Proper suspension geometry is based on the difference between the measurements of a and b. The 108mm that you call measurement c. Meaning it sets the angle of the lower control arm. From its pivot point to the ball joint. To maintain that angle (which will affect bump steer) when you raise the spindle 19mm you need to set that c measurement at 127mm. The 108 plus the 19 of raising the spindle. Otherwise you would reduce the angle of the control arm from the pivot point to ball joint. Bump steer is worsened by not having the steering control arm not parallel with the lower control arm taken from the center of the ball joint to the center of the pivot point. Those two arcs need to be as close as possible so no change to the dimensional measurements. Causing a pull or push on the steering knuckle. Additionally the distance from where the strut mounts on the ball joint to where it sets at the top on the chassis will not change. Maintaining original travel of the shock. That’s stock geometry. That’s why you lower a car with raised spindles vs just changing springs or spring orientation. By maintaining these angles you may not need to raise or lower the steering rack. It would depend on where the knuckle is on the strut. Weather it was raised or not.
