DaewooOfDeath
DaewooOfDeath Dork
12/6/13 5:57 a.m.

If you're not familiar with my project, here's the rundown. I have a 98 Nubira with a 2.0L swap, no swaybars front or rear, 9kg springs at all four corners on bilstein non adjustable shocks. It is a 4 wheel strut car. The bushings are poly. I control roll stiffness front to aft by adjusting the ride height and thus roll centers. I eventually want to eliminate one of those variables with adjustable RCAs but, even now, it works berkeleying awesome.

One of the reasons I'm able to get away with this, I think, is because the Nubira has some unusually high roll centers and I didn't lower the car very much. Considering how happy I am with the results, others might want to consider making high roll centers via RCA or even just raising the ride height.

Problems I had run into before mostly involved jacking in the rear under corner loading. I solved this by lowering the rear ride height and thus the roll center. The only other problem I had was some low speed understeer, but that's gone away with better tires and a slight lowering of the front.

Advantages are as follows:

a. Cornering speeds are stupid. I've had this setup on track three times now and, each time, I've had cornering speeds comparable to other people with the next level up tire. VW GTI on r-comps, I caught him slightly on my 320 wear summer Kuhmos. Kia Koupe on Hoosiers, he was a little, little bit quicker than me through the tight stuff, no faster through the sweepers. S2000 on Contisports, much slower than me on Hankook V12 Evos with a 280 tread wear rating.

b. Tire wear is ridiculously light. I don't drive conservatively on track, if anything I'm prone to over driving. Last time out, I had a four wheel drift going at least once in each of the Korean F1 Circuit's 13 corners during the last session 5 days ago. I look at my tires today and I can't see any evidence this happened.

c. I don't need much camber. 1.5 degrees in the front, 0 in the back and it doesn't roll the tires over at all.

d. It's very, very predictable on the limit.

Sort of controversies:

a: I think high roll centers should be a priority for people tracking strut equipped cars. It tightens up the roll couple and gets you a much better camber curve. So long as you're not jacking under load, I fail to see the down side.

b: I think tuning roll stiffness via roll couple is a BETTER tuning tool than using a swaybar. Swaybars have all sorts of interactions across the axle, with the different motion ratios of the different suspension components. Roll centers interact with nothing but virtual arms and thus can, potentially, be much more consistent.

c: No swaybars means a truly independent suspension. This becomes very noticeable over rumble strips and in bumpy corners when the stuff you normally try to watch out for simply doesn't bother the car.

Definite controversies:

a: I think one reason I'm getting such good cornering speeds is because swaybars convert body roll into weight transfer. Let me restate, I think that if you have swaybars, you are transfering more weight across the axle from the inside tire to the outside tire, thus lessening the mechanical grip available to the system.

b. I think (know) you don't need nearly as much spring to pull this setup off as you'd imagine. My friend's 200 kilo lighter, big swaybar equipped Tiburon runs 14 kg/mm front and 16 kg/mm rear springs and they aren't doing anything unusual. I run 9/9 kg and I don't have body roll problems.

Wally
Wally MegaDork
12/6/13 6:34 a.m.

In class where we ran skinny tires we ran a few circle track cars with no bars. Like you saw the fairly high ride height helps, but as you get bigger stickier tires you will want sway bars. Until stock car radials became popular in the 90s you rarely saw a rear bar even in the cup series.

Wally
Wally MegaDork
12/6/13 6:38 a.m.

I will also assume being a Grand Prix track it is pretty smooth. On rough pavement you may be better of with softer springs and sway bars to soak up the bumps.

wae
wae Reader
12/6/13 6:54 a.m.
DaewooOfDeath wrote: I have a 98 Nubira with a 2.0L swap, no swaybars front or rear, 9kg springs at all four corners on bilstein non adjustable shocks. It is a 4 wheel strut car.

For those of me that are metric-impaired, what's a 9kg spring in old money?

cghstang
cghstang HalfDork
12/6/13 7:51 a.m.

9 kg/mm is about 500 lb/in.

