Alignment Details

Rocwandrer@aol.com wrote:
>
> I was just looking at Randy's alignment spec's on autocross.com.
> O.K. I understand everything there except why toe in in the rear and toe out
> in the front. I thought that max traction was when an axle set had parallel
> wheels? that, according to Fred Puhn, would mean you would want slight toe
> in in the front to compensate for deflection from drag and the opposite in the
> rear due to the push from acceleration, compromising rear braking slightly. I
> am not being critical of your specs, Randy, just trying to understand why this
> is a good setup.

No problem. These are similar to specs used by most really fast MR2
drivers.

The toe setting are not set up for acceleration or braking, but for
cornering. Consider what happens to the car when it enters and exits a
corner.

First toe in on the rear. When you corner, the tire on the outside is
doing most of the work of all four tires. Since it is doing most of the
work, the alignment of that tire is crucial. Toe out on the rear, means
the outside tire's slip angle on cornering is near zero, so the back end
wants to come around more. By adding toe out, you increased the rear
tires slip angle and it fights coming around more. By the same token,
the inside rear tire is already turning. A car with toe out on the rear
should not turn in very quickly. Zero toe may be okay, but in this case,
we are using the toe-in to compensate for the 91/92 cars tendency to
oversteer. This makes the car more predictable.

Toe out on the front. Too high a slip angle on the front tire means the
car will plow. Simple cure for understeer is to decrease the front slip
angle, easily by pulling the steering wheel more open (back to home).
The other way is to have some toe out. The outside tire (again doing
most of the work on cornering) is using it tire patch for adhesion, but
the slip angle hurts you. Now having toe in on the outside tire has an
advantage in quick turn in (it's already trying to turn), but that
advantage gets removed because of whats happening to the inside tire,
and the increased slip angle if there is too much understeer.

The inside tire having toe out is already turning (it's pointed around
the corner more). If the inside tire has toe in, you can see that the
inside tire now has an extreme slip angle on hard cornering (you are
pushing it more sideways).

Then add in, the toe out makes the steering wheel easily center itself
after coming out of turns. So, I will not say you should always have toe
out on the front, but you should not have toe in, and toe out will add
some benefits. It may pay to experiment. I have tried various
combinations, and there is no one set number to use for all
surfaces, speeds, swaybars, tires, and drivers. You need to set
up the car for your situation. I am only trying to give you a
starting point, that has worked for me.

Randy Chase