Alignment or Suspension Related at 100MPH?
 

So, I have a 2016 with the 19" Rays. Car has about 8K Miles. Factory tires that have plenty of meat still left on them. Car is bone stock.

I noticed past 80MPH, the car gets real sensitive to steering input. Like, if I move the damn steering wheel a centimeter, the car has the potential to go from the first lane to the forth lane on the freeway. Going over uneven grooves on the freeway also sets the car into a slight tizzy, it feels uneasy.

I took it for an alignment and wheel/tire balance to a local reputable shop. They used the factory specs, and the car still exhibits the same behavior. They've tried three times to align the car, last time with me in the car, and I still get the same behavior.

What the hell is it? My damn GTi at 100MPH was rock solid!

So the factory tires with the hard sidewalls is what's causing the issue?

Wide tires make tramlining worse. A short wheelbase makes tramlining worse. A light car makes tramlining worse. If you're going to drive a 370Z, you're going to have to put up with tramlining on rutted roads.

The Z has speed-sensitive steering. If you are encountering the problem on flat roads, this feature may not be working properly on your car.

I'll take into service and have them check it out. Thanks.

I have experienced this. It was the toe settings front and rear. Too much toe in. Not all alignment shops are equal. it is even more noticeable in the rain. The car will plow straight (meaning it is twitching left and right in the front).

What should the Toe be on a totally stock car? I read the front Toe can't be adjusted, only the rear is adjustable.

That is the camber and caster that is not adjustable, stock. Toe is. I do not have the alignment specs in front of me. You can search for them on here.

SouthArk's sig above (post 4) has a link to the FSM where you'll be able to find the OE alignment specs

Toe in will increase stability as the thrust are towards the center of the car and the toot (toe out on turns) is less drastic. This is why common auto x setup Yun like -1 degree toe up front but the car is twitchy for anything else.

Both myths are not actual direct causes of tramlining for most cars, and the Z34 chassis in particular. The standard 225 and 245 front tires are not large by normal standards, certainly with the static weight applied to them. Nor is the wheelbase that short, it's longer than both the latest 911's and Caymans and a few other cars at 100 inches and only 8 inches shorter than the a E92 m3 which has a backseat and longer trunk.

As Jhill stated, increasing toe-in will help self centering, but at a cost of slower response with high lock and more tire scrub.

The predominant reason behind the tramlining and wandering is the Caster angles and anti-dive geometry. Camber and toe marginally changes this. From the 350z, Nissan reduced the caster angles by over 3 degrees, and around 3 degrees less than most cars nowadays with standard mcpherson strut designs (6.5-8.5 degrees compared to 4.5-5.5 degrees in the Z34).

This reduces the self centering steering notable in cars like the VW golfs, Ford Focus and 911's. For those who have driven the Alfa 4c will note that car wanders around and squirms over cracks a lot! This car has smaller tires, shorter wheel base and....dot dot daa.. less caster and more anti-dive A-arm tilt.

I've experienced this with toe at 0* in rear; an alignment shop thought they were doing a favor for better roll & tire wear.not!
Rear has 2x as much positive toe as front.
Currently I'm just over 1/16" in front & just above 1/8" rear positive toe.
It's more likely the rear causing it to dance around.

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Be sure & get a print-out of the alignment & you'll see where the problem is.

Exactly, I was leaning towards the caster already but honestly don't feel it to be that bad in stock form so thought he might be feeling something else. However every car I've had has had a quicker go kart feel so I must not mind it but compared with the MB's and other lines I work on in the past, MB being some of the highest with their 8-9 degrees (this is going of memory) the z has very little caster.

Tire pressure comes to mind also.

What are you running?

This has just been my experience with the 370z. It is the only real error that can happen on the stock suspension adjustments. As soon as I got the toe set correctly, no more issues. I drive just as fast on the interstate in the pouring down Georgia/Florida heavy rain as I do when it is dry. This is when it is most noticeable to me.

