Re: IML: Unit-body vs body-on-frame

[Christopher Hoffman <imperial67@xxxxxxxxxxxxx>]

Since you asked, Richard, I'll offer my two cents! These are all just my
opinions, and I'm sure others will disagree.

I certainly don't define "tougher" as "heavier." Just because your '66
weighs more than a '73 does not make it stronger, more durable, or better at
protecting you (even though it IS strong and durable and "tough").

Unit-body designs can be made more rigid because all of the load-bearing
elements can be welded together as a complete 3-dimensional system (so that
something like the roof and firewalls can help support the overall system),
rather than taking what is largely a two-dimensional load-bearing structure
(the frame, which is more subject to torsional flexing on its own) and
bolting it to a largely non-load-bearing body at 8 to 10 points. (And yes,
the body does bear some loads, but not most of the ones generated by the
forces of driving or the weight of the running gear.)

A good measure of toughness might be dimensional stability, meaning the
entire body structure retains its precise shape in every direction under the
rigors of use. By better resisting flexing and twisting, the welds and other
joints are less stressed over time or in an impact, promoting durability and
safety. And one indicator of the ability to do this is high torsional
rigidity, something which unit-bodies can excel in (I say "can" because
there are crappy designs of both unit-bodies and body-on-frame vehicles).

The one place where a body-on-frame setup might hold an advantage is large
trucks, in part because pickups, by nature of being giant open-topped tubs,
cannot provide the same rigidity as a closed car. It's also easier to
manufacture and beef up for varying lengths, configurations and payloads
without having to reengineer the whole body structure for every "duty" range
(1/2-ton, 1-ton, etc.) or variation (pickup, SUV, dump truck, whatever). If
most large SUVs were not based on a pickup, there's be little reason to go
body-on-frame with them (well, GM might not have the expertise to make a
20-foot-long tube of a Suburban as a workable unit-body.. They achieved
their "benchmark" of rigidity in the 90s with the Olds Aurora by making all
the door and trunk openings really small and the sills really big). The
unit-body SUVs have proven themselves sufficiently strong and more rigid
with lighter weight, which adds to more "carlike" handling. But this is
off-topic from an Imperial perspective, so...

All things being approximately equal (from the size of the car to the
engineering expertise of manufacturer), I'll take a well-designed unit-body
almost any day. 200 lbs of extra weight is not going to make up for the
increases in strength, rigidity and durability. It's just heavier. That
said, I wouldn't kick a pre-67 Imperial out of my collection just for having
a traditional frame under its lovely sheet metal!
-- 
Chris in LA
67 Crown
78 NYB Salon




On 2/25/05 8:45 AM, Woolf,Richard T(Contractor) (richard.woolf@xxxxxxxxxxxx)
wrote:

> I want someone in the club to define "tougher."
> 
> I find that very hard to believe that a unibody car is stronger than body on
> frame. Considering the size of the frame on my '66. My '66 is built like a
> tank, and is over 200 lbs. more than my '73 which as you all know is a
> unibody car.
> 
> Rich Woolf
> '66 Crown
> '73 LeBaron
> '75 LeBaron 



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