john hennessy wrote:
the spring fixtures at each end of the spring, that being the chassis at one end and the "a" arm at the other, would move equally when the spring was compressed by a bump in the road and the chassis would dip down the same amount as the wheel moves up, but what appears tto happen is that the end of the spring on the "a" arm moves up and the center of the spring moves up half of that
All motion is relative such that what you see as stationary is moving in another frame of reference, and what you see as moving is stationary in another frame of reference. A spring only cares about its own perspective. So as you so observantly noted already, if only one end of the spring appears to move the middle of the spring moves half as far. Thus if you measure from the middle of the spring, both ends of the spring did move an equal distance.
nick47 wrote:
If unsprung weight were somehow zero, the body wouldn't move at all, and the suspension would completely absorb the bump. Occupants of the car wouldn't feel a thing...
Actually unsprung weight is only part of the equation. A theoretical car with zero unsprung weight would most certainly have body movement and the occupants would still absolutely feel it. An overly simplified example would be to consider a car with 300lb/in springs supporting the sprung weight and zero unsprung weight. If the car hits a bump that compresses the spring by 1 inch, the spring would still be transmitting 300lb of force up to the chassis. You are correct that unsprung weight and unsprung vs sprung ratio does play a significant role, since the spring (and shock) must also control the momentum of the 75+lb being thrust upward by the bump in the road.
john hennessy wrote:
my current setting are 1.6 in the front and 1.8 in the rear
Those sound like your method also worked well in bringing you to some pretty reasonable numbers.