stacked spring

Studying the stacked spring setup! Question #1, how does length affect rate. I often read spring rates are based on the strength of compression per inch etc. 4" or 10" no difference. If I were to stack a 5" 400# spring over an 5" 200# spring, is it the same as 4" 400# over an 6" 200# setup? Also, does anyone run stacked spring strictly as a two stage, lock nuts tight at ride height? I'm lead to believe this is common at the left front to keep that 550# spring for dive. Any "quality" answers welcomed, LOL.

1. Spring height does not matter.
2. A staged spring setup allows both to work and it "catches" or stops one spring after a set amount of travel. It is actually used on the RF to allow body roll onto the spring to get the LR to start it's motion before getting onto a stiffer spring. It should ONLY be used in a VERY VERY slick application as if not it will put the car into the wall when the LR drives the chassis through the RF.
Putting one on the LF would only change entry on braking and would upset the car going into the corner at high speeds. Not a real good place for the LF to instantly loose traction.

RF is the most common place for this "dual stage" stacked design. And as ego said, slick track conditions ONLY. The idea being that you tighted the car on entry by allowing it to roll over on the RF easier and then increase forward bite off the corner by allowing the stiffer seconday spring rate to reload the LR as you exit the corner. Much like the bumpstop stuff, this can get real tricky on a track with ANY roughness to it.
A similar setup can be run on the LR in slick conditions.
On a heavy track you can run something like this on the RR to provide for an initially soft spring rate to free corner entry and then a stiffer "secondary" spring rate after the car is laid over to help free on-throttle exit.
There is a science to this dual-stage stuff and a lot of guys are playing with it.

depending where on the car you do this it can be a very helpful tool but your shocks are a big factor in this too i like the stacked springs for the adjustability we use this alot but if it were me i would do alot of testing

Thanks for the replies! How do teams use the stacked spring diff. than the dual stage? Looks as though the springs used are very similar in rates, just seems like dual stage is more precise. Is stacked "safer" as far as geeting started? The more I look into this dual stage the more it presents to me as valving your springs. When I first read about stacked springs it appeared to me as an advantage to be had at the LR, compression capabilities of a 200# spring, rebound of a 133#. Sorry if my post seems a bit sporadic!!

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Originally Posted by pushpush

Thanks for the replies! How do teams use the stacked spring diff. than the dual stage? Looks as though the springs used are very similar in rates, just seems like dual stage is more precise. Is stacked "safer" as far as geeting started? The more I look into this dual stage the more it presents to me as valving your springs. When I first read about stacked springs it appeared to me as an advantage to be had at the LR, compression capabilities of a 200# spring, rebound of a 133#. Sorry if my post seems a bit sporadic!!

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Be careful with the terminology. "Stacked spring" and "dual-stage spring" mean two different things.
The stacked spring deal is pretty simple: you've got two springs that work together to form a different rate. The reason you run two is because a single spring of the desired rate and height would bow on you. Formula of (A*B)/(A+B) gives you your rate which it looks like you understand.
The dual-stage spring starts out like the stacked spring but then you add the jam nut to stop the slider and then the spring below it is the only one used.
And you are correct about that LR setup. You would run something like a 200# 12" spring on bottom and a 200# 4" spring on top with slider between them and the jam nut turned all the way up. Set your ride height and turn the jam nut down to contact the slider and you have exactly what you are talking about: 133# spring in rebound and 200# spring in compression.
The RF setup is essentially the same (with stiffer springs) but with the jam nut backed off to allow compression travel at the lower spring rate. How much you back off the jam nut is a key point of adjustability.