Marc wrote:
> "Matthew S. Whiting" <[email protected]> wrote:
>
>>Marc wrote:
>>
>>>"Matthew S. Whiting" <[email protected]> wrote:
>>>
>>>
>>>>Marc wrote:
>>>>
>>>>
>>>>>"Matthew S. Whiting" <[email protected]> wrote:
>>>>>
>>>>>
>>>>>
>>>>>>Nate Nagel wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Really? I expect that a collision between two SUVs would be more
>>>>>>>dangerous to the vehicles' occupants than a collision between, say, two
>>>>>>>VW Golfs (Golves?) due to the construction of the various vehicles.
>>>>>>
>>>>>>Why do you think that?
>>>>>
>>>>>
>>>>>Because the crash tests that simulate a crash with a deformable object are
>>>>>pretty close to real-world crashes with vehicles of similar weight. In
>>>>>such crashes, medium-small cars (like Golfs and Civics) generally do better
>>>>>than vehicles such as pickups and other heavier trucks.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>The SUVs have a lot more distance between the
>>>>>>drivers and the front of the vehicle meaning that there is more distance
>>>>>>over which to decelerate and this means the deceleration forces could be
>>>>>>drastically less.
>>>>>
>>>>>
>>>>>Could be, but they aren't. Look at actual crash results and get back to
>>>>>us. My favorites are:
>>>>>
>>>>>http://www.iihs.org/vehicle_ratings/ce/html/0110.htm
>>>>>http://www.iihs.org/vehicle_ratings/ce/html/0126.htm
>>>>>
>>>>>I happen to own the car that I linked to...
>>>>
>>>>I wouldn't own a Ford truck. I drive a K1500 Chevy. The ratings on it
>>>>are much better:
>>>>http://www.iihs.org/vehicle_ratings/ce/html/0107.htm
>>>
>>>
>>>Better than the Ford. Still worse than the car.
>>
>>But good where it counts ... injuries expected. I don't care if the
>>truck looks good after the accident or if the passenger space is less
>>after the crash, as long as I don't get hurt. My truck rates the same
>>as your car in all four injury metrics. The passenger space may be
>>smaller in the truck than before the crash, but since it is so much
>>larger than the car's space to start with, it could get reduced by 20%
>>and still be as big as your car.
>>
>>And your dummy hit its head on the B pillar. Even though in this case the
>>acceleration forces from that impact are said to be neglible, it could
>>be much
>>different in the next similar crash.
>
>
> And with a greatly reduced passenger compartment, it is much easier in "the
> next similar crash" for the compartment to compress in a slightly different
> manner and crush the driver.
That's the reality of the real world. Crash worthiness design and
testing are not exact sciences. This is just one reason that crash
tests that use a sample size of one should be taken with a huge grain of
salt!
> The current general consensus is that you want the vehicle outside of the
> passenger compartment to crush as much as possible, but you want the space
> within to crush the least possible. Why? Well, in a much slower crash,
> you are going to lose your use of the doors much more quickly with a
> vehicle that can't keep the compartment together. Some anti-seatbelt nuts
> claim that you are safer if you go in water to not be wearing a seatbelt,
> but the greatest single factor is the doors. If they are jammed shut from
> impact, then the people inside are much more likely to drown (the
> government has claimed that you are more likely to drown in a car if you
> aren't wearing a seatbelt because the injuries are more extensive initially
> and impair the ability to successfully execute an egress from the vehicle,
> but I 've not seen any actual numbers to support this).
I don't disagree with any of this. I didn't see any comment in the
tests regarding door jambing. Seems like they would mention that if it
occurred.
> Also, if you get 20% compression at this specific energy level and the
> Impreza compressed less, at double the energy, the compression should be
> roughly double again. That would mean that you would be squashed in the
> Chevy, but still have a little space left in the Subaru.
Hardly, buckling and other modes of structural failure are anything but
linear. Often the structural element will hold right to the point of
buckling, crushing, etc. and then fail completely. If you knew anything
about structures, you would not have written the above. However, lets
assume that what you wrote above is true. Then...
At twice the energy, the deceleration forces would likely kill the
occupants regardless what the passenger compartment does. And if your
theory above were true, the occupants in the car would suffer much
higher g forces than the truck. Once the crush zone is exhausted and
you reach the passenger cage with the point of impact (barrier,
whatever), if the cage holds intact it means that the g forces will rise
very dramatically at that point. If the Chevy truck continues with
progressive deformation of the passenger space, the g forces will be
lessened greatly.
Matt
