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2 minute(s) of a 612 minute read
3-16-2009
More spring info than you'd ever want 
: The second spring in a 2 stacked springs setup could be "helper" as discussed above, or "tender." The term depends on the function of the spring.
Tender Spring: If the second spring is NOT fully compressed with static load, it is no longer called Helper Spring. It's now a Tender Spring and this stacked springs setup is now much different. A tender spring is actually much stiffer than a helper spring and by definition is not in total bind (fully compressed) like the helper spring at static load when car is not moving.
How is the setup different? It now has 2 effective spring rates, an initial rate, and a second rate. If the main spring rate is a, and the second spring rate is b, then:
Intial rate = b x (a/a + b) (someone checks the math for me 
)
Final rate = a
If you are thinking wait a minute, isn't this just like a progressive spring? Bingo. To make matters more interesting, I have even read that the tender spring could itself be either linear or progressive.
BTW, all after-market coilovers for the Turbo that I've seen have similar configuration to the Bilstein: stacked springs. In the Bilstein, the second spring is a Helper; whether it is Tender or Helper in these other setups, I don't know. I remember reading JIC Cross has a spring rate of 900+ in the rear (extremely high) and keep wondering if it is in fact a Main + Tender setup.
4-12-2009
Before and after TechArt Type I lip:
