I don’t do caster, I do what I call the kingpin inclination angle. It has another name but I can’t remember what it is. Cars don’t have king pins anymore but you can still calculate the angle. If it is right both longitudinally and laterally, then the camber and caster will be right.
Most cars these days it is a moot point because there isn’t any adjustment for the camber and caster.
I do my own for the same reason that TT does, only I paid for six crappy alignments before it sunk in and I started doing my own. Guess I’m a slow learner.
keith–you said, " If it [the kingpin inclination angle] is right both longitudinally and laterally, then the camber and caster will be right." I’m inferring that you’re saying the “longitudinal” kingpin angle is the same thing as the caster angle & that the “lateral” kingpin angle is the same thing as the Steering Axis Inclination (SAI). The problem with assuming that the camber will be right if these 2 angles are OK is that there’s no spec (hardly ever anyway) for the SAI, so you can’t know if this angle is right even if you can actually measure it. One just looks for the LH SAI to be close to the RH SAI, especially if you’ve just whacked a curb or whatever. (If you can measure SAI & caster, I don’t see why you couldn’t measure camber too.)
Just FYI: On an alignment rack the caster angle is determined by how much camber change takes place as the steering wheel turns the front wheels through a given number of degrees.
This post refers to a car with a McPherson strut front suspension design. I stand by what I posted previously. Doing the alignment at home came in handy several times when my old VW broke a driveshaft boot or two, had a failed driveshaft, needed a clutch disk, and a rear main engine seal. The lower “A” frame needs to be disconnected to remove the driver side driveshaft in order to to get the trans off when needed to do the jobs mentioned which loses the alignment. The bolt holes in the “A” frame are larger than the bolts so it’s not easily possible to put it exactly where it was previously. This disconnection will affect toe the most, camber to a lesser extent safe enough to ignore and caster to a negligible amount. I too have the bucks to get it done as with oil changes and other maintenance jobs but have a little fun doing it at home. At least half of the time needed would be otherwise spent driving to and from an alignment shop, shopping on the phone for a place to do it and waiting for others to do the work.
You can get a rough idea of caster angle with an adjustable level against a strut body. This tool entirely lacks the precision for the accuracy needed to measure caster for final alignment purposes but you normally don’t need to know the exact caster angle as per my previous post.
There are, of course, several more alignment and steering design parameters than caster, camber and toe but being able to adjust these three on a vehicle that has not suffered collision damage can go a very long way toward keeping a person and his/her car out of an alignment shop.
Yes, caster is adjustable; have used only the first of two methods as follows:
Elongate the strut mounting holes at the top of a shock tower. Then use larger washers to cover the holes well. You get only one shot at doing this so it must be done right the first time. It can likely not be done again unless you get some repair done to the modified sheet metal but the adjustment will probably not be needed again.
Adjustable caster/camber plates are available.
Thank you Karl for your: “But hey, if you’'re doing alignments in the driveway & your tires aren’t wearing out then you’re doin SOMETHIN right!” affirmation. Our cars drive as well as they should and do not wear tires other than what is normally anticipated. Can’t do better than success!