Help, new wheels scraping on '85 Coupe GT addendum:

[edkellock at juno.com]

Was just under my Coupe GT and the panhard rod orientation
is the reverse of what you describe.  However, as I laid under 
the car and absorbed the geometry of it all, I would agree that
this is the cause of the tendency to rub more on the driver's
side rear.  The passenger side is fixed to the body and with
the axle at normal ride height is is angled downward away
from the undercarriage.  So it would seem that when the axle
is pushed up toward the body the panhard rod would need
to extend further to the driver's side as it pivots on it's 
mounting point to the body.

So it would seem we have somewhat of an explanation,
however not for quattro equipped cars.

Ed
Colorado Springs, CO

On Wed, 29 Nov 2000 17:29:53 -0800 "Fisher, Scott"
<Scott_Fisher at intuit.com> writes:
> Ken Keith gets it on the money, I'll bet:
> 
> > This may have already been addressed, but the panhard bar moves 
> > the axle to _one_ side as the car is lowered, or as the wheels 
> > move up toward the body.  Ideally, one may want to have an 
> > adjustable heim (hime?) joint at the end, to center the axle 
> > at the new ride height.
> 
> You know... when I first read the posting about the car with an
off-center
> rear axle, I wondered about the Panhard rod and couldn't remember which
end
> was connected to the car and which to the axle, so I didn't say
anything.
> But of COURSE -- that's a known behavior of a Panhard rod, that the
> body-to-axle alignment changes as the ride height changes.  I'd be
willing
> to bet a power-window switch (works, just needs cleaning :-) that the
right
> end of the rod connected to the axle and the left to the chassis, yes? 
A
> few quick sketches seem to suggest that's the orientation that results
in
> moving the axle left under compression... unless I've got it exactly
> backwards, of course. :-)
> 
> Anyway, this is almost certainly another reason my undropped car
*doesn't*
> rub and all the dropped cars described on the list *do*.  Next time
it's
> reasonably dry (or I'm in clothes that I don't mind wearing while
crawling
> in wet leaves), I'll peer under the CGT and see if I guessed right
about the
> geometry of the Panhard rod.  But either way, for those of you who have
> lowered your CGTs, you *will* have changed the Panhard rod geometry (as
well
> as the rear trailing arm geometry).  That's not necessarily a bad
thing, but
> it IS something to keep in mind.  There's almost no change you can make
that
> affects only one part of the car's behavior.
> 
> (Doesn't explain the ur-Q that was mentioned as rubbing, however...
that's
> gotta be rim/tire width and offset.)
> 
> Also, to chime in further on the subject of tweaking ride height with
> shocks: some brands of shock *are* known to change a car's ride height.
> This was well documented in the early '90s about Tokico Illuminas; I
ran a
> set on my autocross GTI and the car was slightly taller than a friend
and
> codriver's GTI with Boge shocks.  Both cars were on stock springs and
the
> same tires/wheels, so the only difference was the shock choice.  The
main
> advantage that the Illuminas gave, however, was that I could tune the
rears
> stiffer than the fronts, which changed the car's corner-entry
> characteristics to make it feel as though it had more (or at least
some)
> oversteer in the early part of the corner.  Just the change you want to
make
> in a noseheavy autocrosser, where getting the car to "point" quickly in
a
> corner is half the battle.
> 
> One thing I enjoy about the CGT is that, for a FWD car, there's far
less
> understeer than I'd expect from that looooong 5-cylinder engine hanging
off
> the front.  Kudos to Audi for getting the rear suspension as good as it
is;
> it's a joy to pitch this car into a corner hard, get on the gas, have
the
> weight transfer to the rear and feel the car yaw outward into something
that
> feels very much like a RWD car's drift.  That's the main reason I'm not
> planning on putting in shorter springs -- since this will probably
never be
> a track car, I don't want to upset the rear-end geometry.  
> 
> --Scott Fisher
>   1983 CGT
>   1993 100CSQ
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