Why are car alignments so hard to get right?
In: Engineering
It’s not really hard. The difficulty comes from two aspects. First, the angles need to be extremely precise. A good alignment will have certain angles (especially toe, but also camber) within 0.05 degrees of the ideal value. This is usually done by using plates with specific patterns on them viewed by a static camera. A computer takes pictures of these plates, and calculates the angle. It’s very accurate, but the systems are expensive.
Wheels are also held in place by control arms with rubber bushings. This rubber means that there is flexibility and deflection. The alignment needs to be set so that the angles are correct with no deflection in the bushings, so at a ‘rest state’. This is usually mitigated by doing the alignment with the wheels resting on slip plates, which ride on low friction bearings. This means that you can adjust the angle of the wheels without deforming the bushings. Again, this is specialized equipment, and expensive.
So it’s not necessarily difficult, but it does require expensive equipment.
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