Help with spring rates :/

I'm having a lot of trouble deciding on spring rates. Quick info:

Want to run a dual rate setup (I'm using 10" travel coilovers, and can fit 24" of springs plus the dual rate slider without having to compress them on the shock).
My wheel to shock motion ratio is 1.76:1.
Shock mount location is 10.7" out from pivots.
Wheel location is 18.9" out from pivots.
Shock angle relative to LCA is approximately 76 degrees.
Desired ride height is 5" of droop.
Total travel is 14".
Assumed corner unsprung weight is 1175lbs.
Vehicle is a 2001 4Runner (3.4L).
Suspension is a coilover double A-arm design.

Based on my calculations if I run a 1500lb/in spring on top and a 750lb/in on bottom I can get near my desired ride height, I'll just have to crank the collar down 1.5" and I will get near a final suspension frequency of 1.35hz which I found on Race Dezert. Now the issue is, I just found a thread on TTORA where some guys are saying their suspension frequency was around 0.9-1.0Hz. I'm not sure which source I should use, since barely anyone in the offroading world (according to the internet) discusses suspension frequency. Long story short, should I use a 1.35Hz or ~0.9Hz target? 1.35Hz is easy to hit, under 1.0Hz will be trickier to get the ride height I want but if need be I can always compress the springs before installing them though that's not desirable.

The reason I want dual rates is because I have long enough shocks and want to have a smooth ride onroad as well as off. I value offroad performance over onroad, but if I can get good onroad performance than why not go for it? Any help is appreciated, though I'm not just asking what spring rates does everyone run, I want some technical advice in regards to suspension design for a speed oriented offroad vehicle---which as I said, I'm finding extremely difficult to find good info to reference.

Thanks

 

I'm not a shock spring guru, but have a bit of a grasp on it. You probably saw this cool calculator link in your search
http://www.crawlpedia.com/spring_rate_calculator.htm#dualrate

I'm currently running dual rates on my 10" coilovers, but I didn't try calculating out the since I bought the truck used with them already. I should do all the calcs for fun to see where I'm sitting. One issue I see I don't think you can get a 1500lb/in spring. I think the highest is 800 in any desirable length. Could be wrong here. You will want to run the stiffer spring on the bottom. The reason why is because when you hit your slider stop that lower spring will help stop you before you hit a bump stop. You get that nice heavy loading toward the end of your travel. I think the nature of the dual rates you are going to need to crank them down on a heavy truck. If you need a spring rate of 750 overall maybe dual rates can't work for your application.

I also haven't calculated out natural frequency, but I think it is a preference. 1 will be pretty comfortable and 1.3 will be responsive and a bit firm. From what I learned 1 is your everyday car and 1.3 would be a car that has a sporty feel to it. This is where shock valving comes into play. A softer spring you will have a lower frequency and it is easier to tune your shock. When you get up to the higher numbers shock valving becomes more sensitive meaning you have a narrower tuning margin to work with. How 1.3 measures into this it is a bit hard to say since I've only messed with my truck, but 1.3 sounds to be acceptable to work with.

Not too many people get into the technical aspect of shocks for offroad. Most people just call up a shop and ask for a starting point just from what has worked in the past and trial by error.

 

im at 450 over 600 right now on my first gen.
will probably jump to a 500 lb upper pretty soon

 

Sorry to bump an old thread, but did you ever find a solution? I'm looking to run dual rates but like he said the max rate I'm seeing is only 800ish.

Biggie, if youre running a 450 over 650 youre actually at a 257 spring rate... that's REALLY soft unless youre having the top one hit the spacer at ride height

 

Yes that's correct not much over 800, you can get higher rates but not needed at all on a Tacoma , springs that heavy only needed like on a long travel diesel trucks. Usually all 10" coilovers on tacomas that run dual rates always run a 500 top spring and 600-700 lower. I personally run a 500 over 600 and works great. Yes your right it compresses really quickly and I mainly use the lower spring driving on streets. Heck on all long travel trucks ive seen Silverados and nissans any 10" coilover will only come with 500 top spring.

 

Also keep in mind that the rate is per inch of the spring so it takes 650 or whatever the rate is to deflect just one inch of the spring. It's not as soft as you think.