Alignment or Suspension Related at 100MPH?

gomer_110

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

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'17 Titan Bone Stock

jchammond

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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jchammond

Sent from my iPhone using Tapatalk

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jchammond

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

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Spooler

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.

Need4Speeds

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

jchammond

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

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jchammond

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.

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MaysEffect

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.

jchammond

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.

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MaysEffect

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 .

jchammond

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.

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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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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?