"Tim Wescott" wrote in message
...
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

Right. All else being equal, the most rigid frame is the best frame -- and
torsional rigidity usually is the limiting factor -- but, as you say, the
suspension has to be made to handle the high point loads.

Ladder frames have an advantage for trucks and other utility vehicles in
that they can accommodate different bodies with little extra work.
Otherwise, they're generally antiques. One of the best chassis engineering
books ever written said, in 1962 or thereabouts, that perimeter frames,
particularly ladder frames made from open sections, were obsolete for
passenger vehicles.

The Jeep is an engineering anachronism, but a loveable one that still does
its intended job.

--
Ed Huntress