Hello people,

I was considering getting the Ground Control kit for Integra. I believe the spring specs are:
350/9" front
250/8" rear

OK, here's the problem. (Let me know if I screwed up the calculations)

Integra weight 2700 lbs, 64/36 weight distribution
front tire weight: 864 lbs
rear tire weight: 486 lbs

front motion ratio: 1.5
rear motion ratio: 1.35

front wheel rate w/ 350 springs: 156 lbs/in
rear: 137 lbs/in

front wheel deflection 5.5"
rear: 3.5"

front spring compression 3.7"
rear: 2.4:

9" spring stroke: 5.5", meaning I only have 1.8" travel left at the spring
8" spring stroke: 5", meaning I only have 2.4" travel left

Seems like I don't have a lot of travel left

 

I think you should be calculating your front and rear compression with the chassis weight not the wheel rate because the shocks dont move as much as the wheels.
Which would give you figures of 2.5" front and 2 " rear.
You wont have any problems with springs that long.
Its only when you go really short springs like 5" you might have problems.
I dont get the deflection thing though.
correct me if im wrong peaple.

 

your shocks have to be damn near blown the f- out to get any coil slap. if those springs aren't progressive and there spring rates are really that stiff then you should be fine. your suspension travel will probably slim to nill if you don't track it like crazy.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by suprasayin16 &raquo;</TD></TR><TR><TD CLASS="quote">if those springs aren't progressive and there spring rates are really that stiff then you should be fine. your suspension travel will probably slim to nill if you don't track it like crazy.</TD></TR></TABLE>

I'd like to have a car which has a little more than "slim to nil" suspension travel

 

Ground Control did the math. You will not reach coil bind. And a DC kit is 8" springs in front and 7" in rear.

 

I'd recommend rechecking the spring specs. What ID spring are you using? 4.5" block height seems like an awful lot for a 9" travel spring, as does 3" for an 8" travel 250 lb/in spring. For comparison, an 8" free length 2.5" ID H&R 250 lb/in spring has a block height of 2.68", and a 10" H&R 350 lb/in spring (they don't make a 9") has a block height of 3.86", which should be taller than a 9" spring.

 

These are the numbers for an Eibach ERS spring:
part no, length, id, rate, block height, spring travel
0800.250.0350 8.00 2.50 350 3.30 4.70
1000.250.0350 10.00 2.50 350 4.02 5.98

You're right that Eibach doesn't make a 9" spring in 2.5 ID either, but that's what the GC guy told me over the phone.

In any case, nobody yet has said why the math I did is somehow wrong. I would also like to think that GC would sell a reasonable kit. But with a 350 8" spring in front, and 3.7" static spring compression with just the car's weight, that only leaves me with 1" spring travel, or 1.5" wheel travel. That really sucks.

 

Looking at this a bit closer, I found the error in the math.

Spring rate 350 lbs/in / motion ratio 1.5 = 233 lb/in wheel rate
Spring rate 250 lbs/in / motion ratio 1.35 = 185 lbs/in wheel rate

Front wheel spring deflection = 864 lbs / 233 lbs/in = 3.70"
Rear wheel spring deflection = 486 lbs / 185 lbs/in = 2.63"

That makes it look a whole lot better.

Minor detail: this does not subtract the unsprung weight from the spring deflection, as should really be done. Generally this is ~40-50 lbs per corner, most of which is the weight of the wheel, tire, hub, and spindle.

 

The wheel rate is the spring rate divided by (motion ratio)^2.
And then I think you confused wheel deflection with spring deflection.
But two wrongs make a right, and you still came up with 3.7" spring deflection.


Which still leaves me with only 1" spring travel till coil bind on a 8" spring

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtecvoodoo &raquo;</TD></TR><TR><TD CLASS="quote">Ground Control did the math. You will not reach coil bind. </TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beanbag &raquo;</TD></TR><TR><TD CLASS="quote">
You're right that Eibach doesn't make a 9" spring in 2.5 ID either, but that's what the GC guy told me over the phone.

</TD></TR></TABLE>

We make a 9", 250" ID spring for GC, but not for ourselves.

 

Ok so you dont just work out static spring compression on just weight you do take into account the wheel rate as well?
Can someone confirm this please as im buying a set of springs soon and need to work this out myself.
I thought the spring would compress say 854/350 = 2.44"
If this is true this thread just saved me.

If you do have 1 inch till coil bind and on those spring rates you would not go as low and on most lowered hondas especially on the front you only end up with around 1" of travell(a few mm either way) which would mean they might be a problem but only just depending on travell you have left.
You might need to consider a harder or longer spring.

 

Hello Teg

Due to leverage, you calculate the force on the spring by force on wheel x motion ratio.
It's kind of like how a nut cracker works.

(maybe my definition of motion ratio is inverted. Anyway...)

