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.