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Theory of Operation
MEASURING STEERING ANGLES
The steering angles caster and SAI are dened by physical components of the vehicle suspension, those that
dene the steering axis (such as upper and lower ball joints on a short-arm long-arm suspension). Conven-
tional aligners measure these angles using gravity gauges and the toe system by monitoring the affect these
angles have on those angles as the wheels turn. Once again the 3D Aligner is unique and superior.
The 3D program locates the steering axis directly in 3- dimensional space in the same way it found the vehi-
cle’s spindles. We locate the axis by putting our targets in motion about the axis by turning the wheels. First,
we turn one direction 10 to 13 degrees. The software monitors the movement of the target dots, which scribe
an arc. The program nds the center of each of the 33 arcs, averages, and knows where the steering axis is
located. As with the spindle determination, we check our ndings by turning the wheels the other direction.
If the two steering axis calculations agree, we pass this along to other parts of the software that convert axis
locations to caster and SAI angles referenced to the vehicle plane.
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