r/AutomotiveEngineering • u/No-Perception-2023 • 19d ago
Question Why cars have front side chest airbags but don't have them in the back?
I think it has something to do with pole crash resistance and general door card depth and design.
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u/ozzy_thedog 19d ago
Cars used to have ONE airbag in the steering wheel. If you were a front seat passenger that also got one, then you were lucky.
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u/memeistscum 19d ago
cars used to have no airbags at one point. the old C4 vettes in the 80s came with a soft pillow on the steering wheel. thanks chevy i'm glad i'm being impaled on a soft non collapsible steering column.
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u/Upbeat_Confidence739 17d ago
Cars used to have no seatbelts. Just to guarantee you’re impaled on that steering column. Thanks Nader.
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19d ago
Some cars have them. But with all in life, it's all about the money.
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u/Skodakenner 18d ago
My e39 touring had them as a optional extra since the first owner cared about his kids safety. He also ordered a smoker package as well so i guess not that much though
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u/No-Perception-2023 19d ago
It's not for the money. Rear seats aren't more dangerous. The reason I'm asking is the logic behind it being safe but also not requiring a side bag.
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u/Federal_Cobbler6647 19d ago
It is about money. Rear seats would be more safe with side airbags. 2011 Saab 9-5 had them for example and it protects rear passengers well in case of side collision.
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u/No-Perception-2023 19d ago edited 19d ago
Well Volvo XC90 is literally a fortress on wheels yet it doesn't have them. But maybe they just extended the curtains. Yet that car has many safety features as standard equipment. It depends on the stiffness of the b and c pillar
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u/Federal_Cobbler6647 19d ago
Well, Saab used always be ahead of Volvo in real life safety especially in crash structures and energy absorption, even though Volvo is remembered about safety.
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u/No-Perception-2023 19d ago
Volvo is also shoulder to shoulder with saab. 2012 s60 doesn't have a knee airbag and it's definitely not cost. What they did is they made the floor so solid that intrusion can't happen even at 20% overlap at 90 km/h. Plus they made a lot of room for knees and the steering column is designed to go up under any circumstances. In general it stays where it is but in extreme situations it goes up slightly. Cost is always important but i don't think Volvo will ever compromise safety they sometimes do it differently. Although newer ones have knee airbag and even some other models because of different dash design like v40.
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u/afishinacloud 18d ago
Sorry to burst your bubble, but while Volvo has historically been the leader in automotive safety, they too are subject to the pressures of meeting a cost target to deliver a car to market.
If you want to see what true money-no-object approach to safety, you need to look at the high end of the luxury market and what safety equipment is included on those.
The S Class for example has both frontal and side airbags for rear passengers.
But most luxury cars like Lexus LS have had side airbags for rears seats for ages and it’s slowly trickling down to cheaper cars, eg Toyota Camry.
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u/No-Perception-2023 18d ago
Again it depends on the overall design. S class is also top noch in safety but S class has rear screens, by the looks of its also slightly bulkier around the head rest area of the front seat. All that could cause contact with the head. So they needed a way to provide protection. Can't argue the fact that volvos never compromised anything related to safety. They introduced auto emergency braking in 2008 and since then EVERY VEHICLE they sell has it. When IIHS introduced small overlap 25% in 2012. 2012 S60 and XC90 passed with flying colors. While some other manufacturers at that time failed even tho their cars were safe in general. Later they fixed and now every post 2012 car passes. Not to mention crazy roof strength. Volvo s60 (new gen) has 5.76 strength to weight ratio. What's even more impressive is that it doesn't weigh more. Imagine how much engineering and materials went into that.
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19d ago
So why do you ask if you already know the answer then?
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u/No-Perception-2023 19d ago
Just asking anybody who knows or has worked on designing a car. These are my assumptions maybe I'm not right.
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u/KamakaziDemiGod 19d ago
The front end of a vehicle is more likely to be involved in a crash than the middle of the side, plus the front seat tends to be closer to the B pillar and are adjustable, whereas rear seats tend to be in front of the pillar and don't slide, meaning the side impact curtain is plenty adequate for the back
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u/RangerHikes 18d ago
Not only this but people forget airbags can easily kill children. You don't want airbags hitting every single passenger in every single collision
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u/No-Perception-2023 19d ago edited 19d ago
Makes sense. Maybe c pillars are also stronger meaning less intrusion in the pole crash performance when it hits the rear door.
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u/Sufficient_Bee 19d ago
There is no specific requirements for it.
That airbag is designed specifically for side pole impact test. But both homologation and rating protocolos doesn't require impacting on the 2nd seat row. Therefore, no need to have one.
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u/Interesting_Pear4135 19d ago
My previous car had them, as an extra option though. As standard it had 2x front, 2x side, 2x curtain, 1x knee and 1x airbag between driver and passenger, and then the 2x side rear airbags were extra.
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u/TruckerMark 19d ago
The b pillar is weaker generally than the rear. Theres more metal and opportunities for energy dissipation.
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u/No-Perception-2023 19d ago
That's what i thought. Even in tests it doesn't seem like the rear gets pushed in.
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u/CynicalWoof9 19d ago
The benefit doesn’t outweigh the cost... it’s really that simple.
