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Matching Your Spring Rate to Dampening Rate

4475 Views 18 Replies 9 Participants Last post by  NiteRyd
Does anyone DEFINITELY KNOW the actual dampening rate of the AGX's at the various settings. I installed them on my car yesterday to compliment the prokit, swaybar, tower bar and AVS 100's I put on about a year ago, and the car does feel much better – but I am curious whether anyone knows what the actual rates are though?

I did 25K miles in Atlanta traffic over the last year, and when going over an overpass on the interstate, where the pavement drops about and inch or two for 30 feet and then goes back up, the car really jumped if the stored energy in the compressed spring could no longer be controlled by the stock strut as it was released. I didn’t lose control or anything, but it did start to bug me after a while. People drive FAST in Atl and it is not uncommon to hit overpasses at 70-80+, when the effect can become quite pronounced.

Anyway, I know that guys like to play with the AGX settings, but as far as I am concerned, shocks and springs should work in collaboration and be matched. I set the AGXs at 4 and had some fun hard cornering earlier today, but I was essentially using the shocks as stiffer springs in that case, which is not a good thing to be doing from a part reliability and driving predictability standpoint. I have done some searching and have found some setting numbers and %stronger estimations, but would be curious if anyone knows for sure how the AGXs compare to stock. In my thread from last year, I tested the prokit, so we know how much stronger they are than stock. Can anyone help? I will post the Eibach thread below for referenc, but basically, the rears are about the same and the fronts are 65% stiffer than stock. The drop was 1.2 inches front/rear. Thanks!
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Prokit post from last year.........

I decided to go ahead and install the pro-kit springs this weekend to see how they perform—that way I can evaluate each suspension upgrade individually (springs, shocks, tires, rear strut tower bar). I went to Home Depot to pick up 15-40lb bags of sand, for 600 lbs total for my experiment. The general idea to the experiment is to measure spring rate starting from a normal resting position on the stock and pro-kit springs. The goal was to place additional weight to on the car and measure spring compression in order to approximate spring rate under real progressive force. Placing varying weights on the car, I measured total compression first on the rear, then on the front. Here are the results:

-all inches were converted to decimals to do the calculations
-measurements do not account for possible tire compression
-measurements do not account for minimal weight transition to front/rear of car as weight was added, for example of the 600 lbs. Of weight added to the rear, it is impossible to say exactly how much was transitioned to the front springs.
-my assumption is that the bags of dirt/sand from Home Depot actually weighed 40lbs each. I was not inclined to check it.
-measurements were taken at the wheel well, centered vertically on the center of the rims.

Rear STOCK Measurements:
0 lb. L/R average height = 27.34 inches
400 lbs. L/R average height = 25.79 inches
600 lbs. L/R average height = 25.07 inches
Rear Calculations
From 0lb.- 400lbs., k=f/x = 400/1.55 = 258 lb/in or 129.03 lb/inch per spring
From 0lb – 600lbs., k=f/x = 600/2.27 = 264 lb/in or 132.15 lb/inch per spring
From 400lb – 600lbs, k=f/x = 200/.72 = 277.8 lb/in or 138.8 lb/inch per spring
Spring rate for STOCK REAR SPRINGS are about 130-140 lb/inch and seem slightly progressive—but unsure.

Front STOCK Measurements:
0.0 lbs. L/R average height = 27.41 inches
320 lbs. L/R average height = 26.44 inches
480 lbs. L/R average height = 25.94 inches
Front Calculations
From 0.0lbs. - 320lbs., k=f/x = 320/0.97 = 329.90 lbs/in or 164.95 lbs/inch per spring
From 0.0lbs. – 480lbs., k=f/x = 480/1.47 = 326.53 lbs/in or 163.26 lbs/inch per spring
From 320lbs. – 480lbs., k=f/x = 160/0.5 = 320.0 lbs/in or 160.0 lbs/inch per spring
Spring rate for STOCK FRONT SPRINGS are about 165 lbs/inch and are not progressive

Eibach Prokit Install:
Total drop was about 1.2 inches in the front and rear. I drove the car hard to settle it in, and the car had been on the springs for a couple of weeks anyway..

REAR Eibach:
Placed 200 then 400 lbs in the rear and came out with around 135 lb/in for both weights, so the REAR Pro-Kit is NOT PROGRESSIVE and about the same stiffness as stock (probably about 140 lb/in).

