Nabush

Hello,

I have a 2009 HR 350Z with the following chassis modification :

- BC Racing ER Coilovers, about 5cm lower than stock. (on the track: compression 30/30, rebound 20/30. 12kg spring front 10 kg spring rear)
- Cusco Front Upper Arms
- Stock sway bars
- Enkei RPF1 9.5*18 ET15 wheels
- 265/35 18 Front Toyo R888 tires
- 275/40 18 Rear Toyo R888 tires

I also have AP Racing 6 pots brakes, exhaust (PPE Headers, AAM Single, XYZ,Stillen dual intake, Uprev osiris remap, ), JWT 6 kg flywheel, Odyssey PC925, Recaro Pole position buckets seats, and other oils modification Greedy oil pan, stillen oil cooler etc...

My alignment is the following:

Camber Front : -3.3° (otherwise the tires rub)
Toe in : 0.02° total (i will put back toe out, don't like toe in in the front)

Rear : Camber : -2.5°
Toe in : 0.18° total

The car is fast but edgy... It is very stable on right turns, but scary on left turns, with a lot of oversteer at turn in when i'm at the limit. The traction is quite bad.

I will add a quaife and rear camber adjustable arms, and sways bars in 2016.

I know i have too much camber front and rear. My tire wear is bad, too much wear on the inside front and rear. i will go back to 2.5° front and 1.5° rear, but i'll have to roll my fenders (or more) because of the very wide toyo and the ET15 of the Enkei.

For track use, what to you think of my current settings ? Too much camber no ? I'm considering perhaps to reduce rear camber to -1.0° since my exterior are really good and interiors bad...

What camber rears arms would you buy ? Which sways bars ? Which bushings ?

More importantly, what could cause my snappy oversteer on the right turns ? i heard that the weight balance is quite bad on Z, but stock it is not snappy like that... I originally though it was due to too much camber rear but i'm not sure. The toe in setting at the rear seems sufficient no ?

I don't exactly know what to do to solve this problem.

Here are some video where you can see my oversteer problem :


Here at 1 min and 2min55

VenomGT9

iTrader: (1)

I'd look into getting the sways sooner, along with upgraded endlinks (powergrid or Whiteline)

dkmura

iTrader: (64)

Looked at your vids briefly, and your Z really suffers from a lack of roll stiffness. Swaybars will help that, but you really need to get a tire pyrometer on all four tires to determine what your tire temps are after a track session. Then you can adjust camber to fit. As you say, I suspect your excessive camber is rolling the contact patch quickly at turn-in and the lack of roll stiffness has the Z seeking to swap ends.

If nothing else, this shows what happens when a lot of money is spent without first considering the basics. Swaybars should be one of the FIRST upgrades to be considered for a car going to the track...

MicVelo

First problem: Tires are imbalanced. I don't mean wheel balance, I mean size. Your fronts being as large as they are and rears only a fraction (10mm more) PLUS aspect ratio differences is already a recipe for snap oversteer as the fronts are gripping harder and the rears softer (relatively speaking).

HOWEVER, that's not too bad of a problem that adjustable sway bars can't mitigate. (Which, as David said, should ALWAYS be the first modification to suspension AFTER proper alignment - more on this in a sec) In this situation, I'd tend to think that running a hole 2 front/hole 1 (softer) bias should fix this by slowing the rate at which the rears reach max slip angle.

Speaking of alignment, I see where you have adjustable UCAs up front but no camber adjusters in the rear? How'd you get -2.5deg back there?

And yes, that's FAR too much camber angle all the way around, particularly for the street. (Dedicated track cars might be able to run this on a long track but for dual purpose, ehhhh.... not so much.) Combine that with the toe you're running and you run into "decent turn in but darty, skittish behavior at the apex".

For a car set up dual purpose, I'd keep camber no more than -2.5 in front and closer to -2.0-2.5 MAX in the rear. On toe, I'd bring it back to 0 or even a slight toe in, maybe a 32nd Front and a little more, maybe a 16th in on the rear.

The car will still rotate properly but you stand less chance of overcooking the rears before the front.

Get your bars in, toe adjustment out back THEN bring it to a race shop (or a really competent alignment shop that understands the alignment settings that are "off the books".

In the end, it's all about experimentation. The settings I quoted might not work for the types of courses you run but it's a start and I can almost guarantee that some of the skittishness you're feeling will be reduced or go away altogether. It's basic alignment theory.

Good luck!

Mic

Nabush

Hi,

Thanks for your first answers.

I will try to answer to your questions

First i didn't want to change my roll bars in the first place because i made some research and conclude than stiffer sway bars could cause a loss of grip and traction. It stresses more the outside wheel and overload it. I choose to put harder springs on my suspension. 12kg front and 10kg rear.

i found my car was faster than same Z with aftermarket sway bars. My Z is indeed very fast, or i'm a faster driver than the one i met don't know.

The near square tires setup is praised here, in fact my 265/35 front toyo are in real wider than my 275/40.

But i've quite lost confidence in the car on the left turn, so i keep more margin in these... Perhaps sways bars will help to regain confidence and i'll be faster overall.

Concerning the rear camber i don't have rear camber kit. I'm at -2.5° because the car is very low, it's near the lowest setting in height on the BC ER.

Some collegues told me to take SPL arms, but they are very expensive, and the rigid mount scares me in terms of lifespan of my arms...

I'm considering buying SPC excentrics in the first place to see if i can come close to -1.5° camber rear, and instead of buying 800€ SPL rear arms, buy Whiteline Sways bars with ends links.

