Spring rate, ride height, and ride quality

[NODNARB]

So, here’s the story: we are making some custom shocks for a dude, nothing crazy, just bolt in emulsion 2.5’s with the help of carbon shocks. They’re for a 3rd gen explorer (independent front and rear suspension)

The easy part was getting extended and collapsed lengths to mimic overall length of stock ones with a small “strut spacer” to hopefully be better than that. Already checked cv angles with the small spacer and we are good there, can’t make them exactly stock length anyways because they’re too short to package with a 2.5… anyhoo, one pair of the factory ones has a roughly 350 lb rate but 5” of preload!
I checked using my high tech spring rate testing unit.

So, using the spring as a “scale” we know it takes roughly 1750 lbs of force to hold the truck at current ride height. I don’t think we want to run a 350 lb coil with 5” preload, but do we want to run an 800 lb coil with 2” or so either?

In my limited experience on my personal truck I’ve found better ride quality with a heavier coil and less preload vs lighter coil with more preload but that was a change of 100 lb/in difference in coils. Not 450 lb difference. What to do? I think this is gonna turn into a can of worms that I shouldn’t have opened.

 

[Motiracer38]

That's a progressive wound spring that would not have a linear weight. Did you compress further to verify the spring rate at ride height? Keep pressing as far as you dare and record the load in 1/2in increments or so.

Soft spring rates allow for a compliant ride without feeling jittery or harsh. A 350lb spring loaded to 1750 will require 2100lb to compress another inch where an 800lb spring will need 2550lb. Bottomed out at 4in travel would be 3150 and 4950, respectively. A small bump in rate would be better for an off-road ride but that would be a huge jump.

 

[84Prerunner]

That's a progressive wound spring that would not have a linear weight. Did you compress further to verify the spring rate at ride height? Keep pressing as far as you dare and record the load in 1/2in increments or so.

Soft spring rates allow for a compliant ride without feeling jittery or harsh. A 350lb spring loaded to 1750 will require 2100lb to compress another inch where an 800lb spring will need 2550lb. Bottomed out at 4in travel would be 3150 and 4950, respectively. A small bump in rate would be better for an off-road ride but that would be a huge jump.

I was thinking basically this same exact thing. Need to know how far the stock coil compressed in stock form and gather that full bump rate vs full bump rate of a larger coil with less preload.

 

[NODNARB]

Ok this makes sense. Thanks guys. I can only go to 660 lbs (300kg scale) I think we are going to essentially split the difference and see what this thing rides/sits like and go from there.