Safety of Separate Frame/Body vs Unit Construction

[Crash]

Does anybody know of any objective tests or documentation as to whether a vehicle with separate frame and body is safer than a vehicle with unit body construction?

Crash

[sawyerob]

Does anybody know of any objective tests or documentation as to whether a vehicle with separate frame and body is safer than a vehicle with unit body construction?

Crash

I'd be willing to bet you it will be what individual car your talking about. Some unibody cars hold up quite well in a crash, even better than a vechile with a frame, others don't.

Bottom line is, it's all about design...

[Crash]

*I'd be willing to bet you it will be what individual car your talking about. *Some unibody cars hold up quite well in a crash, even better than a vechile with a frame, others don't.

*Bottom line is, it's all about design...

sawyerbob,

Yep, I'm sure you're right about that. I was just wondering, given equally well-designed vehicles, which method of construction would provide more safety for the occupants.

Crash

[Buck]

It really depends on the vehicles application. Unit body can be , but not
always safer, than ladder frame construction. The TOTAL vehicle weight
LOADED is the detemining factor.

A simple car of modest size can be very safe in unit body where a pick up
or large luxury car really need a ladder frame to carry the weight.

Then it depends on how well the unit or frame engineers did their jobs too.

[chrisser]

Does anybody know of any objective tests or documentation as to whether a vehicle with separate frame and body is safer than a vehicle with unit body construction?

Crash

Vehicle design is a series of compromises.

Unitized bodies lend themselves well to mass production, compact drivetrains (especially transverse front wheel drive), utilitarian suspensions (Macpherson struts), and passenger vehicles.

Body-on-frame vehicles lend themselves well to vehicles which tow or haul, or which are performance-oriented (either in terms of drivetrain power, or suspension design), or which are produced in smaller quantities.

Which is "safer" depends on the lens through which you want to view it.

For example, unitized bodies would be safer than body on frame if you were comparing safety vs material used, or safety vs cost to mass produce.

Body-on-frame would be safer in terms of safety vs performance, or safety vs tow/haul capacity, or safety vs cost to produce in small numbers.

Neither design is inherently safer than the other unless you control for some other parameter. In other words, given unlimited cost, or unlimited materials, either can be made as safe as the other.

Also, generally speaking, larger and heavy vehicles have frames. Safety is most often expressed in terms of collision surviveability, and a lot of that depends on what it is you hit (or hits you). In a vehicle-to-vehicle collision, the vehicle with the most mass wins, and this is generally the framed vehicle.

To be a little more specific, though, in a collision, there are some significant forces involved. The key to how safe the vehicle is (not counting things like intrusions) is how much of the force of collision is absorbed by the vehicle (through deformation, redirection, or impact absorbtion) and how much is absorbed by the driver (through seat belts, air bags, the steering wheel, etc.).

But there's a tradeoff too. At some point, the reaction of the vehicle has to change from self-sacrifice (absorbing collision) to occupant protection (not collapsing the passenger compartment). Larger vehicles have more "stuff" to deform, collapse, bend, whatever to absorb the collision before the passenger compartment integrity becomes a concern.

The point at where that tradeoff occurs is the real key to how safe a vehicle is, given a collision involving some amount of force. The vehicle that can absorb the most force from a collision without compromising the passenger compartment or transmitting the force to the occupants, is the safest, regardless of the path used to get there.