Suspension setup stuff

Hey y'all, it's amateur hour.

I just did some testing with my new coilover suspension on the Daewoo and got some pretty good results. That said, I do have one problem and a question.

The setup is thus:

9kg/mm (slightly less than 500lb/in) springs front and rear.

Bilstiene shock guts, TechPro body/assembly/coilover hardware.

Four wheel struts.

Testing done with no front bar, no rear bar. Not really any deep strategic reason for this other than the fact I broke the old links and hadn't gotten the new ones in yet.

Car weighs about 2500 lbs and runs 195/55/15 performance-y all season Kuhmos.

Test Results:

In tight corners I got mild understeer. The slotted strut mounts seem to be working and the car isn't rolling over onto the side walls. It cocks the inside rear wheel an inch or so and puts down the power much, much better than it did before.

I made a slalom out on an abandoned warehouse parking lot and tested there. In transitions the car felt awesome. Good response, a small amount of well damped body roll in the front, and a useful amount of slip angle in the back. The front would bite, the back would step out a few degrees and then it felt like the entire car hunkered down and shot out of the corner. Smooth or bumpy, it made no difference. Very pleased with this test.

In long smooth corners the handling was very balanced. Mild understeer on the throttle, neutral with maintainance throttle, easily controllable oversteer on trail throttle.

In long bumpy corners things got uglier. Every time I hit a bump it felt like that inside rear tire was touching down. This would cause the car to lurch. Sort of like the wheel touching down was gaining weird toe settings at its full droop. Any guidance on this would be greatly appreciated.

Now for the engineering question:

If the car is working without swaybars does that mean I screwed up with the spring rates, or could it just be a closely coupled CG/roll center? I don't know any performance cars running just on the springs, but mine seems fine that way. At least, I can't imagine the rear swaybar helping the lurch and, from reading the tires, I can't imagine the front swaybar doing anything but causing push.

I just thought of another possible culprit. If I had a seriously floppy chassis, would I get that lurching?

You're sure you're not running out of suspension travel?

Does it dart around in a straight line when you hit bumps?

Swaybars are just there to make up for a lack of roll stiffness provided by the springs. I'm gonna go out on a limb and guess that your new springs are significantly stiffer than the stockers, and guess that the roll rate with the new springs by themselves is probably still higher than the old springs with the sway bar.

As to the weirdness under bumps, I also suggest checking clearance. What I've had suggested to me is to mount up the suspension without the springs, then cycle the wheel through it's full travel, clearancing any place where the wheel is impacting.

SkinnyG wrote: You're sure you're not running out of suspension travel?

I"m positive that's not it. I've spent several hours going fast over speed bumps trying to bottom the car out. I haven't yet. I'm running the coils at full height. The car is only about 1 inch lower than stock and the springs are much, much stiffer.

96DXCivic wrote: Does it dart around in a straight line when you hit bumps?

No.

ReverendDexter wrote: Swaybars are just there to make up for a lack of roll stiffness provided by the springs. I'm gonna go out on a limb and guess that your new springs are significantly stiffer than the stockers, and guess that the roll rate with the new springs by themselves is probably still higher than the old springs with the sway bar. As to the weirdness under bumps, I also suggest checking clearance. What I've had suggested to me is to mount up the suspension without the springs, then cycle the wheel through it's full travel, clearancing any place where the wheel is impacting.

There's much less roll now, actually. I was surprised by that as well. I don't know what the stock rates were, but a 500 lb spring isn't that crazy and I've got very, very little roll.

I'll try clearance testing. I haven't heard any grinding/rubbing, but then the car is kind of loud now.

Yah, so I went back to that tight corner that caused the problems and realize that I'm really an idiot. The lurching had nothing to do with the car and everything to do with the fact that this particular corner has alternating strips of rough and smooth pavement. The first time I went at night, so I just didn't see it.