On Sun, 11 Apr 2010 10:23:22 -0400, "Ed Huntress"
wrote:


"John" wrote in message
.. .
On Sat, 10 Apr 2010 12:11:41 -0400, "Ed Huntress"
wrote:


"John" wrote in message
...
On Fri, 9 Apr 2010 08:30:43 -0400, "Ed Huntress"
wrote:


"John" wrote in message
om...
On Thu, 08 Apr 2010 07:29:27 -0700, Larry Jaques
wrote:

On Thu, 08 Apr 2010 08:20:07 -0600, the infamous Lewis Hartswick
scrawled the following:

I didn't read the whole tirade but Ralph Nadar
is/was an IDIOT. He lost all credibility when
he wrote " Unsafe at any Speed".
What a load of BS.

Yeah, he castrated GM while allowing the VW to go unpunished, despite
the fact that they had more problems than the Corvair, including the
extreme tendency for several to set themselves on fire almost as an
almost daily practice.

No that is not correct. Nader wrote Unsafe at any Speed, which was
pretty much a hatchet job to the extent that totally incorrect
statements were made and even a sketch of how a swing axle works was
deliberately drawn showing the outside wheel in a turn tipping inward
at the bottom, "tuck under" as Nader preferred to it when in fact it
does exactly the opposite, although if you do not understand how the
suspension works it might appear to be correct.

Ah, John, no. I hesitate to interfere with your trashing of Nader g,
but
he was correct. It was commonly called "jacking" among the sports car
fraternity. Anyone who drove an early VW, Corvair, Triumph Spitfire, or
box-stock Porsche 356 (including the original Speedster) will be glad to
relate some horror stories about it for you. d8-)

Some older chassis books can explain and illustrate the same thing. If
you
were actively driving sports cars around, say, 1965, you were very
familiar
with it.

Well, actually the "sports cars" I was tinkering with didn't have
fenders and had wishbone suspension all around. But I did do some work
on swing axle cars and unless you were able to weld the chassis to the
axles body roll, and they all had it caused the inner end of the
inside axle to move downward. Of course the inboard end of the outside
axle moved up :-)

The formula VW guys didn't have problems with "wheel tuck tripping the
car" as Nadar claimed...

They would have if they weren't strapped down with stabillizer bars or
Z-bars. The lower CG made it less likely than in a bug, but you still had
to
strap down the rear. I never saw a FV that didn't have a stabilizer bar in
the rear, although someone probably tried it at one time or another.


No Ed, the whole "wheel tucking" is so much hogwash. Before you reply
draw a little picture. Differential in the middle, attached to the
chassis; axle going our either side firmly attached to the wheels. Now
imagine going around a corner - the chassis/body rotate around an
imaginary line called the "roll Center" that body rolls outward at the
top and the diff goes right along rolling the top of the diff toward
the outside of the corner which moves the axle attaching point down
which in turn causes the wheel to lean inward at the top and outward
at the bottom.

John, enough. Here's a photo of an early, swing-axle Triumph Spitfire
jacking:

http://forums.pelicanparts.com/uploa...1090328641.jpg

Here's a Triumph Herald -- same suspension, higher CG. This is the extreme
case: the inside wheel actually lifts:

http://herald-tips-tricks.wdfiles.co...ilt_herald.jpg

Here's an illustration that shows it:

http://www.rqriley.com/images/fig-17.gif


Your analysis is missing the primary forces at work here, which are the
inward force applied at the bottom of the tire, and the outward force of the
car as it goes through the turn, applied from the pivot point through the
half-axle, to the center of the wheel hub. The couple's effect is to tuck
the tire under the car.

Forget body roll for a moment and just look at how that force couple is
resolved -- by the tire tucking under, and the car "tripping" over the
outside wheel.

That's what happens. Compression of the outer spring from body roll
counteracts it. When forces are low, the body roll usually dominates. As
cornering forces increase, the outside wheel snaps from negative to positive
camber, the pivot point reacts by moving in the only direction it's free to
move -- upward -- and the car jacks.

You can see it clearly in the photos above.


Yes, I can clearly see it in the photos and certainly the wheels are
both positive.

I've read your description a number of times and I think something
besides cornering force is effecting the car.. As you describe it
cornering force alone overcomes every other force and lifts the entire
back of the vehicle enough for the camber, which would have probably
been at least a degree or so negative as a result of body roll to
suddenly go, from your pictures at least 10 degrees positive. But the
Internet is so slow here in the Marina that any research will have to
wait until I get back home to a faster connection.

I had damned Nadar for all these years when he was right......but what
the hell, I'm not going to start lauding him with phrase, I plead the
rights of RCM to continue my own cockamamie view point, evidence to
the contrary be damned :-)


Cheers,

John D. Slocomb
(jdslocombatgmail)