WHEEL ALIGNMENT

FRONT
Unlike the MacPhearson front suspension used on most cars today (Saab 9-3, 9-5!), the (more advanced) double wishbone setup on old 99's has a lot of adjustment possibilities to play around with.
- Toe in: Adjusted by screwing the end-link balljoints in or out of their trackrods
- Camber: Adjusted by adding or removing shims, located between the upper wishbone bracket and the inner wing. More shims = more negative camber.
- Castor: Adjusted by adding or removing shims only at the front or rear end of the bracket. More shims at the front end = more castor.
- KPI (King Pin Inclination): Is affected by the adding/removal of shims.

REAR
After the periodic vehicle-check, some Saab owners have been told, much to their surprise, that the rear wheels were out of alignment. "-But the rear axle has no adjustment possibilities!??" Oh yes it has. A strategicly applied 20 ton hydraulic press will adjust toe in and camber as much as you like. (You'll need to remove the rear axle from the car first)
A misaligned rear axle often means a bent axle tube, caused by someone's careless use of a single point jack. Or hitting something when travelling sideways at 100 Km/h.

GOING BY THE BOOK
According to the HAYNES 0765 -79 to 93 manual, the only adjustable thing is toe-in. Neither camber, castor, KPI, or the rear axle are adjustable. I believe exactly what I want about that.
According to the HAYNES 765 -79 to 83 manual, toe in, camber and castor angles are adjusted as described above. Can they please decide??

WHY ALIGNE ?
The suspension was manufactored and adjusted to the constructor's spec's when the car was new, and is "supposed" to stay that way. The constructor's spec's is always a compromize between attracting inspired drivers who want sharp handling, or making the car suitable and safe for most drivers. Saabs are mostly biased towards the latter category.
- The toe-in setting mostly affects front wheel tyrewear, but also directional stability, especially under heavy braking.
- Playing with the other angles, and altering suspension setup will affect steering wheel lightness (or lack thereof), steering wheel kickback, tyrewear, directional stability, direction change willingness, tramlining, body lean, understeer/oversteer, sneezefactor and more.

Thumbrules:
- Adding anti roll bars will reduce body lean. (And low speed snow traction)
- Adding a front `bar, will make the car understeer more.
- Adding a rear `bar, will make the car oversteer more.
This does not, however, mean that fitting anti roll bars both front and rear will make the car drift more sideways through a bend. It will do quite the opposite: Grip more.
- Stiffer springs will reduce body lean. (and low speed comfort)
- Stiffer front springs will make the car understeer more.
- Stiffer rear springs will make the car oversteer more.
The same principles as for anti roll bars apply here.
- The shockabsorber bounce/rebound settings will affect matters too.
- Increased track-width will increase corner stability and reduce body lean.
- More front negative camber will improve turn-in reaction.
- If you have a "loose" front and a "firm" rear, more rear negative camber will improve rear adhesion, when your inner rear wheel lifts off.
- Different tires have a different "ascew-roll-angle". (The angle between the pointed direction and the travelled direction, at a certain sideways load). This also changes with tirewear. Less rubber left = sharper handling.
- Different wheel dimensions have a different behaviour.
- Stiffer (polyurethane) suspension arm bushings will sharpen the handling. (And increase noise)
- Stiffer steering rack bushings will reduce the sneeze factor.
- Ride height will affect the position of the roll-center, since the angles of the lower and upper front suspention arms (viewed from the front) changes with wheel travel.
- At the rear, roll-center is determined by the angle of the panhard rod. It too changes with ride height.
- Front/rear weight distribution affects under/oversteer balance. There are two types of "weight". The things placed OUTSIDE the wheelbase (in the overhang), and things placed INSIDE the wheelbase.
- Heavy objects placed in the front overhang will make the car resist direction changes. (For our grandparents, this is called "nice&safe stability". For us, this is called "soggy understeer")
- Objects placed within the wheelbase does not affect "direction change resistance" in the same way. This is why sports cars with mid-mounted engines has such sharp handling.
The battery, for instance, is one of the "easy moveable objects".
The engine is not. The windshield washer tank is. The headlight wipers can be ditched. Move the horns!? Mould a fibreglass bonnet? -It all comes down to how much effort you wish to put into balancing the car.

When I say "balancing the car", I mean exactly that. It is easy to get lost, when playing with the wheel angles, if you dont know what you're doing. Dont overdo it, or you'll end up with a car that does NOT handle well. Its only harsh and uncomfortable.

SNEEZEFACTOR
A "safety feature", especially loved by German car constructors. (Opel, VW, Mercedes and such)
It works like this: Drive your car at 100 Km/h (62 Mph) on a two or three lane motorway. Then, VERY rapidly turn the steering wheel 90 degrees to one side, turn it back again, then turn it 90 degrees to the other side, and finally turn it back again. This must be done in a fraction of a second, and in one whole operation whithout any pause inbetween.
With a built-in sneeze factor (very compliant rubber bushings in the steering rack, and elsewhere in the suspension), your car will do absolutely nothing! Perhaps perform a little wiggle at best, but it will stay in the lane you were driving in.

Now you know what your car will do if you have a sneeze attac on a motorway.

Do this in a Lotus Elise (the best performing car of the last century, and so far this too) and you'll have changed lane three times. I believe the steering rack bushings in the Elise are made of aluminium (!)

99 vs 900
As I've mentioned before, the 900 evolved out of the 99, and basically they are similar.
The front suspension is identical, exept for early m82 models, when 99's still had the old type hub/driveshaft assembly (in combination with the new H-engine), and 900's got the new type. The dampers are different, and will not interchange, as 900 dampers have top pin-bolts, instead of eyes. The 900 frame rails are positioned 2 cm furter apart from each other than on the 99. Therefore the 900 has a 2 cm wider front track. I believe the driveshafts are longer too, but I dont know for sure. If anyone has the exact measures, please e-mail me. Wider track is achieved by changing wheels, a different offset is needed.

The rear axles look similar, but the 900 has from 3 to 1cm wider track, depending on model. This is acheaved by a wider axle tube, but the attachement points in the body are identical (as of m75 99). The 900 rear axle also has a slightly diffrent geometry, the upper leading arms are longer. In 1982 Saab rationalized away having to produce two different, similar looking rear axles. The Saab 99 got the 900 rear axle, resulting in a shorter wheelbase.
- A 900 rear axle will bolt straight on to an m75 or newer 99.
- On the pre -75 models, some modifications on the brake hoses are needed, and a panhard rod from a Saab 9000 (!)