Home alignment setup

[Norm Peterson]

It is possible to work with a floor that's slightly out of level as long as it's flat. You have to keep in mind that the cambers that you measure and the casters that you compute will need to be corrected to the actual vehicle attitude. Say the floor slopes 0.1° from one side to the other. That means that -0.5° measured for the wheel on the 'high' side of the floor is really at -0.4°, and -0.5° on the other side is really -0.6°.

From working with a car in which rear toe is adjustable and another car in which rear toe is not adjustable but not zero either (even though the thrust angle is pretty close), I wouldn't put too much faith in a line determined by assuming that any rear wheel is ever parallel to the vehicle centerline. Parallel strings is still the better bet. An adaptation of the SmartStrings approach is one way to ensure that the strings are in fact parallel. Then you can offset the strings from the front and rear wheels, keeping in mind that front and rear track dimensions probably are not identical.

Starting from scratch, I'd probably work rough caster, rough camber, rough toe, then caster, camber, and toe. Remeasure and iterate caster, camber, and toe if necessary. Caster adjustments seem to affect camber more than vice-versa (why you'd do caster first), and "final" toe adjustments have hardly any effect on the other two (why it's saved for last). BTW, make your caster sweeps for the left side and right side independently of each other. At 15° or 20° of front tire steering, Ackermann effects are creeping in, and the 20° that you work to on one side could be a degree or two different on the other (which makes the assumed factor for getting caster from cambers inaccurate and the caster won't be quite what you think it is).

Suppose you don't get the strings quite parallel to centerline. I think what that mostly means is that your steering wheel might end up a little off center on your test drive. Toes should be close enough, since they're still referenced to lines that are parallel, and close enough to being parallel to car centerline that - for the tiny amount of steering involved - Ackermann effects will be essentially nil. So you might have to adjust one tie rod longer and the other shorter by the same number of "wrench flats" a couple of times (this can even be done during your test drive, if done with a little care). Theoretically, equal and opposite tie rod adjustment will hold your toe setting, but in practice you probably won't get them adjusted quite equally. So you'll probably want to check the toe one more time against the strings after you're happy with the steering wheel position.




Norm