That means if the corner weight is 854, the weight on the spring is 854 x 1.5

Looking at my car right now, there is like a 2-3" wheel to fender gap (stock height). I'm pretty sure that my front wheel can compress until it starts tucking into the fender. So I expect at least 3-4" of extra travel. I can't tell how much shock travel I use because the dust cover is blocking the way.
For people who want to "slam" their car, they probably don't worry about coil bind coz they're nearly on the bump stops anyway. We call this scenario "posing".

I think you're right that I need a longer spring, since I plan to run the car near stock height.


Modified by beanbag at 9:07 PM 8/8/2007

 

Ok thanks but im still not sure..because... The leverage effect works on the centre of the tyres contact patch not the coilover assembly....

the shock and spring moves 1" =the chassis=854
the wheel moves 1.5"=contact patch=233

Therefore the wheel will see less force but not the spring...it should be 1.1 on the spring and shock?


Were am i going wrong.

 

If you think about it from the perspective of the lower control arm:
The contact patch holds the car up, so it has the 854 lbs on it. = F ground
You're forgetting about the chassis connection of the lower control arm



Modified by beanbag at 10:22 PM 8/8/2007

wheel rate calculation here:

http://e46m3performance.com/te...x.htm


Modified by beanbag at 10:23 PM 8/8/2007

 

Thanks but the pic gave me a headache (should of listened to my math teacher)

To determine the spring compression and wheel movement at static ride height.(front)
Ill use your corner weights my spring rates.
Corner weight: 864
Spring rate : 800
wheel rate : 356

Wheel movement = 2.4" (864/356)
Spring compression = 1.6" (2.4/1.5)

I can see how the load force on the spring is the weight x 1.5
So do you think that the force is felt less in the car due to the wheel rate or is it the other way round were more force is transfered to the chasis.
What i mean is how would the 800lb spring rate be felt in the car more or less?

I guess you could also calculate your corner weight by knowing the spring rate and length and the amount it compresses when sitting on the ground.

How did i go there?
thanks again.

 

The wheel rate determines the natural frequency, which is related to perception of "harshness".

 

How do you intend to solve your problem?

Ok so my calculations were right then i hope.

And why then is a 800lb spring percieved as super harsh but on a strut suspension with a 350lb spring percieved as not harsh....what is the factor that causes this...anyone.

 

I think I will get a longer spring than what Ground Control "recommends". But first I need to check how much travel I have with my stock suspension.

Your numbers look right to me, but then again, I started this thread because the results looked kind of funny to me. You should get a second opinion. Why don't you have Ground Control "do the math" for you?

I had a conversation with somebody earlier who used to run a GC/Koni Sport setup and moved onto something better (TC Kline).

Me: Does Ground Control know what they are doing when they sp....
Other guy: No

To answer your other question:
Wheel rate
Natural frequency
http://www.team-integra.net/se...D=747

 

I think that ground control would expect most to lower a fair amount.

You will find that standard there is not that much travell.

With a taller spring it will change the suspension range where you will not be able to go as low which is okay for you. But thats not what 99% of peaple who buy coilover kits want. Ensure the length and stiffness of the spring will suit your height range as well.

You could also consider off the shelf standard type springs.

I looked into the frequency thing and there a many factors but in theory a 800lb spring on my honda should feel just as stiff as a 350lb spring in a strut type car with all other things equall......i think.

You saved me with those calculations i have to consider a 160mm spring instead of 140mm...coil bind was around 25mm away.
I am using 60mm id springs from eibach not ground control so GC cannot help me.
I also checked the calculations by dropping the car and measuring the spring length with some other springs i have and it seems to be right i hope...i will email eibach before i purchose though.

thanks and good luck.

 

Thanks, Teg, I think your post basically answered my original question.

 

Thanks again for the info...
I just bought some Konis and am going 2.5', 8' springs 700lbs.
How close is this..

(corner weight)900 multiply 1.5 = 1350

1350/700=49mm static comp.
49mm+40mm bump compression = 99mm
Coil bind eibach=107mm
Coil bind H&R = 109mm

Im 8-10mm off coil bind a 7' spring and its all over.

 

Update on this thread:

I got 300/12" f, 200/12" r

Thanks to vtecvoodoo for the fast shipping and great prices.

Yes, 12" springs. The front and rear are lowered about .5" or so, and I put the koni's on the lowest perch. I can still drop the car another 2-3" in the front if I want, and about another 2" in the rear. In the front, I have another 2-2.5" of shock travel until I hit the CUT bumpstop. Which is fine coz I have another 3.2" of spring travel until coil bind. (I calculated that a 10" spring would only have 1.8" travel left) During driving, I did hit the bumpstop coz they got pushed up into the top hat. Which means that in the same situation, I would have coil bound the 10" springs. Even if I had a 350# spring, it would have coilbound.

In the rear, I also have about 2.5" of shock travel left until hitting the cut bumpstops. Which is also fine because I have 4.6" of spring compression left. If I ever upgrade to 250# rear springs, then a 10" spring would also have been fine.

The moral of the story is to get as long springs as you can.

 

TTT