Looking for a good stack spring starting point

[racefastnow]

What springs would be good for a RF stacked spring setup. looking for the lbs. of each and the height of each spring.

[DEKconsulting]

400/600 is a good start point

[Matt49]

Height of springs depends on the design of the lock out kit you're using.

The most important thing you need to understand is that this setup requires a completely different shock valving profile. You can't just put the springs and lockout kit on your standard RF shock and expect results from this. You also need to understand the starting point for your lock-out nut (gap) which depends greatly on what springs you start with.

[DEKconsulting]

Yes what matt said is correct u need to understand it and how it works but those are the two that i started with both are 7 in Springs

[7uptruckracer]

We have a lot of guys on this over a bump spring. I can't figure out why. We want the cats on the ground . Unless they have opened the gap up so the car travels farther until it get onto the 600-800 whatever they are running on the bottom how is that better then a 308 (500/300) bump spring 2.5 inch stack? I've been racking my brain on this lately. And when you are dojng wheel loadin do you count the static load or just zero out once you reach your static center to center

Height of springs depends on the design of the lock out kit you're using.

The most important thing you need to understand is that this setup requires a completely different shock valving profile. You can't just put the springs and lockout kit on your standard RF shock and expect results from this. You also need to understand the starting point for your lock-out nut (gap) which depends greatly on what springs you start with.

[racefastnow]

I wanna ask a really dumb question. but how does a stack setup with 2 heavier springs end up being ligher rate than one softer spring. for example. a 500/700 is a 291 rate. but uses a 500 and a 700. so, this combo would be lighter than a 400, but both springs are heavier than a 400. something i must not understand about the way springs must work.

[Matt49]

I wanna ask a really dumb question. but how does a stack setup with 2 heavier springs end up being ligher rate than one softer spring. for example. a 500/700 is a 291 rate. but uses a 500 and a 700. so, this combo would be lighter than a 400, but both springs are heavier than a 400. something i must not understand about the way springs must work.

The best way to think of it is to use a simple example to keep the math easy.
Take a 400 rate spring and put 400 pounds on it. It will move 1" because the spring is rated at 400 pound per inch.
If you put another 400 rate spring UNDER that first 400 rate spring, it will compress 1 inch also because it still has to hold up 400 pounds (plus the weight of the other spring but that is negligible). The bottom spring feels a 400 pound load. AND the top spring feels a 400 pound load.
So BOTH 400 rate springs will compress 1 inch if you put 400 pounds on top of them. This means the total rate of the stack is 200 pound per inch since the entire stack compressed 2 inches under 400 pounds of weight. As you start to use springs that are of unequal rates, the math gets complicated but it boils down to the formula we all know.
(AxB)/(A+B)

[95shaw]

Great explanation!!!

[racefastnow]

in your explanation, im a little confused all thought i think you did a good job, haha. doesnt that mean if you stacked 400 on top of another 400 pound spring that each spring would obsorb 200 pounds so each spring would compress half n inch.

so,, when you use the formula, thats the actualy spring rate. so if its less than a single spring its going to behave less than that spring all the way. if in your example you have a 500/1000. which is 333. but it wont act like a single 333 spring correct? im saying if the 2 springs were just stacked on top of each other, negating the locknut. im asking these questions cuz were trying to do something else but its related. like in your example 2(400) springs would they act the same as a single 400. if they were just stacked on top of each other.

Is it because there wound seperately and dont compress together totally thats y this is true. where a single 400 would be obsorbing the load totally?

[Matt49]

in your explanation, im a little confused all thought i think you did a good job, haha. doesnt that mean if you stacked 400 on top of another 400 pound spring that each spring would obsorb 200 pounds so each spring would compress half n inch.

so,, when you use the formula, thats the actualy spring rate. so if its less than a single spring its going to behave less than that spring all the way. if in your example you have a 500/1000. which is 333. but it wont act like a single 333 spring correct? im saying if the 2 springs were just stacked on top of each other, negating the locknut. im asking these questions cuz were trying to do something else but its related. like in your example 2(400) springs would they act the same as a single 400. if they were just stacked on top of each other.

Is it because there wound seperately and dont compress together totally thats y this is true. where a single 400 would be obsorbing the load totally?

