The Z is a weekend track car, this past season I've fell in love with HPDE. This season I've set a benchmark for what I should be at next season as far as confidence and lap times @ a few local tracks. The plan is to get into the 200TW tire gang. However, there is one slight issue I would like to adjust on the car and that is the understeer I am getting. Currently I've thought through a series of ways I can go about fixing the understeer.

Go square set up: currently I am on 18x9.5 + 15 FRONT, 18x10.5 +15 REAR RPF1s, 255/40F 275/40R (set up for street). I want to keep 10.5s all around instead of 9.5s all around mainly because I like the wider stance. I am also lowered on hotchkis springs which will most likely rub if i have 18x10.5 up front (idk?) I also want to keep a 40 sidewall because of looks (again)

I can also keep the staggered set up I have and dial in some camber with adjustable arms

ideally I'd like to run 40 sidewall tires on a square 10.5 +15 wheel. is this possible? what do i sacrifice if no? Just want to figure this out before i buy the tires

 

I would stick to the 9.5's square unless you are making a TON of power.
you can run 275's on 9.5 and it should run fine square.

Also under/oversteer can more easily be adjusted via sway bars and coil overs.


Weigh the car after the wheels. move/remove/transfer weight
I am guessing you are nose heavy.

Are you getting understeer constantlying or on slow turns. fast turns? high speed exits?.

 

Going to a 10.5 square will help reduce understeer by giving your fronts a bit more adhesion. Most of the track settings I see are running on lower tires as well, maybe 275/35 (instead of 275/40) on track setups.

As was mentioned, sway bars (and/or adjustable shocks/c.o.'s can definitely help you fine tune the steering attitude. Dialing in more roll stiffness in the rear (and/or reducing some in the front) will enable the rear tires to reach their max slip angles before the front and create more oversteer.

 

I get a lot of understeer on slow turns and i'm powering out. Why do you ask tho? how can you tell? Also does my tires screetching mean i'm over working and causing understeer? I have just summer tires @ 340TW so they screetch alot.
Do you have coilovers or a shock/spring set up? i have koni yellows that are adjustable. also hotchkis sways that are adjustable. what do you recommend?

 

What are your shock and bar settings F&R now?

 

Some tire noise is good, just means you're using them correctly But there is a difference between how tires sound while gripping and how they sound once they start to lose grip and begin to wash out. If you know what to listen for you can use this feedback to stay at the limit of adhesion without destroying the tires prematurely. Once the tires start to wash out, pushing harder is counter productive. When in doubt repeat the old mantra "slow in, fast out". Turn into the corner a bit slower, a bit later, and setup the car for straighter exit so you can get on the throttle earlier. It's less exciting, but your lap times will go down.

Just fyi, the Nasa spec Z series runs 275/35/18 square setup, I'd stick with that and a 9.5" wide wheel.

 

thanks for the tip! I think i can distinguish between while gripping vs heavy understeer. Under heavy understeer its more of a hard loud sound with heavy fighting on the steering wheel, under just tire slippage its just sounds like a drift event haha. i rly want to stay 10.5 but i'm considering all this

right now i'm using my Koni Yellow sports as is from the box. I have not changed anything because I like how it feels now, minus the understeer coming out of tight corners. my sways i believe are at mid/mid. Again I'm not very knowledgable here. I've done 9 total HPDE days with these settings and feel comfortable but think I can adjust to a better feel. I'm horrible at correcting oversteer and I think I will benefit from a car control clinic or more autocross with traction off (safer enviroment to loose control and learn how to correct than a track at speed). any advice on setting my shocks and sways?

 

In as few words as possible (because this topic is BROAD!):

Well, "mid-mid" on Hotchkis equates to Hole 2 or 3 front (four total) and Hole 2 (three hole) rear. Suggest you soften the front to either softest (hole one, outside end of bar) or hole 2 if it's on hole 3 and try that out with rear bar on hole 2. Fairly balanced set up with that config. Then keep trying different settings until you're happy with handling at your given track.

Rule of thumb for F& R swaybars:

More understeer - stiffer front, softer (or equal) rear by at least one hole
Neutral (for Z car, others will vary) - stiffer front, even stiffer rear than above
More oversteer - softer front, stiffer rear

On that note, consider that different tracks may "like" different setups so you're in for some experimentation. Once you've gotten that figured out, you can further fine tune by staggering the cross weight bias on the bars depending on needs. Meaning, one side might be at mid-stiff and the other side will be on full-stiff. Don't worry about that for now.

