Determining spring rate

After looking on the Moog website for rear coil springs, there is a "load rate" and a "spring rate", which one (or combination) determines how soft or hard the ride will be?
Also, what is the standard spring rate for the base 1996 caprice from the factory (just to use as a reference point)?

Your SPID label should identify each of the springs installed on the vehicle. There is a 3-character alpha code for each spring, usually beginning with a "7" or "9" and two other characters. This can be used by a factory service department to identify exactly what springs are installed for a car with your options.

"Spring rate" determines the relatively linear rate at which a spring resists compression over a given distance, such as pounds per inch. For example, one inch of spring compression requires 350 pounds. The next inch of compression requires 350 pounds, or 700 pounds total. And so on...

Load rate is a less direct method of classifying springs, and takes into consideration the mass of the vehicle plus whatever load you may carry. Typically, it is the total load which you can apply to a stock vehicle while remaining within the stock ride height limits. It's a lot more subjective and less accurate a comparison.

The load rate number is typically a lot higher than the spring rate number, since a spring is usually designed to compress several inches before being at a stock ride height. It may take 1,050 pounds to get a spring to compress a spring three inches from its free length to the stock ride level. Such a spring would have 350 pounds of spring rate but 1,050 pounds of load rate.

Springs with a higher spring rate tend to provide a firmer, flatter, and more controlled ride. Springs with a lower spring rate typically have a softer ride. A relatively "soft" spring with a load rate of 1,000 pounds may have 20" of free length, whereas a "firm" spring with the same load rate might only have 16" of free length. A caprice had fairly long, soft springs, while an Impala SS had fairly short, firm springs. Both vehicles had basically the same effective load rate.

So, the spring rate affects the ride, and the load rate only affects the ride if there is a load in the back that compresses the springs?
How would it ride if I went with softer springs but firmer shocks?

So, the spring rate affects the ride, and the load rate only affects the ride if there is a load in the back that compresses the springs?
How would it ride if I went with softer springs but firmer shocks?

with soft springs and a firm shock like bilstiens you would over work the shocks....the basic caprice springs where the FE1 this is the standard spring/soft ride don't last very long..then you have the FE2 police /9c1 H.D. suspension springs..then you have the FE4 springs this is the same as the FE2 except they are shorter..about 1.5inches or so....

don't use the soft springs you wasting you money and your shocks won't last....there are many places on the internet to get all this info and to order exactly what you require...

I always order the HD suspension from factory when purchasing vehicle...standard springs are bad...

This is what is on my '94 Impala w/WS7 and FE4 options:

6TY - Spring, Left Front, Computer Selected
7TY - Spring, Right Front, Computer Selected
8HL - Spring, Left Rear, Computer Selected
9HL - Spring, Right Rear, Computer Selected

My '96 Impala has the same RPO codes. The paper Alpha tags (if they are intact) show which springs are actually installed at each corner.