Spring rates and Load rates and yeah this is a general question

I am faced with getting some new shocks for my van and I'd like to run this by da guys on the boards here. I figure this knowledge will help a 3S platform a bit too and I bet several of you have vans. lol

Basically the curb weight of the van is 3800lbs. I dunno if thats with full fluids or not, but that would be of course "before added other weight". This is a Ford Windstar, same year as my 3S, 95. The rear springs have always been too soft and mushy... lots of bottoming out etc... Both rear shocks are blown and a lot of guys recommend air springs and I really don't want to fool with that. I just want a set it and forget it option.

Mostly, this is about comfort and I want to "not bottom out" when the van is fully loaded full of people and FULL luggage. I estimate all that to be about another 500lbs in the back and sometimes I tow a small single axle 6x12 cargo trailer that weights 1400lbs. All towing will be likely under 2500lbs total and I really doubt if it'll ever even be that much and I might tow something 2 times a year.

From what I have read most vehicles don't come with variable rate springs in the back or anywhere and instead come with constant/single rate springs. I am considering upgrading the front ones too due to age (do they sag over time???) along with the rears. With all that in mind I've found some options and actual spring rates here:
Moog Suspension Parts - Universal Coil Springs

The part numbers on that page are:
Part Number / End 1 Type / End 2 Type / Inside Diameter / Bar Diameter / Install Height / Load / Spring Rate / Free Height
MOOG-CC875 Pig Tail Pig Tail 4.326 .562 12.00 680 136 17.00
MOOG-CC873 Pig Tail Pig Tail 4.326 .562 12.00 732 136 17.38
MOOG-CC820 Pig Tail Pig Tail 4.000 .718 12.13 1428 366 16.19

Ok, well I've read that the lower the spring rate the softer the ride. Given that I want to be prepared for a full load of luggage and people and not have all that sway and bounce and sometimes tow.... which would you go with? Will the CC820's ride like hell with no load and no people? I called MOOG and he said he had a Windstar and the CC875's were listed as heavy duty. I was going to go with those as I wouldn't think that they'd be much different than the CC873's, but there's also those CC820's.

If I guestimate 900lbs in each rear corner for just van weight alone, and then add 250lbs for each rear corner for added people/luggage load thats 1150lbs per rear corner, which to me would make it seem like the CC873's would be "OFF" a bit on the load rate factor, but OK ON THE SPRING RATE???

My van is rated to tow up to 3500lbs too, not that I will but it would seem the CC820's would take care of the load factor for sure, but I wouldn't want it to make the van seem too damn rough all other times. I just wish I knew the spring/load rate of the OEM Ford rear (or front) springs, but I don't know where to find it.

I went through all this before when I bought a set of KSport coilovers for my 3S and I totally got this wrong so I figured this may be a good lesson here for others too.

Don't tell anyone I found all those spring rates, cause apparently no one wants to list the spring rates because its the bread and butter of the spring industry. :P

LOL - Oh well. I gave it a shot.

CC873 CC875 will ride the same. the 873will ride higher given the same weight in the car. They will both bottom out at the same compression, but it will take more load to bottom out the 873. 820 will probably feel like bouncing ASS, especially if you can't find uprated shocks.

Thanks Pete.

I was looking into the Monroe Sensatrac shocks. I guess I should just go with the 873's and since I'd be going from constant rate springs to variable, that alone should feel a lot better wouldn't ya think?

Odd to me that I have called MOOG twice and asked and they say the CC875 will bottom out before the C873 will, but the CC873 has a higher load rate than the CC875 does. It even lists on RockAuto.com that the CC875 is more "heavy duty" than the CC873, but I wonder if MOOG listed the load/spring rates wrong for these two parts or listed that the 875 is heavy duty when in fact it isn't.

In any case I'm going to trust the numbers I see and despite the 875 saying it is more "heavy duty" the load rate of the 873 is higher and the spring rate of both are the same, so it would appear to me the 873 is more heavy duty than the 875, so again trusting the listed numbers I am going to go with the 873 since I want a heavier duty option.

I know this is a boring ass thread - :) - since its about a van, but these same principles apply to our 3S and any car. :)

Well, not that anyone cares, but the 875 is the more heavy duty. The 873 was listed heavier duty wrongly so on the 3rd party web site I was looking at.