Toe-in
Theory
Toe refers to the amount by which a pair of wheels on an axle vary from being parallel to each other.
The amount of toe can be expressed either by the number of degrees which the wheels are out of parallel,
or more commonly, as the difference between the track widths as measured at the leading and trailing
edges of the tires or wheels.
Toe settings affect three major areas of performance:
tire wear, straight-line stability and corner entry handling characteristics.
Toe-in, or positive toe-in, or just 'toe', is when the fronts of the wheels are closer
together than the backs of the wheels. This creates a stabilizing force; when traveling forward the
wheels are aimed very slightly toward each other, therefore creating a small understeering tendency on
that axle, therefore tending to keep the car going in a straight line. The two downsides of this are (1)
as toe-in increases, the rolling resistance of the tire increases, slowing the car down and (2) it
'mutes' the ability of the car to turn into a corner, creating a little corner-entry understeer.
Zero toe is when the wheels are exactly parallel to each other.
This can cause the car to wander about instead of tracking in a straight line,
but at least there will be minimum rolling resistance.
Toe-out, or negative toe-in (in GPL, shown as a -ve value for toe-in: confused?)
is when the leading edges of the wheels are further apart
than the trailing edges.
This also creates a stabilizing force and rolling resistance, but
does accentuate the ability of a car to turn into a corner,
creating a little corner-entry oversteer.
In theory, you might have a little toe-out on the front wheels because of the
Akerman steering effect.
How does the toe change dynamically during longitudinal weight transfer?
In a rear-wheel drive car under acceleration, the front (non-driven) wheels will
tend to toe themselves out and the rear (driven) wheels will tend to toe themselves in.
(In a front-wheel drive car under power, the fronts tend to toe themselves in,
and rears tend to toe themselves out).
How does the toe change dynamically during lateral weight transfer (cornering)?
I didn't know, so suspension guru Giovanni Tifosi patiently explained it to me.
The summary is that cornering increases the toe-out of the loaded front,
but neither this nor any other dynamic toe change are likely to be modeled in GPL.
Application to GPL
The toe angles I've had to guess at, as I don't know how to get data out
of GPL to set these properly.
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Dr Bunsen Honeydew experiments...
How much does toe, both in/out and front/rear, affect straight line speed?
Theory and intuition suggest that a little toe-in at the front will create the
maximum possible straight line speed.
To verify this, my assistant took the Coventry to Monza and measured Vmax, over an average of four laps,
at two points on the track. We tried, over five four-lap runs, both maximum and
zero toe-in and toe-out at the front and the back. The result?
Maximum speed was not affected at all by any change in toe.
Toe does not affect rolling resistance in GPL; it's not modelled.
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In the real world, you'd typically have about 1/8" (0.125") of toe-in
on the front wheels of a road car, and maybe 1/8" of toe-out on a race car.
Anyway, front toe-out or toe-in? Don't seem to need much of either.
I've found that having zero toe on the front wheels can create a little
corner entry instability, so I generally use a little toe-out, which gives
the front of the car a little 'bite' when turning in. Too much toe-out
on the front also creates some instability, of the twitchy 'oversteery' kind.
Because the back of the car wanders under acceleration (not to be confused
with the abrupt wandering caused by hitting the bump stops), and these cars generally
seem twitchy and unstable, then you need some rear toe-in.
About 1/8" seems to be enough; any more interferes with the rest of the setup.
The overall amount of toe changes the nature of the car.
Having no toe at all makes the car unstable, as does having too much toe.
Also, I've noticed that having an equal amount of toe front/back makes for a
more predictable chassis, so I generally use, or at least start with, -0.125 (1/8" toe out)
on the front and 0.125 (1/8" toe in) on the rear.