On your shocks, I'd start them at dead center/zero. I can't really give you any advice on that since I don't know your tracks. However, you'll again have to do some experimentation. The good news is that Yellows are single adjust rather than having to adjust both jounce and rebound via different ***** and trying to get them matched perfectly for your track. Dial one way for commensurate jounce and rebound control, and if that doesn't work for you, go the other way. But one thing to keep in mind is what I ref'd above for sway bars.... you can also manipulate front and rear roll stiffness with shock adjustment.

 

Just how crucial is a square setup and is the 350Z particularly sensitive that way? This is of interest to me and it looks like it would be to the OP too.

 

yes! I really don't want to buy a pair of 10.5 or 9.5 depending which square I want to go since i'm staggered right now. i would love to stay with my current staggered set up and correct the understeer. There are 2 other Z track guys I am usually with and they run square 9.5. I haven't driven their car but next season that might be a possibility depending on the track we are at.

I would love to keep my staggered
if not
I would like to go 10.5 square (function over form, but i wanna little bit of form!)
if not
square 9.5 it is.

 

the enemy of tracking is weight.
and you already have understeer.
adding extra wheel weight in the front wont help. which is why the people here are telling you to stick to the 9.5's.
My miata runs 14x6 wheels with 205/60/14 tires..

I would stiffen the rear sway bar's one notch and try it again with a square set up.
see if that helps.
followed by weighing the car. and moving /removing weight to balance it more.

The reason i was asking about slow vs fast corners is to see if this is a 100MPH sweeper you plow through and would have suggested looking into aero to correct lift. VS slow speed scrubbing where weight and suspension could change the behavior.

 

The weight distribution for a stock 350Z is 53/47, which is close enough to 50/50 to be considered neutral. Cars with rear weight bias, such as the 911 which are close to 40/60 do benefit from staggered setup to control what would be dangerous oversteer otherwise, but on neutral cars staggered setup is all looks and no function. Of course on race prepped Zs that weight distribution usually ends up even more forward bias, since it's easier to lighten the interior than the engine, so a staggered setup becomes even more detrimental to optimal handling.

I'd like to think that Nissan engineers understood this and made sure the front suspension is capable of running wide enough wheels to do square setups. I give them credit for that, there are too many cars out there where front wheel clearance is a limitation.

 

i am learnt this morning.

 

I think the best tip is how to enter and exit the turn. Just starting off you can add adjust all of these things but the main issue may be the way to take a turn. There's a youtube video I watched about understeer that may be helpful

 

I'll throw an old video of mine on here, it's a few years old so I apologize for crappy quality, but watch the M3 in my rear view, he has more power and more grip than me, but he's too aggressive going into turns and washes out each time, he's not able to get a pass because by the time we get to the next straight he falls way behind. He's fighting the car and abusing the tires, and I'm sure it's very exciting, just not a very fast way of driving.

 

Most common setup for the Z at the track is 9.5 to 10.5 wheels all around and 275/35-18. With that said, my car has RPF1 in 10.5 +15 all around and 275/35-18. It help a bit, but suspension is still needed to get in dialed in. Front camber is a must, and it's also needed to clear the wheel and tire combo

 

Thanks Terra! always good to get some input from you. you said you are running 18x10.5 +15 up front? What is your camber in the front at and are you lowered?

you said you are running 18x10.5 +15 up front. What is your camber in the front at and are you lowered?
I rubbed pretty bad last event where my fender liners were trashed under compression.

Why did you choose this set up over a 9.5 square set up?

 

Most 275/35-18 tires are optimized for a 10.5 inch wheel, the wider wheel opens up the tire all the way and gives the best contact patch with minimal sidewall deflection

Front camber, most of us running this are between -3.3 and -4

then yes my car is lowered about an inch and sits on 16k front springs

 

terrasmak, can you post a picture of that set up? with the 10.5s and that amount of camber? I take it you trailer your car to-and-from the track? I'm doing maybe 100 miles to and from the track (depending on which track) along with 4-5 20-minute sessions. other than that car does not get DD'd. Think i'll wear em out with just that many miles in a year? For this next event, I have a friend who I will see can let me use his 9.5 square and i'll swap after a session to see how much better it feels. If its mildly better i'll stick with 10.5s but if i notice its a huge difference I may go 9.5 square and just get extended lugs and put spacers on

 

I daily drove the car with that much camber for a year, 2 of my common track were 230 miles away and I drove to them. The car has only been on a trailer twice, cause it broke.