Opinion: Suspension Setup

[DTFE30]

Its an early model. Sorry.

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[tinkerputzer]

It's best to get the body body as level as possible. On a late model it will make it look like it has slight reverse rake but that's ok.

[Bimmerman325i]

Early or late model? Seems in the right ballpark for a late.

[DTFE30]

Right now I have 12.5" from center of wheel to the lip of fender and 11.25 in the rear. So abt .75 rake based on the body line. Will raising the front help me out a bit?

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[Bimmerman325i]

The design was originally va 10k/9k setup with a progressive rear spring. Coming on to the front stretch at NHMS was pretty bad. The rear of the car was essentially bucking. Like you could feel it almost pushing you from behind. I think the 10k linear spring up front was acting as a pivot point for the super soft and progressive rear springs. Even on the street bumps at hard acceleration would cause a bouncing motion that would result in the rpms increasing with the frequency of the bounce. This was at every damping setting I tried. I put the new 700# 2.25x5" this spring and set damping to the middle setting front and back. It seems to have helped some but I really haven't been able to really test it. I am running thompson motor speedway next Monday and Tuesday so I will have more information to report following the event. As to changing the dampers, the fronts are all one unit like megan racing so I cant really change it. Sorry if some of my inexperience is not helping diagnose the issue haha.

Ah!

EDIT: I'm going to assume you're not talking about the car not settling instantly, and that it keeps bouncing well after the bump. Otherwise, I agree with FredK's post, momentary unweighting isn't unusual after a bump but if the car feels pogo-stick-y then that's bad. The rest of my post assumes there's a problem, not lack of instant bump absorption.

I'm going to ignore the damper (and my posts) for a moment-- the first issue you had was with your springs. The rates were staggered completely backwards and the linear/progressive combination did you no favors.

Your original rates were around 560/500 lb/in, with the rear being progressive aka way below that rate except near full compression. BMWs love stiffer rears than fronts, usually in the 100-150lb higher range (but not limited to!).

The 750 spring you just installed should make a good difference, but if the ISCs are at all like Koni SAs, they just don't have the damping to control much beyond 700-750lb well. The DAs have a bit higher headroom but not a whole lot more.

Rereading, the "pushing from behind" comment is also a bit weird, check to see if the rear shocks are toast. Having springs like yours aren't optimal but what you're mentioning sounds like a bigger problem that's a bit hard to point to one specific cause.

What are your ride heights, by the way? Lower is not necessarily better, and a flat rake is also not good. All of that can have an undesirable effect on the car's behavior.

I don't think DAs are all that necessary.. not unless you're such a good driver that a tiny change in damping will make a difference in lap times or something.

I really like my Koni Race (SA). Coming from custom valved Bilsteins, it's like riding on a cloud.

shocks/struts are definitely what makes for good ride quality. My rates are still pretty stiff at 500/600.

They're definitely not necessary, and one needs a good sense of setup parameter cause-effect to really utilize it.

The compression adjuster's range definitely isn't a small change in damping; full soft to full hard is a noticeable difference in bump absorption, chassis roll, and the under/oversteer balance. The TCK DAs did not have nearly that range (esp regarding low shaft speed adjustment effects), but their compression adjuster still made a big difference in car balance and comfort. Stiffening up the rear compression 3 or so clicks from my normal setup made it hilariously more tail happy on track. If you've ever done rain autox or track, being able to back rebound off a click and go full soft on compression really helps putting power down.

It's just a tuning tool, and it's a bit much for a beginner, but it is a really useful tool once you get consistent enough to notice and try different settings. They won't make you instantly faster though.

[nando]

I don't think DAs are all that necessary.. not unless you're such a good driver that a tiny change in damping will make a difference in lap times or something.

I really like my Koni Race (SA). Coming from custom valved Bilsteins, it's like riding on a cloud.

shocks/struts are definitely what makes for good ride quality. My rates are still pretty stiff at 500/600.

[FredK]

bucking....sheesh....I wish I could help w/ the dx.

Usually,.....bucking is a sign of the shock not being able to control the spring rate.

I think so too.

12B at NHMS does have a pretty large bump after the apex as you're feeding in power. I guess if you had a magically damped shock it would allow you to just power out smoothly, but most people's track videos you can see that as the car gets unweighted by that bump, the engine revs higher.

If there is oscillation, then your shock is underdamped. If you get jounced and the car settles right after the bump then I really think that's most other people's experience at NHMS.

[JRKOUPE]

bucking....sheesh....I wish I could help w/ the dx.

Usually,.....bucking is a sign of the shock not being able to control the spring rate.

let us know about thompson..its on my list for 2014.


btw...


I run a swapped car...s50.....for the past 6 yrs or so Ive run Hr race and GC valved koni sa's...stock bars.....neg camber frt and rr...3.2/2.5...poly bushings..

car is a pleasure on track but soft for a "track Car"..I drive her to all events.....I bought GC coilvovers(525/700)...but not instlld yet... to be used w/ the same shocks as per GC.

I know GC is an affordable set up that wont compete w/ a high line set up...but for DE's I believe they are more than worthy.....and will allow me to still get better as a driver and not mask too much.

if u r the type to love constantly fiddling then get dbl adjustables....Im more of a set it and forget it type. I just wanna drive the car. Altho I can go faster for sure....Ive never felt at any track..wgi..poco...lrp..njmp...omfg, this set up sux.

