coil overs spring sizes

[itsjay]

Hey everyone.
I am switch out my shocks and going to coil overs.
gonna have eight inch of travel.
what size springs should I use?
I read that the bottom should be 10 inches long but what about the pounds?
I'm thinking 150 for bottoms and 100 for the tops.
Suggestions?

Thanks

[Dale M.]

What is your current suspension setup... Stock VW or custom chassis.... VW shock towers were never designed to take spring/suspension loads...

Dale
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[KrAzY-BaJa]

what size shock body
and 100 is very light

All shocks should have a minimum of twice the travel length in spring length. That means an 8" travel shock should have a minimum of 16" total spring length....either using one 16" spring or a combo of lengths (6" upper and 10" lower for example) to reach the total length.

We typically recommend using a lower (Main) spring that is 2" longer than the shocks travel length, and an upper (Tender) spring that is 2" shorter than the shocks travel length. (ie. A 12" travel shock will use a 14" Main spring and a 10" Tender spring) If the spring rates you need are not available using the longer lower/shorter upper method, you can use 2 equal length springs as needed. (ie. A 12” travel shock can use 2 12” springs)
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[77charger]

I have 8.5 fox 2.0s and use a 10 inch bottom spring and an 8 inch top spring.

My buggy only has about 375-400 pounds on the front end unloaded and i am using a 150 top spring and a 200 bottom. just to give you an idea.
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[itsjay]

thanks for the replies.

[DHale_510]

You want to engineer a solution or just copy what folks like?
If you want to engineer a solution you need to do arithmetic, measure your weights and decide just what kind of use you will see.

2 1/2" springs over 10" long will arc and rub the shock body, so dual springs are popular. Springs shorter than the coil over adjustment rang fall off their seats and do crazy stuff. Tender springs keep this from happening, and plastic junction blocks keep them together and off the shock threads.

Dual springs always result in a spring rate softer than either one. The equation is [rate A + rate B] / [rate A x rate B]. Two 10" x 200#/" springs is a 20" x 100#/" spring.
They will not have the softer rate until it is played out then change to the stiffer rate.
The pair of springs will move together until the softer one fully compresses at around 2/3 of the combined travel [if one is 1/3 stiffer than the other] then the rate goes up to the stiffer rate for the remaining travel. This is sort of a progressive rate. It is better than a true progressive rate since the car always reacts about the same instead of changing all the time. The above example of two same rate springs will run at 100$/" for the whole travel, maybe 15". Remember that the springs have thickness and a 10" spring will only travel 5" to 7".
Preloading the assembly will allow you to adjust for the down travel, at rest loading [ride height], and will keep the stack from unloading without tender springs.

If you drive hard and land your car off jumps [or just make mistakes...], you probably want enough rate and travel to take the force without bending stuff that isn't a spring. So if you have a 2000# [rather light] Baja Bug, you need to take on about 1000# at each wheel, and if you have 10" of travel, you want about 100#/" spring rate as described above. If you expect to land everything on one wheel, maybe twice that is a good idea, at least in the back. The shock can slow things down and help, but it is not a spring.

Most Baja Bugs weigh over 2500# loaded with Duke and Daisey, while Buggies start about half that. Stock Bugs came in at about 2000# empty, maybe 500# of load, and had about 750#/" spring rates. Early Bugs were lighter. None were engineered for airborne stunts.

Since these cars always are relatively rear heavy, the front to back spring rates are seldom the same, and the engineering to solve that problem is all yours to work out, and why there is no simple answer to your simple question.

Dennis