ground control spring rates

[kamotors]

I'm thinking of switching out my H&R race springs and going with a ground control setup.
My question is what spring rates would you recommend for a turbo E30 auto-x setup? My current H&R race setup feels too soft and the rear squats too much.

[IronFreak]

Call Mark at GC, the dude is super cool. has helped me with a lot!

[acolella76]

Seriously, why do people post this question anymore when it gets asked every other day? You're a cool dude, but you've been here for a while. You need to learn to search. My advice to you is either A) search old threads and see what people run (I run 500/~550) or B) call ground control and see what they recommend.

[Robert]

500f/750r

[Earendil]

Seriously, why do people post this question anymore when it gets asked every other day? You're a cool dude, but you've been here for a while. You need to learn to search. My advice to you is either A) search old threads and see what people run (I run 500/~550) or B) call ground control and see what they recommend.

My understanding is that suspension is a highly dynamic thing, consisting of many elements. Not only is the existence of ones exact setup not guaranteed, but assuming it does it's near impossible to find using the search function. What r3v needs is a chart made up of the most common elements that get combined, and post it in a sticky, such as:

Use (autox, track, rally, street, mom-as-passenger)
Shock
Spring rate
Bar size
Weight
Power
Desire to under/over-steer.

That would go a long way to answering those looking for a more typical setup, while also helping those that are looking at something close, but not quite what's on the chart. In the mean time, I don't mind people asking, and I don't mind reading the answers :)

If you are positive that GC is the brand you want and offers a solution, then by all means call the GC experts and tell them what your setup is!

[mulletman]

Off topic: I will be in Reno tomorrow night. You should give me a ride in that ridiculously powerful car of yours.

[acolella76]

My understanding is that suspension is a highly dynamic thing, consisting of many elements. Not only is the existence of ones exact setup not guaranteed, but assuming it does it's near impossible to find using the search function. What r3v needs is a chart made up of the most common elements that get combined, and post it in a sticky, such as:

Use (autox, track, rally, street, mom-as-passenger)
Shock
Spring rate
Bar size
Weight
Power
Desire to under/over-steer.

That would go a long way to answering those looking for a more typical setup, while also helping those that are looking at something close, but not quite what's on the chart. In the mean time, I don't mind people asking, and I don't mind reading the answers :)

If you are positive that GC is the brand you want and offers a solution, then by all means call the GC experts and tell them what your setup is!

Maybe I am the only one who thinks spring rate advice threads get posted all too often. And for what it's worth, there is already a suspension setup thread and it is stickied at the top of the page. Or perhaps I should just start one of my own?



OP, if I were you, this is what I'd do:

450-550 front springs
Convert the rear to coilover and double up on springs. Put a low rate tender spring (about 150-200lbs) and a higher rate spring on top to equal the total spring rate you want (so if you put a 300lb spring on top of a 200lb spring you would effectively have a 500lb rear spring). This acts similarly to progressive rate springs and is helpful in high horsepower car that have trouble putting power down. But I'm just going to guess that you probably don't want to switch to rear CO so you would probably be better off running a spring that is more on the softer side. IMO I would probably look in the 500-600 ballpark.
Of course, sway bars are used for fine tuning to the drivers preference, but disconnecting your rear sway bar will also help put the power to the ground.

[Hellabad]

Convert the rear to coilover and double up on springs. Put a low rate tender spring (about 150-200lbs) and a higher rate spring on top to equal the total spring rate you want (so if you put a 300lb spring on top of a 200lb spring you would effectively have a 500lb rear spring).

Actually, this is not correct. It is very hard to imagine how "stacked springs" work, unless you have spent a lot of time designing electrical circuits. (truth!)


Here is how I would try to explain it:

Imagine two pillows stacked on top of each other. Two pillows are softer than one pillow.

Imagine that one is a feather pillow, and one is a foam pillow. When they are stacked together, they will feel softer than just one pillow.

Through a bunch of mathemagic, the formula ends up like this:

(feather pillow times foam pillow)
divided by
(feather pillow plus foam pillow)
equals
super soft pillow.

for resistors we have:

(300 ohms times 200 ohms)
divided by
(300 ohms plus 200 ohms)
equals
120 ohms

for stacked springs we have:
(300 pounds/inch times 200 pounds/inch)
divided by
(300 pounds/inch plus 200 pounds/inch)
equals 120 pounds per inch

This is really really hard to wrap your head around, so try to imagine the pillow scenario.

If you are very mathematical, then check this link:

http://wiki.answers.com/Q/What_happens_to_resistance_when_resistors_are_wired_in_parallel

here is a link for electrical resistance:

http://www.sengpielaudio.com/calculator-paralresist.htm

Here is a link for actual car springs:

http://www.swayaway.com/calculators/swayawayCalc.php#step7

Ask here if you have more questions. I can't promise I can answer right away, but I can help you understand how these things squish.


Jay (Ground Control)


PS. Just to really make things interesting: The same formula is used for volume of flow through two different sized pieces of tubing.
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[DRTSRFR]

Pillowfight!!

Thank God for the pillow analogies...

Jay has been my suspension mentor for over 20 years. I'd still be an idiot if it weren't for the mental pictures.;)

[kamotors]

Seriously, why do people post this question anymore when it gets asked every other day? You're a cool dude, but you've been here for a while. You need to learn to search. My advice to you is either A) search old threads and see what people run (I run 500/~550) or B) call ground control and see what they recommend.

I was just hoping for an auto-x specific spring rate, I know its asked a lot, most other threads were for DD rates and not higher HP cars.

Off topic: I will be in Reno tomorrow night. You should give me a ride in that ridiculously powerful car of yours.

car doesn't run currently, replacing head with a cammed head.

[lambo]

^^^ That is weird to think about, that the spring rate goes down with a helper spring...is that due to the reaction forces from the springs acting on each other, or something?

[acolella76]

Damn Jay, you just showed me up big time. My boss who used to be a crew chief for IMSA and WC cars said he would just 'stack springs' on cars that were having power down issues, so I assumed it was as simple as stacking and adding. I didn't think there was a mathematical formula for that, so thanks for posting that!

[Earendil]

^^^ That is weird to think about, that the spring rate goes down with a helper spring...is that due to the reaction forces from the springs acting on each other, or something?

It's because... pillow...

If you apply 200 lb to a 200lbs spring, you will have compressed the spring 1 inch, right?
If you then place that compressed spring and weight onto another 200lbs spring guess what, the new bottom spring now has 200lbs* on top of it, so it will ALSO drop an inch.
The spring between the bottom one and the top weight still has 200lbs sitting on top of it, and it has no reason to do anything but stay where it is. The end result is that you put 200lbs and dropped 2 inches, which you would say is a 100lbs spring.

Does that make sense for those that like math a tiny bit more than pillows, but are confused by adding and multiplying? :)

Now, what I suspect would help is if you had one spring embedded inside the other (think M20 valve springs for those that know). In this way, both springs could actually push independently of each other. But I doubt this would give any sort of progressive effect.

*Yes, I know it's actually 200lbs + weight of the spring. I didn't want to complicate things.

[mulletman]

car doesn't run currently, replacing head with a cammed head.

Dammit....

[JeffRR]

Damn Jay, you just showed me up big time. My boss who used to be a crew chief for IMSA and WC cars said he would just 'stack springs' on cars that were having power down issues, so I assumed it was as simple as stacking and adding. I didn't think there was a mathematical formula for that, so thanks for posting that!

He was bumping the roll stiffness distribution foward (increasing understeer), assuming he was talking about "stacking" springs at the rear.