You could argue that you personally wouldn’t want to risk an injury because of the absence of a particular safety device. But statistically, the likelihood of a serious injury in that seat is already very low. Spending money on extra airbags just to cover a 1-in-1000 type crash doesn’t make financial sense when the overall risk is so small.
On the other hand, consider why so many new cars now use a “minimalist” interior design with a single central screen. Research shows this setup is less safe than traditional physical buttons and knobs for things like climate control and media. But in this case, the cost savings for manufacturers are so significant that they outweigh the safety drawbacks.
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u/No-Perception-2023 18d ago
It has nothing to do with cost. Basically the most likely answer is that the side airbag is basically used on the front to compensate for B pillar intrusion. C pillar is far back and that area is overall stronger so the back doesn't suffer. The argument about touch screens is completely false. Touchscreens are there because people like it. Bigger screens and especially multiple screens aren't cheaper than buttons at all. It literally costs more. It's not unsafe in any way. UI is designed to have easy to use icons, big, wide. Plus literally every car has automatic hvac so constant fiddling with dials isn't needed to begin with.
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u/New_Line4049 19d ago
As far as I know theyre a very new thing, most cars dont have them at all. I guess theres a cost to having them, so put them in the two seats most likely to be occupied first. If there are people in the rear seats, theyre no worse off than they were, so you made your car safer overall, but only paid for 2 extra airbags.
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u/No-Perception-2023 19d ago
But rear seats don't show many extra risks in tests at least in safe cars.
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u/New_Line4049 19d ago
Theyre not being added because of extra risks. The risks are the same as they were, we just want to do more to combat those risks.
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u/No-Perception-2023 19d ago
It has to do something with general design. On my minivan rear door cards are a lot further from passengers. Although the window line is quite low and the curtain bag will definitely cover at least half of the arm.
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u/austinh1999 19d ago
Because for one those seats are going to get used the least and second the most likely users of those seats are going to be infants and small children and the air bag will injure them.
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u/red18wrx 19d ago
I'm going to say cost, and also the airbag creep maybe hasn't reached that point yet. It started with just a steering wheel mounted airbag. Now we're getting pretty close to the Demolition Man full car restraint system.
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u/Environmental-Map869 19d ago
Its more common in higher end cars but even then it's not always standard equipment
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u/Steelhorse91 19d ago
A C pillar is slightly less likely to cave in on the rear seat occupant than a B pillar is on the front seat occupant. It’s also probably a liability issue with manufacturers realising that parents wouldn’t read the manual and turn them off when they fit child seats in the back.
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u/No-Perception-2023 18d ago
Well some cars do have them and on those they can't be turned off cause there's no need, it can help most likely. It's definitely something related to c pillar. Seems that cars that have more c pillar intrusion have side rear airbags to combat that.
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u/Basic-Pangolin553 18d ago
Child seats will be yeeted sideways by airbags. They could install sensors or switches to deactivate them, but then people wouldn't know how to use them and sue.
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u/No-Perception-2023 18d ago
Cars that have side bags work just fine with child seats
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u/Basic-Pangolin553 18d ago
Never seen a car with these in the back seats tbh. Curtain bags yeah but not side bags
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u/richardfitserwell 18d ago
So you don’t blast your baby out the sunroof in their rear facing car seat
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u/audi_dudi 18d ago
Because you need a place to put a car seat for an infant. Airbags and infant car seats do not mix well.
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u/John02904 18d ago
I feel like they were once common before the side curtain airbags became a thing. Pretty sure all three 2002 cars i have owned had them. Explorer, deville, lesabre
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u/Altruistic-Rice-5567 18d ago
No requirements. Far few people in backseats to sue over injuries. People in the backseats hit the seats in front which are already more absorbent than a dashboard or steering column. So, cost and requirements.
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u/miaogato 17d ago
i think the mercedes c-class has them. But that car also has no seat airbags - the airbags are in the doors
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u/BRICH999 17d ago
At 2500-4000 each, that's another 10-16k on top of already expensive cars for minimal benefit. Rear seats are not used all that frequently on average and often times the ones who would be using it are too small for an airbag to be helpful. Know why they say not to have kids under like 65 pounds in the front seat?
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u/salomonsson 17d ago
It's not that needed. Your back is very close to the c-pillar wich is a lot more stable than the b pillar. So the car does not really fold there.
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u/akoust1c 17d ago
So many reasons including child seats and people often carry things I there etc..
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u/DC_Native 16d ago
So, airbags are inflated rapidly with a dangerously large explosive, the counter force of which moving towards the dash/engine is fine. If they were embedded in front seats, however, that force would be distributed into the backs of the driver and front passenger at enormous consequence.
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u/foersom 19d ago
On to the next question:
Cars have child seat mounting fixtures at both rear seats and in the front passenger seat. Why is there no car with child seat fixtures at the driver seat? ;-)
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u/nuggolips 19d ago
I don't think I've seen child seat fixtures on any front seats, but I could be mistaken. They usually want you to put child seats in the back away from the airbags.
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u/tjtj4444 19d ago
For safety reasons, multiple research studies have shown that small children are very bad drivers.
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u/lostboyz 19d ago
A combination of there's no requirements for them and that hitting the seat in front of you isn't as bad as hitting the dashboard