rear springs part 2

I spent some more time looking at spring and shock selection.  As the suspension moves up and down, the angle of the spring changes if it is anything other than straight up and down.  I was curious how much spring rate is lost from this travel, as well as how much extra travel length is gained.  It is easy to work out:

From there I made a spreadsheet to evaluate real shocks.  It turns out for anything much beyond 20° initial angle the spring rate falls very quickly for even modest displacement.  I take from this that shocks are inclined to simplify installation, not to gain travel.  That said, I do need to angle them.  The top area needs to be inside the frame rails (not enough room between rail and tire to be outside, not enough height to be under the rail).  If I mount them vertically that far inboard, then there will be too little roll stiffness, and too little roll damping.  So I will need to incline them.

I saw a few inexpensive options:
Jegs double adjustable coil overs (currently $186 each) 6.5 inch travel
QA1 Promastar single adjustable (currently $163 each) 6.25 inch travel
QA1 Aluma matic not adjustable (currently $135 each) 5.125 inches travel

I also wanted to look at how long is the shock is as the car sits (ride height).  The adjustable shocks are significantly longer.  To use a longer shock, I will need to encroach into the truck area and/or mount it lower on the axle which is a potential hazard.  While long travel double adjustables would be cool, I just couldn't justify the extra time, expense and sacrifice to space.  Most other builds I have found seem to go the same route.

Here is what the spring rate loss is over its full travel as a function of install angle which is TBD.  So for example, If I install the shock at a 15° angle from vertical,  The spring rate at full bump will be 15% lower than at full droop, and the total axle travel possible is 5.4 inches.  This is not including the additional loss of spring rate from the initial angle which is ~ 7%.