[s-cars] Understeer vs. oversteer?

[Theodore Chen]

--- Robert Pastore <rpastore at animalfeeds.com> wrote:
> Teddy:
> Put me first on the list for a camber plate Group Buy. I've got the ECS
> offset camber plates on my Avant, and while they've cured the inner tire
> wear problem on the street, I just cannot get much negative camber at all
> and that hurts me on the track.   Wearing the outer shoulder on Hoosiers
> gets expensive!

bob,

watch out, you're making people think i'm running a group buy.  :)  i'm
getting email from people asking me about it.

in my experience, the hoosier R3S03 (and its predecessor, the R2S02)
is very sensitive to proper setup.  R3S03s don't tolerate inadequate
camber very well.  they'll still stick like glue, but their already-short
lives will be shortened even more.

the old BFG comp T/A R1 was designed specifically for use on
production-type cars that typically had little to no negative camber.
it lasted a long time on my mustang, which appears in the dictionary
under "mediocre front suspensions with horrible camber curves".
the kumho v700s i'm running now seem almost as tolerant of poor camber
as the comp T/A R1s were.

until you fix the camber problem, if you want significantly longer
tire life, i'd suggest the kumho v700s.  they'll be slower than the
hoosiers you're running now, though.

how are the ECS plates constructed?  looking at my '92, there doesn't
seem to be a lot of room to move the strut inboard without replacing the
bushing with a spherical bearing.  some basic trigonometry indicates
you could get about 1.5 degrees more negative from the stock location,
which is already maxed out.  after that, i think the bushing is going to
run into sheetmetal of the strut tower.  is there a bump stop on
the shaft of the strut?  i haven't taken this car's suspension apart yet.

it looks like you could get another degree or so by raising the strut
mount, too, but that would affect your strut's position.  if your car
was lowered from stock, this could be a good thing - otherwise, you're
throwing away droop travel.

> The practical problem is that changing camber also changes toe, so every
> "track" to "street" and back setting requires another trip to the alignment
> shop.

i've measured the toe change versus camber change, and it doesn't change
much at all.  on my mustang, adding 1.5 degrees of negative camber
makes it go 1/16" more toe-out (my car is a front-steer configuration),
which is actually more useful for track use because it promotes better
turn-in.

on the S4/S6, with the steering rack behind the balljoints, adding more
negative camber would increase toe-in.  the steering arms look like
they're about 7" from pivot to strut axis.  they're halfway up the
strut, so the camber change would affect toe more on this car than on
my mustang (which has the steering arms down near the hub).

adjusting toe isn't hard, though, and you don't even have to get dirty.
i'd take the car to the alignment shop and have them set up the car for
track use.  mark the settings (camber and toe) with white paint.  then
have them set it up for the street.  mark those settings with yellow
paint.  then you can easily change the settings in the pits without
any measuring tools.

by the way, do the ECS plates add any caster?  more positive caster
increases dynamic camber gain and self-centering action of the steering.

-teddy


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