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Alignment
Posted by stottler (more from stottler) on Thu, 19 Dec 2002 14:23:07
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I'm picking up this thread a little late, so I apologize if I've missed some
of the earlier details, but Peter your comments about the difference in
camber from side-to-side caught my eye.  In general my experience has been
that cross-camber and cross-castor DO matter in terms of how the car
behaves, and I think that this can translate into tire wear problems as the
miles add up.  In general, toe-in has a great affect on straight-line
tracking, which is quite important in a street car, so the toe-in setting is
an attempt to balance straight-line tracking against wear of the outside
edge of the tire, which increases with toe-in.  Castor (front-to-rear angle
of the line through the ball joints to a vertical line) also affects
tracking, which improves as the castor becomes more positive (the line
through the ball joints tilts forward).  The trade-off here is that as
castor increases, turn-in response decreases.  So, one can concieve that if
the two sides are different, the car may behave differently in terms of
tracking to road crown, crosswinds, etc.  Camber is the angle of the line
between the ball joints to a vertical line from side-to-side), with negative
camber meaning the line tilts toward the center of the car.  Increasing
negative camber tends to offset body roll in turning and so keep the tire
closer to vertical when you turn, hence enhancing response.  However, too
much negative camber can cause wear on the inside and instability.

With all that background, my usual approach is to start out with a little
negative camber, about -1° on each side, then get the castor a little
positive, about 1° on each side, and then start with a little toe-in, maybe
1-2mm and see how things behave as far as straight-ahead tracking versus
tire wear.  You may need a little different settings if you drive on crowned
two-lane roads all the time versus all highway driving.  Again, every time I
have had a car with significant missmatch in camber/caster settings between
the two sides (eg: 1° or more), I have had some sort of bad behavior, so I
try to work it down to less that 1/2° difference.  Frankly, this can be a
pain in the neck.  It usually requires iteration on the part of the person
doing the alignment, and they don't want to spend the time; they will just
say 'it's within spec' and that ends the discussion as far as they are
concerned, so it takes some doing to find a shop who will work with you,
especially if you want a setting that's different than the original spec,
which is where I ended up on my 99 Turbo.

I'm sorry, by now I've forgotten which model car you have, Peter.  A lot of
the above can be done with model 93, 95, 96, 97, 99, and C900 cars because
the 'unequal length control arm' suspension is pretty much infinitely
adjustable.  Macpherson strut cars (9000, NG900, 9-3, 9-5, 9-3SS) can be
worse, because alignment is basically 'as built' - the only adjustable part
is the toe-in.  So you get whatever camber and castor you get depending on
how the body welding went that day, how the strut meets tolerance, etc.
Camber/castor adjustment on strut cars require either that a frame shop
start bending the strut towers to get the tops of the struts where they need
to be or that an adjuster plate (Typically a race car part - maybe try
Abbott?) be installed at the top of the strut so that it's position can be
varied with respect to the lower ball joint to adjust camber/castor.  Also,
if a strut car has had any kind of damage, even seemingly minor damage such
as a curb strike, the structure can be out of line and throw things off.  I
think that with 1.6° of cross-camber you are going to see some issues.

I haven't really talked about rear alignment, but it's worth at least an 'as
it is now' measurement to make sure things aren't way off or goofy stuff can
happen.  A car that routinely comes back from alignment with the steering
wheel off-center is a good suspect for rear alignment problems.   Pretty
much all Saabs require a trip to the frame shop to bend stuff to change the
rear alignment.  Don't be afraid of this, it's accepted practice, it's just
hard to find a place to do it.  Again, if you're going to the trouble, stay
on them to make sure they get both sides the same!

A final note, of course, is that all this assumes no wear/play in wheel
bearings, ball joints, tie rod ends, strut bearings and mounts, steering
racks, suspension bushings, etc any/all of which can certainly be suspect in
a car with over 60-70K miles again depending on it's history - a lot of
rough roads and these things start to give up the ghost sooner.

Hope all this helps, a lot of it is based on my experience with a number of
cars both street and track over the years.  Unfortunately, like many things,
'cheap, quick, simple' don't apply too well to getting it sorted out.

Good luck!

Gary Stottler
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