I analyzed the most recent 104 moderate overlap IIHS crash tests done at their facility (that the results were available for by Sept. 25, 2017). The reason for the 104 number is that I could not get data for four vehicles, hence I added four to get an even 100. The tests were on 2007-2017 models, conducted between June 21, 2007 and May 25, 2017. 96 were rated Good overall and 4 were rated Acceptable
The factors I was looking for: when, on average, did the driver airbag deploy, was it fully inflated, and when did the dummy make first contact? How often did the airbag contact the face before full inflation? How often did the dummy go through the airbag to hit the steering wheel? Did the length of time between full inflation and first contact make a difference as to the likelihood of steering wheel contact?
The averages among all 100 vehicles were:
Sternum to the steering wheel - 368.16 mm (14.49 in) - range 328-410 mm (12.91-16.14 in)
Driver airbag deployment - 32.8 ms - range 16-54 ms
Driver airbag full inflation - 63.5 ms - range 34-86 ms
First face to airbag contact - 73.5 ms - range 44-96 ms
Full inflation to airbag contact - 10.0 ms (range -20 to 34 ms)
Negative numbers indicate that the airbag contacted the face before full inflation.
Positive numbers indicate that the dummy contacted the fully inflated airbag.
Of the 100 vehicles:
76 hit a fully inflated airbag and did not hit the steering wheel, or hit it with less than 70 g.
2 hit the airbag as it was "evening out" (the bag was near its fully inflated state) and did not hit the steering wheel, or hit it with less than 70 g.
5 were contacted in the face by the inflating airbag and did not hit the steering wheel, or hit it with less than 70 g.
17 hit a fully inflated airbag but contacted the steering wheel with at least 70 g (enough to mark the head-injury rating down from Good to Acceptable)
Averages of the 83 vehicles where there was no steering wheel contact sufficient to lower the head injury rating from Good:
Sternum to the steering wheel - 367.39 mm (14.46 in) - range 328-410 mm (12.91-16.14 in)
Driver airbag deployment - 33.9 ms - range 20-54 ms
Driver airbag full inflation - 63.9 ms - range 44-86 ms
First face to airbag contact - 73.0 ms - range 44-96 ms
Full inflation to airbag contact - 9.1 ms (range -20 to 32 ms)
Averages of the 17 vehicles where there was steering wheel contact that did lower the head injury rating:
Sternum to the steering wheel - 371.88 mm (14.64 in) - range 348-400 mm (13.70-15.75 in)
Driver airbag deployment - 27.4 ms - range 16-38 ms
Driver airbag full inflation - 61.4 ms - range 34-76 ms
First face to airbag contact - 76.0 ms - range 60-92 ms
Full inflation to airbag contact - 14.6 ms (range 2 to 34 ms)
Results
The results of this analysis would seem to indicate that airbag efficacy declines if too much time passes between full inflation and contact; remember, the millisecond that that bag reaches full inflation, it's losing pressure and thus the ability to resist forward motion from that moment on. A bag that reached its peak pressure 30 milliseconds ago is going to be less firm than one that is at its moment of peak inflation. But other factors, such as the airbag's firmness to begin with, seat belt loads and vehicle deceleration play into this.
However, the greater average amount of time between full inflation and airbag contact for the dummies who hit the steering wheel would suggest that this factor does play a role.
The factors I was looking for: when, on average, did the driver airbag deploy, was it fully inflated, and when did the dummy make first contact? How often did the airbag contact the face before full inflation? How often did the dummy go through the airbag to hit the steering wheel? Did the length of time between full inflation and first contact make a difference as to the likelihood of steering wheel contact?
The averages among all 100 vehicles were:
Sternum to the steering wheel - 368.16 mm (14.49 in) - range 328-410 mm (12.91-16.14 in)
Driver airbag deployment - 32.8 ms - range 16-54 ms
Driver airbag full inflation - 63.5 ms - range 34-86 ms
First face to airbag contact - 73.5 ms - range 44-96 ms
Full inflation to airbag contact - 10.0 ms (range -20 to 34 ms)
Negative numbers indicate that the airbag contacted the face before full inflation.
Positive numbers indicate that the dummy contacted the fully inflated airbag.
Of the 100 vehicles:
76 hit a fully inflated airbag and did not hit the steering wheel, or hit it with less than 70 g.
2 hit the airbag as it was "evening out" (the bag was near its fully inflated state) and did not hit the steering wheel, or hit it with less than 70 g.
5 were contacted in the face by the inflating airbag and did not hit the steering wheel, or hit it with less than 70 g.
17 hit a fully inflated airbag but contacted the steering wheel with at least 70 g (enough to mark the head-injury rating down from Good to Acceptable)
Averages of the 83 vehicles where there was no steering wheel contact sufficient to lower the head injury rating from Good:
Sternum to the steering wheel - 367.39 mm (14.46 in) - range 328-410 mm (12.91-16.14 in)
Driver airbag deployment - 33.9 ms - range 20-54 ms
Driver airbag full inflation - 63.9 ms - range 44-86 ms
First face to airbag contact - 73.0 ms - range 44-96 ms
Full inflation to airbag contact - 9.1 ms (range -20 to 32 ms)
Averages of the 17 vehicles where there was steering wheel contact that did lower the head injury rating:
Sternum to the steering wheel - 371.88 mm (14.64 in) - range 348-400 mm (13.70-15.75 in)
Driver airbag deployment - 27.4 ms - range 16-38 ms
Driver airbag full inflation - 61.4 ms - range 34-76 ms
First face to airbag contact - 76.0 ms - range 60-92 ms
Full inflation to airbag contact - 14.6 ms (range 2 to 34 ms)
Results
The results of this analysis would seem to indicate that airbag efficacy declines if too much time passes between full inflation and contact; remember, the millisecond that that bag reaches full inflation, it's losing pressure and thus the ability to resist forward motion from that moment on. A bag that reached its peak pressure 30 milliseconds ago is going to be less firm than one that is at its moment of peak inflation. But other factors, such as the airbag's firmness to begin with, seat belt loads and vehicle deceleration play into this.
However, the greater average amount of time between full inflation and airbag contact for the dummies who hit the steering wheel would suggest that this factor does play a role.
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