Suspension Upgrade limited edition

[Black88GTA]

Thanks for the offer, I'll be sure to let you know! Likewise, if you need a hand with anything, just shoot me a PM - I'm no master mechanic, but I get by. Plus, I like learning by watching / helping others perform jobs I may need to do at some point.
Got a big project planned - replacement of tie rod assemblies, drag link, idler arm, upper and lower control arms and F+R sway bar bushings. While I have all of that disassembled, I'm replacing all power steering hoses and the belt tensioner, plus I want to figure out my nonfunctional A/C. Have a set of gauges and a leak detection kit on the way. I plan on it being down for a while, hopefully not too long though.

[thelongeride]

Same here...I get by. Let me know...

[Bryson]

Glad it all worked out and it looks great! This is now absolutely the best setup for the average owner in my honest opinion.

Removing the ground flat end of the spring will tend to increase the spring rate slightly from what we determined, so you're probably closer to 750lb/in now, still in the right range.

Thanks for making the post and enjoy!

[e31bev]

I know this thread has been silent for a few years now, but just a quick question if I may..

But Im looking to do something similar to your suspension setup. Right now I have h&r's at the front. I'm thinking about buying a set of 14" x 3" 400lb coils for the rear. I figured once cut I should be able to acheive a 500lb spring rate, which is probably where I want it to be. Do you think this is the right method? Currently, I have cut factory rears and I cut them about a coil in a half, which was too darn low. I had to use those acorn spring boosters to raise it up, which it seems to make it stiffer than if I were to cut the springs for the right height. With the boosters, I'm guessing I'm close to around 400lb rate on the rear springs, as I could my car handles much better.

[dukegrad98]

I'm not seeing how cutting a spring is going to change its rate. It will change your ride height, but not your spring rate.Cheers, John

[8eights]

Sounds logically incorrect but it's true, You cut a 3/4 turn off of a stock rear spring and it will stiffen up to equal that of a rear Eibach. Cut a rear Csi spring the same and you'll regret it, Ask me how I know!(

[dukegrad98]

I guess if the springs are not linear in their rate, then it makes a bit of sense -- if you're able to cut a lower-rate section of the spring from the top or bottom, its overall/average rate could rise. Hadn't put that much thought into it, and was focused on a traditional coil spring with a fixed rate. I'm not a fan of cutting springs in general, but I do understand that sometimes it can be hard to find exactly the spring you want, resulting in compromises. Thanks for the thought exercise.

Cheers, John

[spikec]

I'll chime in to say that I did this mod exactly as he did and my car rides very nicely. It's lowered a bit but has a nice stance imho.

[peezen]

I also just finished this mod, though I haven't put my car on the ground yet! I did the cut from one end only, and cut it to the same length as the Eibach kit spring. I'm excited to see what it looks like. Already had the reinforcement plates and CSI bump stops.

[thelongeride]

I just now saw this old post being revived. Others have tried "my" design and it works. While it is technically OK, ride comfort and height is a personal preference. The design came from calculations I did, using a lot of the research that was done and posted on this forum. My tweak was simple, compared to the work done by the real experts here.
And yes, cutting a linear rate coil spring will increase the spring rate. I also have TRW shocks to install in the future, and I don't expect an increase in the ride height. I would love some feedback from those who have installed TRW. My car is supercharged and she is a mean beast! With my suspension, my car will drift before it rolls, but still is comfy enough for the misses not to complain. My spring was cut to 11.5 inches, but I suggest a higher cut, 12.5 maybe and test, then a final adjustment if needed. Reminder...the look is very subjective (but important) and you can cut again, but you can't add.

[rotomoto712]

The TRWs seemed to have increased my ride height but I also replaced all of the spring seats as well. The front settled nicely but I wound up having to cut an additional .5" off of the rear spring height. As they say YMMV.

[thelongeride]

Thank you for the input. Data on TRW will be good to have and may help others decide. I will comment whenever I install my set.

[dragon850]

I love my TRW shocks with stage 3 Dinan springs!

[e31bev]

I'm swapping out the front h&r's for msport springs, which aren't nearly as low of a drop, because the csi bumper rubs everytime I get on my driveway. I would like do something similar like yours for the rear so that the spring rates work best with the msports. Do u think a pair of 400lb coils 14"x3", cut to about 12", will increase the rate to about 500lb? Or should I work with 450lb springs?

[thelongeride]

Purely on the number you wrote, I would start with the 500# spring. However, there are a few unanswered questions. Why not go with the msport set? If you mean BMW msport, those do match, to as far as I am aware. What is the front spring rate? My answer above is based on you verifying the front rate, and that 500# work. There is balance and frequency, some of which took me a while to get a general basic understanding...very basic. The sway bar and shocks will also determine the final functionality of the system.

