caster & toe questions

[fiero88]

this is specific to an 88. 16x7 wheels all about, 205-55 on front, 225-50 on rear.

original front susp:

-0.5 camber
+4 caster
0 to 1/16 toe in (very little if any)

complaint: wanders on highway, not directionally stable.

Added a bit of toe in and ended up with too much (1/4"), but it was getting dark... so had to accept it for now.

the directional stability of the car is slightly improved, but I noticed a large improvement in overall cornering limits. with the original setup, the car was ok, but would start to plow when pushed. now, with the 1/4" of toe in, the plow is more or less eliminated, the car corners much nicer. previously the car would start to plow silently, whereas now the car will track through a corner (including accelerating out) without requiring additional steering input.

I'm trying to understand what happened - shoudln't too much toe have resulted in a degredation of cornering ability? I did not expect this change.

[donk_316]

can we all assume your suspension is rebuilt and next to new including your steering rack?

[fiero88]

the entire suspension is polyurethane. no rubber bushings anywhere.

balljoints, tierods, and steering rack are in good shape.

Everything has a few miles on it (it is NOT next to new) but otherwise checks out to be in good condition. nothing is mechanically worn out / failing / sloppy.

[TurboGT]

I have had this same problem on my car and it is a 87 GT. I went throught the entire suspension and replaced all the control arm bushings with UHMW poly, and new shocks and springs. I have tried several toe settings and still have the loose feeling on the freway. The car drives great around town and corners awsome and the rack dosnt feel like it has any slop. Here are some pic of what I made to allign my car

[The Dark Side of Will]

When you align for maneuverability, you just have to accept lack of straight line stability. If you want it to be more stable on the highway, try a little more caster.

The increased toe increased your cornering limits because it increased the slip angle of your outside front tire relative to the "average" direction of both tires, which is what determines where the car goes.

I'd put -1.0 camber all around.

[befarrer]

Doesnt having a positive rear toe in (toe out??) increase your cornering, but reduces straight line stability too?

I need to replace all my suspension bushings, I am running stock rubber, except for the upper A-arms, I think all of it is factory install with 170,000miles on it.

[The Dark Side of Will]

Toe out in FRONT reduces stability but increases agility.

Toe out in the REAR causes crashes.

[fiero88]

so If I'm understanding everthing correctly:

adding toe-IN will increased highway stability, increased overall cornering limits, and decreased agility;

whereas adding toe-OUT will decrease highway stability, decrease overall cornering limits, and increase agility;

where highway stability is defined as wander on the highway,
cornering limits is defined as the ultimate steady-state G-force the car can sustain, and increased agility is defined as the willingness of the car to switch direction/manuver.

[Kohburn]

so If I'm understanding everthing correctly:

adding toe-IN will increased highway stability, increased overall cornering limits, and decreased agility;

whereas adding toe-OUT will decrease highway stability, decrease overall cornering limits, and increase agility;

where highway stability is defined as wander on the highway,
cornering limits is defined as the ultimate steady-state G-force the car can sustain, and increased agility is defined as the willingness of the car to switch direction/manuver.

pretty much yes

[The Dark Side of Will]

Front toe won't affect limits so much as it will affect balance. If your car understeers with neutral toe, and then tightens up with increased toe, you ought to be looking at bar and spring rates... with the right wheels, tires, springs & bars you should be able to run slight toe out at the front and not sacrifice limit traction.

[rube]

You didn't say what offset your wheels are. 88s have different wheel offsets front and rear. I had 16x7-40mm all around on my 88 and it was miserable. The front wheels ended up too far out up front and did squirrely things to the handling. Like you said, hunting on the highway, following truck ruts and oh god don't hit a puddle with just one wheel at any speed. Those same wheels are fine on an 84-86.

[The Dark Side of Will]

The 84-87 suspension has a LOT more knuckle offset (lateral scrub radius, steering offset, whatever) than the '88 suspension. The offset requirements for good steering geometry on each are VERY different.