E30 Bouncing in the rear

[Forrest 35]

Okay so I need some suspension experts help with the set up in my E30 track car.

Currently while I am driving on any road (mostly noticable on motorways) that is not flat as a pancake, the rear of the car is bouncing up and down on any sort of imperfection. Kind of hard to explain, but it feels like I am driving a car that has cut springs or no shocks in the rear haha.

Another member on here followed me on a back road the other night and he said it looked really soft and wallowy in the rear.

Also have noticed it getting worse as the rear of the car is now stripped, so less weight sitting on the rear wheels.

My current set up in regards to suspension is as follows:

Eibach 60mm front, 40mm rear

Front and rear strut braces

Koni adjustiable front and rear (3-4000km old)

Urethane sway bar mounts

Urethane subframe mounts

etc etc wank wank wank

The springs in the rear are defintely captive, when I brought the shocks the rebound needed to be lengthened as there was only 20mm travel once bolted in and I need a trolley jack to compress the spring enough to bolt the shock onto the trailing arm.

I have fiddled around with adjusting the hardness settings on the rear shocks and also tyre pressures but it doesn't seem to be getting any better.

Do I need to try a harder spring in the rear? i.e King Spring, also are there any negatives to mixing spring brands front to back? Because the front is perfect as is.

Is there any way to find out the spring rate of the current Eibach springs?

Any help or pointers are appreciated.

Cheers, Nathan

Edited June 2, 2010 by Brams

[pureboiracer 0]

try a different spring mate. if your shock adjustment is not fixint it then put some other springs in... your welcome to borrow the ones out of my racecar if you want. its not going anywhere for a while.... you cant keep them but it will tell you if its the springs or not.

[_ethrty-Andy_ 2122]

how old are the springs?

[Forrest 35]

No idea how old the springs are, might just be worth replacing them, want to think at the moment they have just softened pretty bad.

Any other ideas are appreciated.

[_ethrty-Andy_ 2122]

offers there to borrow my Jamex's as well. ill just throw my cup rears in my carif you want.

+1 to softened springs. it happens.

[JiB 0]

I think you guys might be looking at it slightly off. It depends whether Nathan thinks the spring rate is correct or not. If you want to keep the springs, get different dampers. If you want to keep the dampers change the springs. Have you tried max hard on the rear dampers?

Bouncing is usually a case of being under damped. The series springs are quite soft - am assuming Eibach's are much harder.

This is an example of why it is important to match dampers to the application. Usually you want a damper that is slightly overdamped, just above critical damping.

edit: What are the Eibach's spring rates? They may be wrong for a stripped coupe. Usually ride frequency of non-downforce tintops should be 0.5-1.5Hz IIRC. This is dependent on sprung mass and motion ratios (suspension travel)

Edited June 2, 2010 by JiB

[Forrest 35]

^ Cheers for that Jon, much appreciated.

Well I don't want to replace the shocks as they are brand new, and I don't know the age of the springs(could probably find out, this car has had about 5 bimmersport owners), so would rather change the springs.

I know that H+R's and Jamex's are the softest (from talking to a few people).

Silly question but should there be a certain way up the rear springs should go? From my eyes they looked symmetrical but I can't be so sure, so maybe that isn't helping things.

Better option would be to go to coilovers but can't afford that at this stage.

Hmm, just need to find out the hardest spring rate for a rear E30 spring now.

Oh and to behonest, firming up the dampening in the rear seemed to make it worse, thats according to the bum-dyno. I will try them on full hard but I have been warned to be careful when having them like that on the road.

[JiB 0]

I think you'd want a softer rear spring rate if you have no weight in the rear. If I were you, I'd just get some series springs...the series cars aren't slouches!

And I think you have an LSD right? Maybe get a bigger rear ARB 'cos you can probably put up with greater weight transfer in the rear.

Remember this is all my 2c.

[Forrest 35]

I think you'd want a softer rear spring rate if you have no weight in the rear. If I were you, I'd just get some series springs...the series cars aren't slouches!

And I think you have an LSD right? Maybe get a bigger rear ARB 'cos you can probably put up with greater weight transfer in the rear.

Remember this is all my 2c.

Hmm true, your more of a expert than me.

Yup got a LSD, want to be careful with the ARB though, many of the race series guys don't run em.

[JiB 0]

Hmm true, your more of a expert than me.

Yup got a LSD, want to be careful with the ARB though, many of the race series guys don't run em.

Series cars aren't allowed LSD's...so their setup would be different. But I'm no expert!

I just think that a rear ARB would counter-act any understeer the LSD generates on initial throttle...and don't forget you have a front biased car (if it's stripped out as you say)! The series 6 cyl's have to run loads of weight so they can reduce the front bias...so remember - there are quite a few differences between your setup and a series setup.

I stress again - this is my 2c worth.