Sent from my VS995 using Tapatalk

[e31bev]

I've seen a few 8ers with msport springs all around and the rear looks lower than the front. That's why I intend on cutting a set of coils to raise the back up jus a tad bit while maintaining the proper spring rates equivalent to that of the rear msports, which I believe are 530lbs.

[thelongeride]

As some of you may know I have acquired an 840 with the intent to do some transformation. I am currently upgrading the suspension with Eibach all round. I have two E31 specific Eibach rear lowering springs for sale. These are from the Eibach BMW E31 kit.
Make me a reasonable offer and its yours. I will list on auction website or use them as artwork in my man-cave.

As an update, I still enjoy my supercharged E31.
LSD upgrade 293:1, ratio, Custom Suspension upgrades, Eibach springs 220# front - 730#Eibach Racing rears, shocks, UCA with custom BMW spherical bearings, UUC twin clutch, etc

Here is what I am doing with my second E31.
upgrade suspension Eibach all round 220# in front, 700# in rear, UCA with spherical bearings,
LSD diff upgrade 315:1 ratio
Engine, Transmission!!!!!???

[JDP530]

I have a Ground Control kit in my car and I believe front springs are 440 lb/in and 550 lb/in in the back. I am also running oversize bars front and back. Car has been lowered about 1 1/2".
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[m6bigdog]

Not that is is any of my business, its your car!! But others would not want to follow your led on spring rates!!

So how did you come up with those as acceptable spring rates for an E31 suspension. Coil-over setup has nothing to do with spring rates or suspension wheel rates.
Way too much front spring rate (Eibach fronts are 220lbs/in) and too little rear spring rate for what your installing in the front (CSi rears are 680lbs/in).

The complex E31 5-Link rear suspension geometry require a rear spring that is something like 340% greater than the front.
Sway bars are for correcting the F/R roll stiffness balance not correcting for the wrong spring rates.
One of the E31 message board members ran 430 lb/in front springs with 1200 lb/in rear springs, however it didn't take him long to calm it down to 275 lb/in front and 900 lb/in rear. The 275-900 setup has better pitch/motion behavior than the 430-1200 setup.

IMHO, the E31 suspension with the spring rates you've chosen would have an abundance of understeer from excessive front suspension roll stiffness and the Pitch/Bounce motion would be horrible.
Excessive understeer is dangerous because the car cannot be controlled once the understeer happens at speed (car quits turning) and applying the brakes or getting on the throttle all cause the same problem; more understeer. Letting off the throttle helps a little, but that is usually too little to quickly recover the understeer condition.
All the best.

[JDP530]

Thanks for the info! Ground Control picked the spring rates but they have not put together a kit for this chassis in many years and I don't think they had any notes available on previous kits. I have 'tracked' my car a few times and I was quite happy with handling but i do recall suffering from some understeer at lower speeds. I knew that rear spring rate is much higher but I did not realize how much so I will eventually try some other spring rates in the back. I do know that I have much less body roll now with the current setup.

Car really handles nicely for me on the street/ highway but, I don't push it hard as I do at the track. I don't notice any pitch/ bounce motion either. Before I changed out the suspension the EDC shocks on front were blown and I definitely had lots of bouncing going on.

I haven't driven the car much in the past several months so I haven't tried any different bar settings. I thought I might be able to eliminate the low speed push by adjusting bars front and back but I have not tried that yet.

[m6bigdog]

One thing I just noticed is you are running Koni rear shocks.
I talked to a Koni shock fitment specialist several years ago and they were unable to recommend a rear shock that could be serviced on the E31.
Heck, Koni doesn't even recommend the E32/E34 Sport front strut cartridge on the E31 strut as it is not a direct fit application but it can be fitted.
That I am aware you are the first to have Koni shocks fitted in the rear.
Please post a close-up photo of the Koni label on the rear shock.
You will be a hero of you can crack the nut for the Koni adjustable rear shock for the E31!!

[JDP530]

One thing I just noticed is you are running Koni rear shocks.
I talked to a Koni shock fitment specialist several years ago and they were unable to recommend a rear shock that could be serviced on the E31.
Heck, Koni doesn't even recommend the E32/E34 Sport front strut cartridge on the E31 strut as it is not a direct fit application but it can be fitted.
That I am aware you are the first to have Koni shocks fitted in the rear.
Please post a close-up photo of the Koni label on the rear shock.
You will be a hero of you can crack the nut for the Koni adjustable rear shock for the E31!!