DaewooOfDeath
DaewooOfDeath Dork
12/6/13 8:01 a.m.
wae wrote:
DaewooOfDeath wrote: I have a 98 Nubira with a 2.0L swap, no swaybars front or rear, 9kg springs at all four corners on bilstein non adjustable shocks. It is a 4 wheel strut car.
For those of me that are metric-impaired, what's a 9kg spring in old money?

488 lbs/inch

DaewooOfDeath
DaewooOfDeath Dork
12/6/13 8:02 a.m.
Wally wrote: I will also assume being a Grand Prix track it is pretty smooth. On rough pavement you may be better of with softer springs and sway bars to soak up the bumps.

Works pretty good on broken pavement.

http://www.youtube.com/watch?v=mMzOpzy1j4U

wae
wae Reader
12/6/13 8:15 a.m.

Okay, it's kg/mm. I got it now. Thanks!

Very interesting concept

Swank Force One
Swank Force One MegaDork
12/6/13 8:46 a.m.

Steve Hoelscher is a big fan of running no sway bars in his XP class monstrosities.

iceracer
iceracer UberDork
12/6/13 8:50 a.m.

Since strut suspensions inherently have a low roll center, I am curious as to how you raised it. Or does the car have dual control arms. ?

bluej
bluej Dork
12/6/13 9:32 a.m.

In reply to iceracer:

That's what I was trying to figure out as well..

bluej
bluej Dork
12/6/13 10:09 a.m.

Nvmd, I get it. He's saying that this chassis has higher than average rc's to start vs. Most mcstruts, then since the LCA chassis pivot is fixed relative to the chassis, he adjusts the rc height by raising /lowering the chassis ride height.

Stupid question: can someone define "jacking" for me?

MCarp22
MCarp22 HalfDork
12/6/13 10:23 a.m.
bluej wrote: Stupid question: can someone define "jacking" for me?

This is a condition where, after hitting a bump and compressing the spring, the damper does not allow the spring to return to a neutral position before the next bump is encountered. This is caused by too much rebound force in the dampers.

bluej
bluej Dork
12/6/13 12:17 p.m.

In reply to MCarp22:

ah, got it. thank you!

iceracer
iceracer UberDork
12/6/13 5:39 p.m.

Going from street springs, about 150 lbs. to 500 lbs. will certainly increase the anti-roll properties. Raising the car will raise the roll center but it also raises the CG.

DaewooOfDeath
DaewooOfDeath Dork
12/6/13 5:42 p.m.
iceracer wrote: Since strut suspensions inherently have a low roll center, I am curious as to how you raised it. Or does the car have dual control arms. ?

Not necessarily inherent. Since it's difficult to change the angle of the top of the strut mount, the adjustment is all in the angle of the lower control arm. Let me illustrate.

Now, using these parameters, extrapolate the roll center for this type of suspension with the a-arm considerably higher on the chassis side than the knuckle side.

This ^ is going to have a very high roll center.

There are, effectively, four ways to achieve this:

A: Buy a car where the a-arm is higher on the chassis than the knuckle stock (what I lucked into).

B: Lift your car. (Probably not worth the compromise)

C: Install a roll center adjuster in place of your stock ball joint, thus lowering the a-arm attachment point on the knuckle relative to the chassis.

D: Relocate the chassis a-arm mounting point higher.

bluej wrote: Nvmd, I get it. He's saying that this chassis has higher than average rc's to start vs. Most mcstruts, then since the LCA chassis pivot is fixed relative to the chassis, he adjusts the rc height by raising /lowering the chassis ride height. Stupid question: can someone define "jacking" for me?

You got the adjustment right. I want to eventually install RCAs on all four corners so I can elimintate the ride height variable, but right now, yes, I have to do it with ride height adjustments.

As for jacking. If your LCA is angled down from the chassis to the knuckle enough, side loads will try to push the tire under the chassis. This is the type of jacking to which I refer.

Spitfires don't have struts, obviously, but this jacking in action. Make that strut lca angle too extreme - or in the case of a Nubira, leave it stock and put on better tires! - and you'll get jacking under side loads.

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