ground control spring rates

[Hellabad]

I want to start this by saying I am NOT calling you guys idiots

I know. People from Marietta tend to be gentlemen, so if they think you are an idiot....they just quietly take your money at the pool table.

and we've yet to get a call from an angry customer saying that their towers have collapsed.

Well, you understand my point. When (or IF) the strut tower collapses...then you get a phone call.

And you get a phone call about something breaking, that was made by someone else, 30 years ago. The person who operated the spot welder on the rear tower on that e30 is probably dead by now.

So, to avoid such an awkward situation of finger pointing at the dearly departed, we just ask people to update their sheetmetal to match the 2013 tires. The tire from a Prius in 2013, is a better tire in every way than the Pirelli P600 on a 1988 M3

And that is on E36, E46, and even E92 cars.

These spot welders may or may not be dead or retired by now. The e30 welding crue were hard drinkin', hard livin' men.

Of course, I'm not going to suggest that route since there's no advantage to running a CO rear setup in an E30 (unless like you said there is a roll cage or other serious reinforcement). I would say at a bare minimum something that ties into the diff like a Mason rear strut bar would be adequate.

I completely agree. The "True" rear coilover has less room for tire clearance, harder to adjust damping, weighs more, and has more unsprung weight at the end of the control arm. But they are shinier.

Thoughts?

See above. Thanks for the insights, and the opportunity to comment.

[golde30]

I have ripped the sheet metal off with the mount on an e30, and that was eith stock mounts and some tokiko shocks back in the day. so I believe GC when they say roll bar required. I was just curious.

I do still want to send in my struts for C/O setup. Always wanted the full red pc finish with reinforcements welded into shortened housings. Gotta protect my investment(e30M struts).

[acolella76]

Yes. It is exactly the same as your Zender lip. We took it off the website, because we got tired of explaining what "Must have roll bar" means.

For the record: "Must have roll bar" means:

There are plates, tubes and bars welded from the rear shock tower, to a bar that is arced over the upper interior of the car and is welded.

"Must have roll bar' does NOT mean:

Some guy from bimmerforums said that's wrong and GC are idiots.
They sell them on ebay and they don't say you need a rollbar.
I have a torque wrench, I dont need a roll bar.

So, if you reinforce the load path from your strut towers to an upper structure on your car, GC may sell you a bolt on rear kit, and then I promise not to ask you where I can get that front spoiler.

I want to start this by saying I am NOT calling you guys idiots nor am I saying you are flat out wrong. With that said, I have heard of a lot of people both tracking and daily driving E30s with pin-mount CO rear setups without so much as boxed supports and they have no issues. Additionally, there are cars that have MCS coilovers with a double-shear bracket with no additional bracing and we've yet to get a call from an angry customer saying that their towers have collapsed. And that is on E36, E46, and even E92 cars.

Of course, I'm not going to suggest that route since there's no advantage to running a CO rear setup in an E30 (unless like you said there is a roll cage or other serious reinforcement). I would say at a bare minimum something that ties into the diff like a Mason rear strut bar would be adequate.

Thoughts? I am preparing myself to be schooled by you once more.

[Hellabad]

Bumpin this back up, Mark or Jay, do you guys offer a true real coilover unit for e30s?

Yes. It is exactly the same as your Zender lip. We took it off the website, because we got tired of explaining what "Must have roll bar" means.

For the record: "Must have roll bar" means:

There are plates, tubes and bars welded from the rear shock tower, to a bar that is arced over the upper interior of the car and is welded.

"Must have roll bar' does NOT mean:

Some guy from bimmerforums said that's wrong and GC are idiots.
They sell them on ebay and they don't say you need a rollbar.
I have a torque wrench, I dont need a roll bar.

So, if you reinforce the load path from your strut towers to an upper structure on your car, GC may sell you a bolt on rear kit, and then I promise not to ask you where I can get that front spoiler.

[IronFreak]

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.

And for the sake of the thread, I just bought my setup after talking with Mark at GC, going 550F and 750R.

[IronFreak]

http://www.ground-control-store.com/products/description.php/II=754/CA=8

From GC.

Wait when you say 'real" did you mean "rear"?

[golde30]

Bumpin this back up, Mark or Jay, do you guys offer a true real coilover unit for e30s? I am interested in coilovers again.

Another stereotypical e30 scenario, tired of H&R race/ billy sport combo that replaced an older GC setup to make car more "street friendly". Yeah.

[Earendil]

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

Springs and resistors are all good, but let's not pretend that fluid dynamics has an equation in it even close to that simple :)

[IronFreak]

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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This guy gets hero status!! I just had my mind blown!! You sir are a great teacher!!

[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.

[mulletman]

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

Dammit....

[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.

[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!

[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?

[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.