advances in spring design, comfort-ride suspension can't carry heavy loads and heavy-duty springs ride rough and sit too high when the vehicle is light-loaded. Airbags allow you to tune your suspension under all loads and conditions. Just add or remove air.
Despite our own trouble-free experience with the product, combined with the 20+ years of trouble-free experience by Airbag Man as the manufacturer, from time to time we still get "push back" from some customers when making such a recommendation.
"Nah mate! I don't want airbags! They'll crack ya chassis!"
These customers have usually picked up up the idea from a mate or an internet forum or otherwise a 4WD suspension business that does not have airbags to offer. The rumors perpetuate, and then when you see pictures of vehicles (usually Triton's and D40's) on the internet that have been "bent" because (they've actually been fork-lifted off a boat onto a ramp "makeshift style" in another part of the world) some "cyber experts" will tend to pop up and give their assessment of the situation - "That's airbags for you!"
On occasion, the net will reveal some instances where a vehicle does have chassis damage and happens to have airbags fitted also.... So what is the go here? Do airbags crack chassis or not?
KEEP READING: (CLICK HERE OR ON IMAGE TO VIEW FULL SCALE)
As the summary info in the image above shows, Airbag Man contracted the services of an independent engineering firm for analysis. The testing was performed on the vehicle identified as a "worst case" scenario due to its chassis design compared to the range of other popular dual-cab models. This was the D40 Nissan Navara.
Features of the Chassis Report Testing:
- Loading simulations were carried out with both leaf springs "only" and also with leaf springs combined with airbags.
- Loading cases included heavy tray loads, heavy towball loads, and a combination of both up to vehicle limits PLUS a realistic overload factor.
- Testing simulated loading and operation consistent with offroad use where the suspension movement is substantial, and the towball load is varying, similar to driving over sand dunes.
- The loading case that generated maximum chassis stress was with maximum towball load and maximum remaining tray load, and the simulated failure was identified to correlate with real-world failure modes.
- Chassis stress was greatest above the rear spring hanger, and at a depression on the chassis between the bump stop and front hanger. These points are known failure points on this chassis.
What was the key observation of the testing and analysis?
In the combined "worst case" situation, and all lesser situations, the peak stresses seen by the chassis with airbags installed were equal to, or less than, the stresses with no airbags.
Just in case you skimmed over that point, here it is again:
"In the combined "worst case" situation, and all lesser situations, the peak stresses seen by the chassis with airbags installed were equal to, or less than, the stresses with no airbags."
Key Application Feature:
Airbag Man specifically designs its kits to suit each vehicle application and the load is usually applied where the Original Equipment expects a bump load to occur if bottomed out. This bump load is expected to be a lot higher than normal loads applied.
Brand name and application is important:
It is important to note that the results of the testing are only applicable to Airbag Man airbags, operated and installed correctly, with an important point being that the airbags available travel, spring characteristic, bump response and construction all contribute to their effectiveness. Hence, other brands and methods of attachment may not see the same result, and could in fact cause increased chassis stresses. Airbag Man airbag kits are the result of much R&D. Each kit is vehicle-specific, designed for optimum performance. The Airbag Man catalogue reflects hundreds of different part numbers, including in many cases, different applications for raise-height 4wds.
Why confusion and why the rumors?
Firstly, as above, brand name and engineering design is important. Occasionally after providing someone with a quote for Airbag Man airbags, they will say how they can purchase some other brand on the internet for less. Well, we already know that, but basically if it's not Airbag Man, it's not Airbag Man. We don't want to offer just a "pump up kit" or a cheap copy. From experience, the cheaper kits take steps to help reduce their costs including consolidating the number of bag sizes available (bag height and length) and go for more universal style mounting hardware.
Secondly, chassis cracks or damage occurs when a vehicle owner/driver exceeds the weight and loading recommendations as set out by the vehicle manufacturer. A lot of people think they only have to worry about GVM, but they are many other factors at play. Towing capacity is usually affected by payload capacity (and vice-verse) including the amount of downward pressure on the towball. There are also axle loading specifications that must be considered. Aftermarket trays and trundles are also a consideration for their extra weight. Also, if your vehicle is equipped with an extended-length tray (or service body) remember that any added weight has a mechanical advantage (exaggerated) effect. Basically, the further you move the same weight behind the axle creates a greater load effect due to the leverage.
Finally, certain vehicles have their reported issues. Mitsubishi Triton has also been identified as a problem vehicle. The variant that suffers from chassis failures is the dual-cab version ML/MN. The issue being the design and welding on the forward body mount creates a raised (high) stress point, especially when heavily loaded, towing or carrying overhanging loads.
Ranger and BT-50 PJ/PK and L97M have a similar issue (specific to the extra-cab styles) with a hole through the rail between the cab and chassis mounts. Again this creates a stress raiser that could fail with heavy load carrying and heavy use.
In both cases the suspension system makes little difference to the chassis failures they suffer as the issue is how load is transferred from the body/tray into to the chassis.
The Syngeering Pty Ltd report concluded:
".... AIRBAGS HAVE LITTLE TO NO EFFECT ON THE DISTRIBUTION OF STRESS WITH THE CHASSIS RAILS".... "THE RESULTS INDICATE THAT IN EVERY LOAD CASE INVESTIGATED THE ADDITION OF AN AIRBAG BETWEEN THE CHASSIS RAIL AND LEAF SPRING DOES NOT INCREASE THE MAXIMUM STRESS THROUGH ANY SECTION OF THE CHASSIS RAIL"
So there you go... The rest is up to you.... From now on regarding the use and fitment of airbags will you choose facts or fiction to inform your view?