Alright, I'm scheduling another alignment check at a different shop that's caters to preping cars for autocross events and what not. I'll get a print out this time and post it up here to see what you guys think about the settings.

Sounds good; be sure & have full tank fuel on.

Be sure they don't get crazy with the settings. In some cases a "autocross" setup implies you fudge up the standard alignment for faster steering and decreased roll in the rear. Do not let them go outside of .5 degrees (either direction) in the front and .3 degrees toe-in rear. You will kill your tires and most likely it will not benefit this car much.

As little camber in the rear, increase camber in the front.

Yes, I agree with you.

You need a little more toe in. When your toe setting gets close to zero. The car will fell nervous. The faster you go, the worse it gets.

Dead in the middle of the spec is best. No fudging one way or the other with all settings. As stated above, Autocross and track setups are different. When they get it right you will know right away.

Wait, so do I want zero Toe in the front and back or just a tad bit of Toe In...in the front and Zero Toe in the Back? I'm all confused. Some of you are saying Zero Toe Front and Back and some are saying a little bit of Toe In

2x more +toe in rear than front,,,look at chart & you may want to go between nominal & maximum,,,will give better straight line stability.

I originally had mine at .125"F & .250"Rear....kept a really straight line & gradually backed off till i got .094"F & .188"R-performing nicely.

In relation to the above info. Setting zero toe will allow the front tires to gain more toe out under compression in the front (braking/turning/bump). In addition to this, Adding toe-in on the rear (only) will actually increase the wandering on the front axle as it changes the pivoting angle slightly. As mentioned above, its best to set a bit of toe in on both axles. If you set zero toe front, you will actually get better high speed straight line stability with a bit of toe out in the rear. Under rear compression the car is set to toe in (acceleration/turn/bump). During cruising and hard braking however it may fish tail a bit more.

To mitigate both instances, it's best you get rid of the rubber lca bushings for something a bit stiffer.

Sorry for the oddly worded description. Typing from phone.

Unsure about all the details that Mays says; but little or no toe in rear will make the tail end dance around-especially if you go negative.
Also; I'm pretty sure you supposed to line up the rear before going to the front..& this may sound weird & the alignment shop may not do it....but road test it good & then throw back on the rack..as it seems things will settle.
I performed my own alignment & had to tweak it over a couple week span-to get the drive & measurements I was looking for.
A real learning process.

I was just attempting to explain the dynamics behind what goes on during driving conditions. At most cases we'd be cruising at highway speeds. I concur it will slide around the rear with toe out when cruising. But under acceleration the rear is set to toe in. To be fair, it's not efficient to drive this way in daily conditions. But at the track, its advantageous.

If you are using the string and ruler alignment technique it doesn't matter which axle you do first as long as you are using some form of turn plate under all four wheels. If you're only using turn plates on one axle at a time, then yes, rears first, reset the string, then fronts. In all cases, doing it on uneven ground will result in a incorrect alignment no matter what. 1/2 inch of unevenness is enough to mess up accuracy. Plus J, you have massive tires so i can't imagine this being easy to do :eekdance:.

May's;
It has been a learning experience for sure...no turn plates.
I tweaked a tad every day or 2 & kept up with all of my adjustments made;as the least incorrect adjustment & steering wheel can get mis-aligned.
Treadwear is very good on tires.

Yea that sounds a bit tricky. To make it a bit more accurate . A cheap alternative to professional turn plates would be to use a double stack of thick glossy pvc sheets on top of rubber mats and use oil or soap and water between the two plates.

This was recently covered by motoiq on a project drift car. This will yield better results compared to nothing but rubber to road surface. The downside is that you have to constantly check the alignment of the string.

