Spring rates- how to create a calm E30?

[whitebulat22]

While researching suspension setups and particularly those of E30s, I noticed that many others were having similar experiences to me in my stock eta- less understeer + more oversteer than most things this side of an air-cooled 911. I've heard spec E30 racers remove the rear anti-roll bar entirely in the interest of moving towards neutral balance and better laps.

My personal goal is to create a twisty road / cone course attacking E30 without going too stiff, which seems to be done a lot. I figure to make a high-powered turbo eta setup it would make a lot of sense to install stiffer front than rear springs along with a big front anti-roll bar. In my head I expect this to lead to a slightly less scary experience trying to put all the power down, still having a generally tail happy car that wants to drift in large empty areas.

This world view led to me being surprised when I first saw smart looking people custom ordering E30 springs with more than 50% extra stiffness at the rear. I thought most things equal front and rear was approaching a drift car setup. What are your experiences and preferences for different builds?

For the record I don't actually expect or want a calm E30, unless we're speaking relative to full slideways setups.

[Jaxx_]

Are you saying you want less understeer and more oversteer? and you want a bigger front bar and harder front springs? :-\ Yes, a bigger front bar will help you get the power down, but you'll be understeering quite a lot.


The way I look at it, if you approach a consistent radius corner at the right speed, you want a neutral car. The need for a big front bar is to get ridiculous amounts of speed at the exit. It depends on your preference.

Going with bigger sway bars is the easiest and arguably the best way to change the way the car handles without effecting ride quality (at least for compression along both sides of the axle).

On the road I suggest a little understeer, on the track I suggest a little oversteer. In a neutral car the driver should be able to attack a corner in order to rotate or get power down sooner, depending on the situation.


edit: also the reason you see people ordering a very stiff rear compared to the front is because the trailing arm setup. mechanical advantage and all...

[whitebulat22]

Sorry I meant less understeer more oversteer seems to be what comes from the factory and that it seems like people are having their cars insist on staying that way when modified.

Thanks for pointing out the mechanical advantage / leverage factor and different scenarios, you've helped a new guy today.

[djjerme]

Depends on what you are willing to spend..

What tire compound are you going to run? What is your current cross weight? etc, etc..

It's all about experimentation. Obviously, you have a road-only car and are not trying to eek out every last tenth of a second on a closed course, and will (I pray) not be driving at 10/10th's on the street. So you could probably find something "decent enough" and just adjust your driving to compensate.

The big choice I think you have to decide is if you want to go full coilovers or stick with a stock style setup.

There is plus and minus to both.

Then you also figure in sway bars.

If you are not one who wants to tinker with the setup, then you could probably run the SE30 setup and be happy. Bilstein's are tanks and will last for probably longer then you have your car, and the H&R race springs are predictable and not a teeth rattling setup on the street.

I ran the SE30 setup with the correct sway in front, and a stock eta in the rear (I am not a fan of disconnecting the rear bar, because when you do, you loose ANY benefit you may have from a rear sway. Won't get in to the entire logistics of why this is not desirable, but lets just say, this "fad" is going away in our PRO3 group..)

It wasn't bad, but for me was a little soft when transitioning between tight left and right hand turns at speed, and was getting too much body roll from the front in high speed corners.

I also ran a home made coilover setup built around Bilsteins and running a few different spring rates. The first version was with all stock eta sway bars, and using adjustable end links to preload the front depending on the track. It was a decent setup, and I turned some fast laps in it, but the rear end very much had a tendency to step out on some turns. This was probably due to too soft of shocks in the rear and too small rollbar.

The latest setup used iX shocks in the front, and the SE30 bars all around. It's very planted, and good in transition, but I still have the rear stepping out too much, and have a nasty front wheel hop on some turns. We have come to the conclusion that it's the Bilsteins in the front, they just are too soft for the 650# springs. So I have Koni SA's coming that will be installed before my next race. This along with the AAF bar for the rear, should allow me to dial in the suspension a bit more depending on the track..

As you can see, there is lots of ways to skin that cat, and it really depends on how much time and money you want to spend getting it "just right." The cheaper/easier thing to do, is tighten the loose nut behind the wheel, and just adjust your driving style to the car..

[Artful Dodger]

my e30 is a multi purpose car. I do HPDE, autox, rallyx, and daily drive the car.