FRONT Eibach
I placed 200, then 400, then 480 on the rear and was AMAZED by the results. Even with 480 lbs on the front end, measured compression was only .87 (less than an inch on both sides). The ratio was constant, so I do not believe they are progressive. But do the math – 480lb/.87 inch = 552 lbs/inch or about 275 lb/inch per side. If you doubt it, try it. I did it a couple of times and it came out in about the same range. That’s a pretty huge difference. I did all measurements exactly the same, so I don’t know what to say. Could it be 275? That would make the fronts 65% stiffer than stock. I have no problem believing that, because that’s the way it feels. What do you think?????

From 0lb – 400lbs., k=f/x = 400/.74 = 541 lb/in or 270 lb/inch per spring
From 400lb – 480lbs, k=f/x = 80/.13 = 615 lb/in or 308 lb/inch per spring
From 0lb – 480lbs, k=f/x = 480/.87 = 552 lb/in or .276 lb/inch per spring
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I just emailed KYB and will post up their reply when I recieve it...
I have been wondering the same thing.

When I was running the ProKit with KYBs, it seemed like the shocks set at 2-3 would limit the initial compession when I hit a bigger bump or rut, but that the spring was too week to take it from there, and it would compress too easily.

So I put on Tein S-tech that up the rates 30% front and back over the stock rates.

Have not had to worry about scraping front end due to compression since.

Now I have been fiddling with tire pressure and KYB setting. After many months of different combinations I am running 36 PSI on setting 1 front, and 30 PSI on setting 3 in back.

This feels tight, the least bouncy, and the least punishing on Portlands rough inner city roads. On the smoother freeways the settings don't matter as much.

As far as KYB rates, "firm-firmer-damn firm-f**king firm"...all agreed ?
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I remember last year when you did this test. Again, great work BTW.

I've driven one car with Pro-Kits and Koni's, with P-Zero's, and it felt... different than stock. Slightly stiffer, but not by much. The struts, even though they were just Koni's (relatively soft on the compression side) felt like they were overkill for the Pro-Kit, it was that soft. Also at the time I had 350 lb/in springs (GC's) on my Eclipse, and it felt subjectively 10x stiffer (on the same struts) than that car with the Pro-Kit.

I don't doubt you're results, I'm just still surprised by them.

I've currently got the Tein S-tech springs, and again as an opinion, they are much stiffer (with a similar Koni setup) than the Pro-Kit. Tein claims them to be approx 240 in front.

My opinion (see how I use that word and "subjective" and such a lot ;) ?) on the KYB's is that they were fairly stiff on compression, where many guys complained about it actually, and if also gave people a sense of higher handling capabilities (maybe it did, who knows). But perhaps a little soft on rebound. Your bouncing near the bridges may be a symptom of the spring compressing very quickly and then launching the car, the KYB not controlling it well enough. The Koni's on the other hand are somewhat the opposite. They were somewhat soft on compression, but could be set stiff for rebound. Some guys would bottom out over rough pavement, because each bump would compress the suspension a bit more and the Koni's were too slow to give it back after ~ some number of hits. This may make some springs feel softer - where they control the body roll and absorb the bumps and not the struts. But the high rebound adjustability controlled my GC's without a problem.

I had thought for a long time that the perfect strut might have no comrpession resistance at all, and be very high rebound. It would be matched to some very stiff springs. My GC setup was something like that, and I was always happy with it. I swapped to Tein's because I moved to a section of town that was ridiculous for potholes and crappy pavement, the GC's were just beating me up too much. nowadays I wish I had a setup where I could adjust springs, and strut compression and rebound settings (independantly) at the touch of a button from the dash. Or just pick apart say a new M5, and see what the Germans do.

More info than you wanted probably, but i just love these types of conversations ;)
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I have had the pro kit, KYBs, and ST swaybar for some time, and the KYBs ARE very firm. 4 is like riding in a chariot, the roads around here are horrible.

The worst part of the install (other than rattling in the rear) is that unfortunately, the first few degrees of body roll are not resisted much at all, so the car feels like it's a bobble-head. Once you get past the first few degrees of body roll, it really firms up nice though.

But I've been wondering if stiffer springs would take away that feeling... anyone know? :confused:
Just heard back from KYB. This should definitely be a sticky....

From: KYB
Date: 2004/08/03 Tue PM 03:24:50 EDT
To: Cameron
Subject: RE: [KYB.COM Contact Form] Dampening Rate

The AGX products have the following approximate damping force values.
When adjusted, both rebound and compression damping forces change.