[DTFE30]

You guys are awesome. Thanks for all of the advice. The design was originally va 10k/9k setup with a progressive rear spring. Coming on to the front stretch at NHMS was pretty bad. The rear of the car was essentially bucking. Like you could feel it almost pushing you from behind. I think the 10k linear spring up front was acting as a pivot point for the super soft and progressive rear springs. Even on the street bumps at hard acceleration would cause a bouncing motion that would result in the rpms increasing with the frequency of the bounce. This was at every damping setting I tried. I put the new 700# 2.25x5" this spring and set damping to the middle setting front and back. It seems to have helped some but I really haven't been able to really test it. I am running thompson motor speedway next Monday and Tuesday so I will have more information to report following the event. As to changing the dampers, the fronts are all one unit like megan racing so I cant really change it. Sorry if some of my inexperience is not helping diagnose the issue haha.

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[tinkerputzer]

There is nothing saying you have to run j-stock dampers in stock housings. I had my bilsteins valved to j-stock specs and run them with 2.5" springs up front and 2.25" springs in the rear. I'm quite happy with them for autocross. I dd the car too but roads here are fairly smooth though.

[Bimmerman325i]

Did you run the shortened housings and m3 style end links?

You definitely want to. You gain travel, despite the shorter housings, and the m3 style links do make a small difference in effective anti-roll rate. I would get both modifications done, and then investigate whether you prefer the endlinks on the control arm or on the strut. Many people prefer both, so I'd say try em.

[Bimmerman325i]

You can change the spring rate until the cows come home, but if the damper isn't up to snuff, then you're just wasting your time and alignment funds. The damper is the most important component in a suspension, not the springs, not the sways, not the bushings.

Case in point: I went from TC Kline Doubles to Motion Control Doubles at the same spring rates, and the difference in handling was eye opening. The car was so much more composed over bumps, each click of rebound or compression made a noticeable difference in feel, and the car didn't feel like I was driving a pogo stick down the road. Responsiveness of the car, car chassis movement damping and control, and car balance have all been drastically improved....and that's saying something considering the TCK DA suspension is pretty damn fantastic on its own, especially compared to a stock car.

Compare that experience to the ASTs I had, or the Bilsteins/Eibachs: the car was incredibly uncomfortable, harsh over bumps, bouncy, and just utterly uncompliant and unforgiving. People who don't know better associate stiff and harsh ride with good handling and quick responding suspension but that could not be farther from the truth.

Another data point: we installed a set of JRZ race shocks (with silly high spring rates) on my friend's street Evo MR, to replace the still-good stock Bilsteins. Bone stock car otherwise, sticky street tires, nothing else except the JRZs now. Immediately, without doing any setup tuning, the car was smooth and controlled over bumps and broken up pavement, handling bumps with control and aplomb rather than unsettling the chassis, turn in was dramatically improved, over/understeer balance was improved, the car gripped so much nicer, and ride quality was even improved. The magic here is in the shock, not the springs, not the sways, not in any other part of the suspension.

ISC coils aren't BC or Megan or JOM levels of garbage, but they are still $1k coilovers. The dampers aren't consistent nor even all that good at blowing off bumps and absorbing shocks. If his issue is unsatisfactory handling, the single best thing he could do is swap the dampers for something better.

rant over: having the ability to change spring rate and anti-roll bar rate has little to do with improving ride quality when the primary culprit is poor damper quality and unsatisfactory functionality. You get what you pay for with dampers, so don't skimp.

As far as J-Stock idea goes, I would favor an adjustable coilover. Not being able to adjust springs, ride height, nor damping means the car is easier to set up and forces the driver to focus on driving and not tuning (great for lower-level HPDE), but you eventually will outgrow it. It is a great setup but it is honestly not designed for swapped and modified E30s, with different weight biases, different max/min weights, power, tire, etc. I would instead get a good adjustable suspension, set it to the baseline specs provided by the retailer, and then do a few HPDE before you twiddle knobs. Once you get used to how the car reacts with the new suspension, then start fiddling with it to dial it in to your driving style preference (over/understeer, trail braking, stability, etc). Again, a good damper makes setting up a car easy and simple. A bad damper leaves you chasing your tail and frustrated. It all comes back to the damper.

[Jaxx_]

To me it seems crazy to redo the entire suspension setup if you have swappable coils and adjustable sway bars. I assume you cannot adjust compression/rebound on the current coilovers? Is the concern about mismatched spring rates and shock valving because of ride quality?

I have nearly spec e30 suspension (missing SE30 sway bars) and it's not bad, but not fantastic. It handles everything pretty damn well in my 318, and matching sways and tires appropriately will make up for the imperfections in my opinion. Over harsh bumps it is easy to tell that the springs were not designed to match the valving of bilstein sports.

With all of this said, I think that even with mis-matched dampeners and springs in the rear your car could handle fine. Does the car under or oversteer into or out of a corner? Some of these issues can be fixed simply with sway bar setup(or even alignment!), even if the car is neutral mid-corner.

[matthugie]

I will amend my original opinion and agree with Dodger here. I thought you were still M20 powered if you were thinking Spec E30. If you have a swapped car then don't go with a spec suspension. I swapped out my IE3's and billie sports for a J-stock setup and it's one of the best things I've done to the car. That said, if the roads around you are rough and/or you drive to and from the track over rough roads it can be a bit much after a while. J-stock also is hard to find (except the dampers, Turner still sells them). If you want adjustability then go with a good coil over kit.

[lcoleman]

Better dampers are probably what you're looking for. Is there a way to add a better strut to the setup you have now? Just replacing one part is much cheaper than replacing the whole thing, obviously.

Otherwise: SpecE30, GC, TCK, AST or Ohlins, MCS in ascending order of price (I think).