I am really surprised this didn't kick up

adriver said
I happen to have a 66 B body and a 74 A body on jack stands right now.
So, I slithered under them and did some quick, dirty measurements if anyone is curious.
I'm sure people could find actual Chrysler drawings somewhere.

The A body measurement from the trans cross member frame to the rear frame rail first point of contact (rear frame rail forward flange) is 36.5 inches.
This would be the area that the rocker panels span.
And it measured 33.5 inches from one rear frame rail to the other across the car.

The B body measurement from the trans cross member frame to the rear frame rail first point of contact (rear frame rail forward flange) is 39 inches.
Again, this would be the area that the rocker panels span.
And it measured 34.5 inches from one rear frame rail to the other across the car.

The rear frame rails on both the A and B appear to be 4.5 inches in height.
The gauge of metal APPEARS to be the same on both cars.
I didn't have time to try and measure that as it would be more difficult.

But what was surprising is that the B body rear frame rail was actually narrower than the A body.
The A body is 2 5/8 inches wide.
The B body is 2 1/4 inches wide.
I had to measure that twice to be sure.

Now admittedly there probably are other factors to consider.
Like is is assumed the B body rear for a given type would weight more.

And the B body is more likely to have a high torque heavy motor twisting the front to rear.
All this points to me sticking with my previous assumptions.

View attachment 1715363874 View attachment 1715363875

How I measured this.

View attachment 1715363876

Remember there are 111" and 108" wheel base A-bodies, and the difference is in the floor between the ends of the frame rails. B-bodies are also quite different by year and model. Quite frankly you've made too many assumptions already. The engine thing makes no difference either, remember that A-bodies got Hemi's and at the design stage a big block powerplant would have been considered. The chassis didn't change when they stopped doing factory big blocks.

Honestly I shouldn't have bothered measuring my E-body, it's not a relevant discussion because there are simply too many more variables to consider. The simple fact of the matter is that the number of ribs molded into the floor pan makes a difference in how stiff the car is. The length and height of the roof, the width of the C-pillar, the height of the kick up for the rear axle, the track width and distance between the wheels and the springs, etc, etc, etc.

So, your assumptions are exactly that, assumptions. Your assumptions aren't good ones, because as you put it yourself, there are "other factors to consider". Well, those "other factors to consider" have at least as much of an effect, if not more, on the strength of the chassis as the couple of measurements you took. And that's why this discussion is so silly to begin with. We have a bunch of people, many of whom have no education or training in structural analysis, providing commentary on a subject that is more complicated than they could possibly know. Engineers trained in structural analysis don't make half assed guesses about how strong a structure is, they do a finite element analysis and actually get the facts. The reason for that is that there are plenty of structures that "look good" that fail. Literally every stamped feature in the sheet metal has an effect on how strong the uni-body is overall, even the relatively simple unibody structures of these cars have hundreds of relevant variables.

Mopar-Mitch said
Everyone on here is right about what they have posted. The only thing missing is from the engineering aspect of the unibody design. Safety was built into the design, body's were crash tested and studied for collapseing, we got collapsible steering columns and such, these bodies were studied for taking the shock of a crash, its suprising how similar unibodies are today compaired to the early ones. You would think stiffer is better in a crash, but not so when it comes to metal compressing and folding up.

The design and construction of these cars is RADICALLY different than a modern unibody. The only real thing they share is the fact that they're both unibodies. The crash performance on these old cars isn't comparable to modern designs, the level of engineering and analysis is on a completely different level now. Even modern unibodies have changed dramatically in recent history, look at the first time that the Insurance Institute for Highway Safety included an 40% offset frontal crash test in 1995. The performance of cars that were considered safe the year before was abysmal. A few years later, many makes and models were performing quite well in the same test. In 2012 they came up with a new 25% offset test, same deal again. Even some cars that performed well in a 40% offset crash did poorly in the new test. But the designs that take that new test into account perform better. And to the untrained eye, those chassis' don't look any different at all.

And as I said before, the safety that was designed into the chassis on these cars was based on how these cars were equipped from the factory. As soon as you start changing things, the amount of power, the amount of traction, the factory design is no longer ideal (assuming it was in the first place, which is a big assumption). I can absolutely guarantee that the factory engineers would not have put out the same design if they had intended these cars to have radial tires. You know why? Because they changed all the designs when radials became factory equipment a few years later.