Jordan wrote:
Tim Wescott wrote:


Steel can be painted or galvanized to not rust, and works pretty darn
well for frames.

The original spec for Land Rover (British version of Jeep) frames was to
make them in steel and galvanize. They didn't do that in production, but
a version for the Australian army called the Perentie did.
http://www.allisons.org/ll/4/LandRover/Perentie/
The chasses were welded up from rectangular section steel, looking
something like a home built.
Don't Jeep frames need to flex somewhat? I saw a bare one sitting on a
garage floor. The owner picked up one corner, and the other three
corners stayed on the floor!

They may, but I'm more inclined to believe that they're supposed to be
reinforced by the body they sit on. Model T Ford frames were quite
flexible, but by design much of the missing torsional strength came from
the bodies -- the '26 T roadster body 'subframe' is more torsionally
rigid than the frame it sits on.

In general if a car is flexing in torsion then the doors won't stay
closed, or at least won't close properly in some circumstances. Also in
general, closed car bodies are much more torsionally rigid than open
ones -- this is why convertibles generally need stronger frames than the
equivalent closed version of the same car, and why they are often a few
hundred pounds heavier.

But certainly if you take a frame that's made to flex and make it
inflexible you'd better know what you're doing, or the next thing
that'll happen will be that suspension parts will rip themselves off of
the thing. (IIRC the early Fords would rip up their body mounts when
you hot rodded them or drove them hard for long periods of time, for the
same reason).

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com