Concerning the toe in in front, i don't like it, the car feels numb on turn in, and not really better when i go out of the turn. With a little toe out it feels more reactive.

What do you think ?

Sorry if some terms are wrong, but i'm french, i sometime lack technical vocabulary in English

Nabush

Here is a pic of my car in action.

For me it's clear i have too much camber, the outside of the tire is not enough in contact with the ground. No ?

dkmura

iTrader: (64)

Those photos don't do much except show you have too much camber dialed in. As for swaybars, your understanding of them is flawed. As the car rolls into a turn, swaybars progressively begin to work. Unless you stiffen them too much, there is no loss of grip or traction. Mic's recommendation for initial swaybar settings is a good starting place. Simply putting harder springs in your Z has made the handling nervous and the car unstable with the tires and suspension settings you've chosen.

Nabush

One thing i forgot to mention concerning the spring : they are standard spring for BC Racing ER coilovers. Before i had BC Racing BR with 10kg front and 8kg rear.

When i said i choose stiffer springs, i meant i changed my BR to ER coilovers the difference is higher spring rates and separate tuning of compression and rebound + external reservoir

Concerning sways bars i read specialized book on chassis tuning, the physic related to it, and saw that too much stiffness on the sway bars has a negative effect on the overall grip. More confidence, but less ultimate grip. So i choose to bypass them. it seems i'm wrong on this...

i'm not the type to do something because other do. I try to understand the basics before doing. (I'm a engineer so it's my nature).

MicVelo

I don't think David was implying any lack of knowledge, just pointing out a slight - and actually based in fact - misconception.

You are correct that too much roll stiffness can and does create instabilty. Watch autocrossers lift the inside wheel -especially FWD - and you can see the dramatic side-side weight xfer in action.

Point he (and others) were making about ADJUSTABLE bars is the main point... To adjust roll stiffness to best suit track (and general road) conditions - GIVEN YOUR SETUP.

SQuaLZ

I thought that sway bars would cause more oversteer, but in my case it did not at all. And the oversteer that I did incur felt way more controllable. With the Nismo sway bars, the car feels more neutral, and you actually feel it "hunch" when you accelerate through a turn. It feels like the weight is transferring more to the wheel that has grip.

Also, since you said that it happens more turning one way versus the other way leads me to believe that you LSD is not operating properly. Is it the OEM VLSD? I noticed you have buttons on your steering wheel so it can't be the open diff.

Nabush

Hi, all europeans Z have lsd and brembos (which i replaced by ap racing)
For now i have the stock VLSD which is crap. Will replace it with a Qaife soon.

Nabush

Yes, it's clear that if take sway bars, i will take some adjustable one, since the bias between front and rear seems to have a dramatic effect for understeer or oversteer.

Do you think guys that my 2.5° camber rear is the cause of my oversteer on turn in ? If so why more on left turn since my alignment is very accurate and equilibrate (exact same values for each wheels)... Weight balance ?

You think that sway bars will reduce the phenomenom alone, without touching the camber?

guitman32

iTrader: (15)

You are probably too low and running out of damper piston travel, as a result you are riding your bump stops which makes the on-limit behavior snappier.

Raise the car a bit, make sure you have the sock length, ride height and corner weights set correctly. Get it on scales.

Upgrade front bar stiffness.

Your damping seems too stiff, but really you need to upgrade to a better suspension anyway.

terrasmak

iTrader: (8)

Yup, looks odd and it might be riding on the bump stops. I wonder if the rear shocks are adjusted long long. Shorten them up and gain some travel.

It's not easy to make a Z oversteer like that, normally the push badly and we are fighting suspension to get then neutral. Last car I dealt with that did that had Stance coilovers installed by Stillen. He had 1/4 inch of bump travel till the stops were engaged.


That rear camber should help on turn in and mid corner traction. I would think it would only be limiting for the on throttle drive out.

Nabush

No man, i adjusted my dampers accordingly to my height. I have about 10cm shock travel before hitting the bump stops, measured when the car is on it's wheels....Or 10cm is not enough travel?

guitman32

iTrader: (15)

Are you sure its 10cm actual piston stroke before hitting the bump stops? You need to first set your shock length, set your ride height, then corner balance it. If you get that all dialed in you may be able to dial down the compression damping some which will probably help the handling.

Nabush

Hi, what exactly is corner balance ?

Concerning shock travel i first adjusted the height to the value i wanted, then adjusted the shock lenght in order to have 10cm piston travel when the whole car is on its wheel.

guitman32

iTrader: (15)

Corner balancing a car is when you put it on scales and adjust the corner weights on each side, specifically to even out crossweight.

It is usually pretty decent from the factory, but when you have completely revised the suspension including ride heights, it can be skewed from that baseline. Especially since you are complaining of asymmetrical handling characteristics, it may help.

First thing you want to do is set the shock body length for adequate piston travel, then adjust your ride height utilizing spring length and preload. Then the last step is to take it in for a corner balance and alignment.

Keep in mind the 350z suspension likes a ride height close to OEM to keep geometry optimal.

OTS systems are usually designed to work within a range of ride heights, but it is easy to miss the mark and end up riding the bump stops.

terrasmak

iTrader: (8)

10cm of up travel ( bump) from your static height. I bet there is less than 15mm of down travel, that would explain things happening on turn in.

03threefiftyz

iTrader: (25)

Car is pretty soft (assuming the rear spring is in the OE Position)...you could be bottoming out the rear shock with 10cm of available travel, especially over bumps.