Alignment or Suspension Related at 100MPH?

MaysEffect

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.

Rusty

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. Been there, survived that.

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浪人 - 殺し屋
"The Difficult Anytime, The Impossible By Appointment Only"
http://www.the370z.com/members-370z-...o-journal.html

MaysEffect

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?

Rusty

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

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浪人 - 殺し屋
"The Difficult Anytime, The Impossible By Appointment Only"
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MaysEffect

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 :

Spooler

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.

cv129

I think Rusty still has stock arms in the rear.

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Setrab | RE-71 | SPL | JRZ | Nismo | ARK | Whiteline | RacingBrake | CJM Oil Pan | Ti shield

MaysEffect

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.

Rusty

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

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.

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浪人 - 殺し屋
"The Difficult Anytime, The Impossible By Appointment Only"
http://www.the370z.com/members-370z-...o-journal.html

Rusty

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.

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.

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.

__________________

浪人 - 殺し屋
"The Difficult Anytime, The Impossible By Appointment Only"
http://www.the370z.com/members-370z-...o-journal.html

MaysEffect

I'm not entirely sure i can give anymore useful information when we are talking about customized setups that go far beyond the normal limitations of the oem setup, certainly one as modified as your own. MY G is bone stock apart from Hankook RS3's in oem size. My other cars are significantly more tuned just because i've had them longer and it was worth the cost. The only 370z's i've driven were also bone stock, so again its not like your setup (so i assume). I've worked on both the G37's and 370z a few times so i am aware of the design hands on. This doesn't change my opinion on the cars in stock form though, and that was my point about normal alignment setups, even aftermarket setups to some extent. I've never attempted to change the handling balance of any car based on alignment setup, i change the alignment only to chase the wear and heat patterns of the tires. Considering my G is stock, there isn't a whole lot to change other than camber in the rear and slight changes in toe in the front. So far my normal changes have been to marginally start to increase toe-in from my base setup depending on how fast the wear is. The last time i changed it, it was sitting at .2 degrees toe-in front, close to zero toe rear. I play around with tire pressures significantly more though before i decide to tweak the alignment. My Normal traffic temps is 37psi front, 35psi rear. Spirited driving, i set around 34f/35r.

I can't speak on your exact issues without knowing the particular driving situations and setup you have. Looking at all the stuff you've done, it's impossible to get an idea on how the car handles without experiencing it myself or seeing it in action. You saying you're experiencing snap oversteer from toe out just doesn't add up without other factors causing it to behave in an unstable manor. However like we previously discussed, the factory Caster angles and rear traction arm geometry already makes it so that the handling response is a bit fast and loose (nervous).

Are you saying you just turn in to the corner and immediately the tail steps out? Was it on throttle, off throttle? Trail braking, no braking? All these different variables dictate weight balance, and all of which can change the amount of load on any given tire and subsequently cause instability. I've never had a situation where the rear has just stepped out unless i provoked it through cornering speed, steering and throttle/braking inputs or simply causing load changes in some form such as hitting a bump or elevation changes through the corner.

I'm not sure we are on the same page as to the definition of snap-over steer if you are implying you have grip and then it lets go, that's just regular oversteer. From your description, it sounds like you are feeling exactly what i described previously. When you load up the rear wheels, the natural tendency is for the outside wheel to start to toe in. This transition state from toe-out to toe-in will feel a bit vague, and it will feel even more loose if your camber settings are not ideal for the tire being used and/or you have a combination of stiff and soft bushings. But saying it let go, doesn't seem accurate if you are saying there was grip through the corner. Some other factor had to cause the loss of traction. A change in throttle/braking input, bump, the tires maximum slip angle was reached and the TIRE let go. But the last point would be more of a problem with static toe in, not toe-out. Most cases it comes from a change in CG and instant roll center. The only situation where i can see that the normal dynamics won't be ideal is if you have stiff/solid bushings for every control arm except the traction arm and upper control arm in the rear. In which case the traction arm would be the only arm moving and the camber and toe arm will be limiting the ability for it to gain toe-in. In which case it may start to toe-out more under load. This doesn't seem ideal, but i can only imagine this would just make the motion of steering a bit digressive. Which i can see would make the car behave in a manor where the amount of rotation is not linear to amount of steering input, making steering with the throttle a bit inconsistent. Is the case with your car?

Saying you experienced snap-oversteer would imply a sudden loss of traction at the rear. This doesn't just happen from toe settings unless they were WAY off. Like 3-10 degrees off. If this is happening, something is broken. Given your knowledge and experience i won't assumed you'd allow this to go unnoticed.

With regards to my experience with snap-oversteer.
The clearest, most dramatic situation i have was when i was going for a "normal" night run through the canyons in Malibu in my mkv r32 a few years ago. To give you an idea of variables. My rear tire pressure was higher than normal at about 42psi rear, 38 psi front (i even checked it beforehand), i had a mismatched squared tire setup 225/45 ZII stars front, DZ101 rears, the camber was set to almost 2 degrees front and rear and toe out front, zero toe rear. The tires were already warmed up from the drive up the canyon (Topanga canyon to the locals reading). I was going back down the hill to PCH, and was evading some guy trying to keep up (not the cops). Going through the down hill section with tight S turns, i picked up the speed on a short straight, and threw the car into a down hill right turn that was slightly cambered inward at about 70mph (way too fast). The car turned in relatively well with only a bit of understeer with steady throttle, then as i straightened out, the rear started to slide out once exiting the corner onto the flat straight. I started to counter the slide with full throttle and a bit of opposite lock. The rear gripped up and i let off the throttle and braked while straightening the steering. Subsequently the car swung back around and spun on a dime and i headed backwards further down the straight before i stopped just before hitting the canyon walls. Post inspection of the tires, the pressure had increased to 41F/45R.

In this situation, i'm confident the alignment setting played a small role in the situation. The variables of tire pressure, too much speed, sudden shift in weight balance and steering input caused the drift and snap oversteer. I already noted before the instance that the car was sliding a bit and felt a bit loose, this wasn't normal for the alignment setup i had and still have today. All of my other situations of snap-oversteer was similar to this with other variables such as running over berms, bumps or inconsistent throttle input.


Hopefully this makes sense. Though i may have put some of you to sleep.