What sets the airbag off?

Hey I guys I recently fitted up a steel Bullbar to my nav, for some reason I thought I'd see something to do with the air bags as I removed it but never did, is there a switch that sets it off? Or does it go off g forces?

As far as I know, there are only two things that can set off the air bag:

1) A collision with an object* at a speed of 35 km/h or higher (measured by speedo and accelerometers)

2) An unlucky person stabbing away at the steering column with a screwdriver trying to remove the airbag

As for how the structure of the vehicle is meant to be for proper deployment I'm not sure. A certain degree of crumple is expected in the front, accommodated by the bullbar if present (hence the need to test them).

It really is best to leave that sort of thing to people qualified to deal with it. I'm not, so I don't play with it - although I have mounted a winch to it.

* The fact that this object is larger than a housefly is left out as it's just bloody common sense. However, I have heard of airbag deployment from hitting a camel, so the limit is somewhere in between.

I'm glad you said that tony, I was worried there was some sort of sensor I might have missed. That's good. It's funny with this heavy steel bar the brackets are half the thickness of the alloy one.

Generally you could say that aluminium is half as strong as steel and only a third of the weight. Depends on the alloys used, of course. Aircraft-grade aluminium is superb and approaching the strength of steel but it's bloody expensive. Ordinary steel is much cheaper and provides more strength, so per $ spent, steel is better in terms of strength. Steel is also far less brittle - it comes down to the structure of the metal. Aluminium has a coarse crystalline structure whereas steel is quite fine - in broad terms, aluminium won't flex very much before it breaks, whereas steel will happily exceed aluminium's flex limits and continue to do that for long after the aluminium has broken.

I'm not sure about all air bag compatible bull bars but with my D22 the bar fits onto the chassis rails over the crushable zone at the front of the chassis bar.

The bar has slots for the bolts and not holes so it can move backwards in an impact allowing the crush zone of the chassis to compress. These slots seem to be the main difference between this air bag compatible bar and the earlier bar which just had bolts holes.

I was told there were no sensors in the crush area where the bar mounts.

I herd airbags go off by froce of 2 magnets been pushed together u no where u turn the magnet around and they want to push against each other with a certent amount of force to push they together and pop goes your airbag that's what I have herd anyway

Not too sure of how they are triggered but do know an impact of 26km/h or greater sets them off.

They will definitely go off if all the electric's get wet.

When my D22 was drowning and i was climbing out the window BANG Lets just say it helped me get out a bit quicker..

thats intresting to know..... how deep under?... could be a real hazard if your trying to cross a river up north somewhere..

joshy said:

thats intresting to know..... how deep under?... could be a real hazard if your trying to cross a river up north somewhere..

Click to expand...

The water was flowing in pretty fast once it was at a stand still, i would say the water level was just below the steering wheel and above the seat when it went BANG, also the stereo came on, the horn started going and the headlights came on.

It may pay to wrap the ECU up if a river crossing looks sketchy, and you have no choice but to try and cross it.

[yt]/watch?v=Cbojfun27pg[/yt] like this guys horn ?? lol

what a complete F%!$wit...... where was he trying to go with putting his drivers wheel up on that ledge!!!! wtf!! there were people yelling, "no not there"hahahaha dickwit

They're usually somewhere in the B-pillar. There is also usually an arming accelerometer which requires a threshold acceleration and arms the airbag circuit, and on top of that a trigger accelerometer which requires a higher acceleration, which fires the airbag.

The crumple zone at the front of the chassis is there to absorb energy at a specific rate, which results in an acceleration which is sufficient to trigger the airbag, but not so excessive that the occupants cannot survive the collision. "Airbag approved" bullbars are not really designed around 'allowing' the airbag to go off; they are designed around not reducing the amount of energy the crumple zone can absorb or increasing the rate at which that energy is absorbed. It just so happens that vehicles that have airbags are also vehicles with crumple zones.