| The reason I say rate is misunderstood and mis-used is because "rate" does not come close to fully defining a spring's load characteristics. The best way to compare springs is with a force vs. displacement chart. The spring rate can then be calculated with the change in force between two points divided between the change in length between the same two points. Progressive rate springs are coiled so that as the spring is compressed, some of the coils will become inactive and cause the spring rate to "progressively" increase in doing so. This is explained by the spring rate formula: R = (Gd^4)/(8D^3Na) Where:
R = rate
G = modulus (material specific)
d = wire diameter
D = mean diameter of spring
Na= number of active coils Since Na is in the denominator, you can see that decreasing Na will cause R to increase. Where in the springs compression stroke, the coil(s) become inactive is entirely geometry related and depends upon the distance between the spring's coils. A tighter coiled design will transition much sooner than a design with more spacing between the coils. When a manufacturer defines their progressive spring with two rates, in my opinion, a lot of information is left out leaving a huge question mark as to it's "load" characteristics. The numbers may look similar to what you are replacing but without a full load vs. displacement chart, you might as well be picking the springs based upon how pretty they look instead. If you're interested, I've load checked my stock TT springs and here's what I found: 
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spring "rate" is misunderstood and mis-used... - 
