Side-impact safety: 2 doors vs 4 doors

[Majarvis]

I have always had this question burning in the back of my mind, what would be structurally safer in a side-impact crash, in the same model of car? A 2 door, or a 4 door?

When I say this, I'm not talking about completely different cars, simply cars that are offered in both 2 door and 4 door versions, like the Honda Civic, for example.

Now, to me, it would seem that a 4 door would be slightly stronger than a 2 door, because of the vertical pillar on guarding the driver, whereas on a 2 door, that pillar is further back, most of the time behind where the driver sits, not protecting the driver.

Would this be a fair assumption, or are there other variables to take into place. For comparison purposes, let's stick to, like I said, models that are offered in both 2 door and 4 door versions, like the Honda Civic, so we are not comparing completely different cars.

Just for a reference, this is the pillar I am referring to: (picture taken from IIHS.org)


On a 2 door model, the pillar would be further back, behind the driver, offering less interior intrusion protection (theoretically, anyway).

 

[Tornado]

Yeah, but there is also less of an opening in the side of the car, making the difference (usually) negligible. On cars with Suicide doors (RX-8, extended cab pick-ups, etc.), I'm not sure though.

 

[Majarvis]

Yeah, but there is also less of an opening in the side of the car, making the difference (usually) negligible. On cars with Suicide doors (RX-8, extended cab pick-ups, etc.), I'm not sure though.

I'm not sure I quite follow you when you say there is "less of an opening."

 

[VIPFREAK]

On a 2 door model, the pillar would be further back, behind the driver, offering less interior intrusion protection (theoretically, anyway).

I think any side impact you're pretty screwed which is why I try to avoid them. I have a 2dr. and I don't feel safer than a 4dr. I'm a smaller target taking up more of the car that they can aim for.

 

[High-Test]

I think 2 doors are safer. usually, there's more rear quarter panel metal, whereas in a 4 door the extra quarter panel space is taken up by a door. (if that came out in a coherent pattern..)

 

[Tornado]

I'm not sure I quite follow you when you say there is "less of an opening."

I mean less space cut out of the side of the car for the doors. EX:
The Civic coupe only has one door cut out of the overall frame, so the bodywork helps support the frame from the side:

The Sedan however, has 2 doors per side, so there is no extra bodywork to help the frame. It, however has a B-Pillar.

But on a Mazda RX-8, there is no extra bodywork or B-Pillar, so you must reinforce the tub and roof of the car more than a normal 4 door to prevent caving in. Theoretically, this approach is least safe, but Mazda went at it in a way so it wouldn'y matter.

 

[Raghavan]

2 doors are safer as they are have stiffer frames as they don't have 2 extra doors that decrease the structural ridgitidy of the whole car, so the coupes would be stronger in a crash.

 

[Majarvis]

I mean less space cut out of the side of the car for the doors. EX:
The Civic coupe only has one door cut out of the overall frame, so the bodywork helps support the frame from the side:

The Sedan however, has 2 doors per side, so there is no extra bodywork to help the frame. It, however has a B-Pillar.

But on a Mazda RX-8, there is no extra bodywork or B-Pillar, so you must reinforce the tub and roof of the car more than a normal 4 door to prevent caving in. Theoretically, this approach is least safe, but Mazda went at it in a way so it wouldn'y matter.

Ahhh, I understand now! Yes, now I understand why a 2 door would hold up better in a side impact, thanks Now that I think of it, no wonder on a 2 door vehicle, the door feels heavier when you open and shut it; not only because it is longer, but it has more reinforcing within it.

 

[Joey D]

I can't imagine that 2-doors are safer...hell my 2-door Blazer is the most unsafe vehicle on the road to date, it's way unsafer then the 4 door model. Why? I haven't go the slightest idea.

 

[VIPFREAK]

Smaller... bigger car hits you and they have more energy because of bigger mass... you in a tin can... you have no chance. At least yours is a truck and not a little car.

 

[Joey D]

True I've been it two accidents with my truck...one fairly serious. I walked away from both with no severe injuries. Guess its not all unsafe.

 

[VIPFREAK]

I'm screwed in a side impact that's all I gotta say. People seem to aim for me too.

 

[niky]

Were you talking about consumer or NHSTA ratings for your truck, Blazin'?

Always thought that those were because of rollover possibility due to the high ride and short wheelbase. (not that it's very high now... ).

Agree with Toro and Raghavan, coupes do tend to be stiffer than four-doors... or even three doors. The extra large driver's door doesn't matter much, with side-impact beams standard these days... plus that makes for more door, actually, to absorb the impact.

 

[Tornado]

The extra large driver's door doesn't matter much, with side-impact beams standard these days... plus that makes for more door, actually, to absorb the impact.

Yeah, but that makes the car structually weaker technically, because a door will never be a sturdy as normal bodywork, as there too many forces acting on it with less space to displace itself. It's similar to the idea of a bunch of pieces welded together are not as strong as one big piece. An area that was naturally a shape is stronger than something made to conform to a shape.

 

[Joey D]

I'm not sure which one it was, but there was an article on yahoo a few months back talking about it, I think I made a thread about it.

 

[Majarvis]

Awesome input guys, thanks

 

[niky]

Yeah, but that makes the car structually weaker technically, because a door will never be a sturdy as normal bodywork, as there too many forces acting on it with less space to displace itself. It's similar to the idea of a bunch of pieces welded together are not as strong as one big piece. An area that was naturally a shape is stronger than something made to conform to a shape.

That's true... thus we argue for the jigsaw that's made of five pieces (hood, trunk, body, 2 doors) instead of one made of seven (4 doors). But then, you're the one who explained it best. 👍

At least newer cars have the side impact beams. Get hit side on in an old one at any speed and you're toast. Oops... an old compact, I mean. Get hit in an old full-sized American, and you might die, but the car will live.

 

[Tornado]

Oops... an old compact, I mean. Get hit in an old full-sized American, and you might die, but the car will live.

I think that's an unfair statement. The Ford Crown Vic hasn't really benn changed in at least 20 years and that's one of the safest cars on the road. But really, you are right. Any car made before 1975 really isn't all that safe at all. Barring a few examples (Tucker Torpedo, Volvo 164, VW Beetle, Tatra T87, etc. You know, all cars that were overengineered ), cars from that era are total deathtraps, with about as much in the way of crumple zones as a concrete divider.

 

[niky]

But to be fair, my dad had a major shunt in one of our old cars back in the 70s (can't remember if it was a Seville or a Caprice). No crumple zones, yes, but I guess the seatbelt saved his life. He wrapped it around a 20-30 year old oak, a big mother-of-a-tree. Wrecked the car, but he didn't get a scratch.

Killed the damn tree, though.

 

[High-Test]

So.. Would I be seriously injured in my 45 year old chevy If I was hit?

 

[Tornado]

So.. Would I be seriously injured in my 45 year old chevy If I was hit?

Yeah, possibly. Especially if it is a unit-body, because they have NO crumple zones (part of the reason they are preferred for Demo Derbies).

 

[High-Test]

Yay!!

And I have Lap belts and a nice steel dash and uncollapsible Steering column!!!

So... I'm screwed!

 

[Majarvis]

So.. Would I be seriously injured in my 45 year old chevy If I was hit?

Definitely, yes (depending on the type of crash of course).

 

[VIPFREAK]

Yes, because unlike cars today you're in a tank so nothing is being absorbed you are gonna absorbe it all. They don't make em like they used to.

 

[High-Test]

So.. when I'm impaled by the steering column, the person I will the car to can drive it home from the crash scene!


No, they don't make 'em like they used to.