[Forrest 35]

The rear half only of the car is stripped due to the move to a drivers harness, the front looks factory.

So I would want a set up to counteract a lighter rear end and a virtually as normal front end set up. The rear does sit alot higher also due to the different spring drop front vs rear also, a 60mm spring would even it out if that makes any difference in terms of dropping the center of gravity in the rear lower to the road.

[pureboiracer 0]

the rear arb in my race car made it hell to drive, the back was so unbelievably twitchy. but the effects of the arb in the back all depend on how your springs and shocks are set up.

its is it a case of the car is sloppy and floating in the back like a boat? or is it nice and stiff in the back so you feel every little bump...? from my experience i have found the e30 handles alot better when the rear is set up quite soft. if it is a case of its super stiff so you feel everything then maybe try a softer spring... if it is sloppy and boat like then maybe a harder spring. imo the series springs are the way to go. but i guess you have to find the happy medium between performance and comfort...

thats just from my experience. take it with a pinch of salt. im no expert.

Edited June 2, 2010 by DRTE30

[Forrest 35]

No comfort issue now, I am going balls out

The car as is, is pretty twitchy in the wet, especially with the rebuilt LSD in it, I actually get scared driving it in the rain.

I might try some kings and also pull off the ARB and see if there is any improvement, I think the addition of the strut braces and less weight in the back is heightening the twitchyness and floatiness I am feeling along with the bouncing.

I remember reading somewhere lately that if the car is soft, it is more of a spring issue rather than a dampening issue.

Nothing like trial and error.

Cheers guys.

[pureboiracer 0]

yeah i find with no arb in the back and an lsd esp in the wet the car is alot more progressive when it starts to loose traction. it doesnt suddenly just go it rolls abit but is alot smoother and alot easier to control.

"I remember reading somewhere lately that if the car is soft, it is more of a spring issue rather than a dampening issue."

^yeah thats usually the case.

[e30plz 1]

New springs and you'll be all g.

[JiB 0]

the rear arb in my race car made it hell to drive, the back was so unbelievably twitchy. but the effects of the arb in the back all depend on how your springs and shocks are set up.

More ARB = usually faster weight transfer too..and it also depends what you're running in the front of the car too...isn't Nathan running an aftermarket front ARB?

New springs and you'll be all g.

Yup, pretty much I think. Do it Nathan.

[_ethrty-Andy_ 2122]

come to think of it, if you end up needing a softer spring (didnt read all the advice so not sure if your after harder or softer), id be happy to straight swap my Jamexs for your rear ones, assuming the Jamex's are softer like you say they are. Ill be compressing either set anyway so its probably better if they are harder to start with for me. Just say the word

[Forrest 35]

Ya I am running a 23mm Whiteline on the front, thoughts? The front is really nice and tight but the rear is loose as a goose atm.

[zenetti 0]

Okay so I need some suspension experts help with the set up in my E30 track car.

The springs in the rear are defintely captive, when I brought the shocks the rebound needed to be lengthened as there was only 20mm travel once bolted in and I need a trolley jack to compress the spring enough to bolt the shock onto the trailing arm.

Any help or pointers are appreciated.

Cheers, Nathan

Going down a different route to everyone else, and after having similar problems in a different car (a lowered RAV4 with shortened shocks ). To me, it still seems like your shocks are too short and are topping out causing it to bounce around (the springs are under too much compression). Have you tried putting your old standard shocks back in and seeing if this makes any difference? Food for thought perhaps.

[Forrest 35]

Going down a different route to everyone else, and after having similar problems in a different car (a lowered RAV4 with shortened shocks ). To me, it still seems like your shocks are too short and are topping out causing it to bounce around (the springs are under too much compression). Have you tried putting your old standard shocks back in and seeing if this makes any difference? Food for thought perhaps.

^ I have thought this. It does go on three wheels pretty easy on the track...

Maybe I should just deal with it...haha

[zenetti 0]

^ I have thought this. It does go on three wheels pretty easy on the track...

Maybe I should just deal with it...haha

Definitely sounds like a shock length problem then rather than spring rate. A customer in a Primera used to have the same issue as well.

Why don't you try changing the shocks back to your old ones to see if the issue disappears?

[JiB 0]

Sounds like Zenetti's on to it. I just assumed your bits were the right length

[Forrest 35]

^ Maybe said bits need lengthening

(Not what she said though )

[Guest Simon*]

Sounds like Zenetti's on to it. I just assumed your bits were the right length

^ Maybe said bits need lengthening

(Not what she said though )

Oh wow Just going to leave this alone

Must .... not .... make ....smartass comment!!!!1!!11

[*Glenn* 854]

I had the same problem on the Ti when Chris shortened my Bilsteins. The bump stops I fitted were too long and the shocks were riding on the bump stops all the time and were not allowing any suspension travel when going over uneven surfaces. It was bloody dangerous untill I put shorter bump stops in.