I am using the Spec E30 suspension. I have found at the track, I like my car without the rear sway bar connected. I think, if i had the choice, simply a lighter rear bar would be preferred. But, I cannot adjust my rear bar any further.
For an autox I like the added rotation, and leave the rear sway bar attached. It gives me less understeer and I feel I can control where I want the car to go more effectively.
on the street, both setups are fine and safe.

hope this helps.

[djjerme]

Find an old eta bar, that's what I was running for the longest time.. I am sure someone is giving one away somewhere..

Oh wait this is R3v - I am sure someone is asking a gawd awful amount of money for an old eta sway.

But seriously.. Shouldn't be hard to find.

[Bimmerman325i]

Aim for springs with about 100-150lb stagger front/rear. To have consistent handling you want the rear fairly stiff so as to reduce the geometry changes inherent in the design. I would get adjustable bars on both ends and adjust them to suit your desired balance-- on a most basic level, sways are for balance, springs are for stiffness.

You also want a good shock or you're just lighting money on fire.

This all depends on the tire, alignment, and weight balance of the car, so....yea. There's no easy answer.

[nando]

I think you should probably at least have a basic understanding of E30 suspension geometry before making broad brush statements. obviously you're here to learn or you wouldn't have posted this thread but there's a physical reason the rear springs are always stiffer than the front.

the stiffer rear spring relationship has nothing to do with geometry changes. the leverage ratio in the rear is 2:1 while the front is closer to 1:1. That's the reason why the rear springs are always stiffer than the front on an E30. a 500lb rear spring is effectively 250lb because of the 2:1 ratio. if you ran 500 front and rear, your rear springs would be nearly half as stiff as the front. the car would handle and drive poorly.

I've never heard of a stock E30 being more oversteer prone. most cars including E30s understeer from the factory. if yours is oversteering a lot and it's stock, something is either worn out or you are lifting off the throttle mid corner.

I'd start with replacing all your 25+ year old suspension bushings and then do some more reading.

[whitebulat22]

Thanks everybody for sharing experiences, I am unaware when the shocks were last replaced and im fairly sure no bushing on this car has ever been replaced so I will be starting by getting poly bushings everywhere. Shocks are working fine but may have uneven aging front and rear.

I would like to just tidy up the car, save, and buy bc br coils with custom spring rates and adjustable height dampingand camber but I won't have the experience to decide springrate myself. I would feel alright going 100 to 150 lbs harder in rear and using my other adjustments as needed if I want to change my balance. Does this sound like a reasonable plan ?

I would probably spitball something like 7k front 10 or 11k rear so the rear is effectively a bit softer. I'm excited for that because it seems to encourage weight transfer to the rear for straight line acceleration, slower front weight transfer under braking and lateral transfer close enough to neutral that I can adjust it for my driving as I go.

[priapism]

Some people remove the rear bar, but I'm pretty sure most racers don't. I run it pretty stiff, personally. I only know of one racer that runs his disconnected, and he has this weird way of driving it to compensate for the increased roll. I don't recommend running it disconnected.

In my experience the stiffer the bar, the less it understeers / more it oversteers, and leaving it disconnected makes turnin sloppy and slow.

[ajhostetter]

This is interesting. I have a '91 318is with an S52 (more weight over the front axle than an M20), and run my car with Vogtland lowering springs and Bilstein Sport shocks. I have GC touring camber plates up front (-2 degrees) and am stock in the rear. I have an IE 25mm bar on the most aggressive setting up front with no rear bar. On the track, the car is perfectly balanced IMO. I can get it to rotate easily and really steer it with the right foot. My experience/.02

[Smelser]

running on dirt we have NO sway bars, we WANT the body roll to transfer weight to the rear corner.

I have springs that are too stiff. I looked around and have found a place here in Canada that will MAKE my springs for me. more I get the cheaper it is. I am looking into the weight range of 125-175 lb rear springs. two are 80 a peice, 4 are 60 a peice and 6 are 40 each.
our compression working height in the car is about 5.25-5.75" so we are going with 6" free height springs.

if you wanna go really soft PM me and I can order extra springs to that weight.

[nrubenstein]

The number one reason why a stock eta is loose is because the suspension bushings and dampers are trashed. You need a reasonably well sorted suspension and then you will be fine.

Also, trash tires can play a role here, as well. A lot of E30s are running on positively terrifying tire setups.