Relative Value
1 - Same as Factory (100%)
2 - Same as our GR2 products (10~15% firmer than Factory --115%)
3 - 50% firmer than #2 (172%)
4 - 30% firmer than #3 (223%)

For an eight position adjustable product, the damping force values are
approx. the following: With #2 being Factory at a relative value of 100,

#1 = 95 (5% softer than Factory)
#2 = 100 (Factory damping force)
#3 = 107.5 (7.5% firmer than Factory)
#4 = 115 (15% firmer than Factory)(GR-2)
#5 = 143.5 (43.5% firmer than Factory)
#6 = 172 (72% firmer than Factory)
#7 = 197.5 (97.5 firmer than Factory)
#8 = 223 (123 % firmerthan Factory)

When using Eibach Prokit springs recommended setting on a 1~4 is no
lower than 2, 1~8 no lower than 4.
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Getting back to the original question, I assume that it's best to match the spring rate to the shock rate. I further assume that Eibach knows a thing or two about springs, and based upon the weight distribution and suspension setup of our car, they decided that the ProKit would work best if it lowered the center of gravity 1.2 inches and stiffened the front 65%. That being the case, it looks like the best complimentary setting for the AGX with the ProKit should be #3 in the front and #2 in the rear (or perhaps #1) -- which I don't think anyone is running. May seem strange, but the logic is there, unless I am missing something.
Makes sense.

I think people run the reverse for other reasons than Eibach had in mind. I bet if you were somehow able to talk to an Eibach engineer, and asked - "OK, I know your street / normal usage rates, what about... autocross?" that youd probably get a different answer. one closer to what a lot of people are running.

My opinion - a few guys are racing and have played with the settings. They post the info. Lots of other people read it and try the settings as well. Seems to work, who knows. Eventually it's considered to be the standard, whether it's really the best settings or not.
Yes, if you want to maintain similar handling characteristics to how the car is set up from the factory, then those settings would be good. The car will ride relatively nice that way.

For instance, I usually turn my Tokicos down to 2 from four whenever I have friends in the car. It makes an AMAZING difference in ride quality. It also makes things scary if I enter a turn and forget that I've turned 'em down.
As mentioned, I do 50 miles a day in Atlanta traffic. Tried 1#'s all around Monday, #2's Tueday, #3's Wed, and #4's to work today. #4 is fun, but just not practicle. On the way home, I dialed in #3F and #2R, and that is where things will stay for daily driving -- it does seem to be the best match. I just signed up for a weekend autocross event here in Atlanta....guess what number they'll be on :eek3: It will finally give me a chance to test all the suspension mods. Well, I guess that about finishes up this thread. I hope members find it useful now and down the road.
This is just FYI. The front springs from the pro-kit cant keep you off of the bump stops alone. With the factory front sway bar in and the front right bump stop removed entirely, the strut bottomed out into the bottom of the upper strut mount and the tire hit the top of the wheel well plastic. This occoured in a left hand turn on a relatively smooth autocross track. If you add the 1-1.5 inch bump stop, you only run out of travel sooner, you just dont hear the bottoming.
You're talking about stock shocks or something stiffer?
To tell you the truth, i dont realy remember. It was either stockers or shortened koni inserts. If i had to guess, id say it was on the stockers.
so how do you guys feel about kyb agx's with sportlines?
LOL Holy thread from the dead, batman.

The sportlines are a little bit lower than the pro-kits, but they aren't significantly stiffer. If you want sharp handling, look elsewhere.
There is a reason for the dead thread madness. I had some front end damage and picked up some fog lamps JW this weekend and we were talking shop. I put the AGXs on 2.5 years ago as you can see and have tried all of the settings. I autocrossed once all set on #4 and forgot to set them back before getting on the highway. I had a headache and lower back pain by the time I got home :) Overall, I have been happy with the setup. I used to keep the fronts on 2 and rears on 1, but now go with 1 all around. Even at #1, the ride is still significantly harder and flatter than stock. Long story short, front stock shocks CANNOT handle any aftermarket springs for more than a few months...if you are going to change the front shocks, change the backs...and based upon my experience with changing the settings and the email from AGX above, you can probably use their shocks with any springs and do well.
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I also have done a lot of playing around with my settings after reading this tread several years back. I found that despite the stock settings or the 3F and 2R. That I perfer the inverse with 2F and 3R when doing spirited driving (as it keeps the fronts planted) and 2 all around for the daily driving routine.

Overall the above information is still very good, thanks again EclipseSeeker for getting this information from KYB.
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