Rockweiler

I'm looking for help on suspension tuning, something I really suck at! Here's my current set-up:

Tires and wheels: 255/35-18 Potenza RE-11 on Forgestar F14 18x9.5 all around.
Suspension: Bilstein PSS9 coilovers, set at midway point for damping, approximately
3/4 inch drop in rear vs 1 inch in front. (Don't ask me why!!)
Car has had an alignment and gave it a 2 degree camber all around (mostly for tire clearance purposes).

Now the initial idea of going to a square set-up was to reduce the understeer typical of this car and induce a "little" more over steer (which I'm more used to). However in sharp angle turns the oversteer is now more than I'm comfortable with. The front now writes checks that the rear can't cash!!

Other than going back to a staggered set-up (which I don't plan on doing since the upgrades are new from this year) is there a way to tune the suspension to ring in some of that excessive oversteer? Damping? Ride height? Roll bars? Like I said I don't know much in that area.

grubinski

Take off the rear sway bar ... it's free, see how you like it.

DrivenAP2

Are you talking about autocross? If so, try running with the rear shocks turned all the way down and the front turned all the way up, find the pressure your tires are rolling over on correctly in the rear and run a psi or 2 more up front. fill your gas tank before an event... these really helped me get my times down... removing the rear sway ( witch I did ) was a good change. I would try the other things first, only because it's IMO the rear bar is a big change. If the other things aren't enough remove the bar. besides the tank of gas, they are all free.

These are all things I have tried and had success with, I run a square setup as well. Even if your not Auto-crossing it should help.

jr94513

What year is the vehicle? Kind of hard to help you without specifying what you have

Gottabfast

I'm assuming you're talking about lower speed high angle turns and the oversteer comes on when you get on the throttle out of the corner. Is there a difference turning left vs turning right? (corner weight issue?)

Tire pressure will affect your ultimate amount of grip, so that's the first thing to find.
If you feel like there's a lot of roll and then it snaps, maybe the sway bar will help.
What do your rear toe settings look like?
You may be able to play with damping rates to manage weight transfer during acceleration and cornering to slow it down and make it more manageable. If all else fails, you can take some grip from the front so it evens out the slip angles (maybe less front camber).

Rockweiler

Sorry for the lack of pertinent info guys, wasn't sure what was relevant and what wasn't. I'm a total neophyte in suspension tuning.

My S is a 2007, all stock except for the mods listed above and a catback. I do not Autocross (but do plan on a few track days) but yes it is in lower speed, sharp angle corners that I experience heavy oversteer, both left and right. And the rear really doesn't need much power to lose traction in those circumstances. Toe is on spec for the year and model (don't have my printout sheet with me).

Thanks for the suggestions so far!

Sebring AP1

You can drop the rear ride height some more to get a little more grip on exit. You should also add a front sway bar.

Also the bilstein setup is engineered around a staggered tire setup, so you're not going to want to run the same setting front and rear. Run the front stiffer than the rear until you like the balance. Do 2 clicks towards stiff on the front - drive and test, repeat until you're happy.

I'd get a front sway bar regardless.

Rockweiler

Thanks for the advice and I'll certainly try those things ... however I would like to understand what I'll be doing to the car on an engineering/physics/vehicle dynamics level so that I can better tune it for different driving conditions.

Ex: What does removing the rear sway bar do to the car to achieve more rear grip? Same for adding a front sway bar? Front vs rear rear damping settings? What are the forces at work in those mods?

Sebring AP1

Don't remove the rear sway bar.

The front bar is going to stiffen the front and limit roll, and in turn the rear will do more of the work, which produces more rear grip.

Damping settings work similarly. Stiffer front = more rear grip // stiffer rear = more front grip. If you have oversteer issues stiffen front/soften rear and vice versa for understeer.

This is literally as basic I can get into it without typing a lot of information but for most club racers/HPDE goer's this is all you need to understand.

-=Zeqs=-

What is the toe settings on your car? Camber is important, but toe shouldn't be overlooked either.

Also, pay attention to Sebring AP1's points. He's generally spot on from experience.