You probably know this already but...
Make sure your tires are in good shape, worn front tires are going to cause you to understeer all day everyday.
Maybe look at this from a tuning perspective.
1. First choose the right wheel and tire setup
2. Choose your coilovers and alignment
3. Adjust your rebound and compression
4. Use swaybars to fine tune the handling.
If any one of those are off, like the first one...you're going to end up compensating for it elsewhere.
Stock stagger creates enough understeer at the limit that it's more than just a nuisance. Increasing that stagger is only going to further exaggerate it. You want to reduce understeer at the source of the problem? Go to a square wheel and tire setup. Any tire in my opinion over 285 is overkill for this car, especially if it's NA.
The car will rotate easier and you'll be able to control that rotation much better with throttle input. Anything else you do will be masking the inherent nature of that configuration. Although I know you said you don't want to mess with your compression and rebound settings. If you stiffen the rear it should make the car want to oversteer more and by that logic I would not recommend removing the rear sway bar as it will induce more understeer.
If you can...get a true square setup.
If you cant...play with your coilover compression and rebound but write down what they are currently set at so you don't lose that baseline.
Then...stiffen the rear a bit more from what it is now, maybe move in 1 or 2 click increments, see if the understeer has gotten better until you've reached your ideal setting.
If it's still understeering, maybe then see about setting up your sway bar to a stiffer setting. You are running up against your wheel and tire setup and I would not recommend you try to mess around with your alignment too much to try and fix this because your setup is going to be all over the place. Might as well start with the wheels and tires and do it right from step 1 onward.
__________________
nismo| EVO-R High Wing | Stillen Gen 3 CAI | SEIBON TS Hood | Z1 34 Row Oil Cooler | VMR 810 Wheels | Endless MX72 Pads | Sabelt GT-140 Seat | Fly1Motorsports RS1 Fenders | Hotchkis Front Sway Bar | Berk HFC |
|