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Steering axis inclination (SAI) and toe-out-on-turns are not adjustable angles and only used for checking for bent parts. Usually, if the steering axis inclination is off, either the upper or lower control arm is bent and possibly the spindle. It would depend on what the reading was, for example you could not usually cause a control arm to lengthen so if it was showing too much negative the top would be in too far and thus the upper control arm bent. Just the opposite for bottom or camber/included angle (SAI) too positive, then the bottom too far in or lower control arm bent. Not to mention it could possibly be the spindle also. If the toe-out-on-turn is off then the spindle is bent where the arm reaches out to hold the outer tie rod.
It all depends on how hard the curb is hit. Most of the time a simple camber/caster adjustment will bring it back within specs, if not something is bent too far. Everytime something is hit it bends, the adjustments are there to compensate for minor adjustments.
The strut technically in this case would be the same as the upper control arm since it won't have an upper control arm if there is a strut there.
If you ever looked at the upper and lower balljoints you would notice that they are nowhere close to being the same distance from the vehicle center. The camber is actually measuring the tire. The angle that the upper balljoint or in the case of a strut the spot where it connects and most likely different manufacturers have different ways of measuring would be the included angle, add or subtract from that the camber for SAI.
You asked, "Why or how is the cam neg anyway?" Answer, if the top gets bent in. Whether or not the upper control arm or strut.
Camber is adjustable on just about every vehicle as well as toe. Caster not all vehicles have an adjusment but wit the invention of aftermarket cam bolts, strut plates, etc they can be made adjustable.
What year, make,model engine are you working on? I will look up what specs I can.
The very first thing to do when checking alignments is checking parts for being worn or loose, checking tire air pressure, ride height. Different cars have different SAI specs.
For example here is the alignments specs for the 1970 Chevelle, note the different SAI specs. Also, what they call wheel pivot ratio is the same thing as toe-out-on-turn.
Thanks for the accept. Here's a tip for you. Here is how an instructor taught me years ago to do an alignment without a machine, just incase you wanted to know.