Opinion: Suspension Setup

[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.

[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.

[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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[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.

[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.

[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.

[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.

[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]

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

[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.

[DTFE30]

Its an early model. Sorry.

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