When going around a corner near the limit, the Z exhibits very bad understeer. All the tires are planted except for the front tire on whatever side I am turning to. I currently have 275/40 and 245/40 T1-S on the stock 18" rims with eibach sways. The front sway is set on soft (only 2 settings) and the rear is set on medium. What should I try to fix the understeer?

 

what trim Z do you have?

Where are your tire pressures?

 

Performance

38front 33rear

 

Quit going into corners so hot.

 

If it were just entering the corner I would understand, but it is entering, through the center, and exiting the corner where it understeers.

 

well, as an aside, 33 psi is way too low to run on T1S's IMHO, but on to your question

Biggest issue I see is your rear tires are a bit big for that wheel. Another thing worth looking into is front camber and toe, so see where it is now in relation to stock

I am running the same tires, at 38 psi all around, on 8.5 front 9.5 rears. Granted I've got a ton of suspension mods, but even with the stock struts and RSR springs, the car was pretty neutral overall.

 

I'm no expert but I concur with the rear tire size/pressure being the issue. I believe the outside rear tire's sidewall is rolling over, cause the inside front tire to lift, thus understeer until the weight is again transferred to the front inside wheel.

 

I'm running the same size tires all around with 350evo sway set to medium front and rear and I still have understeer (36 psi front, 33 rear). I'm changing the rear to stiff for my next autocross on Sunday. The real problem (in my opinion) is that the car really needs more camber in the front. Since it isn't adjustable from the factory, a set of adjustable upper a-arms for the front are high on my list of mods.

 

Just out of curiosity, as I no very little about this stuff, why the difference in tire pressure?
Doesn't less pressure equate to more sidewall flex and more traction?
Should a wider tire run less pressure?
Have you tried a 265 or even a 255 rear?

 

To increase camber you could drop it with some springs without getting into too much trouble. I remember when I had the Eibach springs my front camber was ~-1.7 and rear was the same. After I put on the JICs and dropped the car 1.5 to 1.75" the front camber was ~-2.2 and the rear (I had kinetix rear arms) was set to -2. You could also stiffen up the rear sway as high as it will go. You are really fighting the inevitable though, how much adjustibility do you want? How much are you going to track the car? How much do you want to spend chasing this problem? I learned the hard way that you should have a specific goal in mind. By the way, anyone wanna buy my 14" Stoptech kit?

 

stumpmj, what size and brand tires and wheels are you running?

 

Running such a difference in tire size is really asking for more push. (Johnlotusboy told me switching from the factory two-size differential to a one-size made a noticeable difference in the car's balance.) Lower rear pressures ought at least help with turn-in, but that's still a 'work-around.' You should try cranking up your rear bar. Minimizing rear toe should help some, also. The number one thing I did to make my car handle 'properly' was front camber.

I was running my Stillen bars middle in front and full stiff rear and things were pretty good, then I installed the Kinetix a-arms... whoa, momma, THIS, is how it's supposed to be! Of course, you can easily get to the point where you are using up front tires at an alarming rate...

For daily driving I would change the relationship between front and rear camber (more front than rear), and get the Konis.

 

your driving could also be a big factor. how exactly are you taking corners?

 

There are many ways to get the car to rotate to minimize understeer. Try adjusting your driving technique by throwing more weight on to the front tires when you enter a turn (i.e. trail braking). I'd suggest throttle-steer, but I know with a 275 rear, the car simply sticks too much.

I run 245 / 275 RA1s, and the car now tends to push a bit, so I've had to change my driving style. At low speed corners (<50mph), the car can be a bit difficult to rotate, but at high speed corners, I find it to be quite neutral. I may take off my STP at my next track event so I can let the front end twist a little more, which may help on the car's balance on low speed turns.

As for tire pressures, I normally keep my rears about 1-2psi lower than the fronts. Since the rears are the torque wheels, they'll tend to heat up a little more.

 

Put your rear sway bar on it's stiffest/hardest setting. If that still doesn't help learn how to 'pitch' the car into a turn. Even on cars set up for oversteer if you go into a corner sloppy it will understeer.

 

1. You didn't mention your alignment settings at all...hugely important. There's not a ton you can do with the stock suspension, but adjusting toe will make a big difference. Right now, I'm running
Front Toe: 0
Rear Toe: In .025”
You may want to try a little toe out on the front and 0 in the rear if you want the car to turn in more.

2. I found a 5lb pressure stagger just about right for my old setup front to rear like you have them set. I was using Kumho MX's though, so it will be diiferent on your car.

3. As others have said, stiffening up the rear sway and softening up the front will give you more oversteer. However, you may not be able to get as much weight transfer and traction out of the rear when you do this.

4. Running a set of 255's all the way around would make a big difference...not so wide that they are numb on steering feel, and not so wide in the back that you can't break traction with throttle if you want to.

Here's a basic guide to suspension tuning...there are lots and lots of ways to experiment. Remember...CHANGE ONLY ONE THING AT A TIME AND TAKE NOTES!

http://www.susquehanna.com/susq/othe....htm#alignment