If you set the rear toe on the Z to zero or more negative toe. You'll get into a handling problem called snap-over steering. The settling is nice for getting the Z to rotate in a corner on the track, and the Z feels nervous going straight. But at max grip in a corner. There is no warning of the rear letting go. It just goes. :eek: Been there, survived that. :driving:

There are several other factors that would cause snap oversteer, not just toe-out in the rear. In most cases, toe out would actually limit snap oversteer or sliding as the inner tire is countering rotation depending on how much toe-out is set. If we are talking about 1 degree from zero, then neither case would be a primary reason for this issue. The Z being a multilink rear setup with rubber bushings like most cars, the design is set to reduce toe-out under load on the outside wheel. If you are getting snap oversteer you are most likely dealing with weight transfer problems.

Unless you have a solid/stiff bushings in the rear, the outer tire in most cases is gaining to in. Increased static toe-in would just create more understeer at the limit.

What was the situation where you were sliding or getting snap oversteer with toe out?

How much actual track time you have with the Z. Because your answers sound like they're coming from a book, or google. :icon14:

I have track time and driving experience with several cars, with varying suspension designs and chassis weight. Whether the information came from a book or experience, the dynamics behind the geometry of this car and my own are still factual, that's all i was saying. Not to mention i've gone through about 100 alignment changes over 3 cars in the past 2 years. All of which have different suspension designs and bushing materials. I'm not trying to blow smoke up anyone's rear. It's genuine passion in the subject.

You made a point about toe settings causing SNAP oversteer, when in reality this factor alone can't possibly cause this phenomenon. That's why i asked for you to recount the situation you have in mind. I'm willing to bet cash that several other factors came into play for you to have such a situation. I already agreed upon the fact said alignment can cause basic stability problems in certain situations.

But you're right though, i did get a lot of information from books and research. A couple thousand dollars worth of information and training to be fair :rolleyes::

I don't want to answer for Rusty but I beat money he has SPL bushings in the back just like he does the front. No rubber bushings for him.

I think Rusty still has stock arms in the rear.

In any case, if you have stiff or solid bushings, the direction of travel won't change, you'll just be limiting the amount of change under load. Tires with less grip won't benefit from this as the tires have to do more work and can slip more. I didn't see the OP stating he had an aggressive suspension setup. In the case of toe-in or toe-out the tire can slip and cause a quick loss of traction with a stiff bushing setup.

Sorry for the late reply. Been traveling. Using my hotspot for internet. For some reason, it's slow as Hotrodz around a track. :eek: :rofl2: :stirthepot: Drove from Pittsburgh to Greeley Co. across I80. :eek: Be here until the 25th. Then drive back home. :driving: And my arm is killing me. :icon14:

I have most of the SPL catalog in the rear. Just haven't done a write up on it yet. Still deciding on a few pieces, and budget. Planning on write up when I have everything. ;)

I'm pickin' your brains to see what you have up there. How much work have you done with the Z? What alignment settings you've tried? Have you switched out/changed suspension parts? And which parts? What tire/rim comb you using? If you have knowledge up there that can help us track rats. I'm going to pry it out of you. :werd:

I've gone through 20+ alignment settings on my Z to get where I'm at now. Have a killer setting for track but tires life isn't good for the street and the Z is nervous as sh!t. Have a street setting that won't work well on the track, but tire life is great. The setting right now is a compromise between the two. I can tweek farther if I want to. Which I may do over the winter.

Snap-oversteer. Have you ever experienced it? The Z is good at telling you on what's going on if you take the time to listen. I can load the rear to the point of loosing grip, and feel it start to slide. With the toe at zero, or a hair +. The Z tells me everything. But when I had the toe -. I loose that feeling. The rear will load. When I expect it to start to slide. It will hang a little longer, then let go right now without any warning. It's not good looking at the driver behind you. Eyeball to eyeball. :eek:

Alot of the track info for the Z that you read on. Was done by pro level drivers. Like BGTV8, clintfocus, Mike, Shamu, BJ, etc. I'm not up to their level, but I can hold my own.