What are good spring lengths & rates for E30 Ground Control w/ M50

[CMG]

I have multiple sets of Ground Control Eibach springs and I am trying to get a good idea of what range would be good for this car. I don't mind experimenting but would at least like to eliminate what won't work. It is an E30 Sedan w/ M50 so a little more weight in front. I am using the basic Koni & Sleeves GC kit with GC mounts front and rear, and using 2.5" springs. Car will not be slammed and don't want a stiff ride. Let me know what is a general range for spring lengths and rates for E30, thanks.

[JGood]

6-8”, any spring rate you desire. Typical sport springs would be 200lb, 400 and up will be fairly stiff, but that’s obviously subjective.

I’m running 6” 450lb on my m60 e30, the housing were shortened as well.

I just installed 8” 225lb springs on my Lemons e30 with full length housings, I’d say it’s very similar to H&R sports for height and spring rate, adjusted all the way down.

[CMG]

Ok thanks for the info. Do you usually use similar or same size/rate for front and rear?

[JGood]

No, sorry, for some reason I only gave consideration to the front in my last post.

I'm running 450f/600r, but again, that'll be stiffer then what you'd want. If you went with 200-300f, I'd assume 400ish rear would be balanced.

Here is an e30 spring rate list, you should be able to make a determination from this:



Spring---------------------Front(lb/in.)------------------Rear(lb/in.)

Stock 325i*-----------------------106-------------------------245
Stock 325is*----------------------118-------------------------265
Stock 325ix*----------------------106-------------------------308
Stock M3*-------------------------114------------------------314
Stock M3--------------------------140------------------------250
Dinan Sport-----------------------172-------------------------300
H&R OE Sport---------------------180-------------------------380
H&R Sport-------------------------180------------------------380
H&R Sport (29664)---------------200--------------------------285
H&R Race-------------------------315------------------------ 570
H&R Coilovers***----------------340--------------------------380
Eibach Pro-Kit--------------------114 --------------------------280-326 progressive
Eibach Race----------------------160--------------------------445
IE SIII----------------------------315--------------------------570
Koni Coilovers-------------------342----------------------------407
Cosmo Coilovers----------------450-----------------------------560
Tokico----------------------------165--------------------------265
TMS J-Stock**-------------------680--------------------------1026
Alpina(est.)---------------------~200-------------------------~350
FK 60/60 cup kit-----------------379----------------------------379
Vogtland Standard***--------115/197---------------------------360
Vogtland CS***---------------137/200--------------------------400
Vogtland--------------------------225--------------------------360
Intrax-----------------------------126--------------------------250
King Springs "Low" -------- KDFL-01 220----------------KDRBL-14 440

[CMG]

Sweet, thanks for the info.

[CMG]

Finally got around to deciphering all my coilover springs (these are all 2.5" ID ones). The ones that I pulled off the car were not too bad nvh wise even though suspension was blown and it was fairly low. I pulled off the front: 6" and 500lb., and the rear 5.5" and 465lb. The other springs I have that would be options are: 6" and 370lb., 7" and 246lb., and 6" and 800lb. I think I might try front 7" and 246lb. for starters, it is easy to swap out rear springs. I have the GC coilover kit that uses modified front strut housing and inserts and the 6" springs and when off the car the top hat is a couple inches above the spring and the spring is loose. If I put in the 7" I can adjust the collars down a little bit and still retain the same height, and gain more damping from the shock since it won't be compressed as much initially. Does that sound right?

[JGood]

No, you will have the same shock travel. The shock will bottom out long before the spring, so it would not matter if you use a short spring with the perches higher, or a longer spring with the perches lower. That said, your shorter spring (6" 370lb) is stiffer than your longer spring (7" 246lb), so it's not really a fair comparison. If they were adjusted to the same static height, the 7" spring would bottom out easier then then 6".

I think the rear 465lb 5.5" springs would be a good combo with those 7" 246lb fronts. That should give you something between H&R Sports and H&R Races, with the benefit of ride height adjustability. If you want something a bit stiffer, the 370lb 6" fronts and 500lb 6" rears would be good.

You also want to make sure you have a shock that is more matched to these springs then an OEM shock. Bilstein sports, Koni, etc...

[CMG]

Out of curiousity I got some info from GC to see what they thought about spring rates. There is no standard GC set up for E30, they have all kinds of spring options but what they recommended for street car with basic GC coilovers was 375/475. Once I get the car done and adjusted I'll be able to have a better opinion about some different rates. I'll have to refresh my memory on physics and springs. The inner diameter does not matter but the rate and height do, and the damping of the spring does play a role too because it is an opposing vector to the load on the spring.

[CMG]

So I messed around with the springs and it pretty much backs up what JGood said. All the springs I used were 2.5" diameter, and sizes between 5.5"-8" can fit depending on what height you set the car. IMO stiffer springs should be shorter and softer springs should be longer (i.e. 7-8" for 200-300 lbs. and 5.5-7" for 300-600lbs.) For me the goldilocks combo ended up being 6" front and 370 lbs., and 5.5" rear and 485 lbs. I am using them with billies and car is only moderately low.

[e30s50dan]

Damn...those J stock's

[2mAn]

Damn...those J stock's

I daily drive my E30 on J-stocks and its not as bad as it seems. Its a progressive spring and with a matched Bilstein shock, I really like it. Even in LAs shitty streets

[varg]

It blows my mind when people say H&R Race or similar is too stiff when I comfortably DD a car with 450lb/in front and 650lb/in back, and Koni SA shocks. I don't think you could go much higher than this with Koni SAs though unless you had them revalved.

[mitchlikesbikes]

It blows my mind when people say H&R Race or similar is too stiff when I comfortably DD a car with 450lb/in front and 650lb/in back, and Koni SA shocks. I don't think you could go much higher than this with Koni SAs though unless you had them revalved.

I am going to be running 445/600 with Koni SA this spring. Good to hear it isn't overly stiff

[E30335i]

I daily drive my E30 on J-stocks and its not as bad as it seems. Its a progressive spring and with a matched Bilstein shock, I really like it. Even in LAs shitty streets

2x rides amazing. Passed my rocky, pothole, messed up, alley test


Sent from my iPhone using Tapatalk

[CMG]

Stiff springs are great when they are properly matched with the rest of the suspension and car. I have other cars where I went the fully stiff route, so that's why I kept this car kind of mellow. FYI my car has all around fresh OEM bushings and ball joints and I used OEM front strut mounts instead of camber plates. Other than the GC coils the only other stiff parts I used were poly offset FCAB, JTD RSM, IE rear sway bar bolt on mounts, and solid F&R strut bars.

I have a pair of the older version GC front camber plates that I was thinking about using but can't seem to figure out how to mount. Anybody happen to know a link with good pics of how they mount to the tower?

(FYI I also have a spare GC coilover set for sale, check my FS thread)