Just think in terms of the weight.
Think about it like this...
If you take a 400 pound/inch rate spring on the ground and put 400 pounds of lead on top of it, we all agree that it would compress 1 inch.
If you put ANOTHER 400 pound spring between the 400 pound spring on the ground and the 400 pounds of lead, there is STILL 400 pounds of weight on top of the 400 pound spring on the ground that it has to support. It will compress 1 inch. It doesn't KNOW that the 400 pound spring between it and the 400 pounds of lead is ALSO supporting the weight (and compressing 1 inch itself). It only knows that there is 400 pounds above it and a ground that won't move below it. So it compresses 1 inch. The spring in the middle has a spring below it that (once compressed) isn't moving and 400 pounds above it. So it compresses 1 inch.
The two springs are two independent systems and don't work together. All that the lock nut does is eliminate one of the springs from the total equation. Two 400s stacked together will behave like a single 200 until when compressed from the bottom of the bottom to the top of the top. When the jam nut hits, you are eliminating the top spring and now compressing from the bottom of the bottom to the top of the bottom so you're back on a single 400 pound spring.

[Matt49]

Maybe a better way to think of it is to remember how a spring works in the first place. A springs rate is determined by strength of material, wire diameter, and number of active coils. Increasing wire diameter increases rate and increasing active coils DECREASES rate. In our example of two 400 pound springs, all you've done by stacking two springs on top of one another is increase the number of active coils of the "total" spring. Wire diameter stayed the same and strength of material stayed the same but you doubled the number of active coils which halves the effective spring rate.
And before you ask, no, the length of the springs doesn't matter. If you were to stack a 12 inch 400 pound spring and a 4 inch 400 pound spring you would notice one thing very quickly: The wire diameter of the shorter spring is MUCH less and it has to be to achieve the same rate because the number of active coils is less. The number of active coils makes the spring stiffer so the wire diameter goes down to soften it back up.

[racefastnow]

sent a private message Matt49

[7uptruckracer]

Wanna take a crack at my question

Maybe a better way to think of it is to remember how a spring works in the first place. A springs rate is determined by strength of material, wire diameter, and number of active coils. Increasing wire diameter increases rate and increasing active coils DECREASES rate. In our example of two 400 pound springs, all you've done by stacking two springs on top of one another is increase the number of active coils of the "total" spring. Wire diameter stayed the same and strength of material stayed the same but you doubled the number of active coils which halves the effective spring rate.
And before you ask, no, the length of the springs doesn't matter. If you were to stack a 12 inch 400 pound spring and a 4 inch 400 pound spring you would notice one thing very quickly: The wire diameter of the shorter spring is MUCH less and it has to be to achieve the same rate because the number of active coils is less. The number of active coils makes the spring stiffer so the wire diameter goes down to soften it back up.

[Matt49]

We have a lot of guys on this over a bump spring. I can't figure out why. We want the cats on the ground . Unless they have opened the gap up so the car travels farther until it get onto the 600-800 whatever they are running on the bottom how is that better then a 308 (500/300) bump spring 2.5 inch stack? I've been racking my brain on this lately. And when you are dojng wheel loadin do you count the static load or just zero out once you reach your static center to center

I'm not sure I completely understand the question. What exactly are we comparing? The "308 (500/300) bump spring 2.5 inch stack" part is where I got lost.
When you say bump spring I assume you mean the little spring inside the coil-over spring that sits down on the lower shock perch. The disadvantage to them is that they are a VERY heavy spring rate and limited travel so it's harder to get the transition you might want. But perhaps better than a bump stop as all bumps stops are extremely progressive.

[7uptruckracer]

I'm not sure I completely understand the question. What exactly are we comparing? The "308 (500/300) bump spring 2.5 inch stack" part is where I got lost.
When you say bump spring I assume you mean the little spring inside the coil-over spring that sits down on the lower shock perch. The disadvantage to them is that they are a VERY heavy spring rate and limited travel so it's harder to get the transition you might want. But perhaps better than a bump stop as all bumps stops are extremely progressive.

I have a PAC Bump spring stack it's two 1" springs a 500 and a 800 and with the cups it ends up being a 2.5 tall assembly with a top and bottom cup and a divider cup so that's where I got that number. My question is basically what are the dual stages setting gap at these days. We want the nose on the ground but traveling so far and running a lockout stack I don't see how they are getting the nose on the ground without more gap when we use to run so they don't lockout To a still spring too soon

[fastford]

I have a PAC Bump spring stack it's two 1" springs a 500 and a 800 and with the cups it ends up being a 2.5 tall assembly with a top and bottom cup and a divider cup so that's where I got that number. My question is basically what are the dual stages setting gap at these days. We want the nose on the ground but traveling so far and running a lockout stack I don't see how they are getting the nose on the ground without more gap when we use to run so they don't lockout To a still spring too soon

what rate primary spring are you using with this set up? I left the bump stop for the two stage stacked set up to help on a rougher track, but have been thinking of trying a bump spring set up to try and find a happy medium , didn't contemplate using a stacked bump spring though.....