GC has the Konis built to their specification. Those on the front are built to fit the modified and shortened struts so that chassis can be lowered. I did have some issues fitting rear springs because the upper perch did not fit correctly over the protruding spring alignment nipple but the guys at GC were easy to work with and they solved the problems and modified perches in just a day or two. The upper perch was too shallow and would not seat so they made a deeper perch. And, the bottom threaded perch did not fit and needed a shoulder to locate in hole of lower control arm. The lower perch uses a large bolt and washer to secure it to the control arm.

Looks like the rear shocks are a standard product for Koni, but I have no idea if valving is the same: 30-7436

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[thelongeride]

I have a Ground Control kit in my car and I believe front springs are 440 lb/in and 550 lb/in in the back. I am also running oversize bars front and back. Car has been lowered about 1 1/2".
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I would get back to GC with the direct concerns raised by m6bigdog. Your rates are a bit off. I came to 220 / 750 FR ratio after quite a bit of research. I have it listed as 220/730, but Bryson, a much smarter engineer than me, stated that I was closer to 750 on the rear. Is GC able to provide 275/900 or 275 / 950 instead?

[JDP530]

I would get back to GC with the direct concerns raised by m6bigdog. Your rates are a bit off. I came to 220 / 750 FR ratio after quite a bit of research. I have it listed as 220/730, but Bryson, a much smarter engineer than me, stated that I was closer to 750 on the rear. Is GC able to provide 275/900 or 275 / 950 instead?

GC uses stock Eibach springs and they have a huge selection of spring rates and lengths to try out. I don't know that I would want to go down on the front spring rate because I want to eliminate as much body roll as possible and maintain a comfortable ride. It would be interesting to experiment with the different spring rates on the back. Maybe I will consult with GC and see what their engineers suggest. Thanks,

[m6bigdog]

GC uses stock Eibach springs and they have a huge selection of spring rates and lengths to try out. I don't know that I would want to go down on the front spring rate because I want to eliminate as much body roll as possible and maintain a comfortable ride. It would be interesting to experiment with the different spring rates on the back. Maybe I will consult with GC and see what their engineers suggest. Thanks,

You will want to be realistic!!
There is no such thing as: "eliminate as much body roll as possible and maintain a comfortable ride". Body roll is part of the suspension dynamics from center of gravity and weight transfer. To eliminate body roll without changing the suspension geometry means stiff springs, swaybars to get the roll stiffness up and that produces a stiff less-comfortable ride.
Also, if the GC engineers gave you the 440 front & 550 rear spring rates for your 8, why would go back to see what else they have to say, as those rates are not suspension engineered rates for an E31!!! that is a hack job - most likely using rates for a BMW with a rear coil over shock like an E24, E28, E32, E34, E38 etc.!! Never for a E31 with the 5-Link rear suspension.
As I indicated above; the close ball park number is: rear spring need to be about 3.4 times the front spring rate.

For reference the stock E31 springs are" 123/400 lb/in (3.24) with quite a bit of understeer.
If you want super stiff go with Bryson's the 275/900 rates (3.27).
If you want a more comfortable stiff ride go with the "thelongeride" rates 220/750 (3.4)or CSi rates 200/670 (3.35).
Want to use the 550 rear spring go get a 160-170 lb/in spring for the front (3.4-3.11) .
However, you also need to work with the suspension travel you have set-up given the ride height and GC parts. The less suspension travel the higher the spring rate. Because coil-bind or hitting the bump stops will upset the suspension dynamics engineering and steering control!! Rule of thumb; doubling the sprung weight should not cause suspension to bottom out. FYI, the E31 has approximately 500 lbs front and 450 lbs rear spring weight/wheel. Unfortunately, this is where the calculation of "wheel rate" comes in and that is very different than spring rate.
If you want a good sport ride? the Euro M-Sport rates 170/530 (works if your "suspension travel" with the GC suspension parts isn't significantly reduced from stock values.
The M-Sport spring rates will make the road trip comfortable yet scoot around the corners without noticeable body roll with the correct swaybar setup.

The problem with just picking any rate and ride height is the front and rear suspension dynamics will not work together and in a real (even low speed) panic and/or emergency maneuver the suspension will not perform i.e. a car that is non-responsive to steering input - not fun!!
I run the Euro M-Sport rates, Gen-II K-Bars (28.5/20mm) and EDC shocks. I have been the #2 car on many mountain-road BMW club drive and I can stay right behind the M3 or M-Coup lead car.

The suspension performance engineering task isn't about high spring rates and roll stiffness, it's about control, a suspension that is pitch/bounce motion balanced, neutral-steer with a tad of throttle induced oversteer is a must for a controllable "at any speed" setup. This will have, Great road trip comfort and cornering capability for any driving level.