13. Parallelogram suspension. If the double A-arm suspension is geometrically made by a parallel- ogram then, the wheel will always remain perpendicular to the road. This is the best design to have uniform tire wear. M d a b C. N 03 B FIGURE 7.68. A parallelogram double A-arm suspension. A parallelogram suspension however, has a variable track when the load of the car changes or the wheel moves up and down. The maxi- mum track of a vehicle with such a suspension occurs when the upper and lower arms of the suspension are parallel to the ground such as the one illustrated in Figure 7.68. Calculate and show the track changes of the suspension for z +25 cm. =