too much understeer now!
 

I put 9x19 and 9x11 wheels with 255/35 and 295/30 hankooks with eibach springs and now have too much understeer. the alignment specs post spring install show -1.3deg and -1.4deg camber in the front.

can I get more negative camber out of the front with the stock bits? if so, what is suggested to relieve the understeer based off the tire sizes I am running? also, at what point do I start getting tire wear because of too much negative camber?

would sway bars help my situation at all?

thanks.

Stiffer rear sway bar will help.

:iagree:

You could also try removing the front strut bar.

could also run a couple psi more tire pressure in the rear... some combination of the above... curious why you went with such small tires on the front

Strange, when you lower the car you automatically get more negative camber. In the front that should give you better turn in. You can get a front camber kit to add more negative camber in front...closer to -2.0.

I wouldn't remove the front strut tower bar. Reducing structural rigidity is not the answer.

I do run a couple more psi in the rear.

255/35's are a perfect fit for the 9" wheel.

I think the problem is strictly do to the tire size ratio between front and rear. there's just too much in the rear, which makes the front push. I'll probably just get a camber kit I guess.

Did you change the offset significantly? Changing the track, especially if you didn't change it evenly in the front and back, may have affected your handling.

The 2 inch wheel width stagger is doing you in.

Increase front camber to -2.0 degrees using a camber kit. You'll go through tires a little faster if you do a lot of highway but it won't be that bad. Sway bars would probably only make it worse as pretty much all the aftermarket kits increase the front bar stiffness more than the rear. You could also try widening the front track by adding front spacers or narrowing the rear track by removing spacers if you used any there.

yah, wat offset are you running? your rear might be pushed out too far vs your front.

running 19x9 +24 front, 19x11 +23 rear offsets. I think this is the most aggressive fit you can get from forgestar. I too think it's more of a issue with 9" in the front and 11" in the rear and the resulting tire width differences. I'm just wondering if a camber kit can help this if I went to -2.0? I do commute a lot in this car, 70 miles per day.

I have the Forgestars but I have the 10" wheels up front, 11" in the rear.

What are you running for tire?

When do you experience the understeer, is it turn-in or mid corner?

I don't think they make a 19x10 wheel anymore.

I have the Hankook V12 tires.

understeer is turn-in, really all the time. I just feel all the weight of the car on the front wheels and in the steering. it pushes a lot.

More negative camber up front should help with the turn-in, but really it's going to be difficult to overcome that amount of tire stagger. Ideally you would maintain the OEM ratio or decrease it.

FWIW, you can fit up to a 275 width tire on a 9" wheel.

You could also leave the OEM sway bar up front and run a stiffer rear bar, but that will mostly help center-off.

I think you should change the tire size to one of these combo.

F 255-40-19 R 285-35-19

or

F 275-35-19 R 305-30-19

I prefer the first one since 2nd combo is way too much in my onpinion for the stock setup and power.
Generally speaking, if you over size the tire too much, you might get a nicer look, but you not only eat at your power but it can also tend to numb the feel of the vehicle.

neither of those sizes are good though for the wheel though. a 275 on the front is going to be bulging like crazy and a 285 on the rear is going to be stretched quite a bit. my 295's on the rear are already too small for the wheel.

question, how do other makers get away with an even bigger stagger? porsche has a huge stagger in the 997 and it obviously handles very well.

The Porsche needs that stagger as it has the weight of the engine over the rear wheels.

Over the years the 911s have always been notoriously "loose" cars due to their rear-engine design. Porsche engineers have done a lot to balance the car out with each redesign, and part of that includes quite a large stagger. :tup:

it seems like 275/35 and 305/30 would be a combo made in Hankook that keeps the diameters in sync, but that's only gaining me 10mm less of a stagger. wonder how much of a difference that would make?

It should feel better. You'll have 40mm more contact area up front for better turn in. You still might want to run a little more negative camber but I think you'll have a much better base than you do right now.

Yeah, the weight distribution of the 911 Carerra is 38% front, 62% rear. The large stagger is designed to induce understeer and stop people from going sideways into the nearest tree. There is a reason they used to call the 911 Turbo the "Widowmaker". For the Z you want a 20mm to 30mm stager at most.

anyone have pics of a 275/35 on a 9" wheel? it seems like that will be bulging like crazy. a 255/35 is a perfect fit. I thought I saw pics of a 265 on a 9" and even that looked like too much.

Check my picture gallery.

It is difficult to say, but if your only mods are Eibach springs and tires, then the only thing that I can think of that messes up the handling characteristics of the vehicle is the tire size. Non Nismo Eibach spring rate in my opinion is fairly balanced out and I dont think that is the cause of the difference in performance. Now I have never seen an eibach springs I can only tell your from numbers. But for example if your rears are progressive and your fronts are more linear of a spring then that can also be the cause of the understeer.

:iagree:

Yea, good advice above. I really think the way to balance the Z is to run as close to square as you can get with some adjustable sway bars to tweak that balance. Some of us (me) still prefer to go off the corner frontwards as opposed to backwards.

:icon18:

Good 'ole NASCAR explanation of oversteer/understeer:

Oversteer: You hit the wall with the rear end first.

Understeer: You hit the wall with the front end first.

:icon18:

yeah I don't mind a little understeer but it's at the point now of performing quite a bit worse than a stock Z. I was on highway 17 (for the bay area folk) and it was a little scary going into some of those corners staring right at that center cement divide.

would a .6" difference between tire diameter front to rear be an issue? I've heard with some cars it can play tricks with the ABS.

I'm wondering if I might just throw some 275's on the front and leave my rear 295's...

the front would be 26.6" and the rear would be 26" tall.

Try driving the car with the VDC on and off and see if it makes a difference.

But probably your biggest issue is simply that you have too much rear tire. You've actually increased the front track relative to the rear, which should reduce understeer. You could play with raising the front tire pressure relative to the rear pressure. Sounds like what you're doing currently is the opposite of what you're supposed to do:

Tire Tech Information - Air Pressure for Competition Tires

Also, take a look at your springs and see if you can't figure out their rates. Eibach often prints them on there. You should also be able to tell if they're progressively wound by looking at them. Progressive springs will have a non-uniform winding. There's a chance that the front spring rates were increased relative to the rear rates, which would increase understeer.

This is Zat_Zuma's ride. He's got 275 front and 305 rear on stock sport Rays.
http://www.the370z.com/members/djpat...mm-spacers.jpg

wow, those fronts are really bulging.

No they're not.

Yes, they are.

No there not. It is just the design of the tire lip.

I run the OEM wheels with
255x30 Front
295x30 Rear
Toyo R888 tires on the track. I haven't experienced any understeer with the OEM suspension whatsoever. Pretty much point and go. With the springs and different wheel sizes there are a bunch of changes happening at once. If you still have your OEM wheels I'd swap out and see if the problem persists. Try and fix this by very small adjustments at a time…..just my 2 cents.

I turned VDC off tonight and believe it or not that made a noticeable difference for the better. it's still not great, but much better than it was. I'll do some more testing with it to be certain.

I'm puzzled...how would turning VDC off improve understeer?

no idea, but I take the same route every day and it seemed better to me with it off.

The VDC system uses the brakes (I believe) to try and compensate for things like wheel spin. If he changed tire diameters significantly from stock, the VDC system may rear that as wheel slip due to differences in the rotational speed of the tires.

Next, try raising the front tires a bit and lowering the rears.