Re: caster??

[Steve Stegmann <stegmann@domain.elided>]

On Thu, 15 Apr 1999, Kurt Musgrave wrote:

> We talk quite a bit about the effects of caster.  A couple questions, what
> is the effect of too much caster.  Why did IH design the Scout with 0º
> caster in the first place.  They must have had a reason for that initial
> design, they didn't change it till 80, right?  Why??
> 
> Kurt
> 
Little known fact.  Until the late 70's very few cars had any caster,
maybe 1 degree.  Chevy was investigating how to make their cars, Monte
Carlo was the immediate subject, handle and feel more like a Mercedes.
They stopped with the fact that MB used a lot of caster (4 deg maybe)
to give their cars good self centering.  This was cheap and easy to do
without really changing anything of substance or spending any money.
Illusion without depth has always been a GM hallmark.  It is what sells.
One reason they have beaten Ford and Chrysler for years.  They understand
what it takes to sell.  Image, and advertising, not innovation and
engineering.  People buy what they can see.  IH could have learned a lot
here too.

They didn't bother with the rest of the analysis which has been
"discovered" in the last 5 years.  For years the thing which made the MB
cars feel like they did was a design in which chassis rigidity and
strength was paramount.  They weren't light by any means, MB's are
generally heavy.  But they were tight - didn't rattle.  And the suspension
worked much better than average because it was attached to a car that
didn't flex.  A lot of this was learned with the 300 SL series which was
fairly light and very rigid.  But it got this way with a "birdcage frame" 
which was made of 1/2 to 3/4 inch tubing running all throughout the
bodywork. Actually only part of the framework was made that way. 'Course
if you hit it, there were very few shops that could or wanted to bother
fixing it. 

When Ford designed the latest Taurus they had been studying the effects of
chassis rigidity, resonance of the whole car structure, frequency of
vibration sources, etc.

What they came up with was the Contour and the latest Taurus.  These cars
have great detail attention paid to chassis rigidity.  The effect is quite
striking when you consider it.  The easiest comparison is the Taurus.
Tests of the old and new side by side have left the writers stunned.  The
effect on handling on poor roads is amazing.  The new ones are much quiter
in general, better isolation.  What really surprised Car and Driver was
the fact that the new Tarus has 50 (fifty!) pounds less sound deadener,
and it's quiter.  The chassis weighs less, it's just designed better.

What they have discovered is that by spending some engineering making the
frame *much* more rigid, they can do all of the following at the same
time.

 1- Raise the resonant frequency of the chassis way above the typical
frequency of wheel induced noises.  (tar strips, chuck holes, tread noise,
road surface noise)  Amazingly lots of noise goes away and doesn't require
damping

2- The handling is immediately improved since the suspension is working
from a stiff chassis and isn't flexing all over creation.

3- The car can be made lighter

4-  The car has a much more solid feel. "Feels like it was machined out of
a single block" they used to say of the old MB's

5- Assembly goes much easier and cheaper since the parts fit better since
the chassis doesn't flex.  Automatic inprovement in fit & finish  (what
the Japs did so well)  Fewer rejected parts that don't fit.

6- They can hold tolerances on hole locations much better, cheaper too.

7- As the miles pile up the vehicles don't seem to develope rattles as
easily.  

8- Won't do a damn thing for corrosion resistance though  (IH realated)

I've noticed that when driving my Contour, hitting tar strips with fully
inflated tires, I hate soft tires, that the chassis actually "rings" like
a bell at each shock.  It isn't very loud, you have to really listen,
normal customers will never hear it. The whole character of the sound made
by the chassis is different. All the rumbling is simply not there.

If you look at it from the bottom of the car, you will notice that a lot
of money has been spent down here where the customer can't see it.
Compared to the older cars there is a heavier subframe for the suspension
and engine, with much more full welding and less spot welding.  You can
also see where they have spent money to decouple the wheels from the rest
of the vehicle.

All of this is applied to current trucks too.  Have you noticed in the 4x4
mags that when crossing a ditch at and angle, the bed and cab on the new
trucks stay aligned much better than and '70s truck.  Some of them would
have 2 inches of motion between the bed and cab. 

That's how come the new trucks are actually as tough as ever and much
quieter.

Preach mode off!

Steve

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Steven A. Stegmann
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